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An improved absorption refrigeration system for recovering two waste heat with different temperatures: Parametric analysis and comparative study
Abstract
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.
... Integration of an absorption chiller with a combustion engine with the objective of utilizing waste energy from the internal combustion engines to drive the absorption system is reported on (Chun et al., 2023;Dadpour et al., 2022), while many other researchers considered the implementation of solar energy to run absorption chiller systems (Mendiburu et al., 2023;Nedaei et al., 2022). Also, numerous investigations focused on absorption chillers which are run with waste heat (Villa et al., 2023;Lu et al., 2023;Zhou et al., 2021a;Bai et al., 2022Bai et al., , 2021b. Many studies reported the integration of a power generation system with absorption chillers with the objective of multi-generation, such as cooling energy, electric power, and desalination (Mugdadi and Al-Nimr, 2023;Kerme et al., 2020;Anand et al., 2022;Mokhtari et al., 2023;Yao et al., 2022;Xu et al., 2022;Esmaeilion et al., 2022;Ehyaei et al., 2021). ...
Dehumidification of industrial flue gas with a membrane condenser requires cooling energy so that the water in the flue gas will recover as it gets condensed due to the cooling process. In this study, the utilization of the waste heat energy of the flue gas to drive an absorption refrigeration cycle is suggested. In return, the cooling energy of the refrigeration cycle is utilized to cool the flue gas before it is admitted to the membrane condenser. The thermal analysis of the refrigeration cycle is carried out by considering a numerical heat transfer analysis at the desorber. The energy and mass balance of the whole refrigeration cycle is carried out based on thermodynamic governing equations. Furthermore, the water recovery process of the membrane condenser which is integrated with the absorption refrigeration cycle is studied. The numerical modeling of the refrigeration cycle and the membrane condenser are combined to investigate the operating parameters of the system. The influence of inlet temperature and mass flow rate of the feed flue gas on the performance of both the refrigeration cycle and membrane condenser is studied.
... For all systems, two distinct mass flow rates were specified for NH 3 -H 2 O solution and water, with values of 1.4948 × 10 -2 kgs −1 and 1.2410 × 10 -2 kgs −1 , respectively. The boundary conditions are also supported by recent studies in the literature [37,38]. Lu et al. [38] demonstrated that the COP and exergy efficiency reach their highest values when the boiler region temperature is between 150℃-160℃. ...
Global warming, inadequate natural sources and an energy crisis are significant concerns in this century. In this context, it has become important to use efficient energy technologies and reduce energy consumption in the cooling industry. In recent years, Diffusion Absorption Refrigeration (DAR) systems have been widely studied as good alternatives to vapor compression cooling systems. In this article, the heat exchanger part located in the boiler-bubble pump region of the DAR system was numerically modeled to determine its behavior. In addition to modeling, five different working fluids were utilized in the DAR system experimentally. The first test was performed utilizing 25% NH3-H2O by mass without nanoparticles. The other four tests were repeated by adding 1% and 2% (by weight) zinc oxide (ZnO) and graphene oxide (GO) nanoparticles into 25% NH3-H2O solution, respectively. The numerically obtained results showed no significant increase in the use of ZnO nanoparticles by 1% or 2%. It was seen that GO nanoparticles made a more meaningful difference in the heat transfer increment than the ZnO nanoparticles. Furthermore, experimental results showed that the utilization of nanoparticles in a 25% NH3-H2O solution assists in disappearing refrigerant. Generally, it was determined that adding nanoparticles to the base fluid eliminates the effects of temperature changes in the system.
... (2) The solutions at the outlet of the generator, the condenser, the absorber, the LP evaporator, and the IP evaporator are saturated (Bai et al., 2022). (3) The purity of refrigerant is higher than 99.99% (Lu et al., 2021) to avoid temperature glides during evaporation. ...
... The continuous generation of greenhouse gas emissions from the conventional energy related activities has motivated many researchers to develop systems that do not involve ozone depleting-working fluid. In view of the above energy challenges, the recent developments in the ammonia-water based thermal systems such as absorption based cooling [1], power [2], cogeneration [3] and trigeneration systems [4] attracted significant attention due to its cleaner approach. The ammonia-water system has a provision to club its standalone cycles into an integrated system. ...
