Single-effect Absorption Refrigeration System Research Articles

Research on geothermal-driven single-effect absorption refrigeration systems with different working fluids: energy and exergy analysis

Abstract Geothermal energy is not only environmentally friendly and has low carbon but also represents a nonintermittent technology. It is anticipated that its utilization in human society will experience rapid growth in the coming decades. Absorption refrigeration can be employed for the recovery of geothermal resources. However, the low performance of absorption refrigeration systems has hindered their development. In order to advance absorption refrigeration technology suitable for geothermal energy recovery, this study developed a mathematical model for an absorption refrigeration system using 55% lithium bromide (LiBr) and 35% lithium chloride (LiCl) solutions as working fluids. The impact of various parameters, including cooling water conditions, chilled water conditions, heat source parameters, and working fluid concentration, on the thermodynamic performance, system efficiency, and exergy efficiency of a single-effect absorption refrigeration system was analyzed. The results reveal that the cooling water inlet temperature and flow, chilled water inlet temperature, heat source inlet temperature, and working fluid concentration are the primary factors affecting the thermodynamic performance and exergy efficiency of the absorption refrigeration system. The coefficient of performance (COP) of the system increases with higher cooling water flow, chilled water inlet temperature, and working fluid concentration, but decreases with higher cooling water inlet temperature. Within a certain temperature range, the COP increases with higher heat source temperature. The effective COP (ECOP) increases with higher cooling water inlet temperature, cooling water flow, chilled water inlet temperature, and working fluid concentration, while it decreases with higher heat source temperature. The highest COP values for the LiBr and LiCl solution single-effect absorption refrigeration systems are 0.795 and 0.785, respectively, while the highest ECOP values are 0.694 and 0.684, respectively.

The performance of [Emim]Br/H2O as a working pair in the absorption refrigeration system

The energy efficiency of the single-effect absorption refrigeration systems (ARS) using ionic liquid (IL) [Emim]Br as an absorbent and water as a refrigerant is evaluated in this study. The thermodynamic properties of the mixture, such as vapor pressures and excess enthalpies, are calculated using the non-random two-liquid (NRTL) activity coefficient model. The coefficient of performance (COP) is estimated with fixed temperatures for the evaporator, absorber, condenser, and generator, set at 10, 30, 40, and 100 °C, respectively. It is found that the COP of the single-effect ARS using [Emim]Br-H2O as the working pair is about 0.8, which is slightly lower than that obtained with LiBr-H2O (0.83), but much higher than that of H2O-NH3 (0.65) systems. The effect of generator temperature on COP has the same trend as that of other IL working pairs. The influence of each component temperature on the system’s performance is investigated, and it is found that the single-effect ARS performs very well under different conditions with [Emim]Br - H2O as the working pair.

Energetic and Exergetic Analysis of a Solar-Driven Single-Effect Absorption Refrigeration System Using LiBr + LiCl/H2O Solution Mixture

Abstract Comprising an eco-friendly blueprint, absorption refrigeration systems have attracted a lot of interest as they can use biomass, solar and geothermal energy sources which can mitigate climate change. The current study presents a methodology based on energy and analysis for solar-driven single-effect absorption refrigeration systems, which offer a 50-kW cooling capacity. This study proposes a new mixture ratio of LiBr + LiCl (mass ratio of 2:1)/H2O solution and compared it to LiBr/H2O thermodynamically. Based on the climate data of Kocaeli province in Turkey, an evacuated tube collector is employed to benefit from solar energy to meet the generator heat load of the system. Although at an evaporator temperature of 5 °C, enhanced thermodynamic performance is evident with the use of the LiBr + LiCl/H2O system, and a diminished solar collector area is required compared to the system utilizing LiBr/H2O; there is a level of attrition relating to the impact of the former with a single degree rise in evaporator temperature. However, this remained at a greater value than for the latter system. The final results pointed out that LiBr + LiCl/H2O has a 48.93% lower circulation ratio, 8.81% higher coefficient of performance (COP) of chiller, 8.88% higher solar COP, 8.96% higher exergy efficiency of chiller, 8.90% higher exergy efficiency of solar-driven system, 8.92% lower solar collector area, and 8.91% lower storage tank volume than LiBr/H2O system in the investigated operating temperature ranges. The final results of the present study can be safely tested in the experimental design of single-effect absorption chillers.

