Condensation heat transfer coefficients of enhanced tubes with alternative refrigerants for CFC11 and CFC12Coefficients de transfert de chaleur de condensation de tubes à surface augmentée fonctionnant avec des frigorigènes de remplacement de CFC11 et de CFC12

In this study, condensation heat transfer coefficients (HTCs) of a plain tube, low fin tube, and Turbo-C tube were measured for the low pressure refrigerants CFC11 and HCFC123 and for the medium pressure refrigerants CFC12 and HFC134a. All data were taken at the vapor temperature of 39°C with a wall subcooling of 3–8°C. Test results showed that the HTCs of HFC123, an alternative for CFC11, were 8.2–19.2% lower than those of CFC11 for all the tubes tested. On the other hand, the HTCs of HFC134a, an alternative for CFC12, were 0.0–31.8% higher than those of CFC12 for all the tubes tested. For all refrigerants tested, the Turbo-C tube showed the highest HTCs among the tubes tested showing almost an 8 times increase in HTCs as compared to the plain tube. Nusselt's prediction equation yielded a 12% deviation for the plain tube data while Beatty and Katz's prediction equation yielded a 20.0% deviation for the low fin tube data.     

Experimental investigation of the performance of R22, R407C and R410A in several capillary tubes for air-conditioners

The objective of this study is to present test results and to develop a dimensionless correlation on the basis of the experimental data of adiabatic capillary tubes for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Several capillary tubes with different length and inner diameter were selected as test sections. Mass flow rate through the capillary tube was measured for several condensing temperatures and various degrees of subcooling at the inlet of each capillary tube. Experimental conditions for the condensing temperatures were selected as 40, 45 and 50°C, and the degrees of subcooling were adjusted to 1.5, 5 and 10°C. Mass flow rates of R407C and R410A were compared with those of R22 for the same test conditions. The results for straight capillary tubes were also compared with those of coiled capillary tubes. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tubes was presented based on extensive experimental data for R22, R407C and R410A. Dimensionless parameters were chosen considering the effects of tube geometry, capillary tube inlet conditions, and refrigerant properties. Dimensionless correlation predicted experimental data within relative deviations ranging from −12% to +12% for every test condition for R22, R407C and R410A. The predictions by the developed correlation were in good agreement with the results in the open literature.     

A generalized correlation for the characteristics of adiabatic capillary tubes

The capillary tube is often served as an expansion device in small refrigeration and air-conditioning systems. In this paper, a generalized correlation for predicting the refrigerant mass flow rate through the adiabatic capillary tube is developed with approximate analytic solutions based on the extensive data for R12, R22, R134a, R290, R600a, R410A, R407C, and R404A, in which a homogeneous equilibrium model for two-phase flow is employed, and there is a subcooled liquid or saturated two-phase mixture at the inlet of the capillary tubes. The collected database about capillary tubes covers the inner diameter from 0.5 mm to 2 mm, the tube length from 0.5 m to 5 m, the condensing temperature from 20 °C to 60 °C, the subcooling from 0 °C to 20 °C, and the quality from 0 to 0.3 at the inlet. Assessments for the correlation are made with some experimental data for R12, R22, R134a, R290, R407C, R410A, and R404A obtained from the open literature and some existing correlations based on the experimental database also. The present correlation yields an average deviation of −0.83% and a standard deviation of 9.02% from the database.     

Flow condensation heat transfer coefficients of R22, R134a, R407C, and R410A inside plain and microfin tubes

Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A inside horizontal plain and microfin tubes of 9.52 mm outside diameter and 1 m length were measured at the condensation temperature of 40 °C with mass fluxes of 100, 200, and 300 kg m⁻² s⁻¹ and a heat flux of 7.7–7.9 kW m⁻². For a plain tube, HTCs of R134a and R410A were similar to those of R22 while HTCs of R407C are 11–15% lower than those of R22. For a microfin tube, HTCs of R134a were similar to those of R22 while HTCs of R407C and R410A were 23–53% and 10–21% lower than those of R22. For a plain tube, our correlation agreed well with the present data for all refrigerants exhibiting a mean deviation of 11.6%. Finally, HTCs of a microfin tube were 2–3 times higher than those of a plain tube and the heat transfer enhancement factor decreased as the mass flux increased for all refrigerants tested.     

