Evolving an optimal composition of HFC407C/HC290/HC600a mixture as an alternative to HCFC22 in window air conditioners

Countries that have ratified Montreal Protocol have to phase out HCFC22 in the near future due to its ozone depleting potential (ODP) and hence new eco-friendly refrigerants are being evolved as substitutes. At Present HFC407C is one of the promising drop-in substitutes for HCFC22. But it is immiscible with mineral oil and hence polyol ester (POE) oil is recommended. Since POE oil is highly hygroscopic in nature it is not user friendly. However such oil immiscibility issue of HFC134a has been overcome [M. Janssen, F. Engels, The use of HFC134a with mineral oil in hermetic cooling equipment, Report 95403, No. 07, presented in the 19th International Congress of Refrigeration, The Hague, 1995] by the addition of HC blend to it, which also resulted in performance improvements. In the present work an attempt has been made to study the possibility of using HFC407C/HC290/HC600a refrigerant mixture as a substitute for HCFC22 in a window air conditioner and to evolve an optimal composition for the mixture. Experiments were carried out in a room calorimeter setup fitted with 1050 W capacity window air-conditioner. Condenser inlet air temperatures were held constant at 30, 35, 40 and 45 °C, while evaporator inlet air temperatures were varied over a range viz. 21, 23, 25, 27 and 29 °C during the experimentation. The HC percentage was also varied from 10 to 25% in steps of 5%. The new refrigerant mixtures demand longer condenser length to decrease the high discharge pressure matching with HCFC22 systems and hence the length has been increased while testing the mixtures. This also resulted in better heat transfer in condenser. The performance analysis revealed that the new refrigerant mixture performed better than that of HCFC22. It has in fact been found that the new mixture can improve the actual COP by 8 to 11% and hence it can reduce the energy consumption by 5 to 10.5%. The overall performance has proved that the new refrigerant mixture could be an excellent substitute for HCFC22.     

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.     

Thermodynamic performance of R502 alternative refrigerant mixtures for low temperature and transport applications

In this study, two pure hydrocarbon refrigerants, R1270 (propylene) and R290 (propane), and three binary mixtures composed of R1270, R290 and R152a were tested in a refrigerating bench tester with a scroll compressor in an attempt to substitute R502, which is used in most low temperature and transport refrigeration applications. The test bench provided 3–3.5 kW capacity, and water and water/glycol mixture were employed as the secondary heat transfer fluids. All tests were conducted under the same external conditions, resulting in the average saturation temperatures of −28 and 45 °C in the evaporator and condenser, respectively. The test results showed that all refrigerants tested had 9.6–18.7% higher capacity and 17.1–27.3% higher COP than R502. The compressor discharge temperature of R1270 was similar to that of R502, while those of all the other refrigerants were 23.7–27.9 °C lower than that of R502. For all alternative refrigerants, the charge was reduced up to 60% as compared to R502. There, of course, was no problem with mineral oil, since the mixtures were mainly composed of hydrocarbons. Since some of them are mixtures, one can change their compositions a little to suit various needs in many applications without significant deterioration of the performance. Overall, these alternative refrigerants offer better system performance and reliability than R502 and can be used as long term substitutes for R502 due to their excellent environmental properties.     

The testing and evaluation of trial refrigerants: Part 1. System description

This work is a contribution to the discovery and evaluation of new refrigerants. It has been stimulated by the uncertainty created by the Kyoto Protocol over the long‐term availability of the hydroflorocarbons (HFCs) and also by the need for more knowledge of HFC–oil pairings. An economical method for testing refrigerants in terms of coefficient of performance (COP) and evaporative behaviour in a lubricated system is described. Part 1 describes the equipment, its instrumentation and operating procedures. Part 2 discusses the system output for four test refrigerants: two single fluids R134a and R22 and two test non‐azeotropic blends each having a glide of around 9 K. Study of R22 was confined to evaporative behaviour. The ranking of refrigerants by COP and boiling length is given and the generality of use of these rankings is discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

The Use of New Refrigerants in Compact Heat Exchangers for the Refrigeration Industry

The present article reports on the results of experimental research carried out on compact plate heat exchangers, currently used as evaporators and condensers in refrigeration loops. The research was aimed at getting information on the thermal efficiency of the heat exchangers, under reference commercial conditions, when using new ozone-friendly refrigerants to replace CFCs and HCFCs. Specifically, the influence of some thermal-hydraulic parameters on the heat flux and the overall heat transfer coefficient are investigated for evaporators, using R134a, R407C, and R410A, three fluids proposed to replace R22, and HCFC, currently the most common refrigerant used in residential and commercial air conditioning equipment. Moreover, in this article a new thermodynamic method has been applied with the purpose of defining the saturation temperature and investigating the other main parameters for mixtures in the two-phase region for the fluids R407C and R410A, which are blends of, respectively, three and two pure refrigerants.     

