Double-effect Parallel Research Articles

Energy and exergy analyses of a recompression supercritical CO2 cycle combined with a double-effect parallel absorption refrigeration cycle

In this study, a new cogeneration system is presented that can make optimal use of the waste heat from the sCO2 power cycle using a double-effect parallel absorption refrigeration cycle (DEARC), generating electricity and refrigeration simultaneously. A comparative study between the proposed (sCO2/DEARC) system and the stand-alone sCO2 power system is conducted to show its advantages and potential. The performances of the sCO2 and sCO2/DEARC systems are evaluated from the energetic and exergetic points of view using an in-house developed thermodynamic simulation platform via Engineering Equation Solver (EES) software. Variables such as pressure ratio, turbine inlet temperature, and evaporator temperature are also used for parametric analysis. The results indicate that the proposed system can generate of 132.72 MW cooling capacity. Also, the results show that the proposed sCO2/DEARC system can achieve a 55.8% and 5.2% improvement in thermal efficiency and exergy efficiency, respectively, with a negligible decrease in net power output (Wnet) compared to the stand-alone sCO2 power plant.

Energy, Exergy and Economic Analysis of Absorption Chiller Systems: A Case Study for a Wood Pencil Factory

This study examines the use of absorption chiller systems in a designated industrial facility having waste heat by conducting energy, exergy and economic analyses. The absorption chiller systems namely single-effect, double-effect series, double-effect parallel and double-effect reverse parallel were analysed to determine the best alternative for the wood pencil factory. The results indicated that the COP of the single-effect absorption chiller systems is changed from 0.758 to 0.763 when the temperature of the generator was increased from 89 ºC to 125 ºC. However, the exergetic performance of the single-effect absorption chiller system decreased by 40% in the same generator temperature range. On the other hand, COP of all double-effect absorption chiller systems increased about 8 % when the generator temperature was changed from 116 ºC to 155 ºC while the exergetic performance of all double absorption chiller systems decreased by around 14% for the same generator temperature range. The COP and exergetic efficiency values of the double-effect parallel system were found to be higher than other absorption systems at all generator temperature values. Overall, this study recommends that the double-effect parallel absorption chiller systems can be preferred for the factories having waste heat source wood chips. The average payback period of the system was also found to be 1.4 years. Furthermore, this study shows that double-effect parallel absorption chiller systems can be proposed for the facilities having wood chips waste sources instead of double-effect reverse parallel absorption chiller systems since they are easy to operate and have lower maintenance costs.

Energy, Exergy and Economic Analysis of Absorption Chiller Systems: A Case Study for a Wood Pencil Factory

This study examines the use of absorption chiller systems in a designated industrial facility having waste heat by conducting energy, exergy and economic analyses. The absorption chiller systems namely single-effect, double-effect series, double-effect parallel and double-effect reverse parallel were analysed to determine the best alternative for the wood pencil factory. The results indicated that the COP of the single-effect absorption chiller systems is changed from 0.758 to 0.763 when the temperature of the generator was increased from 89 ºC to 125 ºC. However, the exergetic performance of the single-effect absorption chiller system decreased by 40% in the same generator temperature range. On the other hand, COP of all double-effect absorption chiller systems increased about 8 % when the generator temperature was changed from 116 ºC to 155 ºC while the exergetic performance of all double absorption chiller systems decreased by around 14% for the same generator temperature range. The COP and exergetic efficiency values of the double-effect parallel system were found to be higher than other absorption systems at all generator temperature values. Overall, this study recommends that the double-effect parallel absorption chiller systems can be preferred for the factories having waste heat source wood chips. The average payback period of the system was also found to be 1.4 years. Furthermore, this study shows that double-effect parallel absorption chiller systems can be proposed for the facilities having wood chips waste sources instead of double-effect reverse parallel absorption chiller systems since they are easy to operate and have lower maintenance costs.

