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A review of absorption refrigeration technologies

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Abstract

This paper provides a literature review on absorption refrigeration technology. A number of research options such as various types of absorption refrigeration systems, research on working fluids, and improvement of absorption processes are discussed.

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... The third technology investigated is the combined cooling heat power (CCHP) technology. The CCHP system is designed to supply additional energy to the cooling load in a conventional CHP system [34][35][36][37][38][39] (Ach) as a component of the EH to supply energy to the cooling load [40,41]. In [42], the CCHP structure, including the Ach, is described, and an optimal hourly operation process for each component is proposed. ...
... An optimal energy operating system incorporating reliability and economics for each system will be considered. [4], [7], [9], [20], [21], [25], [26], [28], [32], [39], [40], [41], [47], [48], [49], [51], [55], [57], [60], [61], [76], [77], [79], [80], [110], [111], [127], [128], [129], [130], [131], [132], [133], [134], [135], [137], [138] CCHP [29], [31], [33], [34], [36], [43], [45], [52], [64], [71], [72], [75], [136], [139] P2G [2], [5], [6], [8], [9], [11], [13], [16], [17], [30], [32], [36], [38], [43], [77], [88], [89], [138], [140] TABLE V FIG [ 2,5,7,8,9,10,11,12] REFERENCES Energy conversion mode [29], [30], [31], [32], [33], [34], [36], [37], [39], [40], [43], [45], [46], [47], [48], [49], [51], [52], [55], [56], [59], [60], [61], [62], [64], [71], [72], [75], [86], [127], [128], [129], [130], [131], [132], [133], [134], [135], [136], [137], [138], [139], [140] Multi energy to Cooling [4], [10], [12], [13], [14], [15], [19], [21], [23], [25], [26], [27], [28], [29], [30], [31], [32], [36], [40], [43], [45], [62], [64], [71], [72,] [131], [134], [136], [140] Multi energy to Hydrogen [17], [14], [137] Gas boiler [8], [32], [35], [40], [42], [45], [46], [47], [51], [62], [63], [92], [93], [96], [95], [96], [97], [102], [105], [117], [123], [125] Electric heat pump [20], [26], [39], [49], [73], [79], [92], [103], [106], [123] Furnace [18], [61], [102] Electric boiler [46], [50], [73] Combustion engine [23], [63], [73] Electrolyzer [8], [10], [16], [18], [49], [50], [85], [104], Fuel cell [10], [16], [18], [49], [50], [77], [85], [104], [122] Gas turbine [18], [35], [36], [38], [42], [47], [61], [96], [97], [103], [109] Absorption chiller [23], [34], [35], [36], [42], [47], [62], [108], [109], [134] Electric chiller [23], [35], [45], [46], [63], [73], [96], [97], [105] Aircondition [40], [ 42], [47], [95], [96], [97], [103], [134] [4], [9], [10], [12], [13], [15], [17], [18], [19], [20], [23], [25], [29], [32], [33], [36], [45], [47], [48], [49], [52], [56], [60], [71], [86], [100], [128], [129], [131], [135], [136], [137], [138], [140] TES [4], [7], [10], [12], [13], [14], [18], [19], [20], [21], [23], [25], [29], [31], [33], [36], [41], [45], [47], [52], [56], [64], [71], [72], [75], [86], [91], [100], [127], [128], [129], [131], [132], [134], [135], [137], [139], [140] IES [4], [10], [13], [21], [23], [36], [41], [45], [46], [52], [63], [75] HES [2], [14], [16], [17], [30], [32], [38], [77], [137] NGS [3], [6], [14], [43], [84] ...
... An optimal energy operating system incorporating reliability and economics for each system will be considered. [4], [7], [9], [20], [21], [25], [26], [28], [32], [39], [40], [41], [47], [48], [49], [51], [55], [57], [60], [61], [76], [77], [79], [80], [110], [111], [127], [128], [129], [130], [131], [132], [133], [134], [135], [137], [138] CCHP [29], [31], [33], [34], [36], [43], [45], [52], [64], [71], [72], [75], [136], [139] P2G [2], [5], [6], [8], [9], [11], [13], [16], [17], [30], [32], [36], [38], [43], [77], [88], [89], [138], [140] TABLE V FIG [ 2,5,7,8,9,10,11,12] REFERENCES Energy conversion mode [29], [30], [31], [32], [33], [34], [36], [37], [39], [40], [43], [45], [46], [47], [48], [49], [51], [52], [55], [56], [59], [60], [61], [62], [64], [71], [72], [75], [86], [127], [128], [129], [130], [131], [132], [133], [134], [135], [136], [137], [138], [139], [140] Multi energy to Cooling [4], [10], [12], [13], [14], [15], [19], [21], [23], [25], [26], [27], [28], [29], [30], [31], [32], [36], [40], [43], [45], [62], [64], [71], [72,] [131], [134], [136], [140] Multi energy to Hydrogen [17], [14], [137] Gas boiler [8], [32], [35], [40], [42], [45], [46], [47], [51], [62], [63], [92], [93], [96], [95], [96], [97], [102], [105], [117], [123], [125] Electric heat pump [20], [26], [39], [49], [73], [79], [92], [103], [106], [123] Furnace [18], [61], [102] Electric boiler [46], [50], [73] Combustion engine [23], [63], [73] Electrolyzer [8], [10], [16], [18], [49], [50], [85], [104], Fuel cell [10], [16], [18], [49], [50], [77], [85], [104], [122] Gas turbine [18], [35], [36], [38], [42], [47], [61], [96], [97], [103], [109] Absorption chiller [23], [34], [35], [36], [42], [47], [62], [108], [109], [134] Electric chiller [23], [35], [45], [46], [63], [73], [96], [97], [105] Aircondition [40], [ 42], [47], [95], [96], [97], [103], [134] [4], [9], [10], [12], [13], [15], [17], [18], [19], [20], [23], [25], [29], [32], [33], [36], [45], [47], [48], [49], [52], [56], [60], [71], [86], [100], [128], [129], [131], [135], [136], [137], [138], [140] TES [4], [7], [10], [12], [13], [14], [18], [19], [20], [21], [23], [25], [29], [31], [33], [36], [41], [45], [47], [52], [56], [64], [71], [72], [75], [86], [91], [100], [127], [128], [129], [131], [132], [134], [135], [137], [139], [140] IES [4], [10], [13], [21], [23], [36], [41], [45], [46], [52], [63], [75] HES [2], [14], [16], [17], [30], [32], [38], [77], [137] NGS [3], [6], [14], [43], [84] ...
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The increasing penetration of renewable resources causes some challenges like the electric power demand prediction uncertainty and energy surplus. Energy storage systems (ESS) are promising solutions for these challenges. However, considering the marginal capacity of ESSs according to the installation area and the economic portion of ESSs according to the installation capacity, the use of battery ESSs to reduce surplus energy is not efficient and has practical limitations. To efficiently resolve the challenges, a multi-energy system (MES) that is capable of operating different energy sources, such as natural gas storage (NGS), thermal energy storage (TES), ice energy storage (IES), and hydrogen energy storage (HES) has been proposed. The centerpiece of converting and managing multiple energy sources associated with the MES is the energy hub (EH). In this paper, we reviewed and compared the performance of existing ESSs and the MES, and the results have demonstrated the superiority of the MES. In addition, EHs that include power-to-gas, combined heat power, and combined cooling heat power, have been examined based on their structural characteristics. A review of the methods and the primary purpose of MES is also highlighted in this paper.
... However, absorption chillers predominantly use ammonia or water as working refrigerants, and both are classified as environmentally friendly refrigerants with ODP and GWP equal to zero. Thence, thermally driven refrigeration systems have two distinctive features over the DX systems: the use of environmentally friendly refrigerants and the ability to utilize low-grade heat sources to drive the system [2]. Those two features make the thermally driven systems more attractive from an environmental perspective [3]. ...
... Moreover, other studies contained reviews of different improvements in absorption refrigeration systems. Besides the aforementioned enhancement aspects, the authors stated some conclusions: For instance, multi-effect cycles are more promising than single-effect ones [2,22], combined vapor compression-absorption refrigeration systems outperform the conventional ARS [23], and the need for improving the design of the distillation column, rectifying column, and most importantly the stripping section within the generator [21]. The authors also recommended to apply the above modifications on domestic refrigerators and air conditioners, increase the stripping stages of the desorber, and using working solutions that prevent corrosion and utilize nanoparticles. ...
... Various techniques are proposed to avoid crystallization. For instance, the use of a ternary mixture like LiBr+ZnBr 2 /H 2 O improves the solution solubility [2]. Moreover, Liao and Radermacher [49] believe that increasing the chilled water temperature and/or reducing the exhaust temperature are effective control strategies to prevent crystallization in integrated cooling-heating power systems. ...
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... However, for optimal performance, this design necessitates a high recirculation rate. Another unique method is the absorption of a vapour-refrigerant in a liquid cover on cooled revolving discs [15]. As a result, the absorption of the spinning discs for a given surface area is significantly greater than in a standard configuration. ...
... The lower temperature section rejects heat out to the surroundings and the rich-refrigerant solution is preheated in the higher temperature section of the absorber. Thus, 10% COP is improved due to decrease in heat input to the generator [15]. The absorber's liquid refrigerant is sent to the ammonia reservoir before being routed to the chiller through the economizer and expansion valve. ...
... The percentage of weak solutions in states 1-3 will stay unchanged, as will the percentage of strong solutions in states 4-6. "Temperatures at Thermodynamic States 11,12,13,14,15,16,17, and 18 represent the external water circuit used to give heat to the system's components", as shown in Figure 1. The inlet and outlet temperatures of the major components of the absorption system is illustrated in Table 2. ...
Article
Experiments on an enhanced “Generator-Absorber-Heat Exchanger” (GAX) Vapour Absorption System (VAS) for cooling purposes were carried out using water-ammonia in present study. The new experimental setup was fabricated using modern and complex technologies for the GAX absorption system which includes tiny heat exchangers, allowing the system to be both compact and efficient. The coefficient of performance (COP) of a system was analyzed for different temperatures of Generator, Condenser, Evaporator and Absorber. The results show that the maximum performance (COP=0.63) is achieved at 25℃ Generator temperature. The system has a low carbon footprint because it does not use effluent water or tower electricity and invention enables the recovery of hot air, which may then be used for several drying applications, including agricultural drying, resulting in a fully cascaded system with a three-fold increase in Coefficient of Performance (COP). A modified VAS-GAX absorption system in present analysis be a good fit for high-performance modern cooling applications.
... Over the past few decades, a number of studies were conducted on absorption refrigeration. Srikhirin et al. [10] reviewed the research on working pairs before 2001. They pointed out that there are more than 40 refrigerant compounds and 200 absorbent compounds available, but the most widely used working pairs are still LiBr-H2O and NH3-H2O. ...
... Pe Hy j (10) In the above equation, ∆P is the pressure drop of the pump, which generally contains pipeline pressure drop and heat exchanger pressure drop, as shown in Equation (11). ...