Formation Conditions of Clathrates Between HFC Alternative Refrigerants and Water

There are two promising candidates as alternative refrigerants for air-conditioners and heat pumps. The first is R407C, which is composed of HFC-32 (23 mass%), HFC-125 (25 mass%), and HFC-134a (52 mass%). The second is R410A, which is composed of HFC-32 (50 mass%) and HFC-125 (50 mass%). In this study, formation conditions of clathrate compounds between water and HFC alternative refrigerants such as HFC-32, HFC-125, HFC-134a, and their mixtures, R407C and R410A, were investigated. Phase diagrams of clathrates of these HFC alternative refrigerants and their mixtures were determined. From the phase diagrams, the critical decomposition temperature and the critical decomposition pressure were determined. The relationship between the critical decomposition points for the clathrates of HFC-32, HFC-125, HFC-134a, R410A, and R407C were studied. It is found that R407C and R410A form clathrate compounds with water under the evaporating temperature condition in the refrigeration cycle of air-conditioners and heat pumps.     

R32/R134a和R407C用于变浓度热泵系统的实验

为了解决R32/R134a应用于变浓度热泵系统存在的排气温度过高问题,提出使用三元混合工质R407C用于该系统中.以R32/R134a和R407C作为工质在变浓度容量调节热泵系统中进行了吸气压力不变时的变浓度实验.实验结果表明,R407C在本系统中变浓度范围低于R32/R134a,但R407C的排气温度和耗功均低于R32/R134a,具有良好的变浓度调节潜力.     

Condensation heat transfer coefficients of R22, R407C, and R410A on a horizontal plain, low fin, and turbo-C tubes

In this study, condensation heat transfer coefficients (HTCs) were measured on a horizontal plain tube, low fin tube, and Turbo-C tube at the saturated vapor temperature of 39 °C for R22, R407C, and R410A with the wall subcooling of 3–8 °C. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation HTCs were up to 50% lower than those of R22. For R407C, as the wall subcooling increased, condensation HTCs decreased on a plain tube while they increased on both low fin and turbo-C tubes. This was due to the lessening effect of the vapor diffusion film with a rapid increase in condensation rate on enhanced tubes. On the other hand, condensation HTCs of R410A, almost an azeotrope, were similar to those of R22. For all refrigerants tested, condensation HTCs of turbo-C tube were the highest among the tubes tested showing a 3–8 times increase as compared to those of a plain tube.     

HFC-161及其应用

介绍ODs替代品HFC-161的性质及应用实例，通过分析与实验说明这些混合制冷剂能够分别替代R410A，R407C，R404A和HFC-134a，均具有环保性能优异、能效比高、用量少、与原系统兼容等特点。     

Performance des mélanges de frigorigènes utilisés pour remplacer le HCFC22

In this study, 14 refrigerant mixtures composed of R32, R125, R134a, R152a, R290 (propane) and R1270 (propylene) were tested in a breadboard heat pump in an attempt to substitute HCFC22 used in residential air-conditioners. The heat pump was of 3.5 kW capacity with water as the heat transfer fluid (HTF) in the evaporator and condenser that are in a counter current flow configuration. All tests were conducted with the HTF temperatures fixed to those found in the ARI test A condition. Test results show that ternary mixtures composed of R32, R125, and R134a have a 4–5% higher coefficient of performance (COP) and capacity than HCFC22. On the other hand, ternary mixtures containing R125, R134a and R152a have both lower COPs and capacities than HCFC22. R32/R134a binary mixtures show a 7% increase in COP with the similar capacity to that of HCFC22 while R290/R134a azeotrope shows a 3–4% increases in both COP and capacity. The compressor discharge temperatures of the mixtures tested are much lower than those of HCFC22, indicating that these mixtures would offer better system reliability and longer life time than HCFC22. Finally, test results with a suction line heat exchanger (SLHX) indicate that SLHX must be used with special care in air-conditioners since its effect is fluid dependent.     

Generalized correlation of refrigerant mass flow rate through adiabatic capillary tubes using artificial neural network

A capillary tube is a common expansion device widely used in small-scale refrigeration and air-conditioning systems. Generalized correlation method for refrigerant flow rate through adiabatic capillary tubes is developed by combining dimensional analysis and artificial neural network (ANN). Dimensional analysis is utilized to provide the generalized dimensionless parameters and reduce the number of input parameters, while a three-layer feedforward ANN is served as a universal approximator of the nonlinear multi-input and single-output function. For ANN training and test, measured data for R12, R134a, R22, R290, R407C, R410A, and R600a in the open literature are employed. The trained ANN with just one hidden neuron is good enough for the training data with average and standard deviations of 0.4 and 6.6%, respectively. By comparison, for two test data sets, the trained ANN gives two different results. It is well interpreted by evaluating the outlier with a homogeneous equilibrium model.     

