A performance comparison of vapour-compression refrigeration system using various alternative refrigerants

A theoretical performance study on a traditional vapour-compression refrigeration system with refrigerant mixtures based on HFC134a, HFC152a, HFC32, HC290, HC1270, HC600, and HC600a was done for various ratios and their results are compared with CFC12, CFC22, and HFC134a as possible alternative replacements. In spite of the HC refrigerants' highly flammable characteristics, they are used in many applications, with attention being paid to the safety of the leakage from the system, as other refrigerants in recent years are not related with any effect on the depletion of the ozone layer and increase in global warming. Theoretical results showed that all of the alternative refrigerants investigated in the analysis have a slightly lower performance coefficient (COP) than CFC12, CFC22, and HFC134a for the condensation temperature of 50 °C and evaporating temperatures ranging between − 30 °C and 10 °C. Refrigerant blends of HC290/HC600a (40/60 by wt.%) instead of CFC12 and HC290/HC1270 (20/80 by wt.%) instead of CFC22 are found to be replacement refrigerants among other alternatives in this paper as a result of the analysis. The effects of the main parameters of performance analysis such as refrigerant type, degree of subcooling, and superheating on the refrigerating effect, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures.     

混合制冷剂HFC152a/HFC125的电冰箱实验研究

对环保节能制冷剂——二元近共沸混合工质HFCl52a／HFC125在电冰箱上应用的制冷循环性能进行了详细的理论计算和分析，并且对该工质灌注式替代CFC12和HFC152a／HCFC22在不同配比和充灌量下的电冰箱主要制冷性能进行了实验研究。实验结果表明：在合适的配比和充灌量下电冰箱制冷性能指标满足国家标准要求。混合制冷剂HFC152a／HFC125优良的环保性能和冰箱制冷性能使它完全适合做新一代的冰箱制冷剂。     

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。     

Applications of nanorefrigerant and nanolubricants in refrigeration,air-conditioning and heat pump systems: A review

Nanorefrigerants are a special type of nanofluids which are mixtures of nanoparticles and refrigerants and have a broad range of applications in diverse fields for instance refrigeration, air conditioning systems, and heat pumps. In this paper thermal–physical properties of nanoparticles suspended in refrigerant and lubricating oils of refrigerating systems were reviewed. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. The results indicate that HFC134a and mineral oil with TiO₂ nanoparticles work normally and safely in the refrigerator with better performance. The energy consumption of the HFC134a refrigerant using mineral oil and nanoparticles mixture as lubricant saved 26.1% energy with 0.1% mass fraction TiO₂ nanoparticles compared to the HFC134a and POE oil system.     

Simulation of a vapour-compression refrigeration cycles using HFC134A and CFC12

A performance comparison analysis of vapour-compression refrigeration systems using refrigerant HFC134a and CFC12 is presented. The analysis is based on computer simulation of actual cycles rather than the ideal cycles. The simulation models for HFC134a and CFC12 are developed on the basis of fluid properties and thermo-hydraulic characteristics obtained from available experimental data and/or correlations. Using the simulation model thus developed, system performance with HFC134a and CFC12 are examined. A comparison of the performance of HFC134a and CFC12 is presented using COP (and compressor power) as a criterion for the same cooling load. Results indicate that the COP for HFC134a is slightly (about 3%) lower than that for a CFC12 system. This means that the power requirement for a HFC134a system is slightly higher than that for CFC12 system for an identical cooling requirement. A comparison of these two systems from a thermodynamic point of view is also presented using exergy loss as a performance evaluation criterion. These results indicate that the HFC134a system is only slightly inferior to the CFC12 systems due to a higher (about 3%) exergy loss with HFC134a.     

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.     

-150℃四级自复叠制冷系统的实验与分析

搭建了一种四级自复叠制冷系统,采用由R600a、R134a、R23、R14、R50和R740等6种工质组成的非共沸混合制冷剂,经过调试与实验,成功得到了-150℃的柜内温度。讨论了该低温箱体的降温特性、压缩机的运行特性和混合工质的节流特性。研究表明,压缩机的吸、排气压力和温度关乎系统能否安全稳定的运行,每级毛细管的长度关乎系统的降温特性。     

Comparative assessment of environment-friendly alternatives to R134a in domestic refrigerators

In the present work, the possibility of using R152a and hydrocarbon refrigerants (such as R290, R1270, R600a, and R600) as alternatives to R134a in domestic refrigerators has been assessed theoretically. The refrigerants are assessed over wider range condensing and evaporator temperatures. The assessment was done with standard parameters such as pressure ratio, volumetric cooling capacity (VCC), coefficient of performance (COP), compressor input power, compressor discharge temperature, and total equivalent warming impact (TEWI). The results obtained showed that pure hydrocarbon refrigerants are not suitable to be used as alternatives to R134a due to its mismatch in VCC. R152a has approximately the same VCC with about 9% higher COP and lower values of operating pressure and compressor input power. The discharge temperature of R152a was higher than that of R134a by about 14–26 K. TEWI of R152a was about 7% lower than that of R134a. The reported results proved that R152a is an energy-efficient and environment-friendly alternative to phase out R134a in domestic refrigerators.     