Simulation, energy and exergy analysis of compressed air energy storage integrated with organic Rankine cycle and single effect absorption refrigeration for trigeneration application

Compressed air energy storage (CAES) is increasingly investigated as a viable technology for balancing electricity supply and demand. The main purpose of CAES is to overcome the intermittent problem when renewable energy is introduced. However, the round-trip efficiency (RTE) of the CAES system commercially developed is still low (around 54 %) and requires further improvement. This study proposed a novel combined cooling, heating and power (CCHP) system, which improves the RTE in two ways: (i) organic Rankine cycle (ORC), which recovers the waste heat and produces extra power; (ii) single effect absorption refrigeration, which delivers cooling capacity with further recovery of waste heat from the flue gas. Steady-state process simulation of the CAES system, ORC and single effect absorption refrigeration system was developed in Aspen Plus® software. The proposed system was evaluated through process, energy, and exergy analysis. The effect of various working parameters on the performance of the CCHP system was also analysed. The results indicated that under design condition, the proposed CCHP system can produce about 206 MW electrical energy, 28 MW heating and 0.2 MW cooling capacity. The RTE of the proposed system (at 66.35%) showed an improvement of 12.35% when compared with the CAES system commercially deployed. The overall exergy efficiency is about 51% and the total exergy destruction of the components of the system is 477 MW. The combustion chamber is responsible for more than half of the exergy destruction.

Thermal analysis of a novel single-effect absorption refrigeration system using water/ionic liquid as working fluids

Based on the demand of improving the cooling performance of traditional absorption refrigeration system, a novel single-effect refrigeration system with assisted compressors using water/ionic liquids as working fluids was comprehensively analyzed. In present work, four kind of ionic liquids:1-butyl-3-methylimidazolium dibutylphosphate [BMIM][DBP], 1-methyl-3-methylimidazolium dimethylphosphate[MMIM][DMP], 1-ethyl-3-methylimidazolium dimethylphosphate [EMIM] [DMP], and 1-ethyl-3-methylimidazolium acetate [EMIM][AC], which was studied as working fluid in absorption system at the first time, was modeled and simulated in both systems. Thermodynamic properties of new single-effect refrigeration system were numerically analyzed by non-random two-liquid models and the mass and energy conservation equations. The effects of compression ratio(pr) and temperature on the COP and exergetic efficiency (ECOP) were graphed and discussed. The simulating results showed the potential of ionic liquids to be used as substitute for traditional working fluids. Moreover, comparison results suggested the system with auxiliary compressors was better than the traditional system for its lower heat source temperature and higher cooling performance. It was better to increase the compression ratio of the compressor located between the absorber and the evaporator than to increase the compression ratio of the compressor located between the generator and the condenser.

Thermodynamic performance analysis of a single-effect absorption refrigeration system operating with water and 1-ethyl-3-methylimidazolium-based ionic liquids mixtures

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.

New environment friendly working pairs of dimethyl ether and ionic liquids for absorption refrigeration with high COP

To overcome the limitations of absorption refrigeration system brought by commercial working pairs of NH3/H2O and H2O/LiBr for the utilization of low-grade heat, a new class of working pairs consisting of dimethyl ether (DME) and ionic liquids (ILs) are developed. The solubilities of DME in three ILs [BMIM][BF4], [BMIM][PF6] and [BMIM][Tf2N] were firstly measured and correlated. Then, COPs of the single-effect absorption refrigeration system (ARS) and absorption-compression hybrid refrigeration system (ACRS) using DME/IL were calculated under different conditions. The maximum COP of ARS using the three DME/IL working pairs can be up to 32.0% larger than that using NH3/H2O, while the maximum COP of ACRS using the three DME/IL working pairs can be up to 38.3% larger than that using NH3/H2O under studied conditions. The three DME/IL working pairs also show much better cooling performance than HFC/IL and HFO/IL working pairs which are R152a/[HMIM][Tf2N] and R1234ze(E)/[HMIM][Tf2N]. In ACRS, DME/ILs can drop the optimal generation temperature in ARS by more than 10 K. DME/ILs are very promising alternative absorption refrigeration working pairs due to the high COP, wide applicability and environmental friendliness.