Energy, Exergy and Economic Analysis of Absorption Chiller Systems: A Case Study for a Wood Pencil Factory

This study examines the use of absorption chiller systems in a designated industrial facility having waste heat by conducting energy, exergy and economic analyses. The absorption chiller systems namely single-effect, double-effect series, double-effect parallel and double-effect reverse parallel were analysed to determine the best alternative for the wood pencil factory. The results indicated that the COP of the single-effect absorption chiller systems is changed from 0.758 to 0.763 when the temperature of the generator was increased from 89 ºC to 125 ºC. However, the exergetic performance of the single-effect absorption chiller system decreased by 40% in the same generator temperature range. On the other hand, COP of all double-effect absorption chiller systems increased about 8 % when the generator temperature was changed from 116 ºC to 155 ºC while the exergetic performance of all double absorption chiller systems decreased by around 14% for the same generator temperature range. The COP and exergetic efficiency values of the double-effect parallel system were found to be higher than other absorption systems at all generator temperature values. Overall, this study recommends that the double-effect parallel absorption chiller systems can be preferred for the factories having waste heat source wood chips. The average payback period of the system was also found to be 1.4 years. Furthermore, this study shows that double-effect parallel absorption chiller systems can be proposed for the facilities having wood chips waste sources instead of double-effect reverse parallel absorption chiller systems since they are easy to operate and have lower maintenance costs.

DEVELOPMENT OF A THERMAL MODEL OF A SOLAR POWERED VAPOUR ABSORPTION REFRIGERATION SUPPORTED GREENHOUSE FOR STRAWBERRY CULTIVATION

In this paper, a novel scheme of a solar powered vapour absorption refrigeration supported greenhouse with indirect evaporative cooler has been proposed. The main objective of this work is to create a favorable microclimatic condition for strawberry cultivation inside the greenhouse for a country with sub-tropical climatic conditions like India when the ambient temperature and humidity are high. The maximum yield of strawberry is achieved for a temperature ranging between 15-25 °C with a relative humidity varying from 55 to 65%. It is quite impossible to achieve a favorable temperature range for strawberry cultivation in the greenhouse under such condition by using the existing greenhouse cooling techniques. A double effect parallel flow LiBr-H2O absorption cooling system along with an IDEC powered through solar energy has been used. A thermal model for the greenhouse has been developed and analyzed for the climatic condition of Kolkata, India. The study reveals that the proposed system can very well maintain a conducive climate for the growth of target plantation for the given location.

Comprehensive exergy analysis and optimization of operating parameters for double effect parallel flow absorption refrigeration Cycle

In this communication, comprehensive exergy analysis has been discussed for double effect parallel flow direct as well as indirect fired vapour absorption refrigeration systems using Lithium bromide-water as working fluid. The temperatures in the main generator and intermediate generator and condenser are optimized parametrically. The solution distribution ratio is also optimized considering exergy coefficient of performance (ECOP) and exergy destruction rate (EDR) as the objective functions. Further, comparison of parallel flow cycle with series flow configuration are presented for same operating parameters. Moreover, the effect of the temperature difference between intermediate generator and intermediate condenser of both the double effect parallel and series flow cycles are discussed. Results indicate that the maximum ECOP of the parallel flow cycle is 3–6% higher than the series flow cycle and minimum EDR is about 4% lower as compared to the series flow configuration. Furthermore, optimum temperature of intermediate generator for parallel flow cycle is significantly lower than the series flow cycle while main generator temperature is higher. Optimum parameters are tabulated for both series and parallel flow cycles, which will help to the design engineers.

