Double-effect Absorption Refrigeration System Research Articles

Energy analysis and economic evaluation of trigeneration system integrating compressed air energy storage system, organic Rankine cycle with different absorption refrigeration systems

In recent years, a concerted effort has been made to reduce reliance on conventional fossil fuels by advancing the use of renewable energy. Nonetheless, the use of renewable energy presents inherent challenges, prominently including intermittency and unpredictability. These obstacles impede the seamless integration and optimal use of renewable energy. A promising solution to address the issues of intermittency and unpredictability in renewable energy is compressed air energy storage (CAES) technology. The performance of CAES can be significantly enhanced through the implementation of a trigeneration system. Some studies have been performed to develop strategies in order to improve the round-trip efficiency (RTE) of the CAES. However, no studies have evaluated the effect of integrating different types of absorption refrigeration systems (ARSs) (different effects and different working media). Steady-state models for CAES, organic Rankine cycle (ORC) and different types of ARSs were developed in Aspen Plus®. All the models were validated in Aspen Plus®. Then process study was conducted to analyse the effects of recuperator outlet temperature and ARS mass flowrate on CCHP system performance. Economic evaluation was performed using Aspen Process Economic Analyser® (APEA). The double-effect ARS is superior to single-effect ARS with the same working medium. The LiBr-H2O is more suitable than NH3-H2O as working medium. The CCHP implemented with double-effect ARS using LiBr-H2O can produce 206 MWe of electrical energy, 7.26 MWth of heating and 27.28 MWth cooling capacity with coefficient of performance (COP) 1.36. The process analysis indicates that COP and RTE increased with the ARS mass flowrate. The levelized cost of electricity (LCOE) of the CCHP-3 system is 31.01 $/MWh, the payback period of the CCHP-3 system is 12.9 years. Overall, this first systematic study comparing different types of ARS for the CCHP system will provide important guidance on the process design and analysis of CCHP.

Thermodynamic and economic evaluation of a non-cascaded dual-temperature compression–absorption–resorption refrigeration system

Thermal processes in many industries require simultaneous cooling at multiple temperatures, highlighting the need for an efficient and cost-effective dual-temperature refrigeration system. This study proposes two novel non-cascaded dual-temperature ejector-assisted compression–absorption–resorption refrigeration cycles (ECARC) to deliver simultaneous refrigeration effects at -5°C and 7°C. These cycles are classified based on the compressor staging with an ejector as ECARC-1 and ECARC-2. The performance simulations of the proposed cycles were carried out at the design conditions and a detailed parametric study was performed to determine the influence of the key operating parameters on the first and the second law coefficients of performance. The proposed novel cycles are more efficient and utilise heat more effectively by consuming up to 60 % less electricity than the conventional multi-evaporator compression refrigeration system, for the same operating conditions and refrigeration capacity. These cycles are also more cost effective with a reduction in their unit production cooling cost by up to 50 % and 25.5% as compared with the state-of-the-art double-effect absorption refrigeration system and the multi-evaporator compression refrigeration system, respectively. Thus, the proposed cycles show excellent thermal and economic advantages for a potential dual-temperature refrigeration system, and the development of these systems contribute towards the decarbonisation of the industrial cooling and heating sector.

Performance Evaluation of LiBr-H2O and LiCl-H2O Working Pairs in Compression-Assisted Double-Effect Absorption Refrigeration Systems for Utilization of Low-Temperature Heat Sources

To improve the performance of conventional double-effect absorption refrigeration systems (DEARS), new series parallel (SP) and reverse parallel (RP) configurations using LiCl-H2O and LiBr-H2O as working fluids, combined with two vapor compressors (VC), are proposed and thermodynamically evaluated. The effects of the distribution ratio (D) and compression ratio (CR) on the system performance are discussed. The results reveal that both configurations can extend the operation ranges of DEARS effectively at a higher distribution ratio, and the performance for low-grade heat source utilization is improved substantially by the use of VC. The compressor positioned between the evaporator and absorber is superior to that between the high-pressure generator and low-pressure generator because of the better performance improvement and larger operating ranges. In all the examined cases, LiCl-H2O systems perform better than LiBr-H2O systems in terms of the coefficient of performance (COP) and exergetic efficiency. At the higher CR of approximately 2, the compression-assisted DEARS can be driven by heat sources below 100 °C with high levels of COPs above 1.16 for the LiBr-H2O working pair and 1.29 for the LiCl-H2O working pair. The system can operate at the optimum condition by adjusting the CR values according to the characteristics of the heat sources.

