Double-effect Absorption Refrigeration Research Articles

Numerical investigation of the thermal performance of compressor-assisted double-effect absorption refrigeration using [mmim]DMP/CH3OH as working fluid

The thermal performance of compressor-assisted double-effect absorption refrigeration (CDAR) was numerically investigated and comprehensively analyzed with 1, 3-dimethylimidazolylium dimethylphosphate/methanol ([mmim]DMP/CH3OH) as working fluid. The CDAR system was modeled and simulated based on the proposed mathematical model of the compression process by considering the mass and energy conservation of each component. The effects of compression ratio and heat source temperature on the system’s operating state, including solution temperature, refrigeration concentration, mass flow, and heat load of each component, were calculated and discussed. Variations in the coefficient of performance and exergy efficiency in four cases were simulated and compared. Results suggested that placing the assisting compressor between the evaporator and absorber was a good option, and placing the assisting compressor between two generators was also acceptable. The exergy losses of each component were calculated and compared. The largest exergy loss occurred in the low-temperature generator and accounted for approximately one-third of the total exergy input. The main reason for the exergy loss in the diffusion absorption refrigeration system was heat transfer with a temperature difference.

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.

Performance analysis of solar assisted multi-effect absorption cooling systems using nanofluids: A comparative analysis

The performance comparison of multi-effect absorption refrigeration systems has been conducted in the present study. The absorption cooling cycles are operated on the solar heat in order to improve the utilization of high temperature heat sources for absorption systems. The absorption refrigeration cycles of multi-effect are modeled and designed for the identical refrigeration capacity along with the similar operating conditions. The engineering equation solver tool is deployed to analyze the coefficient of performance (COP) and exergetic efficiency of the absorption cooling cycles. Performance simulations were carried out over a range of operating conditions, including the effect of heat transfer fluids (nanofluids) used in solar parabolic trough collectors. The COP of the triple effect absorption refrigeration cycle (TEARC) is observed to be 1.752. The COP of the double effect absorption refrigeration cycle (DEARC) is perceived to be 51.9% higher as compared with single effect absorption refrigeration cycle (SEARC) which has a COP of 0.852. The exergetic efficiency of the TEARC is witnessed to be 16% higher than DEARC, and it is 31% higher than SEARC at an evaporator temperature of 7 ̊C. The effect of nanoparticle's (Al2O3) concentration and percentage of weak and strong solutions of LiBr-H2O is also evaluated at design conditions. A high temperature heat reservoir is required to operate the TEARC, whereas, the SEARC and DEARC operate on lower temperatures than triple effect cycle.

Thermodynamic analysis of a novel combined cooling, heating and power system driven by solar energy

A novel combined cooling, heating and power system (CCHP) driven by solar energy is proposed. The system applies an organic Rankine cycle, a double effect lithium bromide-water absorption refrigeration system, and heat exchangers to generate electricity, cooling and heating, respectively. Energy and exergy analyses are conducted to determine system efficiencies and losses. The cycle is compared with similar combined cycle that differs by using a cooling subsystem having a single effect absorption chiller. The effects of some key thermodynamic parameters on the performance of the cycle are examined. The results reveal that, for the same amount of input heat, the usage of a double effect absorption refrigeration system instead of a single effect absorption chiller can raise the amount of cooling power up to 48.5% and consequently can improve the performance of the system. At the same time, heating power rises by 20.5%, resulting in an increase in the cogeneration heat and power efficiency to 96.0%, while net electrical power production declines by 27%. In addition, it is determined that a high exergy destruction rate occurs in the solar collectors.

An exergy based comparative study between LiBr/water absorption refrigeration systems from half effect to triple effect

In this paper a comparative study was performed between five classes of LiBr/water absorption refrigeration systems to investigate the influence of various operating parameters on the coefficient of performance, the thermal loads of the components, the exergetic efficiency and the total change in the exergy of systems. The exergetic analysis of all system’s components was done after their energy analysis. The half effect, single effect, series class of double effect, parallel class of double effect and triple effect absorption refrigeration cycles were compared together in this study. The exergetic evaluation of the thermodynamic flows, which go through this cycle, was performed for a refrigerating capacity 300kW. According to energetic and exergetic analysis, the results showed that the coefficient of performance and exergy efficiency increases from the half effect, to the single, double and triple effect refrigeration system while total exergy change approximately decreases. Furthermore, it was found that there is an optimum generator temperature where the COP and exergy efficiency of the five configurations of absorption refrigeration systems is maximum and the total exergy change becomes minimum.