First and Second Law Analyses of Double Effect Parallel and Series Flow Direct Fired Absorption Cycles for Optimum Operating Parameters

Thermodynamic analysis of double effect parallel and series flow direct fired absorption systems with lithium bromide–water has been carried out for different operating conditions. Temperatures in primary generator (Tg) and secondary generator (Tgs)/secondary condenser (Tcs) are optimized analytically using an iterative technique for maximum coefficient of performance (COP) and minimum energy required. A solution distribution ratio for a parallel flow cycle is also optimized. Source of energy used to drive the cycles is considered as compressed natural gas (CNG) and liquefied petroleum gas (LPG). Exergy destruction rate (EDR) in individual components as well as in the whole cycle along with volume flow rate of LPG and CNG is presented and compared. Results show that maximum COP for the parallel flow cycle is 3–6% higher than the series flow cycle. Also, minimum EDR of the parallel flow cycle is around 4% less while energy consumption is 2–3% low as compared to the series flow cycle.

Optimization of cooling load in the combined vapour absorption–vapour compression refrigeration cycle using exergy analysis

ABSTRACTHeat-based refrigeration in the form of absorption refrigeration can be combined efficiently with the vapour compression refrigeration (VCR) system. Exergy-based optimization of the combination results in maximum benefit from such a combination. A double-effect parallel flow LiBr–H2O absorption cycle is combined with a vapour compression cycle with ammonia as the working fluid. The performance of this system was simulated and optimized using the principle of exergy. Results show that the exergy-optimized combined VAR–VCR system is more energy efficient and hence cost effective than a single classical VCR system.

Mapping of optimum operating condition for LiBr–water refrigeration cycles

In this work, optimum operating condition maps are generated covering wide ranges of refrigeration and sink temperatures for single- and double-effect LiBr–water vapour absorption refrigeration cycle. These optimum condition maps will be useful to choose optimum operating conditions while designing LiBr–water cycle for desired applications. Methodology for generating such maps is discussed in detail, which can also be used for other absorption refrigeration cycles with various working fluids. Three configurations of LiBr–water absorption refrigeration cycles, single effect, double-effect series flow and double-effect parallel flow, are analysed with the most accurate thermodynamic property correlation available in the literature. Sensitivity of cycle performance to various operating variables such as generator, absorber and condenser temperatures is determined. Second law analysis shows that when a higher temperature heat source is available, double-effect cycles are more effective over single effect as they have higher coefficient of performance.

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.

Solar driven double-effect absorption cycles for sub-zero temperatures

This paper presents a theoretical study of a solar driven double-effect absorption system with ammonia–lithium nitrate for sub-zero evaporation temperatures. The performance of a double-effect parallel flow ammonia based absorption system with lithium nitrate as absorbent is investigated. This includes the determination of the effect of the strong solution distribution on performance. A ratio of 0.65 appears to be the most advantageous. The paper also presents the dynamic performance of a double-effect ammonia–lithium nitrate absorption system driven by solar energy under Mediterranean summer conditions. The solar energy is obtained by horizontal N–S parabolic trough solar collectors because they can deliver high temperatures that are required to drive the double-effect absorption system. Simulations of the solar absorption systems with a hot storage are performed in order to supply the cooling load of a pork slaughterhouse with maximum cooling load of 600 kW.

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.

Performance comparison of double-effect parallel-flow and series flow water–lithium bromide absorption systems

The double-effect parallel flow absorption refrigeration cycle with water–lithium bromide as working fluid is analysed based on the concept of equilibrium temperature at the low pressure generator. Coefficient of performance (COP) and its sensitivity to operating conditions are compared with those for series flow cycle. Maximum attainable COP for parallel flow cycle is greater than that for series flow cycle throughout the range of operating conditions considered here. Performance of parallel flow system is more sensitive to the effectiveness of low pressure heat exchanger than that of series flow system.

Integration of absorption and vapour-compression systems

This paper describes the integration of different types of absorption systems with vapour-compression systems. The performances of such systems have been analysed thermodynamically using various refrigerant/absorbent pairs. The first part of this paper is concerned with the intermittent absorption system, the intermittent absorption/vapour recompression system and the combined intermittent absorption/vapour compression system. The second part describes the single-effect, the double-effect series and the double-effect parallel continuous absorption systems and their integration with vapour-compression systems.