Evaluation of supplementary/retrofit refrigerants for automobile air-conditioners charged with CFC12Evaluation des frigorigènes supplémentaires / de remplacement pour des systèmes de conditionnement d'air automobiles utilisant du CFC12

In this study, thermodynamic performance of supplementary/retrofit refrigerant mixtures for CFC12 used in existing automobile air-conditioners was examined. A thermodynamic computer analysis of an automobile air-conditioner was carried out for the initial screening of possible mixture candidates, and refrigerant mixtures composed of HCFC22, HFC134a, HCFC142b, RE170 (dimethylether), HC290 (propane), and HC600a (iso-butane) were proposed to supplement CFC12. Also a breadboard type refrigeration test facility was manufactured to verify the performance of the alternative refrigerant mixtures proposed through the computer analysis. Test results showed that HFC134a/RE170 mixture with zero ozone depletion potential is the best long term candidate to supplement CFC12. On the other hand, HCFC22/HFC134a/RE170 and HCFC22/HFC134a/HCFC142b mixtures are good only as short term supplementary/retrofit alternatives since they contain HCFC22. A hydrocarbon mixture of HC290/HC600a showed a good performance but its use in existing automobile air-conditioners should be carefully considered due to its flammability.     

Nucleate boiling heat transfer coefficients of HCFC22, HFC134a, HFC125, and HFC32 on various enhanced tubes

In this study, nucleate boiling heat transfer coefficients (HTCs) of HCFC22, HFC134a, HFC125, HFC32 were measured on a low fin, Turbo-B, and Thermoexcel-E tubes. All data were taken at the liquid pool temperature of 7 °C on horizontal tubes of 152 mm length and 18.6–18.8 mm outside diameter at heat fluxes of 10–80 kW m⁻² with an interval of 10 kW m⁻² in the decreasing order of heat flux. For a plain and low fin tubes, refrigerants with higher vapor pressures showed higher nucleate boiling HTCs consistently. This was due to the fact that the wall superheat required to activate given size cavities became smaller as pressure increased. For Turbo-B and Thermoexcel-E tubes, HFC125 showed a peculiar behavior exhibiting much reduced HTCs due to its high reduced pressure. The heat transfer enhancement ratios of the low fin, Turbo-B, and Thermoexcel-E tubes were 1.09–1.68, 1.77–5.41, 1.64–8.77 respectively in the range of heat fluxes tested.     

Viscosity of Alternative Refrigerants R407C and R407E in the Vapor Phase from 298.15 to 423.15 K

This paper presents new measurements of the viscosity of gaseous R407C (23 mass% HFC-32, 25 mass% HFC-125, 52 mass% HFC-143a) and R407E (25 mass% HFC-32, 15 mass% HFC-125, 60 mass% HFC-143a). The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K. The densities of these two fluid mixtures were calculated with the equation-of-state model in REFPROP. The viscosity at normal pressures was analyzed with the extended law of corresponding states developed by Kestin et al., and the scaling parameters needed in the analysis were obtained from our previous studies for the viscosity of the binary mixtures consisting of HFC-32, HFC-125, and HFC-134a. The modified Enskog theory developed by Vesovic and Wakeham (V-W method) was applied to predict the viscosity for the ternary gaseous HFC mixtures under pressure. As for the calculation of pseudo-radial distribution functions in mixtures, a method based on the equation of state for hard-sphere fluid mixtures proposed by Carnahan-Starling was applied. It was found that the V-W method can predict the viscosity of R407C and R407E without any additional parameters for the ternary mixture.     

Electrical properties of CFC- and HCFC-substitutes

Electrical properties of refrigerants are of importance as soon as bushings are surrounded by a refrigerant. This is the case e. g. for hermetic sealed motor compressors as well as for some control devices such as liquid level control units or capacity controls for compressors. This paper presents a survey of existing data for HFC refrigerants and presents new measurements for those HFC blends that have been identified as long term replacements for CFCs and HCFCs. The data collection includes permittivity, electrical conductivity and breakdown voltage. Values are given for the HFC blends R404A, R407C, R410A and R507 as well as for R134a.     