Performance Comparison between an Absorption-compression Hybrid Refrigeration System and a Double-effect Absorption Refrigeration Sys-tem

Conventional absorption refrigeration systems (ARSs), which are mainly driven by heat, have a competitive primary energy efficiency (PEE) compared with chillers driven by electricity. In the typical ARS, a large quantity of high-temperature heat is supplied into the generator, while a substantial amount of low-temperature heat is rejected to the environment from the condenser, it’s a huge waste. In order to decrease the input heat for generator and enhance the performance of conventional ARS, a kind of absorption-compression hybrid refrigeration system recovering condensation heat for generation (RCHG-ARS) was ever proposed. In the present study, the models of both RCHG-ARS and double-effect absorption refrigeration system (DEARS) are established, and the effects of different parameters on them are simulated and compared with each other. As a conclusion, the PEE of RCHG-ARS can be 29.0% higher than that of DEARS, and RCHG-ARS has a wider working conditions than DEARS due to the existence of the compressor.

High efficiency H2O/LiBr double effect absorption cycles with multi-heat sources for tri-generation application

The objective of this study is to develop a high-efficiency double effect absorption cycle using multi-heat sources for tri-generation (trigen) application. The trigen system produces electricity, heating and cooling loads at the same time. The double-effect absorption refrigeration system consists of two generators, condensers, solution heat exchangers, expansion valves, an absorber and an evaporator. The cycle simulation is carried out for the H2O/LiBr double effect absorption cycle with multi-heat sources for parallel, serial, reverse, revised serial and revised reverse flow patterns. The absorption refrigeration system uses the high temperature steam and hot water as the multi-heat sources. A new high-efficiency cycle is selected depending on the arrangements of additional heat exchangers. This study recommends HX 2-2 cycle with two additional heat exchangers (SDHHX and DHX) as the best candidate for trigen application. It is concluded that THotwater has much more significant effect on the COP and Q̇E than Tsteam in the HX 2-2 cycle. It is also found that the most important UA to affect the COP is UALG while that to affect Q̇E is UAA.

Integration of biomass gasification with a solid oxide fuel cell in a combined cooling, heating and power system: A thermodynamic and environmental analysis

A biomass-fueled combined cooling, heating and power (CCHP) system is proposed and thermodynamically assessed. The system consists of a biomass gasifier (as the primary energy source), a solid oxide fuel cell (as the power generation unit), a double effect absorption refrigeration cycle (for cooling production) and a HRSG (for steam production for heating purposes). Taking into account the environmental considerations, energy and exergy analyses are conducted for the proposed system and its performance is compared with the corresponding power generation unit and the CHP system. Through a parametric study it is observed that the current density and fuel utilization factor play key roles on the system performance. In addition, considering the system as a combination of three subsystems, i.e. the SOFC, CHP system and CCHP system, an environmental impact assessment in terms of CO2 emission is conducted. Municipal solid waste is examined as biomass and it is observed that maximum exergy efficiency of the CCHP system is 37.92% with a CO2 emission of 20.37 t/MWh which shows an increase of 49.88% in exergy efficiency and 64.02% decrease in CO2 emission, compared to the solo SOFC system. It is concluded that the air heat exchanger and the gasifier are two major sources of irreversibility in the system and the exergy loss is considerable compared to after burners' exergy destruction.

A thermodynamic evaluation on high pressure condenser of double effect absorption refrigeration system

One of the parameters affecting the COP of the absorption system can be considered as the thermal balance between the high pressure condenser (HPC) and the low pressure generator (LPG) since heat rejected from the HPC is utilized as an energy source by the LPG. Condensation of the water vapor in the HPC depends on the heat removal via the LPG. This circumstance is significant for making an appropriate design and a controllable system with high performance in practical applications. For this reason, a thermodynamic analysis for the HPC of a double effect series flow water/lithium bromide absorption refrigeration system was emphasized in this study. A simulation was developed to investigate the energy transfer between the HPC and LPG. The results show that the proper designation of the HPC temperature improves the COP and ECOP due its significant impact, and its value necessarily has to be higher than the outlet temperature of the LPG based on the operating scheme. Furthermore, the COP and ECOP of the absorption system can be raised in the range of 9.72–35.09% in case of 2 °C-temperature increment in the HPC under the described conditions to be applied.