... Losses in the central receiver are mainly of four types namely, emissive, conductive, convective, and reflective heat losses. They are computed using the procedure given by various authors [6,12]. ...
В статье приводится принципиальная схема и принцип работы модернизированного паросилового цикла, в котором процесс конденсации отработавшего после паровой турбины пара заменен на процесс его конденсации, а также принципиальная схема абсорбционного трансформатора, в котором происходят схожие процессы и который взят за основу при разработке схемно-циклового решения модернизированного цикла. С целью разработки оптимизированных схемно-цикловых решений паросилового цикла в статье осуществляется термодинамический анализ различных схемных решений абсорбционных циклов (схема с регенерацией в термохимическом компрессоре, с регенерацией теплоты в основном процессе, схема с дефлегмацией пара). Результаты анализа показали, что наиболее оптимальной схемой абсорбционного термотрансформатора с точки зрения допустимых усложнений схемы и эффективности является схема с дефлегмацией пара и регенерацией теплоты растворов. С целью оптимизации эффективности цикла было осуществлено комбинирование данных схемных решений и также исследована эффективность схемы. По результатам определения наиболее эффективных схем абсорбционных термотрансформаторов в дальнейших исследованиях будут разрабатываться оптимизированные схемные решения для паросилового цикла, при этом будут учитываться особенности функционирования абсорбционных и паросиловых циклов.
The addition of nanoparticles can enhance the mass and heat transfer of basic fluid, also improving the coefficient of performance of the absorption refrigeration system. But the influence of absorption pressure and temperature on the absorption performance of nanofluid are seldom experimental investigated in an actual absorption refrigeration system. Therefore, the TiO2 nanoparticles are added to the NH3 - H2O – LiBr working fluid, and the actual gas-emission range is compared with the theoretical gas-emission range under different absorption pressures and temperatures. The results indicated that the actual gas-emission range increases when the absorption temperature decreases, the absorption pressure increases, or the nanoparticles fraction increases. The ratio of the actual gas-emission range to the theoretical gas-emission range is used to appraise the absorption ability of the nanofluid. And the ratio is increased when the absorption pressure, absorption temperature, or nanoparticles fraction is decreased. Besides, the improvement of that ratio by adding 0.5% TiO2 nanoparticles is bigger at a higher absorption temperature or a lower absorption pressure. At last, a linear formula between the absorption temperature, the absorption pressure, and the fe' / fe are fitted when the TiO2 nanoparticles fraction is 0.5%.
For the sake of making an appropriate choice for the reuse of low grade waste heat, the mechanical heat pump, steam turbine (ST), and organic Rankine cycle (ORC) are modeled by Aspen Plus. The working conditions of 100–150 °C waste heat temperatures, as well as 10–30 °C heat pump temperature lifts are simulated and calculated. The price ratio of electricity to heat is introduced as an important economic variable. The energy and economic performance of the three technologies in low grade waste heat recovery are compared and analyzed based on the exergy efficiency and annual revenue. The results indicate that in terms of the exergy efficiency, the mechanical heat pump is always the best choice. From the perspective of the annual revenue, the mechanical heat pump is the best choice in most cases. The chance that the annual revenue of the ORC and ST is greater than that of the mechanical heat pump arises only when the price ratio of electricity to heat is greater than 5. As for the payback period, all the cycles can meet the requirements of enterprises. A guide of the selection of waste heat recovery technology based on economics is drawn.
Thermoacoustic technology is a promising clean energy solution for the recovery of low-grade heat from renewable energy sources and waste heat. Existing methods for simulating thermoacoustic systems are inconsistent or time-consuming. In this study, a time-saving and reliable time-domain lumped acoustic–electrical analogy model is proposed to investigate the performance of thermoacoustic systems. In the proposed model, each component of a thermoacoustic system is simplified as a lumped acoustic–electrical analogy model. The nonlinear effects of both regenerator and liquid acoustic resistances in gas–liquid resonators are considered to obtain nonlinear dynamic evolution equations. Case studies were performed on a looped heat-driven thermoacoustic refrigerator for low-grade heat recovery to investigate its onset and steady characteristics. The evolutions of the oscillating pressure and volume flow rate were explored, which initially increase rapidly until reaching the saturation state. The minimum onset temperature was 32.5 K at a pressure of 2.5 MPa with hydrogen as the working gas. In addition, the influences of the mean pressure, heating temperature, and cooling temperature on the steady-state system performance with various working fluids were investigated. The results indicated that the cooling power increased significantly with increasing mean pressure, heating temperature, and cooling temperature. A higher working liquid density resulted in a lower onset temperature, lower working frequency, and larger pressure ratio. With the use of helium or hydrogen, the refrigerator performed better in terms of a lower onset temperature and a larger pressure ratio, cooling power, and coefficient of performance. The proposed model provides a new perspective and an effective approach to characterise the onset and steady characteristics of thermoacoustic systems.