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Cascade cooling systems containing different cooling methods (e.g., air cooling, water cooling, refrigerating) are used to satisfy the cooling process of hot streams with large temperature spans. An effective cooling system can significantly save energy and costs. In a cascade cooling system, the heat load distribution between different cooling methods has great impacts on the capital cost and operation cost of the system, but the relative optimization method is not well established. In this work, a cascade cooling system containing waste heat recovery, air cooling, water cooling, absorption refrigeration, and compression refrigeration is proposed. The objective is to find the optimal heat load distribution between different cooling methods with the minimum total annual cost. Aspen Plus and MATLAB were combined to solve the established mathematical optimization model, and the genetic algorithm (GA) in MATLAB was adopted to solve the model. A case study in a polysilicon enterprise was used to illustrate the feasibility and economy of the cascade cooling system. Compared to the base case, which only includes air cooling, water cooling, and compression refrigeration, the cascade cooling system can reduce the total annual cost by USD 931,025·y−1 and save 7,800,820 kWh of electricity per year. It also can recover 3139 kW of low-grade waste heat, and generate and replace a cooling capacity of 2404 kW.
... An absorption chiller is a closed loop cycle that utilizes waste heat to provide cooling. The coefficient of performance (COP) of an absorption chiller ranges between 0.5 and 1.5, whereas modern vapor compression cycles have COPs in excess of 3.0 [119,120]. However, absorption chillers are still frequently used since they can deliver cooling using low-temperature (<100°C) heat source. ...
Thesis
Oil mill sewage sludge (OMWS) is a major environmental problem for olive oil producing countries. Various OMWS elimination strategies have been proposed, in particular rapid pyrolysis which is considered a promising technique and whose main product is bio-oil which finds its application as green diesel in internal combustion engines.In rapid pyrolysis, bio-oil vapors are cooled using a compression refrigeration machine. The objective of the thesis is to integrate an absorption refrigeration machine by recovering the heat of the process, replacing the compression refrigeration machine and thus reducing electricity consumption.It turns out that the sorption refrigeration process allows for better energy efficiency. The ratio of bio-oil exergy to electrical exergy goes from 27 to 102 from the conventional system to the sorption system.An economic analysis is performed to determine the minimum selling price of bio-oil as fuel (MFSP). It is observed that the MFSP is reduced from 3.63 € / GGE to 2.99 € / GGE between the conventional system and the sorption system. The difference comes from the electricity consumption avoided. The economic sensitivity analysis shows that the production cost of bio oil decreases more rapidly than the increase in the investment cost induced by this increase in production.
... The waste heat from the GT exhaust can also be utilized for operating an absorption refrigeration system (ARS) to produce a cooling effect [11]. Mone et al. [12] demonstrated the economic viability of incorporating ARS into a GT-based combined heat and power system (CHP). ...
Chapter
In this chapter, a trigeneration system for the combined production of electricity, process heat, and chilled water is proposed. It includes an intercooled-recuperative gas turbine (IRGT) cycle, a heat recovery steam generator (HRSG), an absorption refrigeration system (ARS), and a reheated-organic Rankine cycle (R-ORC). The ARS operates by using the low-grade heat rejected during the intercooling of the compressed air, while the HRSG and R-ORC operate by using the surplus heat available at the gas turbine exhaust gas. The objective of the present study is to investigate the exergoeconomic and environmental feasibility of incorporating ARS, R-ORC, and HRSG into the IRGT plant using the proposed configuration. According to the results, the net power generated by the proposed trigeneration system is 50.93 MW, with the overall energy and exergy efficiency of 83.14% and 50.65%, respectively. In addition, the HRSG provides 64.43 ton/h of water into saturated steam for process heating, while the ARS generates a 7.73 MW of cooling effect. Moreover, the system and environmental cost rates are measured to be 3,788.5 $/h and 774.26 $/h. The proposed system also has a lower environmental effect than the standalone IRGT cycle since the IRGT cycle’s specific CO2 emission is 522.61 kg/MWh, which is reduced to 244.45 kg/MWh after the incorporation of HRSG, R-ORC, and ARS. Finally, a parametric analysis is conducted to investigate the impact of overall compressor pressure ratio, gas turbine isentropic efficiency, and air compressor isentropic efficiency on the performance of the trigeneration system.
... The basic VARs consist of an absorber, a generator, a solution pump, a condenser, an expansion device, and an evaporator. Given the complex heat and mass transfer processes taking place in absorbers and desorbers, they are acknowledged as key components for VARs [7][8][9]. Therefore, understanding of the behaviour of these components is of the essence to improve the global performance of VAR systems. ...
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The absorber is a key component of absorption cooling systems, and its further development is essential to reduce the size and costs and facilitate the diffusion of absorption cooling systems. Computational fluid dynamics (CFD) can facilitate the characterization of the equipment used in absorption cooling systems at lower costs and complexity, but they must be properly developed and validated to provide reliability. This study provides a detailed description and assessment of a 3D CFD bubble absorber model developed to simulate the absorption process in a vertical double pipe with the NH3/LiNO3 solution. It includes a comprehensive methodology to develop the CFD model and its validation considering the effect of the solution flow and the cooling water temperature on absorber performance parameters such as the absorption mass flux and the solution heat transfer coefficient. The results show that the ‘Volume of Fluid model’ and the ‘Realizable k-epsilon model’ provide the lowest residuals and computational times in the simulations while a good correspondence between the CFD model and the experimental data with errors below 10% and 7% for the absorption mass flux and solution heat transfer coefficient, respectively, was obtained. The maximum absorption rate and heat transfer coefficient were 0.00441 kg m⁻² s⁻¹ and 786 W m⁻² K⁻¹, respectively.
... and is the condensation temperature and the absorption temperature, respectively, is the evaporation temperature and is the generator temperature, in which all these temperatures must be given in the absolute temperature scale, K. Also, Srikhirin et al. (2001) mentioned that the installation of the heat exchanger between both solution streams may improve the COP up to 60 %. In their review, they also detailed possible technologies used in absorption refrigeration machines 2.3 Component size comparison and performance of ARC for several working fluids Boman et al. (2017) investigated the behavior of several working fluids based on their thermodynamic properties and heat transfer characteristic applied in a single-effect absorption refrigeration cycle operating in heating or cooling mode. ...
Thesis
The falling film technology has been widely used in different engineering applications, including in the absorption refrigeration cycles (ARC) because it has a huge potential to be used for heat recovery from thermal sources and from solar energy. Open-source literature review shows different studies over the heat and mass transfer (HMT) behavior for both absorption and generation processes, demanding more experimental results in this field. Moreover, the wettability problems are still present in liquid falling film applications. Therefore, the current work deals with an experimental test rig of an ARC for a 1500 W cooling capacity, allowing to study the absorption process in real operational conditions. Furthermore, the present research study the heat and mass transfer absorption process in a novel configuration, using a horizontal liquid film in ammonia-water mixtures. Firstly, a complete literature review on falling film technology focused on the HMT study in sorption processes was carried out, in which both ammonia-water and lithium bromide-water working fluid were analyzed. Based on that review, a HMT mapping for the most common working fluid was obtained by using a modeling of the absorption refrigeration system. Secondly, a modeling of the ammonia-water absorption process using a new proposal of heat and mass exchanger in which the total wettability is guaranteed was developed. A mathematical model based on the overall balance of mass, ammonia species, and energy equations was carried out. Finally, an ammonia-water absorption refrigeration test was projected, built and tested, in which it allowed studying the ARC as a function of several operational parameters such as strong mass flow rate, generation temperature, weak solution temperature, concentrations, and absorption pressure. Moreover, the horizontal modified liquid film absorber was tested in real operational conditions. According to the theoretical studies, a HMT mapping were obtained for those experimental and analytical correlations, obtaining the possible operating range of the Nusselt number and Sherwood number in some typical operational conditions from ARC's. The heat and mass transfer coefficients were strongly enhanced as the absorption refrigeration cycle achieved vaporization temperatures below 0 °C for ammonia-water working fluid. Moreover, a parametric study of the ammonia-water absorption process was carried out. Absorber heat rate was improved by using lowest surface temperature and lowest liquid film thickness. Also, studies showed absorption heat rejection decreases as a function of the position into the absorber, whose first plate absorbed about 30% of the total heat of absorption. Based on experimental studies, results showed the operation of the ammonia-water absorption refrigeration cycle, achieving temperatures below 0 °C.
... Contact resistances are negligible [73e75]. For both GAX and VAR cycles, a saturated vapour is considered at the exit of the evaporator [76]. ...
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... Ammonia, as a refrigerant, is mostly used in applications using absorption cycles [110]. Absorption systems transfer heat from a cold to a hot source using heat, instead of electricity, as input energy. ...
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Geothermal heat pumps have a widespread diffusion as they are able to deliver relatively higher energy output than other systems for building air-conditioning. The exploitation of low-enthalpy geothermal energy, however, presents crucial sustainability issues. This review investigates the primary forms of the environmental impact of geothermal heat pumps and the strategies for their mitigation. As life-cycle analyses shows that the highest impacts arise from installation and operation stages, most optimization studies focus on system thermodynamics, aiming at maximizing the energy performance via the optimization in the design of the different components interacting with the ground and serviced building. There are environmental studies of great relevance that investigate how the climate and ground properties affect the system sustainability and map the most suitable location for geothermal exploitation. Based on this review, ground-source heat pumps are a promising technology for the decarbonization of the building sector. However, a sustainable design of such systems is more complex than conventional air-conditioning systems, and it needs a holistic and multi-disciplinary approach to include the broad environmental boundaries to fully understand the environmental consequences of their operation.
... The principle of operating the absorption chiller is similar to those for normal VCC. These 3 units (absorber, pump, and generator) are instead of VCC compressor (Srikhirin et al., 2001). ...
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The objectives of this study are to examine the use of the technology of Cooling Air by Solar Energy (CASE), which is used in air-conditioning applications to minimize the consumption of energy, as well as minimize CO2 emissions. The study also aims at providing an overview of different CASE technologies and analyzing the environmental feasibility of selected CASE technologies in Jordan. The methodology used involves a field study of one of the CASE technologies, which has been designed and developed in Jordan, to determine its technical feasibility. The environmental feasibility study has been done on the device used in this work in four scenarios. The results of the analysis of both energy and environmental feasibility have shown that the use of the CASE technology reduces greenhouse gases compared with Vapor Compression Chillers (VCC) that use electricity.Keywords: solar air-cooling; vapor compression chillers; greenhouse gases; energy analysisJEL Classifications: P18, Q40, Q43, Q51DOI: https://doi.org/10.32479/ijeep.11701
... It is interesting to understand how mature and available technology such as absorption refrigeration machines can replace compression machines in the future, to minimize greenhouse gas emissions, complying with the European political roadmap up to 2050. Remarkable studies show the state of the art of these technologies for refrigeration production (Srikhirin et al [29], Kin and Ferreira [30], Talbi and Agnew [31], and Kaynakli and Kilic [32]). More specifically, some authors have investigated the integration of absorption refrigeration machines with systems for supplying the heat necessary for their functioning as a solar source (Ferreira and Kim [33], Desideri et al [34], Ullah et al. [35]), showing how to reduce greenhouse gas emissions. ...