Modeling and parametric analysis of a new combined geothermal plant with hydrogen generation and compression for multigeneration

Geothermal energy is a promising solution to provide multiple outputs at different temperatures and under different conditions. In this current work, a geothermally powered multigeneration cycle is planned, suggested and studied including a Kalina cycle, an organic Rankine cycle, a thermoelectric generators, a double effect absorption refrigeration system, a dryer, a domestic water heater, a multi-effect desalination processes, a greenhouse, and hydrogen production and storage units. The main objective of this study is to generate power, cooling, heating, hot water, drying, greenhouse heating, hydrogen, oxygen, and freshwater in an environmentally harmless approach. An elaborated thermodynamic analysis of the developed research is calculated by energy and exergy efficiency methods. Furthermore, the parametric modeling is employed to calculate the effect of significant variables on the examined study and subsystems' efficiency. Looking the analysis's findings reveal that the evaluated model's net power generation rate is approximately 298 kW. Additionally, the cooling and heating rates of this integrated combined plant are 1169 kW and 1783 kW, respectively. Moreover, the examined plant produces 0.000392 kg/s of hydrogen and 2.77 kg/s of freshwater. Finally, the examined cycle energy and exergy performance is computed as 0.4248 and 0.3826, respectively.

Evaluation of ionic liquids as absorbents for absorption refrigeration systems using hydrofluoro-olefin refrigerant

In this study, we evaluate the use of ILs as absorbents in a double effect absorption refrigeration system using HFO refrigerant. By examining the properties of various refrigerant/absorbent mixtures, we identify the most efficient refrigerant/absorbent pair for the aforementioned absorption refrigeration system. First, we identify a suitable HFO refrigerant for the system. Among the candidates in this study, R1336mzz(Z) and R1234ze(Z) can be used in the absorption refrigeration system because both have low flammability and high critical points. Then, we analyze the characteristics of ILs as absorbents in the absorption refrigeration system. Imidazolium ILs have relatively low viscosities of approximately 20 mPa s at temperatures exceeding 50 °C and high stability. Next, we analyze the characteristics of refrigerant/absorbent pairs. When R1336mzz(Z) and R1234ze(Z) are used as the refrigerant, [OMIM][BF4] have the highest solubilities in oprating conditions. The solubility value of R1234ze(Z) with [OMIM][BF4] is 0.256 at 289.89 kPa and 80 °C, while the solubility value of R1336mzz(Z) with [OMIM][BF4] is 0.154 at 128.02 kPa and 80 °C. Finally, we analyze the performance of the refrigeration system. When the R1234ze(Z)/[OMIM][BF4] is used in the absorption refrigeration system, the COP and cooling capacity of the system exhibit the values of 0.516 and 0.549 kW, respectively.

Performance analysis of a double-effect absorption refrigeration cycle using a low-temperature ethanol solution as the working pair