In the present study, a new solar-based energy system for a self-sustained community is presented and analysed via the principles of thermodynamics. The presented system can meet the electricity demand, cooling load, and hydrogen (for the refueling of the vehicles) in a community by using a solar heliostat system (based on molten salt) in remote areas. Steam Rankine cycle is used to feed the electricity demand while some of the steam is bled out to operate the two-stage ammonia water-based absorption system for the cooling application. The result of the present study shows that with a heliostat area of 6000 m², 372 kW of electricity, 610 kW of cooling capacity, and 7.2 kg/h of hydrogen is generated. Furthermore, exergy analysis results reveal that the maximum exergy destruction takes place in the central receiver (1170 kW) followed by heliostat (980 kW). The performance assessment of the overall presented system is made via exergy and energy efficiencies and estimated as 17.7%, and 38.9% respectively. Effects of some crucial parameters such as direct normal irradiance, evaporator temperature, the bleeding ratio, etc. have been studied on the overall system performance.
Waste heat sources such as flue gas generate large temperature span during recovery process. In order to improve the temperature match with such waste heat sources, a novel absorption refrigeration system with continuous-temperature-changing generation process is proposed. Internal heat recovery process is introduced to both the generator and absorber, and a premixer is added to take the place of the solution heat exchanger in traditional system. A numerical model of the system is built, in which the continuous-temperature-changing generation process is simulated based on a stripping column with heat input at each stage. New parameters are defined and optimized to strengthen the internal heat recovery process, and thus to improve system efficiency. Simulation results show that the system can operate under a large waste heat temperature span of 67.5 K, almost twice of the conventional system. With the evaporation temperature, waste heat inlet temperature, and cooling water temperature at −15 °C, 150 °C and 20 °C, respectively, a maximum COP of 0.93 and exergy efficiency of 49.7% is acquired while the waste heat temperature span is 60 K, showing that the system can acquire larger utilization rate of waste heat with higher system efficiency.
This work investigates the use of a water-ammonia double-lift absorption cycle for low temperature refrigeration driven by low-grade heat, as waste-heat or solar energy. Among the various double-lift cycles, the investigation focuses on the self-adapting two-pump series cycle, using water-ammonia as working pair. At first, by means of a numerical investigation, it is verified that an air cooled unit can operate with driving temperature of 90 °C, air temperature up to 32 °C and brine temperature down to −15 °C. Then, it is discussed how to modify an existing prototype to achieve the mentioned working conditions. The influence of the two restrictors of the refrigerant on the cycle behaviour is discussed in a qualitative manner, pointing out that the restrictor after the condenser sets the intermediate and low pressures and, consequently, the maximum allowed thermal lift. Finally, the prototype performances are experimentally assessed, confirming that the influence of the restrictor between high and intermediate pressure and pointing out that the use of a fixed restrictor prevents the full exploitation of the potential of the cycle. As a consequence, the use of a variable restrictor could represent an option for optimizing the appliance COP in a wide range of thermal lifts.
From 2010 to 2015, three similarly design based absorption chillers have been developed, manufactured and characterized on test benches. The chillers are all ammonia-water thermally driven single effect chiller. They are intended to operate using directly solar thermal energy or using waste heat from Concentrated Solar Plant (CSP). The first one is a laboratory prototype, fully instrumented with a cooling capacity of 5kW. The second one is a pre-industrial version of the first prototype with the same cooling capacity but less instrumented and with a compact design. The last development is a 100kW cooling capacity chiller, with technical choices between the two first prototypes, but design to provide cooling effect at temperatures suitable from air-conditioning to ice making. In this paper, the design principles and the technological choices made for each chiller are described and a comparison of the experimental results is done.
