Performance analysis of a waste‐heat‐powered thermodynamic cycle for multieffect refrigeration

A multieffect refrigeration system that is based on a waste‐heat‐driven organic Rankine cycle that could produce refrigeration output of different magnitudes at different levels of temperature is presented. The proposed system is integration of combined ejector–absorption refrigeration cycle and ejector expansion Joule–Thomson (EJT) cooling cycle that can meet the requirements of air‐conditioning, refrigeration, and cryogenic cooling simultaneously at the expense of industrial waste heat. The variation of the parameters that affect the system performance such as industrial waste heat temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector refrigeration cycle (ERC) and EJT cycles was examined, respectively. It was found that refrigeration output and thermal efficiency of the multieffect cycle decrease considerably with the increase in industrial waste heat temperature, while its exergy efficiency varies marginally. A thermal efficiency value of 22.5% and exergy efficiency value of 8.6% were obtained at an industrial waste heat temperature of 210°C, a turbine inlet pressure of 1.3 MPa, and ejector evaporator temperature of 268 K. Both refrigeration output and thermal efficiency increase with the increase in turbine inlet pressure and ERC evaporator temperature. Change in EJT cycle evaporator temperature shows a little impact on both thermal and exergy efficiency values of the multieffect cycle. Analysis of the results clearly shows that the proposed cycle has an effective potential for cooling production through exploitation of lost energy from the industry. Copyright © 2014 John Wiley & Sons, Ltd.     

First and second law analysis of an ejector expansion Joule–Thomson cryogenic refrigeration cycle

In this paper, a combined first and second law approach is applied to study an ejector expansion Joule–Thomson cryogenic refrigeration cycle. The effects of the evaporator temperature, ejector pressure ratio and compressor function on the coefficient of performance (COP), exergy destruction and the exergetic efficiency have been investigated. The present study has been conducted for the evaporator and compressor temperature in the range of 75–135 and 270–330 K, respectively. The ejector pressure ratio is varied from 1.5 to 5.5. Simulation results show that COP and exergy efficiency increase with increasing evaporator temperature and ejector pressure ratio. In addition, it was found that the increase in the compressor temperature leads to the reduction in the first and second law efficiencies. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermodynamic Analysis of a Mixed Refrigerant Ejector Refrigeration Cycle Operating with Two Vapor-liquid Separators

A mixed refrigerant ejector refrigeration cycle operating with two-stage vapor-liquid separators(MRERC2) is proposed to obtain refrigeration temperature at-40℃. The thermodynamic investigations on performance of MRERC2 using zeotropic mixture refrigerant R23/R134 a are performed, and the comparisons of cycle performance between MRERC2 and MRERC1(MRERC with one-stage vapor-liquid separator) are conducted. The results show that MRERC2 can achieve refrigeration temperature varying between-23.9℃ and-42.0℃ when ejector pressure ratio ranges from 1.6 to 2.3 at the generation temperature of 57.3-84.9℃. The parametric analysis indicates that increasing condensing temperature decreases coefficient of performance(COP) of MRERC2, and increasing ejector pressure ratio and mass fraction of the low boiling point component in the mixed refrigerant can improve COP of MRERC2. The MRERC2 shows its potential in utilizing low grade thermal energy as driving power to obtain low refrigeration temperature for the ejector refrigeration cycle.     

Cycle improvements to ejector‐expansion transcritical CO2 two‐stage refrigeration cycle

In this paper, a new configuration of ejector‐expansion transcritical CO₂ (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. It was found that, compared with the conventional transcritical CO₂ cycle and ejector‐expansion transcritical CO₂ cycle, the simulation results show that the coefficient of performance and second law efficiency of the new cycle were increased by about 55.5 and 26%, respectively, under the operating conditions that evaporator temperature is 10°C, gas cooler outlet temperature is 40°C and gas cooler pressure is optimum pressure. It is also concluded that the entrainment ratio for the new ejector‐expansion TRCC cycle is on average 35% higher than that of the conventional ejector‐expansion TRCC cycle. The analysis results are of significance to provide theoretical basis for design optimization of the transcritical CO₂ refrigeration cycle with an ejector‐expansion device, internal heat exchanger and intercooler. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance characteristics of two combined ejector–absorption cycles