In this paper, a double-effect absorption refrigeration system using a low-temperature working pair, lithium bromide (LiBr)+1-butyl-3-methylimidazolium bromide ([BMIM]Br)/ethanol (C2H5OH), was proposed to reduce the driving heat source temperature and enlarge the operation range to subzero temperatures. Based on the measured thermal properties, the thermodynamic performance of the double-effect absorption refrigeration cycle under different working conditions was calculated by Matlab and compared with that using LiBr/H2O working pair. Results showed that the generation temperature of the refrigeration system using LiBr-[BMIM]Br/C2H5OH was reduced by about 30 K in comparison to LiBr/H2O under the same operating condition. The temperature in the absorber with LiBr-[BMIM]Br/C2H5OH was 40 K higher than its crystallization temperature, whereas LiBr/H2O was only less than 20 K. Moreover, the system using LiBr-[BMIM]Br/C2H5OH was able to successfully work under 273.15 K without crystallization. At a typical operating condition, the COP of the double-effect absorption refrigeration cycle with LiBr-[BMIM]Br/C2H5OH reached 1.47, which was 0.10 higher than that using LiBr/H2O. As a low-temperature working pair, LiBr-[BMIM]Br/C2H5OH showed a great potential in utilizing solar energy and the low-temperature waste heat under severe operating conditions. Furthermore, compared with LiBr/H2O, the refrigeration system had a better economic performance with LiBr-[BMIM]Br/C2H5OH working pair.

Techno-economic evaluation of novel absorption refrigerator-driven membrane distillation plants

Reducing the energy consumption of desalination plants and air-conditioning systems is primely important for efficient systems and less carbon emissions. As thermally driven systems, vapor-absorption refrigeration systems and direct contact membrane distillation plants could be integrated to minimize energy consumption. In this regard, the literature has already proposed the integration of such systems but with using only one desalination plant. Thus, the current study integrates two plants of direct contact membrane distillation with a double-effect absorption refrigeration system. One plant is driven by the refrigerator’s absorber, and the other is run by the condenser. In such a way, all the energy released from the components of the absorption refrigerator (i.e., evaporator for air-conditioning purposes and absorber and condenser for desalination) is useful. Two schemes of the integrated system are proposed with parallel- and series-multistage direct contact membrane distillation plants. For the implemented conditions, it is shown that the proposed systems produce more freshwater than the standalone membrane distillation plants. The economic analysis also demonstrates that the freshwater and cooling effect costs are lower than the standalone systems by more than threefold. Furthermore, the proposed systems show better performance than those reported in the literature. It is also shown that the parallel-multistage integrated system performs more efficiently than the series one under optimal conditions. For instance, the parallel-multistage integrated system has a water production of 1635.0 L/h, a gain-output ratio (GOR) of 2.730, a cooling effect of 117.50 ton of refrigeration (TR), a coefficient of performance (COP) of 1.034, an overall thermal performance (energy utilization factor, EUF) of 3.764, a water cost of 3.530 $/m3, and a cooling cost of 0.0044 $/kWh.

Novel integration of a parallel-multistage direct contact membrane distillation plant with a double-effect absorption refrigeration system

The increasing demand for freshwater and air conditioning triggered the search for more innovative solutions to reduce energy consumption. In this regard, this paper suggests a novel system to drive a direct contact membrane distillation (DCMD) plant by the heat released from the condenser and absorber of a double-effect vapor-absorption refrigeration (VAR) system. The suggested VAR system plays two roles: a heat pump to drive the DCMD plant and a refrigerator for air conditioning purposes. Multiple modules arranged in parallel for one DCMD plant are considered. The integrated system was examined at different conditions, and the performance indicators were represented by freshwater production, cooling capacity, gained output ratio (GOR), coefficient of performance (COP), energy utilization factor (EUF), freshwater cost, and cooling cost. For the best-tuned investigated conditions, the results of produced freshwater, cooling effect, GOR, COP, EUF, freshwater cost, and cooling cost are found as 1315 L/h, 123.4 tons of refrigeration (TR), 2.20, 1.09, 3.28, 4.09 $/m3, and 0.0052 $/kWh, respectively. These performance values outperform the standalone DCMD system by about 2.23 times for produced freshwater, 2.29 times for GOR, 3.42 times for EUF, and 2.82 times for freshwater cost. Compared to a standalone refrigerator, the cooling cost of the integrated system is reduced by 2.88 times with a slight sacrifice in cooling capacity and COP by 0.92 and 0.87 times, respectively. Therefore, the proposed system is an excellent candidate for concurrent production of freshwater and air conditioning.