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Temperatures in the Mediterranean area have gradually risen in the last decades due to climate change, especially in the Italian Peninsula. This phenomenon has increased the cooling needs to ensure thermal comfort in buildings and, consequently, the use of refrigeration machines. Summer air conditioning is carried out mainly using compression machines powered by electricity supplied by the national network. All this contributes to the emission of climate-changing gases. To avoid this disadvantageous chain, compression machines could be replaced by absorption cooling systems powered by solar energy. The energy needs of the buildings in a time are directly proportional to the sum of positive differences between the outdoor air temperature and the indoor set point of the systems (equal to 26°C). The annual sum of hourly temperature differences defined above can be computed for each grid cell thanks to a numerical weather prediction model, namely the Weather Research and Forecasting model, that simulates the hourly temperatures on high-resolution computation grids and over fairly large extents. Maps of cooling consumption for buildings are thus produced. Choosing absorption solar energy-powered systems instead of vapor compression refrigeration systems leads to a drop in electrical energy consumption and therefore in emissions of greenhouse gases. In this work, different hypothetical scenarios of penetration of this technology have been considered. And the subsequent consumption of electricity withdrawn from the national grid has been estimated together with the reduction of greenhouse gas emissions.
... These machines work with four main components: a desorber, a condenser, an evaporator and an absorber, and require two fluids: an absorbent and a refrigerant. The choice of the absorbent-refrigerant couple is based on many criteria [1]- [3]. The working couples can be classified as a function of their refrigerant: NH3, H2O, alcohol, halogenated hydrocarbon and other mediums [4]- [6]. ...
Conference Paper
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As a key component of the absorption machines, this paper focuses on the absorber to review the different analytical and numerical approaches used to analyse the thermal, mass and hydrodynamic phenomena occurring in falling films for both smooth and wavy laminar regimes. As nowadays, researches used the Thermodynamic of Irreversible Processes (TIP) to identify, to locate and to quantify the entropy generation sources, this paper also presents results of the application of the TIP on theses absorber.
... Fig. 18 and Fig. 19 present the hourly generation of cooling by the thermal chiller when many small split ST are deployed in the CC mode to follow the electric load in the test location, without battery storage and with battery storage, respectively. It is seen from Fig. 18 one notes that this generating unit can be operated satisfactorily with low grade heat of temperature less than 100 ℃ to provide cooling [46][47][48], the increase in the capacity of the ST which will reduce the quality of the flue gas, will not strongly affect its performance. ...
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In this study, rule-based energy management strategies (EMS) based on the modifications of the traditional load following (LF) and circuit charging (CC) have been proposed and developed to effectively coordinate the operation of an integrated multi-carrier hybrid energy system. The proposed EMS aim to overcome some of the challenges of the traditional rule-based EMS and broaden their application to the management of complex energy systems. The study deploys a bi-level optimisation scheme to obtain the optimal number of system components that simultaneously minimises the cost, reliability and emissions, in the outer-loop and implements the rule-based EMS in the inner-loop. Also, the results of the optimal system have been simulated for a 48 h timespan, to investigate the effects of the proposed EMS on the Stirling back-up start-ups, battery storage limits, and generation of other energy vectors. The results indicate the deployment of split back-up and batteries minimise the commitment of the back-up, dumped power and emissions. However, the number of start-ups of the back-up increases appreciably by 15.34% and 36%, with the deployment of 2-split and 4-split Stirling, respectively in CC with battery storage. Correspondingly, the operational cost of the system rises as the number of splits increases, but only a slight change in the energy cost is observed, because of the significant reductions in the capacity of the green generators. Interestingly, the batteries record many duty cycles, store less energy and attain lower discharge limits as many small capacity ST back-ups are deployed. Other results demonstrate the additional capabilities of the proposed EMS in handling complex energy systems by the substantial increase in the generation of heating and cooling with increasing splits of the back-up and inclusion of batteries in the optimal system.
... The absorption system can work based on two processes, as explained by Srikhirin et al. [1]. In the first process, two vessels are connected, having a binary solution of a working fluid formed by one part of the refrigerant and the other absorbent, each in a container. ...
... Trombe and Foex [31] developed one of the earliest solar absorption chillers they reported a preliminary experiment with a pilot plant using NH3-H2O. Chinnappa [32] an extra rectifier should be added before the condenser to provide pure refrigerant [33]. A flat plate or evacuated tube solar collector is enough to get the required generator temperature. ...
Thesis
Solar energy has a great ability in cooling and air conditioning as the demand for cooling and air Conditioning increases worldwide. Absorption cooling cycles have the advantage of being environmental friendly and uses either solar or waste heat for cooling with very small electric power. In this thesis a mathematical model was developed using Engineering Equation Solver EES in order to perform an energy & exergy analysis of both single and double effect absorption system. The exergy analysis of the cycle had shown that the double effect absorption systems have several advantages in terms of coefficient of performance (COP) and exergetic coefficient of performance (ECOP) than the single effect absorption system. Results from simulations showed that COP and ECOP have values of 1.19 and 0.26 for the double effect cycle while for a single effect cycle COP and ECOP have values of 0.68 and 0.27, respectively. The exergy loss and exergy destruction for every component had been also calculated. The exergy destruction of both Evaporator and absorber represent about 50 % of the total destruction for both single and double effect. The required minimum generator temperature to operate the system had been evaluated. Analysis results showed that the optimum generator temperature decreases with the evaporator temperature and increases with the condenser temperature. Hence it is possible to determine the optimum generator temperature for various condenser-evaporator temperatures. An optimized function had been developed to determine the optimum operating conditions from the maximum COP point of view. Several runs were carried out using the TRNSYS simulation program on the proposed optimized system under different weather data of three Egyptian cities to investigate the performance of the system. The selected cities were Aswan, Cairo and Marsa Matrouh. Results from the proposed model showed that optimum generator temperature of the absorption chiller was not affected by the climate conditions, it also showed a huge improvement in terms of COP with a value ranging from 0.77 to 0.83 for single effect and from 1.32 to 1.5 for double effect, which is about 15:20 % enhancement.
... System-level modeling has been performed by various investigators for a range of capacities and configurations. It has been well established that increased system complexity will lead to improved coefficients of performance (COPs) [1][2][3][4][5]. Engler et al. [5] showed that maximizing heat recovery within an absorption system leads to improved system COPs. ...
Article
An investigation of the best ways to achieve optimal performance from a waste-heat-driven ammonia–water absorption heat pump over a wide range of operating conditions is presented. Waste heat from an 8-kWe diesel engine generator is recovered using an exhaust gas heat exchanger and delivered to the desorber by a heat transfer fluid loop. The absorber and condenser are hydronically coupled in parallel to an ambient heat exchanger for heat rejection. The evaporator provides chilled water for space-conditioning with a baseline cooling capacity of 2 kW. All heat and mass exchangers employ novel microscale geometries. A detailed thermodynamics model is developed to simulate performance and develop strategies to achieve the best performance in both cooling and heating modes over a range of operating conditions. These parametric studies show that improved coefficients of performance can be achieved by adjusting the coupling fluid temperatures in the evaporator and the condenser/absorber as the ambient temperature varies. With the varying return temperatures, the system is able to provide the 2-kW design cooling capacity for a wide range of ambient temperatures.
... 13 The chemical and thermodynamic characteristics of the working fluid significantly affect AR systems. 14 The AR systems may be powered by a variety of energy fuels, comprising fossil plus renewable energies and excess heat. ...
Article
An innovative polygeneration structure is proposed based on the oxyfuel power generation (OPG) system integration with carbon dioxide (CO2) capture, CO2 power system, NH3/H2O absorption refrigeration (AR) unit, and organic Rankine power (ORP) cycle. In this regard, a combination of solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) is applied to produce the required pure oxygen for the OPG system. The proposed system simultaneously produces 7204 kmol/h hot water, 149.3 kmol/h liquid CO2, and 102.4 MW power in different cycles. Energy and exergy analyses are performed to evaluate the proposed system. The thermodynamic modeling and simulation of power and refrigeration cycles are performed in Aspen HYSYS software, and verified with high accuracy. Also, an integrated SOEC/SOFC simulation has been done using developed computer code in MATLAB programming. The overall electrical efficiency and the AR coefficient of performance are calculated at 31.55% and 0.4803, respectively. In addition, the thermal and exergy efficiencies of the proposed system are 65.10% and 70.60%, respectively. The exergy analysis indicates the combustion chamber's highest exergy destruction with a share of 35.26%. In the next rank, the heat exchangers (26.42%) and turbines (16.98%) have the largest share of degraded exergy among other devices. The sensitivity analysis demonstrates that when the oxygen productivity increases from 9050 to 9275 kg/h, the electrical efficiency in the total integrated structure and the liquid CO2 productivity rise to 34.57% and 6480 kg/h, respectively. Also, by increasing the natural gas entering the proposed structure from 2375 to 2550 kg/h, the exergy efficiency of the structure increases to 71.19% and its thermal efficiency decreases to 58.70%. A novel polygeneration system to produce power, liquid CO2, and heat is introduced. Integration of oxyfuel/ORC/CO2 power plants and absorption cooling unit is applied. A solid oxide fuel cell/electrolyzer technology is used to produce pure oxygen. The electrical and exergy efficiencies of the overall system are 31.55% and 70.60%. The exergy analysis indicates the combustion chamber has the highest exergy destruction.
... Although H 2 O/LiBr shows excellent performance in absorption cycles, crystallization and corrosion are the most severe problems preventing broader applications. For the working pair NH 3 /H 2 O, the drawback of toxicity and difficulty of separation limit its utilization [6]. Hence, searching for high-performance and reliable working pairs has been of great importance to promoting broad applications of AHT systems. ...
Article
Absorption cycles have attracted considerable attention for utilizing renewable energy and waste heat to achieve carbon neutrality. Absorption Heat Transformers (AHTs) using Ionic Liquids (ILs) as absorbents show great potential in avoiding crystallization and corrosion problems. To screen the optimum candidate for AHT systems, a multi-scale computational screening method by Computer-aid Molecular Design (CAMD) is applied, and its feasibility is verified with high accuracies. For 18 typical operating conditions, the optimum IL molecules are identified from 26,360 candidates generated by the CAMD method. The relationship between the AHT cycle performance and IL molecular structures is systematically analyzed to clarify the significant IL structural factors that affect the Coefficient of Performance (COP) primarily. The correlation analysis shows that IL molecules containing main-cations ([C1N], [C1P], or [C1S]), anions ([Br], [Cl], [Lac], or [OAC]), and sub-cations with short alkyls have the highest potential to improve the cycle performance. The optimum ILs screened by the multi-scale CAMD method perform better than the currently investigated ILs, even outperforming LiBr in some specific unfavorable conditions. At an absorber temperature of 120 °C, heat source temperature of 75 °C, and condenser temperature of 25 °C, [C,1,1,1,1,OHN][OAC] yields a COP of 0.458, much higher than LiBr (0.419). By distinguishing the applicable and inapplicable operating conditions, the comparison shows that the applicable operating ranges of the selected ILs are wider than that of LiBr due to their crystallization-free nature. To accelerate the molecular design process in various operating conditions, eight Machine Learning (ML) algorithms are integrated to predict the cycle performance based on molecular descriptors with less computation cost. To verify the accuracy of the proposed multi-scale CAMD approach, experimental results of [C1,1,2,2,OHN][Br], one of the best-performing ILs, are compared with the simulation results of the multi-scale CAMD. The agreement between experiment and simulation illustrates the high accuracy of this screening method. The multi-scale CAMD approach achieves the high-throughput computational screening of optimum ILs for high-efficiency absorption systems.
