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The effects of the ambient air temperature on the performance of the liquid desiccant air-conditioning system.
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In this work a novel energy efficient air-conditioning system utilizing lithium chloride (LiCl) solution as liquid desiccant has been proposed and simulated. The simulation of this system is mainly formulated with two packed columns, one for regenerating the weak desiccant and the other for the dehumidification of ambient air. The air is first dehu...
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Citations
... A generic single stage LDAC system consists of a regenerator, dehumidifier, evaporative cooler, and heat exchangers as shown in figure 1.The design of LDAC components are prepared based on the simulation calculations from the literature [14], [15]. The mathematical formulation of LDAC components is based on energy conservation principle [16], [17] and correlation based analysis [15]. Some of the approaches provided in the literature concerning the modelling of heat and mass transfer processes in LDAC systems in the present work includes NTU methods [18]. ...
Weather extremes are common in recent times due to the increase in global warming caused by climate change. Thus, thermal comfort applications require considerable amount of energy produced annually. While passive methods of thermal comfort provide correct direction towards sustainability, it cannot provide the complete solution for the problem. One such passive method is a liquid desiccant-based air conditioning system which is a well-known technique that can provide the AC effect, but inherent with corrosion and low efficiency issues. Hence, we propose a simple setup with low-cost polymer components designed and fabricated to overcome these problems. The calcium chloride desiccant solution is chosen because it is non-toxic and inexpensive. The system is able to provide air at about 25 °C and RH of 60% with input ambient air at 31 °C and RH of 70%, by consuming 126 W of electrical power for air and water circulation and 752 W for desiccant heating bringing the total energy usage to about 878 W. With the success of the project multistage setup with other working fluids will be tested.
... The effectiveness of systems using liquid desiccant dehumidification followed by direct and indirect evaporative cooling systems was studied by Abdalla and Kamal [24]. Tu et al. [25] and Tu and Ren [26] investigated liquid desiccant dehumidification followed by evaporative cooling systems. Woods and Kozubal [27] conducted sensitivity and parametric analysis to find key design parameters using a numerical model and found an existing compromise between the coefficient of performance and dimensions of a liquid desiccant-based M-cycle airconditioner. ...
Air-conditioning of buildings is more energy-consuming with widely used vapour compression refrigeration systems in hot and humid areas. Alternatively, evaporative cooling does not show much effect in sultry regions because of increased humidity despite the minimum energy consumption. Indirect evaporative cooling is a promising alternative to direct evaporative cooling systems, but it suffers from low cooling effectiveness and is unsuitable for highly humid regions. Considering the above facts an alternative liquid desiccant-assisted modified M-cycle cooling system is proposed and examined numerically in the present work. The proposed cooling and dehumidification system is a simple unit incorporating chemical dehumidification and regenerative evaporative cooling in a single unit. A simultaneous heat and mass transfer model is developed for the numerical analysis. The numerical code is written in MATLAB and is validated with results available in the literature. Further, numerical analysis was carried out for the effect of various parameters on the performance of the proposed cooling system. The study shows an improvement of 19.2% in dew point effectiveness by incorporating an intermediate opening in the plate separating the product air and working air channels.
... Xianhua Ou et al. [7] experiential investigated the heat and mass transfer performance of a liquid desiccant cooling and dehumidification system form the result, with increased chilled water flow rate, desiccant solution flow rate, and concentration, thermal efficiency and moisture efficiency improve. Min Tu. et al. [8] simulated and analyses a novel liquid desiccant air conditioning system. The simulation of this system is formulated with two packed columns, one for regenerating the weak desiccant solution and the other for the dehumidification of the ambient air. ...
The desiccant air conditioning system consists of two processes, namely cooling and dehumidification, in which the air temperature and humidity are controlled in order to provide comfortable thermal conditions. A typical system includes a dehumidifier, indirect evaporative cooler, and regenerator. The desiccant is selected depending on its ability to absorb water vapor present in the air. In this study, calcium chloride solution was used as a desiccant for the desiccant solution regeneration process, and a flat plate solar collector was employed. Different variables, such as the primary air flow rate, desiccant flow rate, and the concentration of the desiccant solution, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant system such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the solution concentration and the flow rate of primary air increase, the moisture removal rate, sensible heat ratio, and mass transfer coefficient increase. A particular value of inlet primary air flow rate (0.18Kg/s), an increase in the inlet concentration of calcium chloride solution from 0.85 to 0.95 leads to a rise in moisture removal rate, sensible heat ratio, and mass transfer coefficient of (1.1 _1.65) g/s, (0.18-0.25), and (0.01075-0.0123) m/s respectively. While at a certain inlet concentration of a desiccant solution (0.95), increasing the inlet primary air flow rate from 0.1Kg/s to 0.18Kg/s leads to an increase in the moisture removal rate, sensible heat ratio, and mass transfer coefficient o (0.94-1.26) g/s, (0.24-0.26), and(0.0038 -0.011) m/s respectively.