Multi-dimensional assessment and multi-objective optimization of electricity-cooling cogeneration system driven by marine diesel engine waste heat

Although the prosperous shipping industry promotes economic globalization, it causes the environmental issues like air pollution and ecological destruction, due to the emission of harmful substances. Accordingly, many waste heat recovery technologies of ships have been developed and improved, among which the supercritical Brayton cycle has attracted wide attention due to its high energy conversion efficiency. Taking an actual diesel engine as the research object, this study presents four waste heat utilization schemes by combining different supercritical carbon dioxide cycles with a double effect absorption refrigeration system. The indicators of each scheme are calculated from three perspectives of thermodynamics, economy and environment, and the overall evaluation of all schemes is carried out through the analytical hierarchy process. The addition of the refrigeration system to the recuperation supercritical carbon dioxide cycle is considered to be the optimal combination. Parameter study indicates that output power, thermal and exergy efficiency increase with the turbine inlet pressure and temperature. The maximum of these thermodynamic indexes are 5987 kW, 27.35% and 56%, respectively. Furthermore, to lower temperature of high pressure generator is conducive to improving the refrigeration performance and to raise the temperature of low pressure generator also has a similar effect. Before optimization, the capital payback period and product exergoenvironmental impact of the combined system are 6.845 years and 63.023 mPts/s. After operating the optimization program, both of them become 5.81 years and 54.94 mPts/s, which are reduced by 15.12% and 12.83%, respectively.

Energy and exergy analysis of parallel flow double effect H2O-[mmim][DMP] absorption refrigeration system for solar powered district cooling

Solar thermal energy-driven double effect absorption refrigeration system (DE-ARS) for district cooling in smart cities is an efficient, and sustainable alternative for centralized air conditioning and concurrently harnesses low-grade solar energy. This work investigates ionic liquid based H2O-[mmim][DMP] mixture as an alternative working fluid to overcome the drawback of H2O–LiBr driven DE-ARS. The thermodynamic properties of H2O-[mmim][DMP] mixture is evaluated using the excess Gibbs free energy model. Performance modeling and simulation of DE-ARS is based on both energy and exergy analysis by applying the first and second laws of thermodynamic. The performance, and solution circulation ratio of parallel flow DE-ARS is assessed and optimized under various temperatures and solution distribution ratios. In comparison to the conventional H2O–LiBr, the proposed H2O-[mmim][DMP] working fluid achieves 5.22% and 4.95% improvement in COP and ECOP, respectively at Th/Te/Ta/Tc of 140/5/30/30°C . An optimization of generator temperature to achieve maximum COP and ECOP is performed for a wide range of evaporation temperature from 5 to 20°C and Ta/Tc from 30 to 40°C. An optimization of H2O-[mmim][DMP] mixture driven DE-ARS reveals the uppermost COPmax and ECOPmax of 1.81 and 0.69 for Te of 20°C and TaTc=30°C.

Advanced thermo-economic scheme and multi-objective optimization for exploiting the waste heat potentiality of marine natural gas engine

Energy crisis and environmental pollution are great challenges to the sustainable development of human society. In response to increasingly stringent emissions regulations, scientists are actively seeking solutions, such as the exploitation of new energy. In recent years, natural gas has attracted wide attention because of its environmental advantages over the traditional diesel engine. In addition, the higher exhaust temperature of natural gas engine gives it a good potential for waste heat recovery, especially in cascade utilization system. To recover the available energy of natural gas engine at multiple temperatures, an integrated system consisting of supercritical carbon dioxide Brayton cycle, double effect absorption refrigeration system and Kalina cycle is established in this study. After verifying the model accuracy of three sub-cycles, we analyze and discuss the influence of major parameters on system performance in detail, as well as carrying out the dynamic response analysis of waste heat recovery system, After the completion of multi-objective optimization, the thermodynamic and economic analysis indicate that the output power increased by 15.33% and the payback period shortened by 25.6%. Therefore, it can conclude that the new scheme is a practicable approach to recover waste heat of natural gas engines.