Finite-time thermodynamics optimization of an irreversible parallel flow double-effect absorption refrigerator

Finite-time thermodynamics optimization analysis based on the coefficient of performance and the ecological coefficient of performance criteria has been carried out. This was done analytically and numerically for a double-effect parallel flow absorption refrigerator with losses of heat resistance, heat leakage and internal irreversibility. The maximum of the coefficient of performance and the corresponding optimal conditions have been derived analytically. The optimum performance parameters, which maximize the coefficient of performance objective function have been investigated. The effects of irreversibility parameters on the general and optimal performances on the basis of COP and ECOP functions have been discussed. The results obtained may provide the basis for designing real double-effect parallel flow absorption refrigerators.

Energy and exergy analysis of a double effect absorption refrigeration system based on different heat sources

Absorption refrigeration systems are environmental friendly since they can utilize industrial waste heat and/or solar energy. In terms of heat source of the systems, researchers prefer one type heat source usually such as hot water or steam. Some studies can be free from environment. In this study, energy and exergy analysis is performed on a double effect series flow absorption refrigeration system with water/lithium bromide as working fluid pair. The refrigeration system runs on various heat sources such as hot water, hot air and steam via High Pressure Generator (HPG) because of hot water/steam and hot air are the most common available heat source for absorption applications but the first law of thermodynamics may not be sufficient analyze the absorption refrigeration system and to show the difference of utilize for different type heat source. On the other hand operation temperatures of the overall system and its components have a major effect on their performance and functionality. In this regard, a parametric study conducted here to investigate this effect on heat capacity and exergy destruction of the HPG, coefficient of performance (COP) of the system, and mass flow rate of heat sources. Also, a comparative analysis is carried out on several heat sources (e.g. hot water, hot air and steam) in terms of exergy destruction and mass flow rate of heat source. From the analyses it is observed that exergy destruction of the HPG increases at higher temperature of the heat sources, condenser and absorber, and lower temperature of the HPG, LPG and evaporator. This destruction is maximized when hot air heat source is used and minimized with utilizing hot water heat source.

First law analysis of a novel double effect air-cooled non-adiabatic ammonia/salt absorption refrigeration cycle

This paper thermodynamically analyzes an air-cooled type double effect absorption refrigeration system using ammonia/lithium nitrate and ammonia/sodium thiocyanate solutions as working pairs and driven by high temperature heat source such as waste heat energy, innovatively, an air-cooled type non-adiabatic absorber is implemented in the system to improve the cycle performance. Comparing to the single effect absorption refrigeration system, the double effect system is designed not only to directly and efficiently utilize high temperature waste heat energy for cycle performance improvement, but also to greatly extend the application occasion to high ambient temperature condition. Parametric analysis of the present system show that COP of the double effect system is 30–60% higher than the single effect system under air cooling working condition and the high pressure generating temperature of the double effect system can be extended to as high as 220°C. Influences of high pressure generator temperature, low pressure generator temperature, absorber outlet solution temperature as well as other system working parameters on cycle performance are numerically simulated and parametric optimization is provided in the present model. Cycle performance comparison of NH3/LiNO3 system with NH3/NaSCN system has been carried out. According to the simulation results, COP of NH3/NaSCN system is found to be 10–15% higher than that of NH3/LiNO3 system in evaporating temperature range of -10°C<Te<5°C. However in low evaporating temperature conditions, Te⩽-10°C, NH3/LiNO3 systems are found to be more competitive than that of NH3/NaSCN system. The main concern of the present study is that implementation of non-adiabatic absorbers in air-cooled type double effect ammonia/salt absorption refrigeration systems is essential, and only under non-adiabatic absorption conditions can the double effect ammonia/salt system realize miniaturization.