... The supply and return temperatures of the hot water are 120°C and 60°C, respectively. The theory of the LDD can be found in a previous study (Tu et al. 2009). The COP of the LDD is generally in the 1.2-1.5 range, and is assumed to be 1.5 in this paper. ...
The heating requirements for district heating systems decrease sharply during the summer in China, which leads to the heating capacity of these systems remaining idle. To make full use of district heating systems, a novel approach for application of these thermal systems to cooling is proposed in this paper. The proposed system is based on a distributed absorption cooling (DAC) system driven by heat from the combined heat and power system. To investigate its energy-saving effects, the energy efficiency of the proposed DAC system was researched using the primary energy saving ratio (FESR) method. To assess the economic feasibility of the proposed system, the equivalent heating price for this DAC system was derived using economic analysis methods. The weight analysis method was used to analyse the factors affecting the energy efficiency of the DAC system. The research results showed that the energy efficiency and the economic feasibility of the proposed DAC system can be improved by increasing the heating-driven cooling efficiency. A new DAC system (IDAC) was then proposed based on integration of DAC with a heat-driven liquid desiccant dehumidifier (LDD), and the results show that the new system can increase the heating-driven cooling efficiency.
... Tu et al. [29] used the finite-difference model to study the adiabatic dehumidification process, while Luo et al. [30] established the Computational Fluid Dynamics (CFD) technology for the adiabatic and the internally cooled dehumidifiers and demonstrated the importance of considering variable local properties of the desiccant solution. Huang et al. [31] used the finite volume approach to solve the governing equations of a water-cooled membrane-based liquid desiccant dehumidifier and reported that the fully developed Nusselt and Sherwood numbers for the Simple iteration Very good accuracy Design and optimization membrane-based system were 2-3% smaller than those for an adiabatic one. ...
The liquid desiccant air-conditioning system has been identified as a promising technology that has the potential of decoupling and preciously controlling the latent and sensible cooling loads of air-conditioning spaces. The issues of moulds and bacteria growth on the wet surface of chilled water coils of conventional air handling units can be resolved by employing liquid desiccant systems, where moisture is absorbed by antibacterial desiccant solutions instead of condensing at low temperature. Considerable progress has been made by researchers to enhance the dehumidification and cooling performances of liquid desiccant systems, which are coherently presented in this chapter. The thermophysical properties of several liquid desiccants have been evaluated and the opportunities for improving the desired properties by mixing different desiccant materials are explored. Techniques for improving the wettability and flow characteristics of the packing materials are also discussed. In addition, several theoretical models and solution techniques to study heat and mass transfer enhancement opportunities are systematically discussed and compared in this chapter. The potential of a hybrid liquid desiccant system incorporating either a conventional vapour compression system ora vapour absorption chiller is also documented. Finally, some challenges and future research directions are identified and discussed.
... Tu et al. [66] implemented the FD model by [59] on modular computer simulator to study an innovative and less energy demanding LD system utilizing LiCl solution. ...
In this paper, a comprehensive technical review of liquid desiccant (LD) dehumidification and regeneration techniques is presented. The operational features, processes and performance indices of various flow configurations of adiabatic dehumidifier and regenerator are extensively covered. The heat and mass transfer assessment is presented in terms of past experimental and modelling evaluations and procedures. The existing adiabatic dehumidifier/regenerator heat and mass transfer models are categorized into finite difference, effectiveness-number of transfer units and simple empirical correlation models. The respective performance prediction models are critically analysed in details and compared in terms of assumptions, iterative procedures, solution methods, accuracy, computation time, output variables and applications. The solar regenerator models are also highlighted with a focus on the collector module. The ideal settings, formulation procedures, current state-of-the-art and opportunities for improvements are outlined. The review provides meaningful insight into the research status and available opportunities in the LD adiabatic dehumidifier and regenerator modelling and optimization as well as conceptualization of the applicable models. Finally, some very impactful suggestions for improvement and further research are outlined.