Performance variation of an R22 window air conditioner retrofitted with a HFC/HC refrigerant mixture under different ambient conditions over a range of charge quantities

R22 has been generally accepted as the most suitable refrigerant for air conditioners, due to its favorable thermodynamic properties. However, R22 is a controlled substance under the Montreal protocol. M20 is a HFC/HC refrigerant mixture that can be used as a substitute for R22. This paper presents experimental investigation on the performance comparison of a window air conditioner operated with the M20 tested under different refrigerant charge levels and outdoor conditions against that with R22. Experiments were conducted in accordance with BIS procedure in a psychrometric test facility. Refrigerant charge in the air conditioner was systematically varied from 900 to 1600 g in steps of 50 g for R22 and 697 to 1279 g in steps of 39 g [equivalent to 50 g of R22] for the M20. At each charge levels, the outdoor room conditions were changed in accordance with BIS standards. It is observed that R22 is more sensitive to deviations in charge levels as compared to the M20. A decrease in charge level of about 7% reduced the system refrigerating capacity by 11.3% with R22 while with the M20 refrigerant mixture it reduces by 6.9% only. Similarly an overcharge by 7% reduces the refrigerating capacity of the system by 13.8% with R22 while with M20 it reduces by 6.5% only. Thus M20 is less sensitive to charge deviations. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20339     

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.     

Determination of a Vapor Compression Refrigeration System Refrigerant Charge

ＤｅｔｅｒｍｉｎａｔｉｏｎｏｆａＶａｐｏｒＣｏｍｐｒｅｓｓｉｏｎＲｅｆｒｉｇｅｒａｔｉｏｎＳｙｓｔｅｍＲｅｆｒｉｇｅｒａｎｔＣｈａｒｇｅＹａｎｇＣｈｕｎ－Ｘｉｎ；ＤａｎｇＣｈａｏ－Ｂｉｎ（ＩｎｓｔｉｔｕｔｅｏｆＡｉｒＣｏｎｄｉｔｉｏｎｉｎｇａｎｄＲｅ...     

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.     

An experimental analysis of the effect of refrigerant charge level on an automotive refrigeration system

The performance of an automotive refrigeration system is dependent on the refrigerant charge level. Due to inevitable leaks in the system, the amount of refrigerant will decrease over time and thus ultimately reduce the system's performance. A reduction in the amount of refrigerant charge results in excessive compressor cycling, a lower condenser pressure, a higher refrigeration temperature, and an increase in the amount of superheat. This paper identifies and quantifies the individual component losses in an automotive refrigeration system as a function of the refrigerant charge level. A second law analysis, based on nondimensional entropy generation, is carried out to quantify the thermodynamic losses. A passenger vehicle with a cycling-clutch, orifice tube refrigeration system was instrumented to measure various temperatures and pressures, and relative humidity. The data were collected at idle conditions. Thermodynamic equations, which are used to determine the system's thermal performance, are presented. The system's second law efficiency increases 26 % as the amount of refrigerant charge decreases by 44 %. Also the individual component losses are quantified as a function of the refrigerant charge level. The compressor and the condenser losses account for the largest percentage of the total losses, and are of similar magnitude. The evaporator–accumulator and the orifice tube losses account for a smaller percentage of the total losses, and are also of similar magnitude. With a reduction in the refrigerant charge level of 44 %, the losses in the compressor, the condenser, the evaporator–accumulator, and the orifice tube decrease 13 %, 8 %, 10 %, and 33 %, respectively.     

Monitoring hydrofluorocarbon refrigerant leakage from air-conditioning systems in buildings

Hydrofluorocarbons (HFCs) are now widely used in refrigeration and air-conditioning systems. These systems lose refrigerants through leaks and during servicing. This paper discusses the possibility of determining the emission rate of HFCs in buildings by applying tracer-gas techniques. The measurement of the emission rate of an HFC refrigerant (R134a) using the concentration-decay technique was carried out in a single-zone chamber. The results were compared with measurements made using an SF₆ tracer and the Pitot-tube traverse method.     