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Desalination and cogeneration technology for coastal thermal power plants can address severe lack of freshwater and clean heat sources in northern China. However, achieving high productivity, high efficiency and low cost simultaneously is a great challenge for the practical applications of both technologies. In this study, a novel combined heat and water (CHW) system is proposed that combines a district heating system with a freshwater supply system. Compared with previous studies, this study further improves the system efficiency, production capacity and reduces the cost. A practical demonstration project was established at a coastal nuclear power plant in northern China, including a heat-water co-production (HW-CoP) device, a heat-water co-transport (HW-CoT) pipeline and a heat-water separation (HW-SeP) device. A HW-CoP unit can produce 5 tons/hour of freshwater at 95 °C, which fully demonstrates the feasibility and verifies the practical performance of HW-CoP technology. Then, HW-CoT can reduce the heating transportation cost by 40% compared with the conventional heating mode and HW-SeP can further increase the heating supply capacity of the system by 50% compared with the plate heat exchanger. The results show that the new CHW system can consistently produce purer hot freshwater, which means the technologies are fully feasible in practical. Meanwhile, the novel CHW system has an economic heating radius of even more than 350 km compared to gas-fired boilers. In the future, through the use of the new CHW system, the waste heat from coastal power plants in northern China can meet the heating needs of a total of 5 billion square meters of buildings in cities 200–300 km from the coastline and supply more than 3.5 billion tons of freshwater per year, which has a broad application prospect. This paper can be used as a basis to further improve and optimize the district heating system and freshwater supply system in coastal areas.
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Advances in Phyto Chemistry, Textiles, Renewable energy and Industrial Growth
Article
This paper presents the numerical simulation of an efficient ammonia-water single-stage absorption chiller integrating a new combined desorber, able to produce and purify the refrigerant vapor. An experimental campaign was conducted on the pilot plant by varying the main operating parameters, namely the temperatures of external sources and the mass flow rate of the working fluid. Direct experimental measures were analyzed and indirect calculation of other physical quantities was used for tuning of the numerical models. First, a simplified model of the cycle was developed, based on fixed effectiveness and pinch temperatures. Absolute values and tendencies outside nominal working conditions were not sufficiently accurate to predict the performance of the cycle even at the small scale, so more accurate modeling was undertaken. Accordingly, components were characterized by effectiveness, modeled using three operating parameters: the Jakob number (Ja), the number of transfer units (NTU) and the energetic ratio (Ren). The small average errors for calculated effectiveness confirm that these parameters are well suited for the application studied. Global cycle model results showed errors compared to experimental results below 6 % for the COP and 15 % for the cooling power output. The tuned model was used to perform a parametric analysis on the dimension of the components, highlighting the performance improvements/reductions obtainable by increasing/decreasing their size. The use of dimensionless parameters makes this approach well suited for analysis at larger scales of industrial interest, the development of more complex or combined cycles as well as to perform techno-economic or exergo-economic analysis.
Article
3,3,3-Trifluoropropene (R1243zf) and isobutane (R600a) are considered as prominent environmentally-friendly refrigerants, and acetate-based ionic liquids are potential absorbents used in absorption refrigeration cycles. In this work, the dissolving capacities of R1243zf and R600a in one of the acetate-based ionic liquids (1-butyl-3-methylimidazolium acetate, [BMIM][Ac]) were investigated. The measurements were based on isochoric saturation method and the experimental temperature range was from 283.15 K to 343.15 K. The non-random two liquid (NRTL) model and Krichevsky-Kasarnovsky (K-K) model were utilized to model the experimental results, and both models exhibited reasonable deviations. On the basis of solubility data and correlation results, the Henry’s law constants and the mixing thermodynamic properties (mixing enthalpy, mixing entropy and Gibbs energy) for the two mixtures were determined. In addition, the dissolving abilities of R1243zf and R600a in [BMIM][Ac] were compared with the reported results of R1234yf in the literature.
Article
Regarding the working fluids of absorption refrigeration systems, compared with the binary ammonia/water or ammonia/salt solution, the ternary ammonia/lithium nitrate+water solution has some advantages including small viscosities, good heat-transfer efficiency and low crystallization risk. In this paper, four kinds of NH3/LiNO3+H2O solutions with different water component proportions are selected as working fluids, which is No.1(9.6%)<No.2(18.6%)< No.3(27.6%)<No.4(36.9%), and the experimental performance evaluation was conducted on a prototype of absorption refrigeration system driven by exhaust heat. First, experimental tests were carried out with varying operating conditions to evaluate their influences on performance parameters; the detailed experimental parameters operating with No.2 and No.4 working fluids are presented, and the reasons of the experimental results are explained. Then, the experimental results of four ternary working fluids and binary working fluid were compared and analyzed to evaluate the influences of water mass fraction. Compared with NH3/LiNO3, the cooling capacities of No.1, No.2, No.3, No.4 increased by 10.6%, 17.8%, 24.8%, 26.4%, respectively; the logarithmic mean temperature difference of the solution heat exchanger decreased by 1.2K, 2.0K, 2.6K, 3.9K, respectively. The comparison results indicate that, for the working fluid with larger water mass fraction, it has better heat and mass transfer characteristics, the system can produce larger cooling capacities and has lower required driven temperatures of heat sources, but the overall coefficients of performance hardly changed with the water mass fraction. The experiments and comparison results provide significant references in practical applications for the selection of working fluids of the absorption refrigeration systems.
Article
This study focuses on the adsorption heat pump cooling performance enhancement. The corrugated heat exchanger (HEX) has been employed in recent years owing to its excellent heat transfer; however, its filling method require improvement. Therefore, a filling method called dip-coating method is introduced to improve its heat transfer and packing density. The dip-coating method is adapted to accommodate the Wakkanai siliceous shale composite adsorbent, and two types of adsorbent filled-HEX (ad-HEX), i.e., the dip-HEX and dip-filled-HEX, are compared with the conventional ad-HEX of the filled-HEX. The dip-HEX comprises a few mass transfer channels and has a packing density similar to that of the filled-HEX. Meanwhile, the dip-filled-HEX exhibits a 30% higher packing density compared with the filled-HEX. A basic performance experiment is performed, and the results indicate that the dip-HEX outperforms the filled-HEX owing to its higher coefficient of performance (COP) and specific cooling power (SCP). The dip-filled-HEX exhibits a slightly lower SCP than the filled-HEX; however, it exhibits the highest COP among three types of ad-HEXs. Subsequently, mass recovery is applied to enhance the cooling performance. In a typical mass recovery period of 10 s, the COP and SCP of the dip-HEX increases to 0.46 and 0.74 W/g, respectively.
Article
This study proposed a novel micro-scale falling film absorber with its experimental data on a complete absorption refrigeration system. Micro-scale liquid-distributor has been carefully designed and manufactured by special techniques. An experimental system for absorption refrigeration has been established to test the novel absorber. This unique absorber applies ammonia/lithium nitrate as working pair which is considered to own application potential for small-scale absorption refrigeration units. Experimental analysis has been done under various of working conditions for making contrasts. Relationships between significant working parameters and absorption parameters have been discussed. Under series of working conditions, absorption rates ranging from 1.2 to 2.6×10⁻³ kg/(m²·s) have been obtained. Approach to equilibrium factor which characterize the perfection of absorption process ranges from 0.5 to 0.98 while absorption ratio ranges from 0.02 to 0.12. With the increase of Reynolds number from 3 to 52, the mass transfer coefficient rises from 12 to 98×10⁻⁶m/s and Sherwood number ranges from about 30 to 60 respectively. According to the analysis, absorption pressure potential and cooling water temperature are two major factors which enhance the absorption intensity. Absorption pressure potential and inlet solution subcooling degree owns nearly linear relationship with parameters such as absorption rate, absorption ratio and approach to equilibrium factor. However, normalized absorption rate and approach to equilibrium factor gain negative correlations with absorption pressure potential and Reynolds number respectively. Effects of inlet solution flowing features on absorption performance are distinguished under different working condition series. In general, solution flowing intensity inside absorber is a positive factor for absorption process. All the experimental results reveal that, this micro-scale falling film absorber has its priority on absorption perfection and absorption rate for per unit of mass transfer area. Compact structure makes it more valuable for further research and application on small-scale absorption refrigeration unit with the working pair of ammonia/lithium nitrate.
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Advances in Phytochemistry, Textile and Renewable Energy Research for Industrial Growth
Article
The Data Center (DC) and High-Performance Computing (HPC) sector is increasingly becoming one of the single largest energy consuming sectors in the energy system and the demand for new DCs is growing with the rising use of cloud-based services, social media and internet usage in general. DCs and HPC clusters employ energy intensive cooling in order to dissipate the generated heat from the Information Technology (IT) equipment. Conventionally, the cooling is almost exclusively done by air-based systems; however, the use of liquid based cooling has shown potential to increase computational efficiency of the systems and decrease cooling needs by operation above the free cooling limit. Furthermore, the liquid coolant can operate at higher temperatures allowing high temperature waste heat recovery. In addition, load shifting through Latent Thermal Energy Storage (LTES) will allow the non-controllable waste heat resource to be stored seasonally, thereby granting the ability to cover larger District Heating (DH) loads. In this work, a decision support model is developed that will take basic information regarding a HPC cluster or DC as inputs. The decision support model will provide a parameterized output that shows different configurations and design parameters that can be utilized for the system. The main outputs includes yearly energy savings, yearly cost savings and efficiency gains through the Power Usage Efficiency and the Energy Reuse Efficiency. The decision support model is demonstrated in a Danish case study. Electricity savings between 8.14 % and 10.8 % of the total cluster electricity consumption and a waste heat recovery potential of 85 MWh/year to 576 MWh/year are obtained. It is shown that if the DH covered is needed to be self-sufficient the configuration would require an LTES with PCM mass of 500 kg, but system configurations that operate as an addition to an existing local heating source shows increases in yearly energy savings of 332 % compared to self-sufficient configurations. The goal of the decision support model is to assist the design of future waste heat recovery applications through selection of system parameters including coolant temperatures, energy storage design parameters, DH supply temperatures and DH load coverage from the DC or HPC cluster.
Article
Heat capacity and temperature matching between the heat sources and energy system is of vital importance to improve energy efficiency, especially in occasions with multiple temperature-distributed heat sources. In this paper, an improved ammonia-water absorption refrigeration system with additional intermediate-pressure generator and absorber is proposed, aiming at recovering two kinds of heat sources with different grades. To match the heat capacity of two sources, solution distribution to the high- and intermediate-pressure generator can be adjusted. Moreover, heating areas of the two generators are extended from the reboilers to the stripping sections, in order to improve the heat utilization ratio. Simulation study shows that as the solution split ratio to the intermediate-pressure generator increases, the capacity for recovering low-grade heat sources is improved. The coefficient of performance of the proposed system is 5% higher than that of the modified vapor exchange system within a large range of the intermediate pressure. Under the baseline working condition with evaporation temperature of -15°C and condensation temperature of 31°C, a significant increment in exergy efficiency is achieved by the proposed system, which is 32.6% and 56.5% higher than that of the conventional single-effect and conventional vapor exchange system, respectively.