Energy and Exergy Analysis of a Lithium Bromide – Water (LiBr – H2O) Solar Absorption Refrigeration System

Energy and environmental analysis establishes an important role in industrial performance due to the ease at which improvement processes are developed to increase production targets while minimizing the level of pollution and operating costs. Additionally, the exergy destruction analysis defines a clearly structured understanding related to the performance of the thermodynamic cycle. Exergy and energy analysis of the thermodynamic process is investigated based on advanced theories of thermal sciences in order to improve their energy efficiency and to evaluate the exergy destruction developed during their operation. Consequently, thermodynamic efficiency and total exergy destruction studies are used to define the thermodynamic interactions between mechanical devices and to establish the optimal behavior of refrigeration systems under specific operating conditions. This paper performs an energy and exergy analysis of a single effect absorption refrigeration system using a LiBr - H2O solution as working fluid and cooling water for the cycle, considering flat plate solar collectors as heat sources for the absorption refrigeration system. The solar field has been modeled by using a proposed model based on meteorological data, and the cycle is modeled in Aspen Plus® simulation environment, obtaining the thermodynamic properties necessary for the subsequent calculations. Afterwards, some indicators are calculated, such as the Coefficient of Performance (COP), exergy yield and exergy destruction, using Engineering Equation Solver (EES). Consequently, by using MATLAB®, it has been possible to determine the set of parametric variables and operating conditions where a better energy performance of the system can be obtained through optimization algorithms improving the COP from 0.7374 to 0.8097 according to the meteorological conditions of Colombia.

System simulation of air-cooling single effect LiBr absorption refrigerating system driven by solar heat source

Air-cooling single-effect absorption refrigeration system has the characteristics of water saving, space saving and maintenance cost compared with water-cooling. In order to study the characteristics of air-cooled system, this paper uses Aspen Plus to build an air-cooled single-effect LiBr absorption refrigeration system with a cooling capacity of 23kW and adiabatic evaporation and adiabatic absorption, and the influence of temperature on the system at different condensing temperatures is studied. The results show that with the increase of generating temperature, the load increase of solution heat exchanger gradually slows down and then becomes faster, while the load increase of other equipment gradually slows down. After the system COP value rises to a certain value, it basically remains unchanged.

Performance evaluation of an absorption refrigeration system using R1234yf - organic absorbents working fluids

This study proposes the use of hydrofluoroolefins and organic absorbents mixtures as a working fluid pair in a single-effect absorption refrigeration system. In the refrigeration cycle, the 2,3,3,3-tetrafluoropropylene (R1234yf) is used as a refrigerant, and the triethylene glycol dimethyl ether (DMETrEG) and N-methyl-2-pyrrolidone (NMP) are used as absorbents. The working fluid’s thermophysical properties and the verified thermodynamic models are presented in this paper. This study illustrates the effect of the generator temperature (330.15–365.15 K), absorber temperature (293.15–313.15 K) and evaporator temperature (268.15–283.15 K) on the coefficient of performance (COP), the circulation ratio and the solution concentrations. Among the most prominent results of this research are that the COP is between 0.053-0.409 for the mixture containing the DMETrEG, while it is between 0.025-0.333 for the mixture containing NMP. The R1234yf-DMETrEG mixture is recommended based on the overall performance, circulation ratio and stability, followed by R1234yf-NMP mixture. The effectiveness of R1234yf-organic absorbents is lower than those of R134a and R152a with the same absorbents. Therefore, the incorporation of a compressor to assist the absorption cycle can improve the COP of the cycle and extend the operation range of the proposed R1234yf-DMETrEG mixture.

Comprehensive performance analysis and optimization of 1,3-dimethylimidazolylium dimethylphosphate-water binary mixture for a single effect absorption refrigeration system