Double-lift absorption cycles represent a suitable solution for air-cooled thermally driven cooling applications. Among the several existing double-lift configurations, semi-GAX cycles are known as the most promising in terms of efficiency. These cycles incorporate the GAX effect in a pressure staged cycle, by means of a split on the solution leaving the low pressure absorber. Two configurations of the semi-GAX cycle have been proposed in the past, the semi-GAX 1 and the semi-GAX 2. The former achieves the GAX effect between the intermediate and the high pressure levels, the latter between the low and the intermediate. Within this paper, the semi-GAX cycles are numerically investigated at operating conditions suitable for a low temperature driven (e.g., by flat plate solar collectors) air conditioning application. The peculiarities of the two cycles are described and the factors affecting their performances are underlined. The COP resulted to be strongly influenced by the split ratio, which determines the intermediate pressure and the possibility to achieve the GAX effect. If the split ratio is optimized to achieve the maximum COP, the COP is higher for semi-GAX 2 for air temperatures below 27 °C and for semi-GAX 1 above. In both cases, the maximum air temperature which allows a circulation ratio below 15 is 40 °C, with chilled water at 7/12 °C and driving temperature of 90 °C. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
The prototype of an air-cooled double-lift NH3-H2O absorption chiller driven by hot water at low temperature is presented. The main objective of the study is to illustrate the experimental performances of the prototype under different operating conditions. A mathematical model of the cycle is developed, along with a procedure for the identification of otherwise difficult to measure data, with the purpose of providing the complete picture of the internal thermodynamic cycle. The combined experimental and numerical data allowed assessing the effects on the thermodynamic cycle with varying operating conditions. The unit operated steadily with chilled water inlet 12 °C, outlet 7 °C, air temperature between 22 °C and 38 °C, and hot water driving temperatures between 80 °C and 90 °C. The reference cooling capacity at air temperature of 30 °C is 2.5 kW, with thermal COP about 0.3 and electrical COP about 10.
Despite being efficient means of district heating, conventional single-effect absorption heat pumps suffer significant performance deterioration at low ambient temperatures. To solve this problem, an ammonia-water absorption heat pump prototype with intermediate process is designed and built. It utilizes both low-grade heat from the ambient and exhaust heat from natural gas combustion, through the evaporator and intermediate evaporator, respectively. To perform comparison study, the prototype also has the single-effect mode. Experimental results indicate that when the evaporation temperature is 0 °C, the prototype with intermediate process can provide 30 kW heating capacity to heat the water in sequence through the rectifier, condenser and absorber, from 34.24 to 55.09 °C, and the coefficient of performance and primary energy efficiency are 1.66 and 1.28, respectively. When evaporation temperatures reduce to −5, −10 and −15 °C, the coefficient of performances are 1.51, 1.40 and 1.28, respectively, reaching 77%–90% of the simulation values under corresponding working conditions. Compared to the conventional single-effect system, the prototype with intermediate process performs better at lower evaporation temperature, with the coefficient of performance improved by 11%. By replacing the original heat exchangers, the proposed system can be easily applied to the existing heat networks based on gas-fired boilers to improve energy efficiency, and the favorable experimental performance proves that it is a more efficient way of residential district heating, especially in cold regions.
Compared with conventional fuel-direct-burning heating systems, heat-driven absorption heat pump has high efficiency. To further improve the heating performance, generator-absorber heat exchange (GAX) absorption heat pump was developed, but its experimental research was not enough. The parameters tested were usually just COP and heating capacity in the existing literature, the variation of some internal parameters were rarely measured and analyzed. Besides, the latent heat exchange between the generator and the absorber could not continue normally under high thermal lift (TCON-TEVA) and low thermal thrust (TGEN-TABS), instead, more sensible heat is transferred, the temperature overlap decreases or even disappears, and the circulation process of GAX cycle approaches to that of single-effect cycle. This phenomenon is named “cycle degradation”, and is crucial to understand the working principle of GAX for optimal design and control. The cycle degradation was only simulated under low evaporation temperature, but has not been analyzed with experimental data, the influence rules of other external operational parameters on the phenomenon are also not clear. Therefore, a prototype of GAX absorption heat pump is built up, many internal and external parameters are measured and used to investigate the cycle degradation and overall performance under different testing conditions. During the experiment, the COP is in the range of 1.185–1.506, the cycle degradation occurs when the “lifting factor (Eq [18])” is lower than 2.3. Moreover, the performance improves with the increase of driving temperature or low-grade heat source temperature, and deteriorates due to the rise of supply water temperature.