Article
Absorption refrigeration systems (ARS) are thermally-driven technologies used to generate cold utilities. When the working pair H2O/LiBr is used in ARS, severe crystallization and corrosion problems may arise. Aiming to avoid these issues, investigations concerning ionic liquids (ILs) to replace LiBr has been conducted. This paper presents a thermodynamic performance analysis for a single-effect ARS using water and two 1-ethyl-3-methylimidazolium-based ionic liquids as absorbents: 1-ethyl-3-methyl-imidazolium ethylsulfate ([EMIM][EtSO4]) and 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMIM][BF4]), both not yet widely explored for this purpose. Simulations were performed using Engineering Equation Solver (EES) software. Results have shown that H2O/[EMIM][BF4] mixture is clearly unattractive. Particularly at lower temperatures in the absorber and condenser and higher temperatures in the evaporator, H2O/[EMIM][EtSO4] mixture presented COP and exergetic efficiency (ηex) profiles relatively close to those of the conventional H2O/LiBr. For an optimized case, COP and ηex were 8.2% and 19.2% greater for H2O/LiBr than for H2O/[EMIM][EtSO4] which has presented values of 0.764 and 0.114 respectively. For ηex this difference tended to decrease at higher temperatures in the generator, turning H2O/[EMIM][EtSO4] mixture competitive with H2O/LiBr at certain conditions, mainly in view of LiBr crystallization risk. The main contributions of this work regarding ARS studies is performing all the following studies simultaneously: sensitivity analysis, thermodynamic optimization and crystallization risk analysis also considering working pairs that still present some gaps in the literature.
Article
In the current work, thermodynamic examination for cogeneration of electricity and cooling based on a polymer exchange membrane (PEM) fuel cell was carried out. To the waste energy in the fuel cell, an absorption refrigeration unit is employed in two modes with ejector and without ejector. This system includes a PEM-FC, an absorption refrigeration unit, a hydrogen storage tank, an ejector, and an air compressor. The produced thermal energy in the fuel cell is received entirely by a working fluid and is given to the absorption chiller generator. The system simulation was carried out from two perspectives of energy and fuel saving. Findings showed that the energy efficiency of the combined cooling and power (CCP) unit and the CCP system equipped with the ejector (CCP-E) was 63.72% and 78.33%, respectively. It indicated that adding the ejector to the system increases the energy efficiency of the system by 23%. The fuel economy percentages of the CCP system and CCP-E were 44.43% and 45.9%, respectively. The results also showed that adding the ejector in the refrigeration system increases the system performance by up to 44%. The presence of the ejector causes the working fluid flow in the evaporator to increase with the suction of the secondary flow, and the cooling capacity increases significantly. Moreover, with increasing generator and evaporator pressure, the suction ratio of the cooling system equipped with the ejector decreases and increases, respectively.
Article
In rural regions, freshly harvested fruits and vegetables cannot be precooled in time, resulting in enormous economic losses. In this paper, a novel solar-driven compression-assisted desorption chemisorption refrigeration/cold energy storage system for refrigerated warehouses is proposed. Compression-assisted desorption allows flexible adjustment of the desorption temperature of composite sorbent to actively adapt to the instable solar hot water temperature. The desorption reaction can increase compressor suction pressure, which helps to reduce power consumption and improve the coefficient of performance (COP). The chemisorption energy storage module completes its regeneration by day and releases cold energy to refrigerated warehouse at night. This module can change the refrigerating temperature depending on the type of fruits and vegetables, superior to the phase change cold storage technology. Therefore, the system can effectively overcome the problems caused by the instability and intermittency of solar energy. According to the performance test results of the reactor, the COP is 5.5 at a hot water temperature of 90 °C, an evaporating temperature of −10 °C and a condensing temperature of 40 °C, which is higher than the 2.6 of the R404A vapor-compression system. Additionally, its refrigerating capacity can be changed by adjusting the number of reactors operating inside the sorption bed, ranging from 1.52 kW to 5.21 kW. Analysis results indicate that the system can efficiently and consistently meet the precooling needs of freshly harvested fruits and vegetables during the picking season. The payback period is less than one year, considering the economic benefits it brings. Ultimately, the novel system is suitable for refrigerated warehouses in sunny rural regions.
Article
Latent heat based thermal energy storage technology is quite promising due to its reasonable cost and high energy storage capacity. This technology is partially developed. The accelerated transition from non-renewable to renewable energy sources have attracted researchers to shift their focus towards demonstrating thermal energy storage utilizing latent heat at commercial level. Phase change materials utilizing latent heat can store a huge amount of thermal energy within a small temperature range i.e., almost isothermal. In this review of low temperature phase change materials for thermal energy storage, important properties and applications of low temperature phase change materials have been discussed and analyzed. Thermal energy storage technologies are compared in terms of technology readiness levels. Various techniques to improve the heat transfer characteristics of thermal energy storage systems using low temperature phase change materials have also been discussed. Moreover, the use of computational techniques to assess, predict and optimize the performance of the latent energy storage system for different low temperature applications is also presented. In this article, researchers and domestic energy management sector will find comprehensive guidelines for the performance improvement and technology selection for energy management via thermal energy storage.
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Proceedings of the International Conference of Phytochemistry, Textile and Renewable Energy for Sustainable development (ICPTRE 2020), August 12-14, Eldoret, Kenya
Conference Paper
In recent years, research on thermal comfort in the building sector has increasingly focused on renewable energy as an alternative energy. TRNSYS software is used for modeling two types of air conditioning systems. A photovoltaic wage air conditioning system that refers to all air conditioning techniques using electricity produced by photovoltaic panels. The second thermal energy absorption system produced by a vacuum tube solar sensor. In this work, were compared the performance of solar thermal air conditioning and solar photovoltaic air conditioning under the influence of a different conditions, temperature, surface area, auxiliary energy, yield, ring fraction and cost. The results shows that the total energy consumed in the mechanical compression system is very high and up to 170%, compared to the absorption system during the hot season.
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Internal combustion (IC) engines are the major source of motive power in the ships. one of the improvable method is getting waste heat energy of diesel engines and reusing it to produce electricity, cooling and heating. in this study a combined electricity, cooling and heating system based on regenerative Rankine cycle with open feed water heater and absorption refrigeration cycle is offered to recover the waste heat of engine coolant and exhaust gas to generate electricity, cooling and heating. maximum electricity output is 3471 kW and cooling output relevant is 17601 kW. effect of evaporator temperature, condenser temperature, extraction pressure are studied to optimize electricity produced with rankine cycle.
Article
Multi-carrier energy networks (MCENs) have become an engaging research topic during the past few years. Due to the high penetration of renewable energy sources in transmission grids along with the rapid installation of cogeneration units, the interdependency between various energy carriers is increased, and the performance of an individual energy network is exceedingly related to the other ones. Thus, it is inevitable to consider an integrated viewpoint towards the analysis and assessment of energy networks. This paper presents a comprehensive review on MCENs by concentrating on the major contributions in the recent years. An overview on the energy hub concept and its most popular components used in the literature is provided to identify the less utilized devices in this area for further investigations. Then the most popular problems of MCENs are categorized besides their relevant techniques and solutions reported in the literature, focusing on different schemes and with various perspectives. This paves the way for proposing and implementing other well-developed or novel methodologies to cope with these problems. Finally, the future trends of these integrated networks and their main concerns and challenges are discussed for further investigations.
Article
Absorption machines are frequently used for cooling and heating. However, they must be improved to achieve high performance at a lower cost. Being a key component of these machines, this paper focuses on the absorber and specifically on falling film absorber configuration due to its compactness and simple geometry. This paper reviews the different analytical and numerical approaches used to analyze the thermal, mass and hydrodynamic phenomena occurring in falling films for both smooth and wavy-laminar regimes. It shows the significant progress made since 2000 in terms of mathematical models developed and coupling effect resolution. . Research using thermodynamics to identify, locate and quantify the entropy generation sources in falling film absorbers is also presented.
Article
Lithium bromide (LiBr) corrosion on austenitic 316 stainless steel (AISI 316) and copper will largely determine the overall performance of refrigeration compression systems. In this work, the corrosion behavior of AISI 316, copper, and brazed joint was studied in LiBr solution at different temperatures by using the polarization curve and electrical impedance spectroscopy. The morphology and chemical composition of the samples before and after corrosion were characterized to elucidate the corrosion mechanism. The passivation film of AISI 316 stainless steel is more prone to breakdown as the temperature increases, and the corrosion resistance of copper and brazed joint also decreases with the increasing temperature. Zero-resistance ammeter technology was employed to analyze the effect of temperature on galvanic corrosion. The degree of galvanic corrosion increases with temperature for all galvanic pairs (AISI 316-Cu, AISI 316-brazed joint, and Cu-brazed joint). For AISI 316-Cu and AISI 316-brazed joint galvanic pairs, AISI 316 functions as the cathode, while copper or brazed joint serves as the anode. For the Cu-brazed joint pair, the brazed joint is preferred to be corroded at room temperature, whereas at 50 and 75 °C, copper corrosion occurs in priority.
Article
Conventional air conditioning (AC) systems provide simultaneous sensible and latent cooling. This requires air to be cooled below its dew point temperature resulting in low energy efficiency, particularly at low sensible heat ratios where supply air might be reheated. Furthermore, conventional ACs may not be able to simultaneously control the indoor temperature and humidity. These issues have stimulated the research community and industry to pursue advanced cooling technologies like separate sensible and latent cooling (SSLC) technology. This review paper comprehensively discusses the features of different SSLC configurations. It reviews the state-of-the-art of electrically and thermally driven configurations presented over the past two decades using the primary coefficient of performance (COPp) to compare their performance. This review paper also outlines the challenges and opportunities facing SSLC technologies through indicative cost analysis, typical maintenance required, and future energy mixes effect on COPp. It is concluded that the vapor compression cycle (VCC) is more suitable for handling the sensible load, while the desiccant wheel (DW) is a good candidate for handling the latent load. However, DW needs more development at the component and system level for the SSLC to compete with conventional AC systems. Moreover, SSLC is still a developing technology that can benefit from additional prototypes evaluation from the energy and economic point of view to accelerate its commercialization. Finally, it was found that the increased penetration of sustainable energy resources would further support the lead of electrically driven cooling technologies based on the VCC.