Economic optimization of parallel and series configurations of the double effect absorption refrigeration system

Utilization of waste or low grade energy can significantly contribute to the world’s energy demand and reduction of carbon dioxide emissions by employing absorption refrigeration systems. One of the major concerns linked with absorption refrigeration is its low efficiency and high capital cost. In present work, the objective was to develop an economic model for absorption refrigeration system adopting a previously validated thermodynamic model and optimize both the parallel and series configurations. The Thermodynamic and economic model was implemented in MATLAB®. The decision variables including temperatures of all the units of both configurations of absorption refrigeration system, outlet temperatures of cooling water, outlet temperature of chilled water, distribution ratio for parallel configuration and effectiveness of solution heat exchangers were optimized by cost minimization using Genetic Algorithm. All the required constraints, especially the crystallization enthalpy limit, were also included in the optimization problem to discard solutions which were not physically valid. The total annual cost was reduced by 33.48% and 26.26% for series and parallel configuration, respectively. Both solution heat exchangers were eliminated from the flow sheet of both configurations. Thermodynamic and economic performance at optimal operating conditions was found almost same for both configurations.

Novel and efficient integration of a humidification-dehumidification desalination system with an absorption refrigeration system

This paper introduces and evaluates an innovative humidification-dehumidification (HDH) desalination system integrated with a double-effect absorption refrigeration system to produce an abundant amount of freshwater and to provide a cooling effect for air conditioning purposes. The seawater stream of HDH system is used to cool condenser and absorber of the absorption refrigeration system while attaining a sufficient heat to drive the HDH system. The influence of operating conditions on the integrated system performance is investigated. The performance indices are selected to be: gained output ratio (GOR), coefficient of performance (COP), energy performance, freshwater production, and freshwater cost. The system can produce freshwater of 1145 L/h and a cooling capacity of 62.45 TR. The optimal performance indices are found to be 4.54 for GOR, 1.29 for COP, and 5.83 for energy performance. Furthermore, without accounting for the cooling effect, the freshwater cost is estimated to be 2.89 $/m3. In addition to the air conditioning capability, the integrated system performance shows an enhancement of 2.20 times for GOR, 2.21 times for freshwater production, and 8.24 times for water cost reduction over the traditional HDH system.

Dynamic performance comparison of different cascade waste heat recovery systems for internal combustion engine in combined cooling, heating and power

The internal combustion engine is an important prime mover in combined cooling, heating and power systems. However, approximately 30–40% of the input energy is discharged by exhaust; thus, it is significant to recover the exhaust waste heat. Cascade energy-utilisation systems have high efficiencies for exhaust recovery with a large temperature drop. However, waste heat-recovery systems usually work under different conditions and therefore, it is meaningful to study the dynamic performance of cascade systems. In this work, by developing a model library of common components in thermodynamic systems, dynamic simulation models of three cascade systems are established: an electric-cooling cogeneration system (ECCS), a double-effect absorption refrigeration system, and a double-stage organic Rankine cycle. The dynamic response speed and off-design performance of each system are analysed and compared. The results indicate that all the cascade systems respond considerably more slowly than any single-stage cycle, and the ECCS achieves the best off-design performance because both its upper and lower stages (high-temperature organic Rankine cycle and absorption refrigeration) exhibit perfect working condition adaptability, especially the lower stage. Furthermore, the structure of the ECCS is more beneficial for the lower stage to maintain satisfactory off-design performance.

