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.     

Results of an experimental study of an advanced jet-pump refrigerator operating with R245fa

An experimental jet-pump refrigeration system was designed and constructed to assess the performance of R245fa (1,1,1,3,3-pentafluoropropane) as a suitable refrigerant. The paper describes and evaluates the results of experimental tests over a range of operating conditions. In addition, the effects of primary nozzle geometry on jet-pump performance are reported. Performance maps, useful for practical design and control are also provided. Experimental values of coefficient of performance (COP) between 0.25 and 0.7 were obtained. These results demonstrate that low-grade heat can be used to drive efficient jet-pump refrigeration systems, using R245fa as their working fluid, for high temperature applications, such air conditioning.     

混合工质R134a/R23替代R22的可行性研究

叙述了基于新型环保型混合制冷剂R134a/R23替代制冷剂R22的问题,以及通过REFPROP7.5,对混合工质R134a/R23从物性和热力学特性进行的理论计算分析,指出,由质量分数为70%的R134a和质量分数为30%的R23组成的混合制冷剂与R22性能最为接近,在变工况运行条件下,其COP值比R22高8%左右,其冷凝压力比同条件下用R22作为循环工质低21%～36%,理论上完全具有替代R22的可能性。     

Numerical analysis of refrigerant flow along non-adiabatic capillary tubes using a two-fluid model

This work presents a numerical model to simulate steady state refrigerant flow along capillary tube-suction line heat exchangers, commonly used in small refrigeration systems. The flow along the straight and horizontal capillary tube is divided into two regions: a single-phase and a two-phase flow region. The flow is taken as one-dimensional and the metastable flow phenomenon is neglected. The two-fluid model is employed for the two-phase flow region, considering the hydrodynamic and the thermodynamic non-equilibrium between the liquid and vapor phases. Comparisons are made with experimental measurements of the mass flow rate and temperature distribution along capillary tube-suction line heat exchangers working with refrigerant R134a in different operating conditions. The results indicate that the present model provides a good estimation of the refrigerant mass flow rate. Moreover, comparisons with a homogeneous model are also made. Some computational results referring to the quality, void fraction and velocities of each phase are also presented and discussed.     

A new power/cooling cogeneration system using R1234ze(E)/ionic liquid working fluid

A novel power/cooling system integrated with organic Rankine cycle and absorption-compression refrigeration cycle was proposed in order to realize the cascade utilization of low-grade energy. In the proposed system, R1234ze(E) (trans-1,3,3,3-tetrafluoropropene) is used as the working fluid for the organic Rankine cycle subsystem and the binary mixtures of R1234ze(E) with three ionic liquids [HMIM][BF₄], [EMIM][BF₄] and [OMIM][BF₄] are used as working fluid for absorption-compression refrigeration cycle subsystem due to their superior environmental protection property and physicochemical property. Moreover, in order to recover the heat of the exhaust gas from turbine in organic Rankine cycle subsystem, the exhaust gas is mixed with R1234ze(E)/ionic liquid solution directly in desorber, while the heat of refrigerant from desorber is recovered to reduce the heat load of condenser. The proposed system has much higher energy and exergy efficiency and lower heat load of condenser than reference system. Under specific conditions, increases of 0.24 and 0.07 in thermal efficiency and exergy efficiency of reference system can be achieved. The effect of distribution ratio, expansion ratio, heat source temperature, condensation temperature, generation temperature, evaporation temperature and compression ratio were analyzed for better design in actual application.     

Cycle performance study on R32/R125/R161 as an alternative refrigerant to R407C

This paper presents the new ternary non-azeotropic mixture of R32/R125/R161 as an alternative refrigerant to R407C. The physical properties of the ternary mixture are similar to those of R407C, and it is environmental friendly, that is, it has zero ozone-depletion potentials (ODP) and lower global warming potentials (GWP) than R407C. Theoretical cycle performances of R32/R125/R161 and R407C are calculated and analyzed firstly. Based on the theoretical study, experimental tests are performed on a vapor-compression refrigeration system with a rotor compressor which was originally designed for R407C (without any modifications to system components for R407C). Experimental results under different working conditions indicate that the pressure ratio and power consumption of the new refrigerant are lower than those of R407C, and its refrigerating capacity and coefficient of performance (COP) are superior to those of R407C, respectively, and its discharge temperature is slightly higher than that of R407C. Therefore, the new refrigerant R32/R125/R161 could be considered as a promising refrigerant to R407C.     