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Solid waste management is among the environmental challenges facing many industries in the world today. Biogas production is one of the most cost-efficient renewable energy technologies that use biodegradable wastes as feedstock. Furthermore, it is one of the methods for reducing greenhouse gas emission. Cotton Yarn Wastes (CYW) is among the biodegradable wastes that are commonly managed by dumping onto the open land or disposing in sanitary landfills where they undergo anaerobic decomposition. However, CYW could be used as substrate to generate energy in the form of biogas that can be utilized in other activities like powering textiles production. The aim of this study was to investigate the use of CYW as a substrate for biogas production using anaerobic batch reactor. The experiment was carried out in reactors of two-liter capacity. The CYW and inoculum were characterized before and after digestion. The CYW contained 93.18% total solids, 82.48% total volatile solids and 6.82% moisture content while the respective values for digested sludge were 21.61%, 23.61% and 78.38%, respectively. The carbon to nitrogen (C/N) ratio of inoculum was 20.5, which is in the suitable range to keep the anaerobic digestion in a stable condition. However, the CYW had high carbon content; resulting in a C/N ratio of 42.5. The effect of TS concentration at different ratios of CYW on biogas volume produced was investigated. The reactors loading was differentiated using a mixture with concentration corresponding to R1 (1:1), R2 (1:1.5), R3 (1:2), R4 (1:2.5), R5 (1:3), R6 (1:3.5), R7 (1:4), R8 (1:5), R9 (1:6), and R10 (1:10) on TS content basis i.e. 50%, 40%, 33%, 28%, 25%, 22%, 20%, 18%, 14%, and 10% respectively. The total biogas yield was 6307 mL, 6519 mL, 6711 mL, 7178 mL, 4878 mL, 3868 mL, 3720 mL, 3306 mL, 1164 mL, and 932 mL respectively after 36 days. The results indicated that biogas production increased with increase in TS content. The ratio that provided 28% of TS content had the highest biogas yield. The average reduced TVS at the end of digestion was 88.49%. The results of this test indicated that CYW is a suitable substrate for AD due to its high biodegradability. Therefore, the reactors should run at 28% TS, for maximum biogas generation.
Article
Poly-generation systems have attracted a lot of attention due to the increment of efficiency as well as reducing energy penalties, costs and pollutants. Extensive research has been done on these systems in recent years. The current work is done with the aim of simulating an environmentally friendly poly-generation system in the power plant of Shahrood city in Iran. In this way, a poly-generation system is simulated in Aspen Plus software which consists of: I) a gas turbine (GT) for power generation with natural gas fuel of Shahroud power plant, that its flue gas is utilized to supply heat for other cycles and streams, II) a sorption-enhanced chemical looping reforming (SECLR) which simultaneously generates H2 by steam methane reforming (SMR) and uptakes produced CO2 by calcium adsorbent during the carbonation/calcination reactions. In this section, there is also a chemical looping combustion (CLC) based on redox reactions of Ni/NiO to provide heat of the reactors, III) a NH3/H2O absorption refrigeration system to yield the cooling demand, IV) a high-pressure steam generation unit and V) a MEA-based post-combustion CO2 capture unit (PCC) for flue gas. In this system, an attempt has been made to prevent heat loss by internal streams, especially gas turbine exhaust gas, so that energy loss is minimized. Moreover, environmental issues are also prioritized to reduce the CO2 emissions as much as possible. The proposed process is capable of producing 133.3 MW power, 9.875 MW cooling, 50 kg/s high-pressure steam and 0.384 kg/s hydrogen. The mass flow rates of CO2 captured in the SECLR and PCC sections are 2.6 kg/s and 15.35 kg/s, respectively. Moreover, the total energy efficiency of the integrated system is 68.74%. Ultimately, a sensitivity analysis was performed to identify the key parameters and their influence on the process performance.
Article
Experiments in the 1700s eventually led to the invention of absorption heat pumps. Now these pumps are gaining popularity because they can reduce fuel consumption and protect the stratosphere from chlorofluorocarbon refrigerants. Two basic types of heat pumps are common today. One is the electric pump, which is, more precisely, a vapor compression heat pump. The other is an absorption heat pump (AHP). The key thermodynamic difference between them is the energy input required to drive the cycle.
Article
This paper presents an absorption system design process that relies on computer simulations that are validated by experimental findings. An ammonia-water absorption heat pump cycle at 3 refrigeration tons (RT) and chillers at 3.3 RT and 5 RT (10.5 kW, 11.6 kW, and 17.6 kW) were initially modeled and then built and tested. The experimental results were used to calibrate both the cycle simulation and the component simulations, yielding computer design routines that could accurately predict component and cycle performance. Each system was a generator-absorber heat exchange (GAX) cycle, and all were sized for residential and light commercial use, where very little absorption equipment is currently used. The specific findings of the 5 RT (17.6 kW) chiller are presented. Modeling incorporated a heat loss from the gas-fired generator and pressure drops in both the evaporator and absorber. Simulation results and experimental findings agreed closely and validated the modeling method and simulation software.
Article
This paper presents the results of a novel corrosion inhibitor that exhibits improved protection of carbon steel over the inhibitors currently in practice. This inhibitor, formulated in 65 weight percent lithium bromide solution, offers excellent corrosion protection to carbon steel. Corrosion rates were determined using autoclave coupon testing. The corrosion rate in the 300°F to 450°F range was found to be low (1 to 4 mils per year), and the product also showed very low hydrogen generation (0.03 mg/in.2 of carbon steel per week). The metal was protected with a stable and adherent film.
Article
The electrochemical polarization method was used to study the inhibitive action of LiOH, Li 2CrO 4, and BTA, either individually or in different combinations. Afterwards, weight-loss tests planned by orthogonal arrays were carried out to find the optimum condition for the minimum corrosion rate for copper and mild steel in LiBr solution. The results from both polarization and weight-loss tests were consistent for each other in this study. The optimum condition predicted by the orthogonal-array experiments for the minimum corrosion rate is found out by adding 1.5 g/L LiOH, 4.5 g/L Li 2CrO 4, and 100 mg/L BTA, whose efficiency of inhibition is about 83% for copper and 99% for mild steel.
Article
Absorption/compression cycles, also known as vapor-compression cycles with solution circuits, have been known in the literature for about 100 years. The first theoretical investigations were carried out by Altenkirch in 1950 and indicated a large energy-saving potential. Based on this potential and the additional need to replace the ozone-depleting chlorofluorocarbons (CFCs), research activities in the absorption/compression technology have increased rapidly since 1980 and several different experimental plants have been built. This paper gives a detailed overview of the research activities during the last 15 years. More than 40 papers have been reviewed for this purpose. Several different cycle configurations, which have been part of these research activities, are explained in greater detail. The choice of cycle components, i.e., the design of the heat exchangers and compressors, and the choice of working fluids are evaluated. Although several large-scale experimental plants have been operated, there is still considerable work to be done before the absorption/compression technology can be considered a viable alternative solution to the vapor-compression technology.
Article
The generator-absorber heat exchange (GAX) cycle is an absorption heat pump cycle that appears to offer the best potential for an efficient, gas-fired absorption heat pump for residential applications. The GAX cycles under development use the same ammonia-water working fluids and have many of the same components and functions as previous gas-fired absorption air conditioners, but with increased heat recovery and a higher coefficient of performance (COP). The distinguishing feature of the GAX cycle is the unique way that heat recovery is accomplished within the cycle. In this paper, the authors show how a pinch-point analysis technique can be applied to illustrate the operation of a GAX cycle and to highlight its capabilities. Pinch-point analysis, while not commonly used in the heating, ventilating, and air-conditioning (HVAC) industry, is commonly used in the chemical process industries, where internal heat recovery is a key aspect of process design.
Article
A project to review the properties of aqueous solutions of lithium bromide currently published by ASHRAE in the Fundamentals and Equipment Handbooks for the purpose of publishing data consistent with that used by industry in future handbook editions is described. All of the major manufacturers of lithium bromide absorption equipment in the United States participated by supplying their properties data. The review compared vapor pressure and enthalpy data and the sources of the data submitted. A Duhring chart that shows a good correlation with all the data cited has been presented in both English and SI units. An enthalpy-concentration diagram has been constructed that is thermodynamically consistent with the Duhring chart. It is shown in both English and SI units. Means of calculating enthalpy have been described as they apply to any refrigerant-absorbent combination where water is the only volatile constituent. Simple steam table equations, applicable for programmable calculator use, have been developed.
Article
This paper analyzes combined heat and mass transfer during the absorption of water vapor into a lithium bromide-water (LiBr-H2O) liquid film and develops a transient modeling method for a rotating absorber. A horizontal cylinder within a cylinder-type heat exchanger was used. While the outer cylinder is held stationary, the inner cylinder is rotated at an appropriate speed to enhance heat and mass transfer during the absorption process. The effects of the length of the cylinder, diameter of the inner cylinder, clearance between the two cylinders, and angular velocity on the absorber performance were investigated. The results show that the absorption rate decreased with elapsed time for a given angular velocity. Changing the length had a more significant effect in short cylinders than in long cylinders. The time required to absorb all the initial vapor was strongly affected by the diameter at a low angular velocity. The effect of clearance on the time required to absorb the vapor was more considerable at a narrower clearance than at a wider clearance. The optimum angular velocity exists for both thermal and geometric conditions of the rotating absorber.
Article
Absorbent solution film flowing over a cooled horizontal tube is a common configuration for absorption-type chiller units. Here a physical model is presented to analyze the absorption phenomena on the basis of various interactions between the parameters and boundary conditions involved in actual situations. The boundary layer assumptions are used for the transport of momentum, energy, and species in an assumed laminar flowing film. The results by the finite-difference method for a water-LiBr solution are discussed with the aid of contour lines and profiles for various conditions. The results show that (1) for larger flow rates, the heat transfer coefficient improves with the increase of tube diameter, whereas for smaller flow rates, the heat transfer coefficient is large, and (2) an optimum flow rate for a particular tube size can be estimated on the basis of flow rate and total mass flux relation.
Article
This paper develops a model for design of a rectifier in generator-absorber heat exchanger (GAX) heat pump systems with an ammonia-water solution pair. The objectives of this paper are to provide further understanding of the rectification process in ammonia-water systems and serve as a design tool for the rectifier using a stable computation method. Simultaneous heat and mass transfer analysis is performed for the rectification process. Three different geometric configurations of the rectifier, namely, vertical fluted tube, confined cross flow with fluted tube, and coiled smooth tube, are considered in this paper. The effects of the temperature difference between interface and bulk vapor and heat transfer coefficients in each region on the rectifier size are investigated. The importance of the composition of rectifying vapor, z, is studied. The results show that the temperature difference between the interface and the bulk vapor region should be minimized to obtain a rectifier of small size and a high coefficient of performance (COP). During the rectification process, the composition of rectifying vapor should be lower than the liquid concentration, i.e., z < x1. The heat transfer coefficient in the vapor region has a much more dominant effect on the rectifier size than that in the liquid and the coolant regions. Mass transfer has a more significant effect on the rectifier size than heat transfer.
Article
This paper develops a generalized design model using combined heat and mass transfer analysis for components used in absorption heat pump systems. The model can be applied to the design of an absorber, desorber, rectifier, condenser, or evaporator in NH3-H2O absorption heat pump systems. The physical significance of the ammonia composition in the absorbing/desorbing vapor, z, was studied. A composition map was generated by solving the diffusion and mass balance equations simultaneously for each component. It was found that the ammonia concentration in the absorbing/desorbing vapor cannot be found using only the liquid concentration or vapor concentration but must be determined using combined heat and mass transfer analysis. The composition of ammonia, z, should be z < x1 for the rectifier, x1 < z < xvb for condensers, xvb < z for absorbers, xvi < z for desorbers, and x1 < z < xvi for evaporators. The results show that the mass transfer of ammonia and water is in the same direction for the rectifier, evaporator, and condenser, while it may be in the opposite direction for the absorber and desorber. The generalized design model developed in this paper can be used to investigate the effects of variable parameters, such as the heat transfer coefficient in each region, the vapor velocity, and the temperature deviation from the equilibrium, on the performance of each component.