Dynamic Modeling and Simulation for Double Effect Absorption Refrigeration Using [mmim]DMP/CH&lt;sub&gt;3&lt;/sub&gt;OH as Working Pairs

The dynamic modeling and simulation based on components for parallel type and series type absorption refrigeration using novel working pairs [mmim]DMP/CH3OH were conducted. The modified UNIFAC model and Wilson model were used to describe the vapor liquid equilibrium and excess enthalpy of the [mmim]DMP/CH3OH solution, respectively. Under certain assumptions, the dynamic model was developed including the HPG (high pressure generator) model, the LPG (low pressure generator)-condenser model, the absorber-evaporator model and the SHX (solution heat exchanger) model. The effect of exhaust gas inlet temperature and chilled water inlet temperature on the thermodynamic performances were presented and discussed. The best COP of 1.27 and 1.17 for parallel type and series type system, respectively, were observed. The transient responses at step changes of two variables and on experimental conditions were carried out and analyzed, and the latter had been compared with the experimental data in literature. It is indicated that the model well describes the stable and transient characteristics of the double effect absorption refrigeration using [mmim]DMP/CH3OH, and can be employed to enable the further parameter optimization and control design.

Simulation study of the combination of absorption refrigeration and ejector-expansion systems

Recently, in refrigeration industry the use of efficient dual-evaporator refrigeration systems has been paid a lot of attention. These systems sound even more interesting when they are a combination of different kinds of conventional refrigeration systems. In this paper three thermally driven chillers consisting of absorption refrigeration and ejector-expansion transcritical cascade CO2 cycles are proposed and investigated thermodynamically. The systems are called “hybrid dual-evaporator” cycles. The absorption cycle in the systems is either the single-effect or double-effect series-flow or double-effect parallel-flow cycle for each of which a solar collector is considered to supply the required heat in their generator. The performances of hybrid dual-evaporator systems are analyzed and optimized, using the Engineering Equation Solver and applying the principles of conservation of mass and energy as well as the exergy balance to each component of each system. Results indicate that combing the double-effect parallel absorption refrigeration system with ejector-expansion system gives the highest coefficient of performance among the other configurations. However, a combination of single-effect absorption refrigeration system with ejector-expansion cycle may be preferred due to its less complexity and reasonable exergy efficiency. Results also reveal that at optimum generator temperature of 72.92 °C the coefficient of performance and exergy efficiency of hybrid dual-evaporator with single-effect absorption are 1.182 and 0.2564, respectively. In addition, it is observed that increasing the cooling capacity ratio from 1 to 6 results in increases of the coefficient of performance and exergy efficiency of configurations by up to 36.32% and 11.5% respectively.

Exergoeconomic comparison of double effect and combined ejector-double effect absorption refrigeration systems

At a particular temperature range, heat sources are not hot enough to drive lithium bromide double effect absorption refrigeration systems efficiently and are too hot to be used for the single effect systems because of the risk of crystallization. A combined ejector-double effect absorption cycle is a good choice to make effective use of heat sources at this temperature range for refrigeration purposes. In this study, detailed exergoeconomic analyses are performed for series flow double effect and combined ejector double effect systems in order to investigate and compare the influence of various operating parameters on investment costs of the overall systems and product cost flow rates. In addition, the proportion of component costs in the overall systems costs and exergoeconomic results are obtained. The results show that the combined cycle operates more economically compared to the double effect system.

Exergoeconomic analysis of double effect absorption refrigeration systems

Exergoeconomic analyses are reported for three classes of double effect LiBr/water absorption refrigeration systems in order to investigate the influence of various operating parameters on investment costs of the overall systems and product cost flow rates. In addition, the contributions of component costs to the overall costs are obtained for each system and the results of the exergoeconomic analyses of the systems are described. The results reveal the advantages and disadvantages of different configurations of double effect LiBr/water absorption refrigeration systems from an exergoeconomic point of view and are expected to be useful in the selection, design and modification of the structure and operating parameters of such systems.

Use of low grade heat sources in combined ejector–double effect absorption refrigeration systems

At a particular temperature range, heat sources are not hot enough to drive lithium bromide double-effect absorption refrigeration systems efficiently and are too hot to be used for the single effect systems because of the risk of crystallization. To make effective use of heat sources at this temperature range for refrigeration purposes, a combined ejector–double effect absorption cycles are proposed. A computational model is developed to study and compare the effect of operating parameters on the performance of combined and conventional single- and double-effect cycles from the viewpoints of first and second laws of thermodynamics. In addition, because of the importance of crystallization risk in these systems, the effect of varying working conditions on the possibility of crystallization is investigated too. The results show the advantageous performance of the combined cycle compared to that of the single- and double-effect systems at particular ranges of heat source temperature. These temperature ranges are extended at lower evaporator and higher condenser or absorber temperatures.