... The numerical results showed condensation rate was in the range of 0.35-0.5 g/s, which indicated ± 5% deviation from the experimental data [20] . Tu et al. [57] developed a simplified model based on -NTU methods for a liquid desiccant integrated with an evaporative cooling system. The numerical results revealed that with air to dehydrated desiccant mass flow rate ratio in the range of 1-7, the cooling capacity was in the range of 50-250KJ and COP would be in the range of 0.41-0.5. ...
This paper presents a literature review on the recent research progress in liquid desiccant dehumidification and air conditioning systems. The physical features of various liquid desiccant materials and their dehumidification performances have been summarized. With the aim to improve the dehumidification characteristics, mixed solvents desiccants have become research hot topics recently. Various types of dehumidifiers and their integration with liquid desiccant dehumidification system have been reviewed. The combination of liquid desiccant dehumidification system with solar collector, vapour compression system, heat pump system, CHP system, etc. have been grouped and compared. It is shown that the majority of the recent research work for liquid desiccant dehumidification systems has concentrated on numerical simulations, a considerable amount of works are still required for the practical investigations of innovative material (mixed solvents) and hybrid systems.
... Different models were used to introduce the performance of dehumidifier and regenerator performance including theoretical and experimental models [1][2][3]. A modular simulation program with first and second laws of thermodynamics have been proposed by [4] to analyze the effect of several key variables on the performance of a novel hybrid air-conditioning system with lithium chloride as a desiccant in the system. The main results of simulation show that the increasing of the Ts in regenerator can improve the system's performance. ...
... This explains that the model is a suitable to indicate the experiment data with R 2 being higher than 0.90 and 0.95 for the MRR and the ε models respectively. (3)(4)(5), it is clear that MRR increases with decreasing Ta to its minimum level (27°C), the MRR increased when the Wa was increased from 20 to 25 g/kg and at Wa of 25 g/kg, the MRR was achieved at 0.577 g/s. This may be discussed as that the mass transfer potential increases with increase in the humidity ratio of air. ...
... Xiao et al. [30] simulated a dedicated outdoor air system (DOAS) adopting LDS by implementing a dehumidifier model into TRNSYS. Tu et al. [31] developed a program for simulating an LDSevaporative cooler system. Kim et al. [32] implemented the dehumidifier model into EES and integrated the component model into TRNSYS to simulate an LDS-DOAS system. ...
Liquid desiccant systems (LDS) have recently seen an increase in research interest as they can utilize low-grade heat resources and separate the sensible and latent cooling loads by efficiently removing moisture in the air without cooling it to the dew point. However, simulation and analysis of LDS had remained complex and demanding due to the limited resources of LDS simulation tools. This work presents the new LDS module developed in the Sorption system Simulation program (SorpSim), which is an open-source and flexible platform for steady-state simulation and analysis of various sorption systems. First, the new LDS module containing a finite-difference model and an effectiveness-NTU model for the heat and mass transfer in LDS dehumidifier/regenerator component was introduced. Then the simulation results of the new module were verified using data from the literature. Finally, a case study was carried out in SorpSim where an LDS cycle was built and simulated using the new module. The impacts of design and operating parameters on the simulated LDS performance were investigated. The parametric study revealed that a high source temperature improved moisture removal rate (MRR) but reduced the system coefficient of performance (COP); the COP increased monotonically with the desiccant solution recirculation ratio, while the MRR peaked at a ratio of 85%; and an internal solution heat exchanger with UA of 800 W/K was found to be sufficient for optimal performance under high recirculation ratios. The case study demonstrated the LDS module’s capability to facilitate the analysis of LDS design and operation. The LDS module can be further coupled with other component models in SorpSim to simulate and analyze various liquid-desiccant-based systems.
... In other study, Min et al [5] studied a lithium chloride (LiCl) desiccant liquid air conditioning system. A regenerator (dehumidifier) core to regenerate (to dehumidifier) the weak desiccant solution (the ambient air) are simulated. ...
Contrary to the conventional air conditioning systems, the liquid desiccant cooling (LDC) systems are considered efficient systems to control the indoor air conditions. In addition, the LDC technologies are more adequate for the hot and humid climates. In this paper, we present an analytical investigation at assessing the feasibility of a LDC technology under Mediterranean climate. The mathematical equations including the sensible and latent heat transfer equations in both air stream and desiccant solution are presented. The impacts of climatic and operating parameters on the supplied air qualities, moisture removal rate (MRR) and sensible heat ratio (SHR) are evaluated. As a consequence, this study provides a solution to investigate the feasibility of this type of air conditioning technologies under hot and humid climate.