Energy and Exergy Analysis of a Triple Effect Absorption Refrigeration System

Absorbsiyonlu soğutma sistemleri atık ısı kullanarak soğutma yapmanın en etkili yolunu sunmaktadırlar. Bu çalışmada üç etkili bir absorpsiyonlu soğutma sisteminin enerji ve ekserji analizi yapılmıştır. İncelenen sistem seri akışlı ve su – lityum bromür çözeltisiyle çalışmaktadır. Ek olarak üç farklı eşanjör yardımıyla sistem içinde ısı kazanımı sağlanmıştır. Üç etkili absorpsiyonlu soğutma sistemleri çift ve tek etkili absorpsiyonlu soğutma sistemlerinden daha verimlidirler. Ayrıca bu sistemler daha fazla sistem elemanına sahip ve termodinamik açıdan daha karmaşıktırlar. Yapılan analizde düşük basınçlı kaynatıcı sıcaklığına bağlı olarak sistem elemanlarının ekserji yıkımları ve sistemin toplam ekserji yıkımındaki değişim gösterilmektedir. Ayrıca birinci ve ikinci kanun verimliliğinde meydana gelen değişimde analiz sonuçlarına eklenmiştir. Sonuç olarak düşük basınçlı kaynatıcı sıcaklığının artmasıyla sistemin toplam ekserji yıkımında azalma olmuştur. Sistemin toplam ekserji yıkımdaki azalma birinci ve ikinci kanun verimliliklerine artış olarak yansımıştır. Sistem elemanları içerisinde yüksek ve düşük basınçlı kaynatıcıya ait ekserji yıkımında azalma olurken absorbere ait ekserji yıkımında artma olmuştur. Isı geri kazanımı sağlayan eşanjörlere ait ekserji yıkımlarında ise azalma gözlenmiştir.

Experimental evaluation of a 1.x-effect ejector-absorption refrigeration system

In this paper, a 1.x-effect (hybrid ejector-absorption refrigeration working between single-effect and double-effect) cycle is evaluated experimentally. Through the use of the ejector, the external heat sources’ grade is reduced. Part of the refrigerant vapor at the outlet of the low-pressure generator is directly entrained by the refrigerant vapor from the outlet of the high-pressure generator to the condenser. The system with 10 kW cooling load is experimentally studied. The COP of the system is 30.0% higher than a single-effect absorption refrigeration system, and generation temperature is at least 20 °C lower than a double-effect absorption refrigeration system.

Thermodynamic analysis and optimization of double effect absorption refrigeration system using genetic algorithm

Abstract World energy demand is continuously increasing due to population growth, extensive urbanization and rapid industrialization as growth in global energy demand will rise by 30% in 2040. This demand can be met by utilizing traditional and alternative energy resources and by enhancing energy efficiency. The energy efficiency of an energy intensive process may be improved by utilization of waste or low grade energy, design and operation optimization, and running the plant in flexible mode with improved control strategies. Waste heat of an industrial plant can be utilized by employing the so called absorption refrigeration systems (ARS). ARS is capable of utilizing the low quality energy or waste heat which otherwise may have been lost as compared to conventional compression refrigeration system (CRS) where huge quantity of electricity is required for compression of the refrigerant. One of the major concerns associated with ARS is its low efficiency. Efficiency improvement of ARS can be achieved by analyzing and optimizing the various configurations of ARS using any mathematical technique. In the present work, the aim is to analyze and maximize the performance of ARS using exergy efficiency instead of conventional coefficient of performance (COP) approach. Both the series and parallel flow configurations have been considered for the analysis and optimization. Thermodynamic model has been implemented in MATLAB® using the best available correlations for phase equilibria and thermodynamic properties. Operating conditions including temperatures of all the units of both configurations of ARS and distribution ratio for parallel configuration have been optimized. Genetic Algorithm (GA) was used to optimize the operating conditions. The effect of distribution ratio and effectiveness of heat exchanger on the maximum allowable temperature of low pressure generator (LPG) and high pressure generator (HPG) to avoid crystallization has also been evaluated. Exergy efficiency of parallel flow configuration came out to be 6.45% more than that of series flow configuration at nominal operating conditions. At optimal operating conditions, exergy efficiency improved by 11.6% and 20.81% for series and parallel flow configurations, respectively. Furthermore, exergy efficiency for parallel flow configuration is 15.1% higher than series flow configuration at optimal operating conditions. The effect of variation of effectiveness of solution heat exchangers on the optimization results has also been evaluated. Effect of weather conditions, type of energy source, application for solvent cooling and variable cooling load also needs to be considered in future.