The paper describes the performance of an ammonia–water combined ejector–absorption cycle as refrigerator using two simple models. In the first an ejector draws vapour from an evaporator and discharges to a condenser. In the second, an ejector draws vapour from an evaporator and discharges to an absorber. The thermodynamics cycles and ejector operation on the temperature–entropy charts are shown. The thermodynamics of the combined ejector–absorption cycle are simulated by a suitable method and a corresponding computer code, based on analytic functions, describes the behaviour of the binary mixture NH₃–H₂O. It was found from the first model that the refrigerator (theoretical) coefficient of performance (COP) varied from 1.099 to 1.355 when the operation conditions were: generation temperature (237°C), condenser temperature (25.9–30.6°C), absorber temperature (48.6–59.1°C) and evaporator temperature (−1.1–7.7°C). In the second the theoretical COP vary from 0.274 to 0.382 when the operation conditions were: generation temperature (237°C), condenser temperature (91°C), absorber temperature (76.7–81°C) and evaporator temperature (−1.1–7.7°C).     

Exergy analysis of ejector‐refrigeration cycle using water as working fluid

Exergy is based on the second law of thermodynamics and is the only rational basis for evaluating the system performance. The aim of this paper is to study in detail the irreversibilities in the steam‐ejector refrigeration system. The influence of the cycle parameters is analysed on the basis of the first and second law and the results indicated the components with the greater irreversibility. A better quality of the ejector has more effect on the system performance than the better quality of other components, because the ejector at first and the condenser at second have the greater exergy loss of the system. For the refrigeration system the maximum coefficient of performance varying between 0.4 to 0.6 and the second law efficiency remains close to 0.17 for generator pressure 6 bar, condenser temperature 44–50°C and evaporator temperature 4–8°C. Also the study showed that the second law analysis quantitatively visualizes losses within a system and gives clear trends for optimization. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance of hybrid vaccine freezer that combined thermoelectric coolers with vapor compression refrigeration: Experimental assessment

In the medical field, refrigeration systems are used to store and transport vaccines, blood, and other medical supplies that require specific temperature ranges to remain effective. As technology continues to advance, the demand for more efficient and sustainable refrigeration systems is also increasing. The freezer compartment is typically designed to maintain a temperature of −18°C to −23°C for storing frozen items. Consequently, this work aims to develop a hybrid refrigeration system that combines a thermoelectric cooler system (TEC) and a vapor compression refrigeration cycle (VCC) system to achieve lower temperatures than conventional refrigerators. Also, the performance of the proposed hybrid refrigeration system is experimentally assessed with various operating conditions, including varying the voltage delivered to the system. The experimental results exhibited that the temperature inside the freezer room reached −33°C, while the cold side temperature is −47°C. Also, the maximum coefficient of performance of the VCC system, TEC, and hybrid system is 2.07, 1.06, and 0.37, respectively, at a DC voltage applied of 6 V. Moreover, the results revealed that the hybrid system combining a TEC and a VCC system can be a valuable technology for specific applications with low temperatures and limited capacity requirements.     