HCFC22替代物吸收制冷特性的实验研究

报道了吸收制冷系统中R22／DMF、R134a／DMF和R134a＋R32／DMF（R134a和R32分别以1∶1和3∶7摩尔比混合)等四种工质对的实验结果,并进行了比较和分析。结果表明,混合制冷工质对R134a＋R32（3∶7)／DMF在工作压力比R22高出20%的条件下,其系统性能与工质对R22／DMF相当。     

A zero ODP replacement for R12 in a centrifugal compressor: an experimental study using R134a

It is well believed that the hydrofluorocarbons (HFCs) and their mixtures are the most promising candidates to substitute the conventional refrigerants, chlorofluorocarbons (CFCs) and HCFCs which contain chlorine atoms in the molecule. This substitution is necessary for the harmful action of CFCs and of HCFCs toward atmospheric ozone layer damage because the disruption of ozone has been attributed to chlorine. For this reason they must be replaced by more environment‐friendly refrigerants, as the new family, designated as HFCs, that are chlorine free. Centrifugal compressors differ from positive displacement compressors in two major respects: high vapour volume flow for a given physical size and lower pressure ratio. They are particularly suited to applications where differences between evaporator and condenser temperatures are low. The preferred properties for fluids used in centrifugal compressors differ in certain important aspects from those preferred for fluids used in positive displacement units. In particular centrifugal compressors typically utilize fluids such as CFC114, CFC113, CFC12 and CFC11 for which many potential candidate replacements exist; however, for CFC12, HFC134a is the most suitable replacement. A comparison of the refrigerants HFC134a and CFC12 has been carried out and the results from the tests, using data from a refrigerating plant operating with a centrifugal compressor are reported. The chilled water cooling plant, with a refrigerating capacity of 6500 kW is made up of a centrifugal two‐stage compressor, a condenser linked to a cooling tower, an economizer and a flooded evaporator. Experimental results show that a lower coefficient of performance is found when R134a is used as substitute for R12; the difference between the COP values decreases rising the compression ratio. Copyright © 2002 John Wiley & Sons, Ltd.     

R407C as an alternative to R22 in vapour compression plant: an experimental study

The problem of HCFC22 phase-out in refrigeration plants is analysed. A comparison is performed between R22 and R407C. The latter seems a promising drop-in substitute. Indeed, its use in existing plants would only require discharge of mineral oil and refilling with a compatible polyolester oil. The experimental tests are performed in a plant consisting in a water-cooled vapor-compression circuit employed for cooling a water–glycol mixture in a closed-loop system. Both the thermodynamic properties and general performance of R407C are comparable with those of R22. The COP, however, is 5–17% lower. As a consequence, in order to provide the same refrigerating load, a plant working with R407C requires higher electric-power consumption. The operational behaviour of R407C is increasingly better with increasing condensation and evaporation temperature. Therefore, R407C is a good R22 substitute in all applications requiring high evaporation temperatures, such as air-conditioning plants. © 1997 John Wiley & Sons, Ltd.     

Refrigerants as working fluid in a CPC collector system for electric power generation

Compound parabolic concentrators (CPC) achieve highest possible concentration for any acceptance angle. One of the simplest methods of utilizing the energy of the sun to generate electric power is to use a CPC collector system. A truncated CPC can be used without much loss in concentration. Compared with a full CPC the cost of construction of a truncated CPC is much less. A CPC requires only seasonal adjustments. This further reduces the cost of tracking which is required for other types of concentrators. In this paper it has been shown that the refrigerants R11, R12, R113 and R114 can be satisfactorily used as working fluids in CPC collector systems. By using these working fluids, overall conversion efficiency of 9% can be achieved. Other refrigerants R12, B1, R22, R500, R502, R115 and C318 are found not to be suitable as they produce very low overall conversion efficiencies. In order to produce 20 kW of electricity at 1000 W/m² insolation about 920 truncated CPC collectors (2 m length, 0.15 m aperture) with a concentration ratio of 8 are required. This minimum number of collectors would be required at an overall conversion efficiency of 9%.     

Two-phase flow model of refrigerants flowing through helically coiled capillary tubes

This paper presents a numerical study of the flow characteristics of refrigerants flowing through adiabatic helically coiled capillary tubes. The theoretical model is based on conservation of mass, energy and momentum of the fluids in the capillary tube. The two-phase flow model developed was based on the homogeneous flow assumption. The viscosity model was also based on recommendations from the literature. The developed model can be considered as an effective tool for designing and optimizing capillary tubes working with newer alternative refrigerants. The model is validated by comparison with the experimental data of Kim et al. (2002) for R-22, R-407C and R-410A, and Zhou and Zhang (2006) for R-22. The results obtained from the present model show reasonable agreement with the experimental data. The proposed model can be used to design helical capillary tubes working with various refrigerants.     