The energy and exergy analyses of the absorption refrigeration system (ARS) using H2O-[mmim][DMP] mixture were investigated for a wide range of temperature. The equilibrium Duhring (P-T-XIL) and enthalpy (h-T-XIL) of mixture were assessed using the excess Gibbs free non-random two liquid (NRTL) model for a temperature range ??? of 20°C to 140°C and XIL from 0.1 to 0.9. The performance validation of the ARS cycle showed a better coefficient of performance (COP) of 0.834 for H2O-[mmim][DMP] in comparison to NH3-H2O, H2O-LiBr, H2O-[emim][DMP], and H2O-[emim][BF4]. Further, ARS performances with various operating temperatures of the absorber (Ta), condenser (Tc), generator (Tg), and evaporator (Te) were simulated and optimized for a maximum COP and exergetic COP (ECOP). The effects of Tg from 50°C to 150°C and Ta and Tc from 30°C to 50°C on COP and ECOP, the Xa, Xg, and circulation ratio (CR) of the ARS were evaluated and optimized for Te from 5°C to 15°C. The optimization revealed that Tg needed to achieve a maximum COP which was more than that for a maximum ECOP. Therefore, this investigation provides criteria to select low grade heat source temperature. Most of the series flow of the cases of cooling water from the condenser to the absorber was found to be better than the absorber to the condenser.

The parametric study of an absorption refrigeration system single effect with water-lithium bromide

Absorption machines present an interesting alternative to conventional air conditioning systems. The Absorption machines offer an ecological aspect, in terms of the possibility of using solar energy as a heat source, and refrigerant having no ozone –depleting potential or global warning effect reported in literature.
 In this paper a performance of a single effect absorption refrigeration systems of Water-Lithium Bromide are studied, some physical quantities were modelled and Plots, in particular the effect of operating temperatures on the coefficient of performance and the impact of solution exchanger efficiency and the system efficiency.

A simulation study of n-butane absorption refrigeration system using commercial hydrocarbons as absorbents

Abstract A heat-powered single-effect absorption refrigeration system operating with commercial n-butane as a refrigerant and six commercial hydrocarbons (stabilized condensate, light naphtha, heavy naphtha, reformate, light reformate and heavy reformate) as absorbents was studied. The main target of the study was actuating these systems to the available waste heat. Simulation models were created using Aspen HYSYS process simulator. The main parameters of an absorption refrigeration system, using the proposed working fluids, were compared at different evaporator, condenser and absorber temperatures to select the best working fluid. Moreover, a focused interpretation was given to the behavior of the best system at different operating conditions. Furthermore, the effect of both butane recovery and purity, in the generator, on the performance of the best system was investigated. Results revealed that, among the proposed working fluids, the best performance was achieved by butane/heavy naphtha. It could achieve a Coefficient of Performance (COP) of 0.78 at evaporator temperature of 20 °C and both condenser and absorber temperatures of 30 °C. The COP passed through a different maximum value at certain recovery for each evaporator temperature and condenser and absorber temperatures and similar behavior was observed for purity. Low reboiler temperatures were feasible at low butane recoveries with almost the same COP of the high butane recoveries. Generally, Butane/heavy naphtha system could compete effectively with the commercial absorption refrigeration systems, within their range of operating conditions, without experiencing their limitations.

Simulation and comparison of combined ejector-absorption and single effect absorption refrigeration systems

Refrigeration by absorption is gaining more and more importance nowadays especially in applications where the source of energy used in the generator is renewable. However the major problem of this type of refrigeration lies in the COP, which seems to be weaker than compression machines. The use of an ejector is one of the means that can help overcome this problem. In this work, we are interested in the ammonia-water absorption cycle comprising a gas-gas ejector interposed between the generator and the condenser. We suppose that adding a flash tank between the condenser and the evaporator could help improve the entrainment ratio of the ejector. Simulations using the Hysys software are performed in order to look for the optimal conditions for the work of this machine and to make a comparison in terms of performance with single effect cycles. Results showed a significant improvement in the COP and proved therefore that it has better performance than single effect cycles.

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.

Design and Analysis of a Solar Powered Absorption Refrigeration System for Cooling a House in Isparta Province

In the present study, cooling of a duplex house placed in Isparta province by using solar-powered single effect absorption refrigeration system, which uses water-lithium bromide (H2O-LiBr) mixture, was evaluated in details. Firstly, the cooling load of the house was determined as 19.34 kW. In order to provide the cooling load of the house (19.34 kW), the heat required for the generator was calculated as 26.76 kW, and the required collector surface area was determined by considering different types of collectors (flat plate and vacuum tube) to meet this heat capacity. In order to provide the cooling load of the house, the required surface area for the vacuum tube collectors was calculated as 10.32 m2 while it was found as 25.95 m2 for the flat plate collectors. It was concluded that the usage of vacuum tube collector with 57.9% efficiency is more appropriate since the required collector surface area is 15,63 m2 less than the required collector surface area for flat plate collector.

