Theoretical study on an innovative ejector enhanced Joule‐Thomson cycle

This paper describes an innovative ejector enhanced Joule‐Thomson cycle for low‐temperature refrigerators. Since an ejector is introduced into the cycle, the cycle performance is profoundly affected by the pressure lift ratio and entrainment ratio of the ejector. As a case study, the performance characteristic of the novel cycle refrigerator using the non‐azeotropic refrigerant mixture R14/R23 with the molar fraction of 0.6/0.4 is theoretically investigated in detail. The theoretical results show that in a typical refrigeration temperature range from −65°C to −95°C, the novel cycle refrigerator has 24.4%–41.5% improvement in coefficient of performance and 60%–220% enhancement in refrigeration capacity when compared to a basic Joule‐Thomson cycle low‐temperature refrigerator. This achieves a significant advantage as the use of the novel cycle is applied to low‐temperature refrigerators for the medical and commercial applications. Copyright © 2009 John Wiley & Sons, Ltd.     

New refrigeration system using CO vapor-solid as refrigerant

A refrigerant must be in the vapor-liquid phase in a vapor-compression refrigeration system, therefore, CO₂ cannot be used as a refrigerant for temperatures lower than -56°C because solid CO₂ will form under the triple point temperature of -56°C. A refrigeration system with CO₂ vapor-solid particles as refrigerant is put forward, by which a temperature lower than the triple point is achieved. An adjustable nozzle, a sublimator, a high-pressure regulating valve and a low-pressure regulating valve are used to replace the conventional evaporator. Theoretical cycle analysis of the refrigeration system shows that its COP can be 50% higher than that of the conventional one.     

Performance of ejector cooling system with thermal pumping effect using R141b and R365mfc

The ejector cooling system (ECS) is suitable for solar cooling application due to its simple design and low cost. An ECS using a multi-function generator (ECS/MFG) as a thermal pumping device without rotating machines for refrigerant circulation has been designed and tested. The experiment of an ECS/MFG operating at full-cycle while using R141b has shown that the COP_o can reach 0.225 and cooling capacity of 0.75 kW at generator temperature 90 °C, condenser temperature 37 °C, and evaporator temperature 8.5 °C. The present study also redesigned the ejector for working fluid R365mfc in order to replace R141b. This study has shown that R365mfc can replace R141b as the working fluid of ECS/MFG at no payoff of system performance as long as the ejector design is optimized.     

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.     

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.     

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.     

Experimental study on HFC125 critical heat pump

A critical cycle heat pump with HFC125 was studied experimentally. The experimental result indicates that the heat pump with HFC125 can use the general components of the conventional heat pump well. Hot water with wide-range temperature can be conveniently got by the critical heat pump system through water flow control. The COP_h of the critical cycle drops a little when the temperature of outlet water rises from 60 °C to 75 °C. And adding heat recovering exchanger cannot improve the performance of the cycle, but can reduce the working pressure of the cycle. Comparing with the CO₂ trans-critical heat pump, HFC125 critical heat pump has a better performance of refrigeration, lower working pressure, which is especially suitable for dual-function of supplying hot water and refrigeration in the civil and industrial buildings.     

Theoretical study of a transcritical ejector refrigeration cycle with refrigerant R143a

In this paper, a transcritical ejector refrigeration cycle (TERC) using refrigerant R143a as working fluid is proposed to improve the performance of the ejector refrigeration systems driven by low-grade thermal energy. This method adopts an adequate combination of thermal and mechanical energy through the operation of the transcritical process for generator to enhance the performance of the conventional ejector refrigeration cycle (ERC) at the cost of additional driving mechanical energy. The performance characteristics of the TERC are investigated based on theoretical simulations. The TERC is also compared with the conventional ERC using refrigerant R134a. The study shows that when utilizing the low-grade thermal energy, the TERC yields significant increase in COP by adding auxiliary mechanical energy of the cycle pump and has a higher potential in making effective use of the low-grade thermal energy with gradient temperature, such as solar energy gained by a flat plate or evacuated tube solar collector. This also indicates that the TERC is an attractive alternative to the ejector refrigeration systems driven by low-grade thermal energy. Further experimental work for the TERC may be launched in the near future to verify practical applications.     

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.     