An algorithmic approach towards finding better refrigerant substitutes of CFCs in terms of the second law of thermodynamics

In this study, rational efficiency (RE) and component based irreversibility ratios of a cooling system based on the second law of thermodynamics using HFC and HC based pure refrigerants, such as, R32, R125, R134a, R143a, R152a, R290, R600a and their binary and ternary mixtures, along with R12, R22 and R502 (i.e. CFCs) have been numerically calculated. The effect of temperature glide, occurring at the condenser and evaporator, on the RE of the cooling system has been evaluated. The calculations are based on a constant cooling load on a cooling system with suction/line heat exchanger (SLHE). To be able to calculate the performance of the cooling system, an algorithm that uses the state point properties provided by REFPROP has been employed. We have targeted finding better mixture substitutes in terms of rational efficiency. For example, despite the suggestions in the literature; for R22, the mass percentage level of 20/80 of R32/R134a has provided the best RE level. The highest irreversibility (in percentages) is found at the condenser. The results also suggest that for both binary and ternary mixtures, a general trend of increases in RE level is observed against temperature glide increases occurring at this system component.     

Performance comparison of CFCs with their substitutes using artificial neural network

In order to decrease global pollution due to chlorofluorocarbons (CFCs), the usage of HFC‐ and HC‐based refrigerants and their mixtures are considered instead of CFCs (R12, R22, and R502). This was confirmed by an international consensus (i.e. Montreal Protocol signed in 1987). This paper offers to determine coefficient of performance (COP) and total irreversibility (TI) values of vapour‐compression refrigeration system with different refrigerants and their mixtures mentioned above using artificial neural networks (ANN). In order to train the network, COPs and TIs of refrigerants and their some binary, ternary and quartet mixtures of different ratios have been calculated in a vapour‐compression refrigeration system with liquid/suction line heat exchanger. In the calculations thermodynamic properties of refrigerants have been taken from REFPROP 6.01 which was prepared based on Helmholtz energy equation of state. To achieve this, a new software has been written in FORTRAN programming language using sub‐programs of REFPROP, and all related calculations have been performed using this software using constant temperature method as reference. Scaled conjugate gradient, Pola–Ribiere conjugate gradient, and Levenberg–Marquardt learning algorithms and logistic sigmoid transfer function were used in the network. Mixing ratios of refrigerants, and evaporator temperature were used as input layer; COP and TI values were used as output layer. It is shown that R² values are about 0.9999, maximum errors for training and test data are smaller than 2 and 3%, respectively. It is concluded that, ANNs can be used for prediction of COP and TI as an accurate method in the systems. Copyright © 2004 John Wiley & Sons, Ltd.     

An experimental evaluation of the vapour compression plant performances in presence of R407C leaks using an electronic expansion valve

Chlorofluorocarbons and hydrofluorocarbons (HFCs) used as working fluids in the vapour compression plants, have to be replaced by new substances because of their ozone depletion potential. Zeotropic mixture of HFCs refrigerants that are environment-friendly substances are often employed. The zeotropic mixtures with a large glide temperature could cause problems in the refrigeration control system when a leak occurs because their composition modifies. This paper presents a comparison of the energetic performances, in presence of leaks, when a thermostatic valve and an electronic expansion valve are used in a refrigeration plant, working with the zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass)—this is the most suitable substitute of the HCFC22. The vapour leaks are simulated at the inlet of the evaporator and at the liquid receiver. Experimental results show that a good adaptability to mixture leaks is related to the electronic expansion valve, while better energetic performances are obtained using the thermostatic expansion valve as long as it is usable.     

Energy efficiency analysis of a new ternary HFC alternative

In this paper, energy efficiency results are presented for a new HFC ternary blend proposed as a substitute for CFC 502 and HCFC 22. The blend is composed of R-23/R-32/R-125. Performance evaluation test results were obtained after an experimental heat pump set up with a 3 kW rotary compressor. The refrigerants tested in this study under different conditions were HCFC-22, as a reference base refrigerant and R-410a (HFC-32/HFC-125), R-407c (HFC-32/HFC-125/HFC-134a), as well as quaternary mixture; HFC-32/HFC-125/HFC-143a/HFC-134a. The experimental data showed that our proposed HFC ternary blend R-23/R-32/R-125 has superior performance compared to other proposed HFC alternatives such as R-410a and R-407c, under the same conditions. Pressure ratios and head pressures were compatible with new compressors to be used in new systems. Furthermore, experimental results demonstrated that the ternary blend R-23/R-32/R-125 is the best performing replacement for R-22 in heat pump applications and low temperature equipment. Experiments also showed that the heat pump system using R-23/R-32/R-125 was stable and experienced reasonable head pressures. © 1997 John Wiley & Sons, Ltd.     