In this paper, optimal design/operating conditions are presented by considering the cost-effectiveness and operability of a single-stage ammonia/water absorption refrigerator (AAR) via exergy analysis. Chemical exergy change constitutes complexity with respect to exergy analysis of absorption systems. In the study, Gibbs free energy is considered in the exergy analysis to precisely evaluate the absorption and rectification processes including chemical exergy change. The theoretical maximum exergy efficiency of AAR and the influence of its design/operating conditions on exergy efficiency/destructions are investigated under an ideal condition. The analysis indicates the importance of the evaporator outlet liquid (bleed) ammonia mass fraction and the desorber temperature. A condition of bleed mass fraction control is illustrated. In addition, the study involves performing a sensitivity analysis of design parameters (pinch temperatures) with respect to exergy efficiency and optimal desorber temperature. Finally, design conditions that maximize exergy efficiency per cost are derived relative to the sum of thermal conductance as a cost parameter. The study demonstrates the potential for downsizing the AAR without reducing exergy efficiency. The results indicate that approximately 39% total thermal conductance reduction, maintaining nominal efficiency, or 19% total thermal conductance reduction with an exergy efficiency increase of 16% are expected when compared to those in a commercial AAR.
Absorption chiller is a widely used technology owing to its capability to utilize low grade thermal energy including solar thermal energy and waste heat. Yet, most solar absorption cooling systems need cooling tower to dissipate heat rejection into ambient. The use of cooling tower increases both the initial investment and water consumption, which can be improved by air-cooled solar absorption cooling system. In this paper, to give the best absorption cycle options under different conditions, five absorption refrigeration cycles suitable for air-cooled solar cooling including three double lift absorption cycles and two semi-GAX (Generator-Absorber heat eXchange) absorption cycles were compared. Steady-state simulation is carried out. Efficiencies of these cycles were calculated with LiBr-water and water-ammonia working pairs in the scenario of air-cooled solar cooling. Heat source temperatures of 75–100 °C from non-concentrating solar collector and air temperatures of 20–40 °C were considered. Both air-conditioning condition with evaporation temperature of 5 °C and sub-zero condition with −10 °C were discussed. It is found that mass-coupled semi-GAX absorption cycle with ammonia-water is suitable for air-conditioning with higher heat source temperatures, mass-coupled double lift absorption cycle with water-LiBr is suitable for air-conditioning with lower heat source temperature and mass-coupled double lift absorption cycle with ammonia-water is suitable for sub-zero conditions.
The present paper aims at exploring a hybrid absorption-compression heat pump (HAC-HP) to upgrade and recover the industrial waste heat in the temperature range of 60°C–120°C. The new HAC-HP system proposed has a condenser, an evaporator, and one more solution pump, compared to the conventional HAC-HP system, to allow flexible utilization of energy sources of electricity and waste heat. In the system proposed, the pressure of ammonia-water vapor desorbed in the generator can be elevated by two routes; one is via the compression of compressor while the other is via the condenser, the solution pump, and the evaporator. The results show that more ammonia-water vapor flowing through the compressor leads to a substantial higher energy efficiency due to the higher quality of electricity, however, only a slight change on the system exergy efficiency is noticed. The temperature lift increases with the increasing system recirculation flow ratio, however, the system energy and exergy efficiencies drop towards zero. The suitable operation ranges of HAC-HP are recommended for the waste heat at 60°C, 80°C, 100°C, and 120°C. The recirculation flow ratio should be lower than 9, 6, 5, and 4 respectively for these waste heat, while the temperature lifts are in the range of 9.8°C–27.7 °C, 14.9°C–44.1 °C, 24.4°C–64.1°C, and 40.7°C–85.7°C, respectively, and the system energy efficiency are 0.35–0.93, 0.32–0.90, 0.25–0.85, and 0.14–0.76.