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.

Performance comparison of two absorption-compression hybrid refrigeration systems using R1234yf/ionic liquid as working pair

R1234yf (2,3,3,3-tetrafluoroprop-1-ene)/ionic liquid is a kind of environment-friendly working pair, which can overcome the disadvantages of H2O/LiBr and NH3/H2O. In this work, three new working pairs R1234yf/[HMIM][TfO], R1234yf/[HMIM][PF6], R1234yf/[HMIM][BF4] were proposed and new solubility data for them were determined. Two new absorption-compression hybrid refrigeration systems were proposed to improve the cooling performances of the single-effect absorption refrigeration system using R1234yf/[HMIM][TfO], R1234yf/[HMIM][PF6] and R1234yf/[HMIM][BF4] as working pair. The effects of compressor position, compression ratio (r), generation temperature (Tg), evaporation temperature (Te), condensation temperature (Tc) and absorption temperature (Ta) on the coefficient of performance (COP) and circulation ratio (f) were analyzed. Comparison result shows that the two systems can effectively improve the cooling performance of the single-effect absorption refrigeration system including increasing COP, reducing the heat load of condenser and f, and enlarge the operation range of Tg, Ta, and Te. Putting compressor between evaporator and absorber is a better choice than putting it between generator and condenser. R1234yf/[HMIM][TfO] shows better cooling performance than R1234yf/[HMIM][PF6] and R1234yf/[HMIM][BF4] due to its favorable thermophysical properties.

Absorption refrigeration system using engine exhaust gas as an energy source

A single-effect absorption refrigeration system that uses LiBr-water solution and engine exhaust gas is investigated. The generator is a spiral fin-and-tube heat exchanger, while the condenser, evaporator, and absorber are shell and coil heat exchangers. Experiments are conducted at engine speeds of 1000, 1200, 1400, and 1600 rpm; expansion valve opening percentages of 54.5%, 72.7%, and 90.9% at the separator outlet and 3.41%, 4.55%, and 5.68% at the condenser outlet; refrigerant temperatures at the condenser outlet of 25, 30, and 35 °C; and LiBr-water solution flow rates of 0.35 and 0.7 LPM. The results show that the system could work with an engine speed of 1200–1400 rpm. The cooling load and coefficient of performance (COP) increase with increasing engine speed. The highest COP of 0.275 is reached at an engine speed of 1400 rpm, opening percentage of 72.7% at the separator outlet and 4.55% at the condenser outlet, water temperature of 25 °C at the condenser outlet, and LiBr-water flow rate of 0.7 LPM. The decreased refrigerant temperature at the condenser outlet helps to increase both cooling load and COP. The increase of the LiBr-water solution flow rate helps to increase cooling load but decrease COP.

VARIABLE CAPACITY ABSORPTION COOLING SYSTEM PERFORMANCE FOR BUILDING APPLICATION

The increasing energy costs and environmental awareness call for a shift towards some interesting energy alternatives preferably the use of renewable energy. The present study investigates the impact of varying cooling capacity and other operating parameters in a single-effect absorption refrigeration system, using the concept of energy and exergy as a building heating/cooling alternative. The solar heat is used as an input to the generator of absorption refrigeration system. The results obtained from investigation revealed that variation in cooling capacity influences coefficient of performance (COP), exergy loss in different components as well as exergy efficiency. The values of COPcooling and COPheating lies in the range of 0.71-0.89 and 1.71-1.89 respectively for variations in cooling capacities ranging from 1 TR to 20 TR at maximum generator temperature of 80oC. However, exergy efficiency of the system lies in the range of 0.32-0.41 for same variation in cooling capacities. It has also been established that an increase in evaporator temperature and at maximum cooling capacity both COPcooling and COPheating shows an increasing trend. The exergy efficiency also shows maximum value at the highest cooling capacity at a particular evaporator temperature which further with an increase in evaporator temperature shows a decreasing trend. The irreversibility behavior in all the components i.e., solution heat exchanger, absorber, generator, evaporator and condenser shows an expected trend with the variation in cooling capacity. Hence, use of the above mentioned system as a heating and/or cooling alternative for buildings is suggested.