Enhancement of LNG plant propane cycle through waste heat powered absorption cooling

In liquefied natural gas (LNG) plants utilizing sea water for process cooling, both the efficiency and production capacity of the propane cycle decrease with increasing sea water temperature. To address this issue, several propane cycle enhancement approaches are investigated in this study, which require minimal modification of the existing plant configuration. These approaches rely on the use of gas turbine waste heat powered water/lithium bromide absorption cooling to either (i) subcool propane after the propane cycle condenser, or (ii) reduce propane cycle condensing pressure through pre-cooling of condenser cooling water. In the second approach, two alternative methods of pre-cooling condenser cooling water are considered, which consist of an open sea water loop, and a closed fresh water loop. In addition for all cases, three candidate absorption chiller configurations are evaluated, namely single-effect, double-effect, and cascaded double- and single-effect chillers. The thermodynamic performance of each propane cycle enhancement scheme, integrated in an actual LNG plant in the Persian Gulf, is evaluated using actual plant operating data. Subcooling propane after the propane cycle condenser is found to improve propane cycle total coefficient of performance (COPT) and cooling capacity by 13% and 23%, respectively. The necessary cooling load could be provided by either a single-effect, double-effect or cascaded and single- and double-effect absorption refrigeration cycle recovering waste heat from a single gas turbine operated at full load. Reducing propane condensing pressure using a closed fresh water condenser cooling loop is found result in propane cycle COPT and cooling capacity enhancements of 63% and 22%, respectively, but would require substantially higher capital investment than for propane subcooling, due to higher cooling load and thus higher waste heat requirements. Considering the present trend of short process enhancement payback periods in the natural gas industry, subcooling propane after the propane cycle condenser is recommended as the preferred option to boost propane cycle performance.

Analysis of crystallization risk in double effect absorption refrigeration systems

Absorption refrigeration systems are an alternative to vapor compression ones in cooling and refrigeration applications. In comparison with single effect absorption units, double effect systems have improved performance. Also, they are more available commercially than the other multi effect absorption cycles. An important challenge in the operation of such systems is the possibility of crystallization within them. This is especially true in developing air-cooled absorption systems, which are attractive because cooling tower and associated installation and maintenance issues can be avoided. Therefore, distinguishing the working conditions that may cause crystallization can be useful in the design and control of these systems. In this paper a computational model has been developed to study and compare the effects of operating parameters on crystallization phenomena in three classes of double effect lithium bromide–water absorption refrigeration systems (series, parallel and reverse parallel) with identical refrigeration capacities. It is shown that the range of operating conditions without crystallization risks in the parallel and the reverse parallel configurations is wider than those of the series flow system. ► We study crystallization of double effect absorption refrigeration systems. ► We consider series, parallel and reverse parallel cycles. ► We study the effect of operating conditions on crystallization. ► We choose optimum distribution ratio for parallel and reverse parallel systems. ► Crystallization possibility is low in parallel and reverse parallel cycles.

Simulation research on an EAX (Evaporator-Absorber-Exchange) absorption refrigeration cycle

There are some heat sources whose temperature is much higher than the limited generation temperature of conventional single effect absorption refrigeration cycle but lower than that of conventional double effect absorption refrigeration cycle. These heat sources can not be utilized efficiently by prior cycles. To make efficient use of these heat sources, this paper proposed an EAX (Evaporator-Absorber-Exchange) absorption refrigeration cycle. The proposed cycle can make use of the condensing heat of the vapor separated from high temperature generator to make additional refrigeration. Therefore, the COP (Coefficient of Performance) of the proposed cycle is much higher than that of the conventional single effect cycle. Simulation results show that the COP of the EAX cycle can be 40% higher than that of the conventional single effect cycle at some simulated conditions. ►This paper proposed a novel EAX absorption refrigeration cycle. ►The proposed cycle can make efficient use of the heat source which can not be utilized efficiently by conventional single effect cycle or conventional double effect cycle. ►The proposed cycle can make use of the condensing heat of the vapor separated from high temperature generator to make additional refrigeration. Therefore, its COP is much higher than that of the conventional single effect cycle. ►Relative increasing ratio (η) increases as the temperature of heat source increases. When the temperature of heat source reaches to 145 °C, η is higher than 40%. ►η increases as evaporation temperature increases. When the evaporation temperature reaches to 11 °C, η is higher than 40%.