An improved absorption refrigeration cycle driven by unsteady thermal sources below 100°C

This paper deals with an improved absorption refrigeration cycle with staged absorption. Instead of having only one absorber, the improved cycle uses a series of absorbers among which one is cooled by the external medium and the others are cooled by refrigerant at staged pressures between the evaporation pressure and condensation pressure. Ammonia–lithium nitrates (NH₃–LiNO₃) are selected as the working fluids and the calculation results for the two‐staged cycle and the three‐staged cycle are analysed in detail. It is demonstrated that the improved cycle is able to steadily run when driven by low‐grade thermal sources as low as 65°C, and to produce deep refrigeration temperature as low as −40°C. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical Simulation of the Performance of a Capillary Thermal Driven Ejector Refrigerator

A capillary driven ejector refrigerator is a new refrigeration system that can use solar energy and other low-grade heat sources. In this paper, the performance of the refrigeration system is simulated numerically by use of an iteration algorithm and block exchanging technology for all unit models. The flow and heat transfer characteristics in a solar collector, generator, ejector, condenser, and evaporator are analyzed and calculated. The results show that when the generating temperature is higher than 75–80°C and the environmental temperature is lower than 35°C, the system can work normally; the coefficient of performance of this refrigeration system is in the range of 0.05–0.15 by use of water as a refrigerant. The cooling capacity and COP increase with an increasing generative temperature and decreasing condensing pressure.     

Energy and exergy analysis of novel solar bi‐ejector refrigeration system with injector

Energy and exergy balances were done on a novel solar bi‐ejector refrigeration system with R123, whose circulation pump is replaced by an injector. The analysis result of the novel system was compared with that of the original one. The effect of operation condition on system energy efficiency, exergy efficiency and exergy loss was analyzed, and the dynamic performance of a designed solar bi‐ejector refrigeration system was also studied. The comparative results indicate that under the same operating condition, the novel system and the original system have equal energy efficiency, exergy efficiency and exergy loss, and the only difference between them is the exergy losses of the generators and the added injector. The other conclusions mainly include: the solar collector has the largest exergy loss rate of over 90% and for the bi‐ejector refrigeration subcycle, the ejector has the largest exergy loss rate of about 5%; the total exergy loss changes inversely proportional to the evaporation temperature and positively proportional to the condensation temperature; when the other parameters are fixed, there exists an optimum generation temperature, at which the overall energy and exergy efficiencies are both the maximum and the total exergy loss is the minimum. The study points out the direction for optimizing the novel solar bi‐ejector refrigeration system. Copyright © 2009 John Wiley & Sons, Ltd.     

Exergy analysis of Joule–Thomson cryogenic refrigeration cycle with an ejector

In this paper, exergy method is applied to analyze the ejector expansion Joule–Thomson (EJT) cryogenic refrigeration cycle. The exergy destruction rate in each component of the EJT cycle is evaluated in detail. The effect of some main parameters on the exergy destruction and exergetic efficiency of the cycle is also investigated. The most significant exergy destruction rates in the cycle are in the compressor and ejector. The ejector pressure ratio and compressor isothermal efficiency have a significant effect on the exergetic efficiency of the EJT cycle. The exergy analysis results show the EJT cycle has an obvious increase in the exergetic efficiency compared to the basic Joule–Thomson refrigeration cycle. A significant advantage from the use of the ejector is that the total exergy destruction of the EJT cycle can be reduced due to much more decreasing of the exergy destruction rates in the compressor and expansion valve. The exergy analysis also reconfirms that applying an ejector is a very important approach to improve the performance of the Joule–Thomson cryogenic refrigeration cycle.     

Temperature–enthalpy/entropy charts of combined ejector–absorption cycle using NH3–H2O

This paper describes the performance of an ammonia–water combine ejector–absorption cycle as refrigerator and heat pump. This combination brings together the advantages of absorption and ejector systems. Also, thermodynamic cycles on the temperature–enthalpy and temperature–entropy charts are shown. The thermodynamics of the combined ejector–absorption cycles are simulated by a suitable method and a corresponding computer code, based on analytic functions describing the behaviour of the binary mixture NH₃–H₂O. It is found that in the case of the refrigerator and heat pump, the theoretical coefficient of performance (COP) or the theoretical heat gain factor (HGF) vary from 1.6 to 90.4 per cent and 0.7 to 37.6 per cent, greater than those of the conventional absorption system, respectively. The operation conditions were: generator temperature (205.5 to 237.1°C), condenser temperature (25.9 to 37.4°C) and evaporator temperature (−8.4 to 5°C). Copyright © 2000 John Wiley & Sons, Ltd.     