This paper presents the development and experimental study of an ammonia water absorption refrigeration prototype for waste heat utilization of diesel engine exhaust. Side cooling rectification and side heating generation are designed to achieve desirable heat matching for better internal heat recovery thus improving the system performance. An active open heat pipe method is applied for taking the exhaust heat to make the heat input stable. The condensation and absorption processes are combined in one unit and cooled by circulated precooled solution. Small diameter tube bundle heat exchangers with large specific surface area are employed for all components. Both the features make the system bulk small. The experimental results show that the operation of the system is reliable with a sharp variation of the exhaust condition. The prototype produces cooling capacity of 33.8 kW and the system thermal COP reaches 0.53 under the test conditions that the temperatures of the cooling water, secondary refrigerant and exhaust inlet are 26.1oC, -15.2oC and 567oC, respectively. The novel design of the prototype is proved to be valid and its concept can be extended to other applications.
Absorption-compression refrigeration cycle is widely studied for its energy saving potential. In this paper, a comparative study on a novel absorption-compression cycle with an evaporator-subcooler (ES) and a conventional absorption-compression refrigeration cycle with an evaporator-condenser (EC) has been done for the first time. The comparative investigation is based on energy, exergy, economic and environmental (4E) analyses. The results show EC saves 22.5% more electric energy than ES at the cost of consuming 4.6 times more low-grade heat energy than ES. EC has a higher COP, but has a lower COPg, which takes into account both electric power and low-grade heat power. From the exergy analysis, the exergy efficiency of ES is 31.6%, 54.1% higher than EC’s (20.5%), indicating ES has a much better exergy performance. The economic analysis shows that when waste heat is used, EC has a better economic performance and when solar heat is used, ES has better practical application potential. The effect of electricity price and CO2 tax rate on economic performance is also studied. The better cycle for different electricity price and CO2 tax rate are recommended. The results and understanding of the two cycles can be used as the basis for cycle selection and design.
In this paper, different absorption refrigeration cycles are reviewed. The couplings for absorption cycle construction are summarized. Based on the coupling characteristics, the absorption cycles are classified into the following categories: single effect cycle, external-circuit coupling cycles, internal-circuit coupling cycles and the cycle combined with ejector/compressor. Cycles constructed through external-circuit coupling refer to the multiple stage cycles. In these cycles, the external-circuit heat and mass couplings are employed to improve the cycle performance or temperature lift. Cycles constructed through internal-circuit coupling refer to the GAX cycles. In these cycles, the internal-circuit heat couplings are employed to enhance the cycle flexibility and internal heat recovery. The internal-circuit mass couplings are employed to enlarge the GAX temperature overlap. In the combined cycles, ejector or compressor are integrated to improve the cooling output or decrease the driven temperature. The configurations and theoretical COP of these cycles are introduced with diagrams. Related literatures are reviewed. © 2015 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
CCHP (combined cooling heating and power) system based on ICE (internal combustion engine) has been widely used. A key issue is to efficiently recover the jacket water and exhaust gas waste heat for refrigeration. In this work, a mixed effect absorption chiller (AC), which couples single effect and double effect processes together, is investigated to recover these two kinds of waste heat simultaneously. The high pressure generator is powered by exhaust gas while one low pressure generator is powered by jacket water waste heat. Thermodynamic characteristics and off-design performance are simulated. Considering thermodynamic constraints, the start point temperature in low pressure generator should be 77°Cor lower. For a 16 kW ICE, the cooling output can reach 34.4 kW with COP of 0.96 and exergy efficiency of 0.186. Comparing with double effect or single effect AC, it can make a better use of different waste heat in CCHP system.
To increase the use efficiency of available thermal energy in the waste gas/water, a novel high-efficient absorption refrigeration cycle regarded as an improved single-effect/double-lift configuration is proposed. The improved cycle using an evaporator/absorber (E/A) promotes the coefficient of performance and reduces the irreversible loss. Water–lithium bromide is used as the working pair and a simulation study under the steady working conditions is conducted. The results show that the temperature of waste gas discharged is about 20 °C lower than that of the conventional single-effect cycle and the novel cycle we proposed can achieve more cooling capacity per unit mass of waste gas/water at the simulated working conditions.