R744/R600a热泵热水器系统性能实验研究

为了研究环保混合制冷剂R744/R600a应用于热泵系统的可行性,在直热式水源热泵系统实验台上对R744充注质量分数在3%～11%的五种工况进行了实验研究。实验结果表明:R744充注质量分数的变化对热泵系统的COP_h、制热量和排气温度等性能参数均产生显著的影响;在热泵名义工况下,混合工质的最优R744充注质量分数为7%,其对应的系统COP_h和制热量相比R600a系统均明显提高,而其排气温度则明显降低。     

Numerical analysis of an air condenser working with the refrigerant fluid R407C

As CFC (clorofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants which have been used as refrigerants in a vapour compression refrigeration system were know to provide a principal cause to ozone depletion and global warming, production and use of these refrigerants have been restricted. Therefore, new alternative refrigerants should be searched for, which fit to the requirements in an air conditioner or a heat pump, and refrigerant mixtures which are composed of HFC (hydrofluorocarbon) refrigerants having zero ODP (ozone depletion potential) are now being suggested as drop-in or mid-term replacement. However also these refrigerants, as the CFC and HCFC refrigerants, present a greenhouse effect.The zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass) represents a substitute of the HCFC22 for high evaporation temperature applications as the air-conditioning.Aim of the paper is a numerical–experimental analysis for an air condenser working with the non azeotropic mixture R407C in steady-state conditions. A homogeneous model for the condensing refrigerant is considered to forecast the performances of the condenser; this model is capable of predicting the distributions of the refrigerant temperature, the velocity, the void fraction, the tube wall temperature and the air temperature along the test condenser. Obviously in the refrigerant de-superheating phase the numerical analysis becomes very simple. A comparison with the measurements on an air condenser mounted in an air channel linked to a vapour compression plant is discussed. The results show that the simplified model provides a reasonable estimation of the steady-state response and that this model is useful to design purposes.     

R1234ze(E)与R134a在水平双侧强化管外的凝结换热对比实验

搭建了水平单管降膜蒸发试验台,以第四代制冷剂R1234ze(E)和第三代制冷剂R134a作为工质,在新型水平双侧强化管管外分别进行了改变管内水速、热流密度和冷凝温度条件的凝结换热实验。使用Wilson-Gnielinski图解法计算得到管内表面传热系数h_i,进一步采用热阻分离法分离出两种制冷剂的管外表面传热系数,并分析了管内冷却水水速、冷凝温度和壁面过冷度的变化对其换热性能的影响。实验结果表明:同根实验管下不同制冷剂凝结换热性能的差异与制冷剂物性与强化管结构之间的匹配特性有关,实验管型下,R1234ze(E)的管外凝结换热性能高于R134a。     

Experimental investigation of solar concentrating collectors in a refrigerant ejector refrigeration machine

This paper presents an experimental study of energy output and efficiency of solar collectors in a refrigerant ejector refrigeration machine using R113 as the refrigerant. Based on a theoretical study, the oil transformer is used as a working fluid in the solar system. The concentrating collectors show encouraging results for operating the system. The maximum collector efficiency was 20%. The system can be used for both cooling and heating purposes. © 1997 John Wiley & Sons, Ltd.     