Article
A vapor compression cycle with a solution circuit and desorber/absorber heat exchange (DAHX) has been investigated experimentally using the ammonia/water mixture. A breadboard heat pump was designed and built to measure the cycle performance. COPs in the range of 1.2-1.8 were obtained experimentally for a temperature lift between 60 and 80°C. The cooling capacities were between 7 and 12 kW, which increased with an increase of the ammonia concentration. The pressure ratios encountered were in the range of 2-6. A COP of 1.44 at the temperature lift of 79°C was recorded with a cooling capacity at 10.25 kW. The experimental results are compared to that of the single-stage and two-stage cycle. The two-stage system had the highest temperature lift (110-120°C) and the lowest COP (0.69-1.04). The single-stage system has the highest COP (2.2-3.5) but the lowest temperature lift (40°C). Also, a solution bypass between the Absorber I outlet and Desorber II inlet was proposed to improve the cycle performance. The experimental results showed that the COP varied in the range of 1-2%, while the temperature lift increased by the range between 0 and 6°C. In addition, the analysis of the test result uncertainties was made.
Article
A computer program was developed for an ammonia-water-based generator absorber heat exchange (GAX) component that simulates the simultaneous heat and mass transfer for coexisting liquid film absorption and flow boiling desorption. Key input parameters were identified and used to simulate the variations of heat and mass transfer coefficients, total amounts of heat and mass transferred, temperature and concentration driving forces, and the temperatures of different phases. The simulated temperature profiles were found to match well with experimentally obtained profiles for different vapor and liquid flow rates. The simulated values of the absorption-side vapor-phase flow rates were found to approach zero near the end of the GAX component, showing another close match with the experimental boundary condition. The simulations of the coupled heat and mass transfer processes are useful for detecting the presence of pinch points, appropriate sizing of equipment, realistic estimation of the coefficient of performance (COP) and the efficiency, and determining the individual phase flow rates. The insight developed from these simulations enhances the understanding of the heat and mass exchanger behavior and thus contributes to a reliable and efficient design. The simulation program is of a general nature, applicable to the design of dephlegmators and other heat and mass exchangers beyond those involved in GAX heat pumps.
Article
Solar ponds provide inexpensive means for collecting and storing solar heat at temperatures below 100°C (212°F). The most common application of this heat to date has been the generation of electric power. Due to the thermodynamic limitation set by the relatively low source temperature, the overall efficiency of the electricity generation process is on the order of 1%. This work is concerned with the use of heat from solar ponds to generate process steam, which can be performed at relatively high efficiency. The use of an absorption heat transformer makes it possible to produce low-grade steam from the pond's heat at a coefficient of performance (COP) of about 0.5. This paper describes the operation of the heat transformation process and provides quantitative results on efficiencies and temperatures of the output steam.
Article
The paper provides literature review on absorption refrigerators and heat pumps. Basic background on single-effect absorption systems, double-effect absorption systems, absorption heat transformer are discussed. The paper also provides discussion on advanced systems and working fluids. It is hoped that this contribution will stimulate wider interest in the technology of absorption refrigeration.
Article
The vapor pressures of concentrated aqueous lithium bromide solutions were measured at temperatures ranging from 120°C to 210°C. Five solutions of salt mass fractions-0.437, 0.494, 0549, 0.608, and 0.652-were investigated. A novel representation of salt solution vapor pressure over a large range of temperature and concentrations using a minimum number of parameters was developed. The data from this study were successfully correlated using the proposed model. Previously published vapor pressure measurements were also reviewed and checked for consistency. The results of this work will allow the development of more reliable P-T-x charts for aqueous lithium bromide solutions over a large range of conditions.
Article
In this paper a computer program named AMMWAT is introduced. AMMWAT calculates the thermodynamic properties of ammonia-water solutions. A combination of convenience and good accuracy makes AMMWAT a powerful new tool for absorption system analysis. The program is based on a previously published Gibbs free energy formulation. A series of comparisons between the property predictions of AMMWAT and ammonia-water literature data are provided. Estimates of the accuracy of the properties obtained using AMMWAT are given based on these comparisons. Additional details of the Gibbs free energy formulation are provided of the Gibbs free energy formulation are provided beyond these given in the original source. For illustration purposes, AMMWAT is used to calculate the performance of an absorption cycle and the results are compared against standard methods of analysis.
Article
Thermophysical data on water-ammonia mixtures are briefly reviewed. A method for computing the thermodynamic properties of mixtures from the properties of the pure components is used to extend the properties to the regions of interest. Derived properties cover pressures 1 to 1600 psia, temperatures minus 80 to 930 F, and ammonia fractions 0 to 1, and are in agreement with available measurements. The method assumes the mixture to behave as an ideal solution in the vapor phase and as an actual one in the liquid phase. Electrolytic effects and chemical reactions are assumed absent. The equations used are listed. H-X, S-X and T-X diagrams are included. A tentative table of saturated and superheated properties of the ammonia-water system is available.
Article
The surface has been treated as perfectly smooth in the analysis of absorption of water vapor into falling film of aqueous lithium bromide solution. However, waves or disturbances begin to appear at Ref of 20. In this paper, the influence of the waves is analyzed numerically by assuming sinusoidal wave motion over the falling film. The velocity profile inside the film is determined following Kapitza's analysis. The wave velocity and the wavelength are determined from Pierson and Whitaker's equations derived from the stability analysis. The wave amplitude is assumed to be 30% of the average film thickness. The liquid surface is immobilized by coordinate transformation and the basic equations are further changed to eliminate the cross derivative terms by Shyy et al.'s method. The results are compared with those for a laminar flow with a smooth surface. It is found that the absorption rates increase by a factor of 1.7-2.4 over the Ref range of 20-100.
Article
A comparative study of different working fluid combinations with R22 as refrigerant and six absorbents, namely, DMF, DMA, NMP, DMEDEG, DMETEG and DMETrEG, in a vapour absorption heat transformer is made. DMA and NMP are preferable solvents for R22 to obtain high heat delivery temperatures, low circulation ratios and high coefficients of performance. It is observed that the cumulative change in enthalpy of mixing at absorber conditions significantly influences the performance of the system.
Article
The free choice of operating temperatures in absorption systems is limited by the Gibbs phase rule and the thermodynamic properties of the working pair. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpybased coeffecients of performance have been presented for Ammonia-lithium nitrate absorption systems for cooling. The interactions of operating temperatures have been illustrated graphically.
Article
Up to now the industrial systems for energy recovery at the level of 130°C have been using water solutions of lithium bromide. These solutions present two problems: risks of crystallisation and corrosion. To avoid these risks, the system water-glycerol has been selected.The interest of the proposed can be seen through the theoretical simulation of the absorption heat pump cycle. The simulation results indicate that it is possible to achieve an energy upgrading of 50°C at the absorber. The efficiency coefficient depends on the high and low pressure, but not too much on the performance of the condenser. High values of low pressure lead to the best performance.
Article
A novel absorption cycle, with a significantly higher temperature lift than current technology, is under development. The cycle is based on an aqueous ternary hydroxide working fluid consisting of sodium, potassium and caesium hydroxide in the proportions 40:36:24 (NaOH:KOH:CsOH). The higher temperature lift is made possible by the unique properties of this solution. The ternary hydroxide blend is used to shift the crystallization curve to provide the high lift. High lift is needed in many applications and often cannot be achieved by conventional absorption systems. Water heating is one application where the high lift feature is necessary. Development efforts to date have included thermophysical property measurements on the ternary hydroxide system, heat and mass transfer measurements in absorption and vapour generation and cycle design calculations.RésuméUn nouveau cycle à absorption, avec une élévation de température significativement plus élevée que celle permise par la technologie actuelle, est en cours de développement. Le cycle utilise comme fluide actif une solution aqueuse d'hydroxyde ternaire composée d'hydroxyde de sodium, potassium et césium dans les proportions suivantes : 40/36/24 (NaOH/KOH/CsOH). Une élévation plus grande de température est due aux propriétés propres à cette solution. Ce mélange permet de modifier la courbe de cristallisation et d'obtenir une élévation de température importante, nécessaires dans maintes applications que, bien souvent, on ne peut atteindre avec les systèmes classiques à absorption. Le chauffage de l'eau est une de ces applications. Les efforts jusqu'à ce jour ont porté sur la mesure des propriétés thermophysiques du système d'hydroxyde ternaire, sur celle du transfert de chaleur et de masse au cours de l'absorption et de la génération de vapeur et sur les calculs de conception du cycle.
Article
In this study, experiments have been performed for water vapour absorption into 50 and 60 mass% aqueous lithium bromide solution films flowing down a vertical surface to investigate the effects of liquid diffusivity values, molecular properties of the concentrated solutions and non-absorbable gases. The experimental results for wavy films over a film Reynolds number range of 15–90 indicate larger dimensionless mass transfer rates than for strictly laminar flow when the diffusivity of water in a concentrated lithium bromide solution is less than that in a dilute solution. The complete set of results shows that the physical property data for lithium bromide solutions including the diffusivities measured by Kashiwagi are sufficient to explain mass transfer behavior.RésuméDans cette étude, on a effectué des expériences sur l'absorption de vapeur d'eau dans une solution aqueuse de bromure de lithium (50% à 60% en masse) en forme de film en écoulement sur une surface verticale, afin d'étudier les effets des gaz non absorbés, des valeurs de diffusivité de liquide, ainsi que les propriétés moleculaires des solutions concentrèes. Les résultats expérimentaux pour les films ondulés sur une gamme de nombres de Reynolds allant de 15 à 90 laissent supposer que les taux sans dimension de transfert massique sont plus importants que dans le cas d'un écoulement strictment laminaire, lorsque le diffusivité de l'eau dans une solution concentrée de bromure de lithium est moins importante que celle d'une solution diluèe. L'ensemble des résultats montre que les données sur les propriétés physiques des solutions de bromure de lithium, y compris les diffusivités mesurées par Kashiwag, sont suffisantes pour expliquer le comportement du transfert de masse.
Article
A simulation model of a gas-fired, bivalent parallel air-to-water absorption heat pump with LiBr/ZnBrâ/CHâOH and a ''condensing'' boiler for domestic heating is presented. Because of the low pressure of the mixture, all components are constructed as horizontal tube bundles over which liquid flows in falling films. The only exception for the mixture heat exchanger, which is plate type. Under optimal conditions, the heat pump of specified dimensions has a seasonal average COP of 1.2 to 1.5, corresponding to energy savings of 24% to 36%.
Article
This paper reports on a novel ejector boosted single–effect absorption-recompression refrigeration cycle. In this cycle, a steam generator, ejector and a concentrator replace the high and low pressure generators (concentrators) used in conventional double-effect absorption cycle machines, to re-concentrate the absorbent solution. The ejector here acts like a heat-pump to enhance the concentration process by increasing the flow of leaving vapour and by increasing the quantity of heat input at the concentrator. The paper provides a qualitative and quantitative description of the novel cycle and discusses design choices that lead to optimum matching of the absorbent concentrator and ejector. The important role the ejector plays in this novel refrigeration cycle is discussed and some experimental data are presented. An experimental lithium bromide refrigerator based on this cycle is described.