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 study on the evaporation and pressure drop of low‐temperature refrigerant blends in porous media

An experimental investigation on the performance of different low‐temperature refrigerant blends is presented in this work. Five different low‐temperature refrigerant blends are put on display to replace the R22 refrigerant, which has a high ozone depletion potential. These five blends are R404A, R407C, R410A, R417A, and R422A. Different performance studies have been performed on these alternative refrigerants to replace R22. A comparative experimental performance study is performed during the evaporation of these refrigerant blends in porous media. A porous metallic heat transfer medium is used with different porosities (40%, 43%, and 45%) in the evaporator during the test experiments. The evaporator superheat and the condenser subcool are maintained constant throughout the experiments at 8°C (±0.5°C) and 6°C (±0.5°C), respectively. The condensing temperature is kept constant at 38.5°C, and the mean evaporating temperatures were selected to be from ?33 to ?18°C. The effect of the above‐mentioned given operating conditions on the compressor discharge temperature, evaporation pressure drop, evaporation capacity, and coefficient of performance of these five low‐temperature refrigerant blends has been analyzed for different porosities. This experimental study showed that the refrigerant R422A can give a similar or greater performance to R22 and R404A with a global warming effect and zero ozone depleting potential.     

Performance enhancement of a split air conditioner using porous material inside the evaporator pipes

In this experimental study, a porous material is used inside the pipes of the evaporator as the main heat exchanging device in the air conditioning cycle. The used porous material consists of stainless steel balls of different diameters. As a case study, refrigerant R454B, which is a drop-in replacement to refrigerant R410A, is used as a working fluid in the air conditioner thermodynamic cycle. Four different porosities were used during the experimental tests; 100% (empty tube), 46%, 40%, and 33%. This study investigated the influence of variation of porosity as well as outside air temperature and refrigerant evaporation temperature on the cycle coefficient of performance, evaporation capacity, pressure drop, and power consumption during the compression process. Measured evaporation temperatures and indoor temperatures during tests were in the range of 1.5–12°C and 18–25°C, respectively. The use of porous material in the evaporation heat exchanger resulted in a considerable increase in the cycle evaporation capacity and coefficient of performance. Varying porosity from 100% to 33% resulted in an average percent increase of cycle evaporation capacity and coefficient of performance by 48.8% and 84.3%, respectively. Also, decreasing porosity from 100% to 33% resulted in an average percent increase in power consumption during the compression process by about 27%. An average percent increase of power consumption of compressor by about 25.9% is also reported, when evaporation temperature increased from 1.5°C to 12°C. Increasing outside air temperature from 27.1°C to 39.5°C resulted in decreasing evaporation capacity and coefficient of performance by 35.2% and 34.5%, respectively, and in increasing compressor power consumption by about 14.3%. A considerable pressure drop was recorded during the evaporation process when using porous material. The volumetric evaporation capacity, as well as compressor discharge temperature, are increased by increasing evaporating temperature and by decreasing evaporator porosity. The increase in air ambient temperature resulted in a considerable increase in refrigerant mass flow rate.     

Research on performance of mixed absorption refrigeration for solar air-conditioning

A novel lithium bromide/water mixed absorption refrigeration cycle that is suitable for the utilization of solar air-conditioning and can overcome the drawbacks of low system overall efficiency of traditional solar absorption refrigeration air-condition systems is presented. The accessorial high pressure generator was added in the cycle. The lithium bromide solution flowing out from the high pressure generator was mixed with the solution from the low pressure absorber to increase lithium bromide solution concentration and decrease pressure in the high pressure absorber. The performance of a mixed absorption refrigeration cycle was analyzed. The theoretical analysis shows that the highest COP is 0.61, while the highest available temperature difference of heat resource is 33.2°C. The whole coefficient of performance of the solar air-conditioning using mixed absorption cycle is 94.5% higher than that of two-stage absorption. The advantages of solar air-conditioning can be markedly made use of by the cycle.     

Experimental performance of a silica gel–water adsorption chiller

A newly developed adsorption water chiller is described and tested. In this adsorption refrigeration cycle system, there is no refrigerant valve. Thus, the problem of mass transfer resistance occurring in the conventional systems when methanol or water is used as refrigerant and resulting in pressure drop during the flow of refrigerant inside the tubing is eliminated. To make the utilization of low heat source with temperature ranging from 70 to 95 °C possible, silica gel–water was selected as working pair. The experimental results proved that it is able to produce a cooling power of 6.3 kW with a COP of about 0.4. The test results demonstrate that, through the heat recovery, the COP can be increased by 34.4% while mass recovery has the effect of increasing the cooling power by 13.7% and the COP by 18.3%. The performances of the system were analyzed for varied condensation temperature and for varied evaporation temperature. Based on the first prototype, the second prototype is designed and manufactured to improve the performance. Primary test results demonstrate that the performance is highly improved. It has a COP of about 0.5 and cooling power 9 kW for 13 °C evaporation temperature.     