Energy influence of the IHX with R22 drop-in and long-term substitutes in refrigeration plants

This work focuses on the investigation of new drop-in or long-term refrigerants for low evaporating temperatures that can be used as substitutes for HCFC-22, which is gradually being phased-out. This process is already in progress in European countries (Regulation CE-1005/2009) and has been accelerated in Article 5 Countries of the Montreal Protocol. Specifically, in this work the energy influence of the suction line/liquid line heat exchanger on the new substitute fluids is addressed from an experimental approach.The study has been based on experimental measurements in a single-stage vapour compression refrigeration plant, which has been tested in the same external conditions operating with and without an Internal Heat Exchanger (IHX). The energy influence of the IHX working with R22 and three potential substitutes for low temperature applications, the chlorine-free drop-in fluids R417B and R422A and the chlorine-free long-term substitute R404A has been analysed.From the experimental results, reductions in capacity and COP have been observed when R22 is replaced by the drop-in fluids, although the presence of an IHX can help to lessen these reductions. Furthermore, the criteria that are usually employed to determine the energy advantage or disadvantage of the use of the IHX with the new refrigerants have been tested, the results confirming that they remain valid for them.     

Non-adiabatic capillary tube flow: a homogeneous model and process description

This paper presents a homogeneous model of refrigerant flow through capillary tube–suction line heat exchangers, which are widely used in small vapour compression refrigeration systems. The homogeneous model is based on fundamental conservation equations of mass, momentum and energy. These equations are solved simultaneously through iterative process. Churchill’s correlation [3] is used to calculate single-phase friction factors and Lin et al. [6] correlation for two-phase friction factors. The single-phase heat transfer coefficient is calculated by Gnielinski’s equation [5] while two-phase flow heat transfer coefficient is assumed to be infinite. The model is validated with previous experimental and analytical results. The present model can be used in either design calculation (calculate the capillary tube length for given refrigerant mass flow rate) or simulation calculation (calculate the refrigerant mass flow rate for given capillary tube length). The simulation model is used to understand the refrigerant flow behaviour inside the non-adiabatic capillary tubes.     

A flexible numerical model to study an active magnetic refrigerator for near room temperature applications

Magnetic refrigeration is an emerging technology based on the magnetocaloric effect in solid-state refrigerants. This technology offers a smaller global environmental impact than the refrigeration obtained by means of the classical vapor compression machines operating with fluids such as HFCs. The Active Magnetic Regenerative Refrigeration (AMRR) is currently the most studied ant tested magnetic cycle. It combines the regenerative properties of a high specific heat solid porous matrix with the ability of performing thermo-magnetic cycles thanks to the magnetocaloric property of the refrigerant; while a fluid pulsing through the regenerator works as a heat transfer medium. An active magnetic regenerator can provide larger temperature spans making up for the local small temperature variation of the refrigerant. In the present paper, a practical model for predicting the performance and efficiency of an AMRR cycle has been developed. The model evaluates both the refrigerant properties and the entire cycle of an AMR operating in conformity with a Brayton regenerative cycle. The magnetocaloric material of choice is gadolinium, while the heat transfer medium is liquid water. With this model can be predicted the refrigeration capacity, the power consumption and consequently the Coefficient of Performance. The results show a greater COP when compared to a classical vapor compression plant working between the same temperature levels.     

PERFORMANCE ANALYSIS OF VAPOUR COMPRESSION REFRIGERATION WITH R22/R124/R152a REFRIGERANT

In this paper, the performance of vapour compression refrigeration with R22/R124/R152a as the refrigerant is presented. A mathematical model of the system characteristics is developed and the simulated results agreed quite well with those of the experiments. The model was also used to analyse the most suitable composition of the refrigerant. It was found that the required composition was obtained when the mass fraction of R22 was in the range 0.2–0.4. © 1997 by John Wiley & Sons, Ltd.     

Shell-and-tube evaporator model performance with different two-phase flow heat transfer correlations. Experimental analysis using R134a and R1234yf

This work presents a model of a shell-and-tube evaporator using R1234yf and R134a as working fluids. The model uses the effectiveness-NTU method to predict the evaporation pressure and the refrigerant and secondary fluid temperatures at the evaporator outlet, using as inputs the geometry of the evaporator, the refrigerant mass flow rate and evaporator inlet enthalpy, and the secondary fluid volumetric flow rate and evaporator inlet temperature. The model performance is evaluated using different two-phase flow heat transfer correlations through model outputs, comparing predicted and experimental data. The output parameter with maximum deviations between the predicted and experimental data is the evaporating pressure, being the deviations in outlet temperatures less than 3%. The evaporator model using Kandlikar's correlation obtains the highest precision and the lowest absolute mean error, with 4.87% in the evaporating pressure, 0.45% in the refrigerant outlet temperature and 0.03% in the secondary fluid outlet temperature.     