An air-cooled two-stage NH3-H2O absorption refrigeration system is proposed for potential application of residential small scale cooling system driven by solar heated hot water. It can reduce the initial fabrication and maintenance costs of both the solar collection system and the absorption chiller. An experimental prototype for 2 kW cooling capacity has been built to investigate the feasibility and performance of the proposed system. The experimental results indicate that the prototype operates smoothly and steadily. When the prototype is driven by 85 °C hot water with an evaporating temperature of 8 °C and ambient air temperature of 29 °C, its thermal COP and electric efficacy (ε) reach 0.21 and 5.1, respectively. COP stabilizes within the range of 0.18–0.25, and ε varies between 3.6 and 5.1 under air-conditioning conditions in summer, which are the right applications of air-cooled two-stage absorption systems. The study reveals the technical feasibility of the air-cooled two-stage NH3-H2O absorption system. It provides a way to develop low-cost small bulk solar absorption air-conditioning systems for residential applications.
Practical experience in working with ammonia–water absorption systems shows that the ammonia purification process is a crucial issue in order to obtain an efficient and reliable system. In this paper, the detrimental effects of the residual water content in the vapour refrigerant are described and quantified based on the system design variables that determine the effectiveness of the purification process. The study has been performed considering a single stage system with a distillation column with complete condensation. The ammonia purification effectiveness of the column is analysed in terms of the efficiencies in the stripping and rectifying sections and the reflux ratio. By varying the efficiencies from 0 to 1, systems with neither the rectifying nor stripping section, with either the rectifying or stripping section, or with both sections can be considered. The impact of the ammonia purification process on the absorption system performance is studied based on the column efficiencies and reflux ratio; and its effects on refrigerant concentration, system COP, system pressures and main system mass flow rates and concentrations are analysed. When the highest efficiency rectifying sections are used a combination of generation temperature and reflux ratio which leads to optimum COP values is found. The analysis covers different operating conditions with air and water cooled systems from refrigeration to air conditioning applications by changing the evaporation temperature. The importance of rectification in each kind of application is evaluated.
The objective of this study is to propose and evaluate advanced absorption cycles for the coefficient of performance (COP) improvement and temperature lift enhancement applications. The characteristics of each cycle are assessed from the viewpoints of the ideal cycle COP and its applications. The advanced cycles for the COP improvement are categorized according to their heat recovery method: condensation heat recovery, absorption heat recovery, and condensation/absorption heat recovery. In H2O-LiBr systems, the number of effects and the number of stages can be improved by adding a third or a fourth component to the solution pairs. The performance of NH3 H2O systems can be improved by internal heat recovery due to their thermal characteristics such as temperature gliding. NH3-H2O cycles can be combined with adsorption cycles and power generation cycles for waste heat utilization, performance improvement, panel heating and low temperature applications. The H2O-LiBr cycle is better from the high COP viewpoints for the evaporation temperature over 0°C while the NH3-H2O cycle is better from the viewpoint of low temperature applications. This study suggests that the cycle performance would be significantly improved by combining the advanced H2O-LiBr and NH3-H2O cycles.
At present, much interest is being shown in absorption refrigeration cycles driven by low temperature heat sources, such as solar energy or low-grade waste-heat. Double-lift absorption cycles working with ammonia-water have been recommended for refrigeration applications which require cold at 0°C and which are activated by waste heat between 70 and 100°C. This paper discusses the potential of the organic fluid mixtures trifluoroethanol (TFE)-tetraethylenglycol dimethylether (TEGDME or E181) and methanol-TEGDME as working pairs in series flow and vapour exchange double-lift absorption cycles. The ammonia-water mixture was used for comparison purposes. The results show that the performances of these cycles improve significantly when they have the above mentioned organic fluid mixtures as working pairs. For example, the coefficient of performance of the vapour exchange cycle working with TFE-TEGDME is 15% higher than with ammonia-water. In this study, we used a modular software package, which we developed for the thermodynamic properties and cycles simulation of absorption systems.
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.
Waste heat powered absorption refrigeration is an economical and environmentally beneficial means of providing refrigeration. When the temperature is too low to power a conventional single effect absorption cycle, the double-lift cycle is needed. This paper describes several recently conceptualized double-lift cycles that incorporate internal heat exchange between the intermediate pressure absorber and the high pressure generator (termed semi-GAX). Computer modeling identified their key performance parameters. Compared to conventional double-lift cycles, the semi-GAX cycles enjoy a 20% increase in coefficient of performance, and require less total heat duty, implying lower first cost
Self-adapting multi-stage absorption heat pump, has generator generating vapor from fluid, separator liquid outlet feeding evaporator via line, and vapor outlet of separator opening into intermediate pressure absorber unit
- M Guerra
- M Quiela