Choice of absorbent-refrigerant mixtures

Twenty-six absorbent—refrigerant combinations, holding good promise as fluid systems, have been considered for single stage absorption air conditioning system. These fluids have been compared on the basis of solution characteristics, life expectancy characteristics and refrigeration cycle characteristics. The mass flow rates of rich and poor solutions per ton of refrigeration capacity and the coefficient of performance (CP) were compared for an evaporator temperature of 5°C, absorber and condenser temperatures of 35°C and a generator temperature of 120°C (low grade energy sources). More than half of the waste energy available in industry happens to be at a temperatures below 200°C. Other types of low grade thermal energy such as solar energy and geothermal energy can be used in operating vapour absorption refrigeration and air-conditioning systems.     

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.     

Investigation of the effect of superheating on the performance of a refrigeration system using low temperature different refrigerant blends in porous media

A comparative experimental investigation on the effect of superheating of R‐22, R‐404A, R‐407C, and R‐422A as low‐temperature refrigerant blends on the performance of a vapor compression refrigeration system is conducted. Empty and porous evaporators with porosities of (40%, 43%, and 45%) are used during the tests, to predict good alternatives to the refrigerant R‐22, which has high ozone depletion potential and high global warming potential. Condensation, evaporation temperatures, degree of subcool are kept constants at 40°C, ?26°C, and 6°C (±0.5°C), respectively. The effect of superheating on the compressor discharge temperature, evaporating pressure drop, evaporating capacity, volumetric refrigeration capacity and coefficient of performance (COP) of these refrigerants has been analyzed. Refrigerants, R‐422A and R‐404A showed greater performances than that of R‐22. The percentages of increase in evaporation capacities of R‐407c, R‐22, R‐404A, and R‐422A are approximately 144%, 168%, 146.3%, and 161.5%, respectively, when changing the degrees of superheat from 6°C to 16°C and changing the porosity from empty evaporator to 40%. The percentages of increase in COP are approximately 319%, 320%, 312%, and 350%, respectively. The percentages of increase in evaporation capacities of R‐422A and R‐404A when compared with R‐22 under the same conditions are 18.6% and 8.8%, respectively, while the percentages of increase in COP when compared with R‐22 are 17% and 12%, respectively.     

An exergy analysis of a solar-driven ejector refrigeration system

Exergy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m², an evaporator temperature of 10 °C, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 °C as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 °C.     

First and second law investigations of a new solar‐assisted thermodynamic cycle for triple effect refrigeration

This investigation is persuaded for the first and second law analyses of a new solar‐driven triple‐effect refrigeration cycle using Duratherm 600 oil (Duratherm Extended Life Fluid, NY, USA) as the heat transfer fluid is performed. The proposed cycle is an integration of ejector, absorption, and cascaded refrigeration cycles that could produce refrigeration output of different magnitude at different temperature simultaneously. Both exergy destruction and losses in each component and hence in the overall system are determined to identify the causes and locations of the thermodynamic imperfection. The effects of some influenced parameters such as hot oil outlet temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector and cascaded refrigeration cycle have been observed on the first and second law performances. It is found that maximum irreversibility occurs in central receiver as 52.5% and the second largest irreversibility of 25% occurs in heliostat field. The second law efficiency of the solar driven triple effect refrigeration cycle is 2%, which is much lower than its first law efficiency of 11.5%. Analysis clearly shows that performance evaluation based on the first law analysis is inadequate and hence, more meaningful evaluation must be included in the second law analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of the two-phase ejector expansion refrigeration cycle

This paper is a continuation of the authors’ previous work. The paper presents new experimental data of the system performance of the two-phase ejector refrigeration cycle (TPERC). The TPERC uses a two-phase ejector as an expansion device while the conventional refrigeration cycle (CRC) uses an expansion valve. The TPERC enables the evaporator to be flooded with refrigerant, resulting in a higher refrigerant-side heat transfer coefficient. The experimental study shows that the TPERC gives a higher cooling capacity and a higher coefficient of performance. Moreover, the pressure ratio and the discharge temperature of the compressor of the TPERC are lower than those of the CRC.