Performance Assessment and Solution Procedure for Series Flow Double-Effect Absorption Refrigeration Systems Under Critical Operating Constraints

In this study, the effects of critical operational constraints on the operational domain of a double-effect lithium bromide/water absorption refrigeration system and its performance were investigated. These constraints were determined as the equivalence state of concentrations, the thermal unbalance between the system components of high-pressure condenser and low-pressure generator, freezing and crystallization risk of lithium bromide/water solution. For the system analysis, a simulation program was developed, and its detailed solution procedure was presented. The program outputs were initially validated with the literature. Subsequently, parametric studies were conducted for broad ranges of the component temperatures. The results demonstrate that the considered constraints were essential for acceptable design and the operational control of double-effect absorption refrigeration systems. The simulations will help to figure out under which operating conditions a double-effect absorption refrigeration system functions effectively and what kind of control strategies are essentially required to increase the coefficient of performance. Based on the operation scenario of fixed high-pressure generator temperature, the proposed system can enhance the coefficient of performance up to 31% and 84% as compared to its counterparts which function under the variable high-pressure generator temperature and the pinch point temperature difference (5 K between the high-pressure condenser and the low-pressure generator), respectively.

Multi-objective optimization of double effect series and parallel flow water–lithium chloride and water–lithium bromide absorption refrigeration systems

In this study, multi-objective optimization of the series and parallel flow type double effect absorption refrigeration systems is presented. Genetic algorithm is used to find the optimal solutions and the Pareto-optimal fronts. First, a thermodynamic model is developed to simulate the double effect series and parallel flow configurations with water–lithium chloride and water–lithium bromide solution pairs. Energy and exergy balances are applied to evaluate coefficient of performance, exergy efficiency and irreversible losses in the system components separately for the two working fluid pairs. Next, optimization is done considering coefficient of performance, exergy efficiency and the total system irreversibility rate as objective functions. The low and high pressure generator temperatures are taken as decision variables in the series configuration while for the parallel system; additionally the distribution ratio is also taken as a decision parameter. The optimization is done for four different cases of fixed evaporator, absorber and condenser temperatures. For each case, the optimal decision parameter values are determined for both the water–lithium chloride and water–lithium bromide operated double effect series and parallel configurations. The optimized coefficients of performance were found slightly lower for water–lithium chloride. Contrary to this, the optimal exergy efficiencies were more and the total system irreversibility were less for water–lithium chloride. Further, the optimal performances of the double effect water–lithium chloride systems were obtained comparatively at lower generator temperatures than those of the water–lithium bromide systems.

Ammonia lithium nitrate and ammonia sodium thiocyanate double effect absorption refrigeration systems: Thermodynamic analysis

This paper presents a comparison of the performance for three configurations of double effect absorption refrigeration systems with single effect one using ammonia lithium nitrate (NH3/LiNO3) and ammonia sodium thiocyanate (NH3/NaSCN) as working solutions. The effect of operating parameters on COP and exergetic efficiency of the cycles is investigated. In order to avoid error in estimation of solutions enthalpy and entropy at high temperatures, linear equations for specific heat of solutions are obtained from correlating the experimental data. Furthermore, the effects of operating parameters on crystallization possibility are studied. The COP of double effect systems are maximum 60% more, but exergetic efficiency is maximum 16% less than those for single effect cycles. The NH3/LiNO3 systems compared to the NH3/NaSCN systems can perform at lower generator temperatures with higher COP and exergetic efficiency. Operating range of NH3/LiNO3 system is wider, since it is limited for NH3/NaSCN cycle because of crystallization occurrence.