Experimental study on the performance of a heat pump system with refrigerant mixtures’ composition change

An experimental study on the capacity control of a heat pump system has been performed using refrigerant mixtures of R32/134a. A test apparatus was made of a refrigeration part and two different types of composition changing parts; a single separator system and a separator–rectifier combined system. Analysis of the separation process was made for a basic single separator system. In order to pursue a wider range of composition change, a separator–rectifier combined system with packed-type distillation column was designed with Raschig ring as packing material. The composition changing part was connected to the condenser outlet and the evaporator inlet. Heating capacity, cooling capacity, and coefficient of performance (COP) of the system were measured under heating and cooling conditions. When the single separator system was used as a composition changing part, the range of composition change in the refrigeration system was approximately 13%. Around 26% of composition change was obtained using the separator–rectifier combined system. From the composition change with the separator–rectifier combined system, the capacity improved from 2.6 to 3.4 kW in the cooling test and from 1.8 to 2.4 kW in the heating test. As the composition of R32 increases, heating and cooling capacities were improved, whereas the value of COP with the refrigerant mixture is enhanced due to a temperature glide effect. It is concluded that the system capacity can be adjusted to meet load requirements by controlling the composition of the refrigerant mixture.     

A review on recent developments in new refrigerant mixtures for vapour compression‐based refrigeration,air‐conditioning and heat pump units

In the present paper, an attempt has been made to review the performance of new refrigerant mixtures employed in vapour compression‐based refrigeration, air‐conditioning and heat pump units. The studies reported with refrigerant mixtures are categorized into six groups as follows: (i) hydrocarbon (HC), (ii) hydroflurocarbons (HFC), (iii) HFC/HC, (iv) hydrochloroflurocarbons (HCFC), (v) carbon dioxide (R744) and (vi) ammonia (R717). This paper explores the studies reported with new refrigerant mixtures in domestic refrigerators, commercial refrigeration systems, air conditioners, heat pumps, chillers and in automobile air conditioners. In addition, the technical difficulties faced with new refrigerant mixtures, further research needs in this field and future refrigerant options for new upcoming systems have been discussed in detail. This paper concludes that HC based refrigerant mixtures are identified as a long‐term alternative to phase out the existing halogenated refrigerants in the vapour compression‐based systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical Analysis of Optimal Subcooling for Single Vapor-Compression Refrigeration Systems

A finite temperature difference heat transfer method and irreversibility analysis have been developed for investigating the effects of subcooling on coefficient of performance, cooling water pressure drop of condenser, and heat exchanger area for R1234yf, R1234ze, R22, R134a, and R410A in a single vapor-compression refrigeration system. In order to satisfy the increasing cooling load for subcooling in a condenser, the heat exchanger size or cooling water pumping power that corresponds to initial cost or operating cost, respectively, is increased. The optimum degree of subcooling in a refrigeration system with superior performance and least initial cost or operating cost is obtained numerically. The results show that the maximum coefficient of initial cost saving and coefficient of operating cost saving and their corresponding optimum degree of subcooling increase with condensation temperature. At a higher inlet temperature of cooling water, the optimum degree of subcooling turns out to be smaller for all refrigerants. The results are expected to facilitate the prospective design of a vapor-compression refrigeration system for using alternative refrigerants.     

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。     

Development and transient performance results of a single stage activated carbon – HFC 134a closed cycle adsorption cooling system

A laboratory model of a thermally driven adsorption refrigeration system with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC 134a) as the refrigerant was developed. The single stage compression system has an ensemble of four adsorbers packed with Maxsorb II specimen of activated carbon that provide a near continuous flow which caters to a cooling load of up to 5 W in the 5–18 °C region. The objective was to utilise the low grade thermal energy to drive a refrigeration system that can be used to cool some critical electronic components. The laboratory model was tested for its performance at various cooling loads with the heat source temperature from 73 to 93 °C. The pressure transients during heating and cooling phases were traced. The cyclic steady state and transient performance data are presented.     

Theoretical assessments of HFC134a and alternatives to CFC12 as working fluids for heat pumps

HFC134a has been identified as an alternative to CFC12 for refrigeration applications. Significant progress has been made in the use of HFC134a for refrigeration. This paper analyses the suitability of HFC134a along with those of HCFC22, HCFC124, HFC134, HCFC142b and HFC152a as alternatives to CFC12 for heat-pump applications. Some basic and derived thermodynamic data have been used for a comparative assessment. HFC134a appears to be the closest alternative to CFC12, but HFC152a is likely to be a better alternative from an energy point of view.