A combined power and ejector refrigeration cycle for low temperature heat sources

A combined power and ejector refrigeration cycle for low temperature heat sources is under investigation in this paper. The proposed cycle combines the organic Rankine cycle and the ejector refrigeration cycle. The ejector is driven by the exhausts from the turbine to produce power and refrigeration simultaneously. A simulation was carried out to analyze the cycle performance using R245fa as the working fluid. A thermal efficiency of 34.1%, an effective efficiency of 18.7% and an exergy efficiency of 56.8% can be obtained at a generating temperature of 395 K, a condensing temperature of 298 K and an evaporating temperature of 280 K. Simulation results show that the proposed cycle has a big potential to produce refrigeration and most exergy losses take place in the ejector.     

Experimental investigation of a combined ejector-absorption refrigerator

This paper describes an experimental study of a novel heat-operated refrigeration cycle, ‘combined ejector-absorption refrigeration cycle’. In this novel cycle, an ejector was placed between a generator and a condenser of a conventional single-effect absorption refrigerator. The high-pressure vapour refrigerant produced in the generator section was used as the motive fluid for the ejector which entrained low-pressure refrigerant vapour from the evaporator and discharged it to the condenser. This was shown to significantly increase the cooling capacity and COP of the novel refrigerator above that of a conventional absorption unit with little increase in system complexity. © 1998 John Wiley & Sons, Ltd.     

Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator

R134a is the most widely used refrigerant in domestic refrigerators. It must be phased out soon according to Kyoto protocol due to its high global warming potential (GWP) of 1300. In the present work, an experimental investigation has been made with hydrocarbon refrigerant mixture (composed of R290 and R600a in the ratio of 45.2:54.8 by weight) as an alternative to R134a in a 200 l single evaporator domestic refrigerator. Continuous running tests were performed under different ambient temperatures (24, 28, 32, 38 and 43 °C), while cycling running (ON/OFF) tests were carried out only at 32 °C ambient temperature. The results showed that the hydrocarbon mixture has lower values of energy consumption; pull down time and ON time ratio by about 11.1%, 11.6% and 13.2%, respectively, with 3.25–3.6% higher coefficient of performance (COP). The discharge temperature of hydrocarbon mixture was found to be 8.5 to 13.4 K lower than that of R134a. The overall performance has proved that the above hydrocarbon refrigerant mixture could be the best long term alternative to phase out R134a.     

Research on a combined adsorption heating and cooling system

A combined cycle capable of heating and adsorption refrigeration is proposed, and the experimental prototype has been installed. The system consists of a heater, a water bath, an activated carbon–methanol adsorption bed and a ice box. This system has been tested with electric heating, and has been found that with 61 MJ heating, the 120 kg water in the bath can be heated up from 22 to 92 °C meanwhile 9 kg ice of −1.5 °C is made. The calculated COP_system is 0.0591 and COP_cycle is 0.41. After reconstruction to a real hybrid household water heater–refrigerator, when 55 MJ heating is added to 120 kg 21 °C water, and the condensing temperature is controlled at about 30 °C, the result is the 4 kg water contained inside the methanol refrigerant evaporator was iced to −2 °C, the cooling capacity of the ice and the refrigerant in the evaporator will maintain the 100 l cold box for about three days below 5 °C. The experiments show the potentials of the application of the solar powered hybrid water heater and refrigerator. Theoretical simulation has been done, which is in good agreement with experimental results. This research shows that the hybrid solar water heating and ice making is reasonable, and the combined cycle of heating and cooling is meaningful for real applications of adsorption systems.     