Article
In absorption refrigeration technology, it is well known that the water vapor absorption into the lithium bromide (LiBr) aqueous solution is enhanced by the addition of surfactant. The Marangoni effect plays a role but its mechanism is not clearly understood yet. In the present study, the existence of instability due to Marangoni effect was investigated using the linear stability analysis, based on the salting out effect. Then the vapor absorption augmentation was estimated by the numerical simulation of cellular convection. Both theoretical results qualitatively agree well with the experimental ones.
Article
After a short characterization of today's advanced absorption cooling systems, of multi-effect and generator-absorber heat exchange (GAX) type, this work introduces polybranched regenerative GAX cycles (PBR(GAX)). They combine the advantages of four cycles: GAX, branched GAX, regenerative GAX, and those with rectification heat recovery. The general case of n-stage PBR, working with volatile or non-volatile absorbents, is thermodynamically modelled. The model is applied to cycles with one to three stages working with the NH3H2OLiBr combination, selected according to a special criterion, which has in view to maximize the GAX effect. The thermal match in the GAX device is verified using our own complete algorithm. The results highlight the net superiority of the cooling COP of PBR relative to any other published GAX or multi-effect cycles. Compared with those with vapour exchange, operated with NH3H2O, one of the best GAX cycles till now, a three-stage PBR has 1.25–1.9 times higher COP values and represents 71–82% of the Carnot cooling efficiency for lifts varying between 68 and 47°C. The PBR cycles are capable of simultaneously delivering cold and warm water, at 50–70°C. Compared with a double-effect cycle, provided with rectification heat recovery, a two-stage PBR is constructively simpler and thermally with about 40% more performance.
Article
The paper describes a novel absorption device suitable for inclusion in a compact sized absorption heat pump. Current research is concentrated on the isothermal falling film absorber for which calculations are presented to show the necessarily laminar nature of such films. The importance of film surface lifetime to the absorption process is highlighted and an expression derived for the lifetime of falling films around horizontal tubes. A mean of mechanically reducing the film surface lifetime within an adiabatic absorper is explained. An absorbent film is picked up by a disc spinning on a horizontal axis and semi-submerged in a pool of concentrated absorbent. Surface renewal occurs on each revolution, from which it is shown how the absorption coefficient is related to the disc speed. Initial experimental results are discussed and reasons for deviation from the theory suggested. Absorption coefficients about seven times those of films falling under gravity are shown to be achievable, and an equation relating the required absorber size to the rotational speed is proposed.
Article
An experimental plant for the determination of heat and mass trasfer rates in falling films has been constructed constructed at the Department of Chemical Engineering at the Royal Isntitute of Technology in Stockholm, Sweden. Vertical tubes have been evaluate according to their heat and mass transfer rates. The distances between the film mixing points have been calculated using a numerical wave model.RésuméOn a construit on installation expérimentale pour déterminer les taux de transfert de chaleur et de masse, dans des films tombants, au Départment de Génie Chimique de l'Institut Royal de Technologie de Stockholm, Suède. On a évalué des tubes verticaux en fonction de leurs taux de transfert de chaleur et de masse. Les distances entre points de mélange du film ont été calculées avec un modéle oscillatoire numérique.
Article
Experimental measurements of pressure, temperature and concentration have been made for R22 and five absorbents, i.e. N-N-dimethyl acetamide, cyclohexanone, diethylene glycol, aniline and xylene in the temperature range 0–100°C and concentration range 0.05–0.95 mole fraction of R22. These experimental vapour pressure data have been correlated for each pair separately by fifteen constant polynomials. These experimental data have been found to compare well with the authors' theoretical model.RésuméLes auteurs ont réalisé des mesures expérimentales de la pression, de la température et de la concentration pour le R22 et cinq absorbants: le , le cyclohexanone, le diéthylène glycol, l'aniline et le xylène à des températures de 0 à 100°C et à des concentrations en fraction molaire de R22 de 0,05 à 0,95 moles. Les pressions de vapeur expérimentales ont été correlées séparément pour chaque couple par 15 polynômes constants. On a trouvé que ces résultats expérimentaux soutenaient bien la comparaison avec le modéle théorique des auteurs.
Article
A heat transformer with self-circulation has been constructed. The self-circulation is reached according to the thermosiphon principle. The pressure difference in the apparatus is achieved through a difference in hydrostatic pressures. Results of the test runs with the working fluid system H2O/NaOH are presented and discussed.RésuméUn transformateur de chaleur à auto-circulation a été construit. L'auto-circulation est obtenue selon le principe du thermosiphon. La différence de pression dans l'appareil résulte de la différence des pressions hydrostatiques. On présente et on discute les résultats d'essais avec le couple H2O/NaOH.
Article
Multi-effect absorption head pump cycles are promising to yield cooling performances which far exceed the performance of single-stage cycles. In this paper, several types of cycles are analysed. For this purpose, the respective multi-effect cycle is decomposed into elementary building blocks of single-stage absorption cycles with known performance. The multi-effect cycle is a superposition of the elementary cycles. Its performance is predicted by using the performance of the elementary cycles as parameters. The flexibility which is attained by the construction of multi-effect cycles from single-stage building blocks allows the design of highly efficient cycles according to the specific properties of competing working fluids. So, out of a wide range of possibilities, a quick choice of efficient cycles which fit the requirements of a specific application with today's working pairs can be made. A preliminary selection of the optimal cycle configuration can be made. Also, the potential of new working pairs can be validated. Out of a wide range of highly efficient absorption chiller cycles several promising machines are discussed.
Article
Performances of four versions of a two-stage vapour compression heat pump with solution circuits (VCHSC) are compared. The VCHSC represents a cascade system that requires only one compressor. Performance curves for the best cycle, the modified version with a bleed line and a desuperheater are obtained and studied in detail. The four cycles are compared for the same total UA value (product of overall heat transfer coefficient and area) including all heat exchangers while pumping heat from an average desorber temperature of -2.5-degrees-C to an average absorber temperature of 105-degrees-C. Simulation results show that the cycle with a bleed line and a desuperheater has 40 to 50% higher cooling COPs and 30 to 40% higher cooling loads as compared to the cycle with a rectifier. Both the rectifier and the bleed line cycles show an increase of up to 20% in the cooling COP and capacity by adding a desuperheater. Performance curves are obtained by simulating the best cycle at various weak solution concentrations in the low temperature loop and different solution pump flow rates. The parameters studied are the cooling COP, the solution heat exchanger effectiveness, the pressure ratio, the solution temperature glides in the absorbers and desorbers, the low temperature desorber load and the distribution of the UA value. Cooling COPs up to 1.05 and pressure ratios as low as 7.05 are obtained for the modified VCHSC. The cooling COPs are twice as much and the pressure ratios are two thirds less of what would be found in a conventional single-stage vapour compression system. Changing the weak solution concentration in the low temperature loop from 40 to 80 wt% ammonia increased the cooling load by four times. The results indicate that the two-stage VCHSC with a bleed line and a desuperheater can work at temperatures above 100-degrees-C and achieve temperature lifts of more than 100 K with well known and environmentally safe refrigerants.
Article
R 22-DEGDME is chosen as the prime working fluid pair for residential gas-fired absorption heat pumps.The vapour pressures and the heat capacities of mixtures are measured for various concentrations and temperatures and are correlated by a Rankine equation and a polynomial, respectively. The heats of mixing are measured at 10°C, and are correlated by a Redlich-Kister type polynomial.Based on these data, the pressure-temperature-concentration diagram and the enthalpy-concentration diagram are drawn, which make analysis of the absorption cycles possible.RésuméOn donne les raisons du choix du couple R 22-DEGDME (diéthylène glycol diméthyl éther) comme étant le plus approprié à l'utilisation domestique de ces pompes à chaleur à gaz, les autres solvants envisagés sont énumérés tableau 1.On décrit l'appareil de mesure de la pression de vapeur de mélanges de liquides connus (Fig. 1), la capacité thermique à volume constant de mélanges de liquides connus (Fig.3) et la chaleur de mélange (Fig.5). Dans chaque cas on présente les résultats forme d'équations de corrélation dont on indique les constantes dans une série de tableaux.On présente aussi les résultats dans deux diagrammes. La Fig. 7 donne une série de courbes de pression de vapeur pour les solutions de R 22-DEGDME par intervalles de 5% de fraction molaire. La Fig. 8 présente un diagramme enthalpieconcentration de la phase liquide de −40 à 200°C.
Article
This Paper deals with theoretical and experimental investigations on the triple fluid vapour absorption refrigerator (TFVAR) in relation to the gas circuit, thermo-siphon and inert gas charge pressure. The charges of the various fluids were estimated. Helium seems to be a better inert gas than hydrogen. A compact absorber design is proposed.RésuméCet article traite des recherches théoriques et expérimentales sur le réfrigérateur à absorption de vapeur à trois fluides (TFVAR) en relation avec le circuit de gaz, le thermosiphon et la pression de charge en gaz inerte. Les charges des divers fluides ont été estimées. L'hélium semble un gaz inerte préférable à l'hydrogéne. On propose un absorbeur de faible encombrement.
Article
A set of five equations describing vapour-liquid equilibrium properties of the ammonia-water system is presented. They are intended for use in the design of absorption processes. Using variable dependences of technical relevance the equations make it possible to avoid iterative evaluations. The equations were constructed by fitting critically assessed experimental data using simple functional forms. They cover the region within which absorption cycles commonly used operate most often. The enthalpy of the gas phase has been calculated in the ideal mixture approximation. The results are presented in the form of an enthalpy-concentration diagram.
Conference Paper
This paper describes a model of the absorption process in a falling film ammonia-water absorber. The model consists of two ordinary, first-order differential equations with suitable inlet and interface conditions. The model was validated by comparing its predictions to experimental data. The objective of the work was to define strategies to enhance the absorption process in order to downsize absorbers. It was found that in most situations of practical interest, the mass transfer process in the falling film controls the absorption rate. The possibility of water evaporation and migration in the absorber is discussed, outlining how it can degrade performance. 16 refs., 5 figs., 4 tabs.
Conference Paper
There are a number of known absorption cycles capable of triple-effect'' refrigeration. Among the basic triple-effect cycles only one particular cycle is able to use ammonia-water (NH{sub 3}/H{sub 2}O) as the absorption fluid pair. This cycle uses two condensers and two absorbers to achieve the triple effect.'' This paper presents several basic triple-effect cycles superimposed on NH{sub 3}/H{sub 2}O pressure-temperature-concentration equilibrium diagrams (PTX) showing that only one particular cycle can use NH{sub 3}/H{sub 2}O. Calculations are presented showing the relative performance of a conventional double-effect cycle using NH{sub 3}/H{sub 2}O and the performance of this triple-effect cycle using NH{sub 3}/H{sub 2}O on a comparable basis. The triple-effect cycle is predicted to have 18% higher cooling efficiency (COP = 1.41 compared to COP = 1.2 for a double-effect), lower pressure (701 psi instead of 1000 psi), significantly reduced pumping power (less than one half that of the double-effect cycle), and potentially lower construction cost (33% less total heat exchange needed). Practical implications for this triple-effect cycle are discussed. 15 refs., 9 figs., 1 tab.