Performance evaluation of R404A and R507A refrigerant mixtures in an experimental double-stage vapour compression plant

As a result of the ban of the CFC fluids in 2000 and the future limitation of HCFC fluids, which manufacture limit is the year 2010, refrigerant producers have been working to develop different mixtures, mainly based on HFC fluids, which emulate the properties of the former refrigerants used in refrigeration plants. At the moment, the HFC-404A and the HFC-507A are the more widely used fluids in Europe as replacement of the CFC-502 in plants operating at low temperatures. This work presents the experimental evaluation, from an energy point of view, of both refrigerants in the same refrigeration plant, which corresponds to a double-stage vapour compression plant driven by a compound compressor. The characterization was made for an evaporating temperature range between −36 and −20 °C for a constant condensing temperature of 40 °C.     

Predicting Methods for Flow Boiling Heat Transfer of a Non-Azeotropic Mixture Inside a Single Microchannel

At this time, a widely accepted model that can predict flow boiling heat transfer in microchannels with different fluids, geometries, and operative conditions is still missing. Depending on the working fluid, a predicting correlation can lead to accurate estimation or give rise to errors up to 50% and higher. The situation is further complicated when the working fluid is a zeotropic mixture of two components, due to the additional mass transfer resistance that must be estimated. In the recent years much attention has been paid to the possible use of fluorinated propene isomers in substitution for high-global-warming-potential refrigerants. The available hydrofluoroolefins cannot cover all the air-conditioning, heat pump, and refrigeration applications when used as pure fluids because their thermodynamic properties are not suitable for all the operating conditions, and therefore some solutions may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. The adoption of new mixtures poses the problem of how to extend the correlations developed for pure fluids to the case of flow boiling of mixtures in microchannels. In this work, a mixture of R1234ze(E) and R32 (0.5/0.5 by mass) has been considered: The local heat transfer coefficient during flow boiling of this mixture in a single microchannel with 0.96 mm diameter has been measured at a pressure of 14 bar, which corresponds to a bubble temperature of around 26°C. This flow boiling database, encompassing more than 300 experimental points at different values of mass velocity, heat flux, and vapor quality, is compared with available correlations in the literature. The introduction of a correction to account for the additional mass transfer resistance is discussed, and such correction is found to be necessary and proper to provide a correct sizing of the evaporator.     

地源热泵用R22及替代工质热力性能研究

采用CSD方程，针对地源热泵的供暖和空调两种运行工况，对R22及替代工质的系统循环热力性能进行计算，分析和检验R22某些替代工质是否适应于地源热泵，并推荐合适工质。     

An experimental investigation of the global environmental impact of the R22 retrofit with R422D

In recent years a new refrigerant, R422D, has been introduced as substitute of R22 for refrigeration systems. This new fluid is an easy-to-use, non-ozone-depleting HFC refrigerant and, differently from its predecessor (R407C), it is compatible with mineral oil. However, R422D has a very high GWP, and it tends to worsen the efficiency of retrofitted R22 systems. Consequently, even if R422D respects the limits of Montreal Protocol, its global environmental impact could be high. In this paper, we report an experimental analysis in terms of TEWI aimed to identify the global environmental impact of R22 systems retrofitted with R422D. For this purpose, we considered a direct expansion refrigerator for commercial applications and we investigated energy consumption with the temperature of the cold reservoir set to −5, 0, 5, 10 °C. The experimental investigation confirmed that the system, when retrofitted with R422D, leads to an increase of TEWI. Therefore an optimization analysis aimed to eco-friendly scenarios was performed.     

NH3／CO2超市制冷系统的分析研究

介绍了利用自然工质NH_3和CO_2的复叠式超市制冷系统,通过对NH_3/CO_2超市制冷系统与R22和R404A超市制冷系统的分析比较,得出NH_3/CO_2超市制冷系统较R22和R404A超市制冷系统有明显的优势;自然工质NH_3/CO_2复叠式超市制冷系统,不仅节约能源,而且保护环境,是很有发展前景的绿色环保制冷系统。     

Two‐phase flow boiling characteristics of alternatives to R‐22 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two‐phase flow boiling of alternative zeotropic refrigerant mixtures to R‐22, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R‐507, R‐404A, R‐408A, R‐407C, and R‐410A. The experimental data showed that R‐22 has the highest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R‐410A has the highest pressure among the blends under investigation for Reynolds number greater than 3.5×10⁴. However, for Reynolds number less than 3.6×10⁴, it appears from the data that R‐22 has the highest pressure drop compared to other refrigerants under investigation. Copyright © 2000 John Wiley & Sons, Ltd.