An investigation on the absorption–compression hybrid refrigeration cycle driven by gases and power from vehicle engines

A novel absorption–compression hybrid refrigeration cycle (ACHRC) driven by gases and power from vehicle engines is proposed in this article, in which R124–dimethylacetamide is used as working fluid. The ACHRC composes the absorption refrigeration subcycle powered by exhaust gases and the compression refrigeration subcycle driven by power from both automotive engines. It can also meet the technical requirements for vehicle air‐conditioning systems. The thermal calculation for the ACHRC was performed under the given operating conditions in which the temperatures of cooling air, condensation and evaporation are 35 °C, 55 °C and 3 °C, respectively, and the coach air‐conditioning load is 30 kW. The operating characteristics of the ACHRC, which vary with the generator load ratio and cooling air temperature, have been simulated and analyzed. The simulation results show that the maximum integration coefficient of performance of the ACHRC can reach 14.85 under the given operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

An experimental investigation of steam ejector refrigeration system powered by extra low temperature heat source

A steam ejector refrigeration system is a low capital cost solution for utilizing industrial waste heat or solar energy. When the heat source temperature is lower than 80 °C, the utilization of the thermal energy from such a low-temperature heat source can be a considerable challenge. In this investigation, an experimental prototype for the steam ejector refrigeration system was designed and manufactured, which can operate using extra low-temperature heat source below 80 °C. The effects of the operation temperature, the nozzle exit position (NXP) and the diameter of the constant area section on the working performance of the steam ejector were investigated at generating temperatures ranging from 40 °C to 70 °C. Three ejectors with a same de Laval nozzle for the primary nozzle and three different constant-area sections were designed and fabricated. The experimental results show that a steam ejector can function for a certain configuration size of the steam ejector with a generating temperature ranging from 40 °C to 70 °C and an evaporating temperature of 10 °C. For a given NXP, the system COP and cooling capacity of the steam ejector decreased until inoperative as the diameter of the constant area section reduced. The results of this investigation provided a good solution for the refrigeration application of the steam ejector refrigeration system powered by an extra low-temperature heat source.     

An irreversible thermodynamic model for solar absorption refrigerator

A solar refrigerator is made of a solar collector and a refrigeration system. Real solar refrigerators usually operate between two limits, maximum coefficient of performance (COP) and maximum cooling load. A new model is presented to describe an irreversible absorption refrigerator, in which not only the irreversibilities of heat conduction but also those resulting from friction, eddy and other irreversible effects inside the working fluid are considered. The influence of these irreversible effects on the performance of an absorption refrigerator with continuous flow is investigated. The analytical expressions of the optimal refrigeration coefficient and the cooling rate of the refrigerator are derived. The predictions of the model are compared with semi-empirical cycle model of single-stage absorption refrigeration machines. The results obtained here can describe the optimal performance of a four temperature level absorption refrigeration affected simultaneously by the internal and external irreversibilities and provide the theoretical bases for the optimal design and operation of real absorption refrigerators operating between four temperature levels.     

Experimental study on an absorption refrigeration system at low temperatures

The heat-driven auto-cascade absorption refrigeration cycle can be used at low temperatures, and a novel auto-cascade absorption refrigeration system is proposed to gain better performances with a refrigerating temperature as low as −50 °C. The new system uses a mixture of R23 + R32 + R134a/DMF as its working pair and its characteristic study is carried out under different operational conditions. It has successfully obtained a refrigerating temperature of −47.2 °C under the generating temperature of 163 °C. This refrigerating temperature is far lower than that of a traditional absorption refrigeration system with the same working pair, and it is also lower than that of an auto-cascade absorption refrigeration system using R32 + R134a/DMF as its working pair. From the experimental results, it is clearly seen that this new system shows a rapider lowering rate of refrigerating temperature than that of an auto-cascade absorption refrigeration system using R23 + R134a/DMF as its working pair. The results of experimental analyses imply that this new absorption refrigeration system can be used in the deep-freezing as low as −50 °C by utilizing low-potential thermal power. Its potential of industrial application might be greater than that of an auto-cascade absorption refrigeration system using R23 + R134a/DMF as its working pair in the future.