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.     

SrCl_2-NH_3化学吸附式制冷工质对吸附特性的研究

对以SrCl2 为吸附剂、NH3 为致冷剂所组成的化学吸附式制冷工质对的吸附性能进行了研究 ,得到了吸附等温线、回归出吸附等温方程并对化学吸附过程机理进行了探讨。研究结果表明 ,SrCl2 NH3 工质对的吸附制冷量大 ,适宜太阳能或低品位余热驱动 ,是性能优良的工质对。     

冷热组合型超市系统的设计与经济性分析

设计了冷热组合型超市系统,利用CO2跨临界循环对空间夏季供冷和冬季供热,采用R290/CO2复叠式制冷循环对食品冷冻冷藏,同时回收CO2跨临界循环高温气体散发的热量和R290/CO2复叠式制冷循环R290高温循环气体的冷凝热,实现夏季空间供冷、食品制冷的同时供应生活热水,冬季空间供暖、食品制冷的同时供应生活热水,及春秋季节食品制冷同时供应生活热水。并与供冷、供暖、食品制冷和供应生活热水分别进行的常规R404A超市系统的能效相比较,得出冷热组合型超市系统的能耗大大降低,能效明显增加,不仅节约能源,而且保护环境,是很有发展前景的绿色环保系统。     

Prospect Evaluation of Low-GWP Refrigerants R1233zd(E) and R1336mzz(Z) Used in Solar-Driven Ejector-Vapor Compression Hybrid Refrigeration System

In this paper, the entrainment ratio, pump work, heat loads of heat exchangers and COPthermal were theoretically evaluated for a solar-driven ejector-vapor compression hybrid refrigeration system with R1233 zd(E) and R1336 mzz(Z) as the working fluids. The evaluation of the utilization potentials of R1233 zd(E) and R1336 mzz(Z) was presented by comparing the system performance with that of R245 fa, a commonly used refrigerant in the ejector system. The results indicated that the systems with R1233 zd(E) and R1336 mzz(Z) had a higher entrainment ratio and lower pump work. The pump works when using R1233 zd(E) and R1336 mzz(Z) can be up to 14.59% and 38.05% lower than those of R245 fa, respectively. Meanwhile, the system showed the highest COP_(thermal) utilizing R1233 zd(E) followed by that of R245 fa, with the R1336 mzz(Z) system having the lowest value. The differences between R1233 zd(E) and R1336 mzz(Z) systems, R1233 zd(E) and R245 fa systems were 4.33% and 2.0%, respectively. This paper was expected to provide a good reference for the utilizing prospect of R1233 zd(E) and R1336 mzz(Z) in ejector refrigeration systems.     

Study on a solar-driven ejection absorption refrigeration cycle

This paper deals with a solar-driven ejection absorption refrigeration (EAR) cycle with reabsorption of the strong solution and pressure boost of the weak solution. The physical model is described and the corresponding thermodynamic calculation is performed with the working pair NH₃–LiNO₃. It is demonstrated that the EAR cycle has obvious advantages as compared with the conventional absorption refrigeration cycle: (1) the controllable high absorption pressure allows for substantially high coefficients of performance by the action of a liquid–gas ejector in which the low-pressure refrigerant vapour is injected and pressurized as a result of the ejection of high-pressure solution; (2) internal steady operation can be realized for refrigeration cycles driven by unsteady heat sources, especially for solar energy, by adjusting the power input consumed by solution pumps under the condition of economical and reasonable utilization of electric energy. © 1998 John Wiley & Sons, Ltd.