Condensation heat transfer of a pure fluid and binary mixture outside a bundle of smooth horizontal tubes. Comparison of experimental results and a classical model

The condensation of pure HFC134a and different zeotropic mixtures with pure HFC134a and HFC23 on the outside of a bundle of smooth tubes was studied. The local heat transfer coefficient for each row was experimentally determined using a test section composed by a 13×3 staggered bundle of smooth copper tubes, measuring cooling water temperature in the inlet and the outlet of each tube, and measuring the vapour temperature along the bundle. All data were taken at the inlet vapour temperature of 40°C with a wall subcooling ranging from 4 to 26 K. The heat flux was varied from 5 to 30 kW/m² and the cooling water flow rate from 120 to 300 l/h for each tube. The visualisation of the HFC134a condensate flow by means of transparent glass tubes reveals specific flow patterns and explains the difference between the measured values of the heat transfer coefficient and the calculated values from Nusselt's theory. On the other hand, the experimental heat transfer data with the binary mixtures HFC23-HFC134a show the important effects of temperature glide and the strong decrease of the heat transfer coefficient in comparison with the pure HFC134a data. The measured values with the different zeotropic mixtures were compared with the data calculated with the classical condensation model based on the equilibrium model. An improvement of this model is proposed.     

Performance evaluation of environmentally benign refrigerants in heat pumps 2: An experimental study with HFC134a

The performance characteristics of HFC134a in an industrial (water to water) heat-pump test facility at Electricité de France with a twin-screw compressor are presented. The performance of HFC134a has been studied in terms of performance parameters of the compressor (e.g. its volumetric and isentropic efficiencies) and of the heat-pump system (e.g. coefficient of performance and volumetric heating capacity) with a view to using it in new installations for low to medium temperature (< 70°C) applications as well as to replacing CFC12 in existing installations. The influence of degree of superheat on the miscibility of HFC134a with ester oil and on the viscosity of the oil-refrigerant mixture has also been studied for various discharge pressures.     

An experimental study on HC290 and a commercial liquefied petroleum gas (LPG) mix as suitable replacements for HCFC22

This paper presents an experimental study on the performance of hydrocarbon refrigerants, namely propane and a liquefied petroleum gas (LPG) mix as suitable replacements for the widely used refrigerant HCFC22 in refrigeration and heat pump applications. A cylinder of commercially available LPG from New Zealand market was obtained for this study. The composition of the specific LPG mix (by mass fraction) was propane (HC290)—98.95%, ethane (HC170)—1.007%, iso-butane (HC600a)—0.0397% and other constituents in small proportions. Experiments were carried out in a laboratory heat pump test facility with maximum condenser capacity of approximately 15 kW. Condensing temperatures were held constant at 35, 45 and 55°C, while evaporating temperatures were varied over a wide range from − 15 to + 15°C. All tests were carried out at constant degree of superheat (about 1 K) and subcooling (about 8 K). All appropriate precautions were observed against any leaks or fire.The analysis revealed that the hydrocarbon refrigerants performed better than HCFC22 but with a small loss of condenser capacity. The mass flow rate and compressor discharge temperature were found to be significantly lower than HCFC22. The performance of the specific LPG mix tested was found to be better than HC290 at higher condensing temperatures but poorer at a lower condensing temperature. No adverse effects were found with the LPG mix despite the presence of little moisture (less than 0.01%) in its composition. The study reveals that LPG of the tested composition (i.e. predominantly a mixture of propane, ethane and iso-butane) can be an excellent refrigerant in heat pump/refrigeration applications.     

HCFC123与HFC134a离心式冷水机组特性比较

从离心式冷水机组的特性角度出发,阐述冷水机组2种替代制冷剂HFC134a和HCFC123的选择使用,比较分析这2种制冷剂的性能,及其机组性能和其他一些因素。其中制冷剂的环境特性包括毒性、GWP和ODP等。机组性能特性包括产品能耗比及单位质量制冷量比的比较等。其他特性包括产品尺寸、使用维护等。综合考虑上述因素,尤其应考虑2007年9月修订的《蒙特利尔议定书》加速淘汰HCFCs的现实要求,认为在我国对新的离心机组使用HCFC123应持十分谨慎的态度。     

Modelling of reciprocating and scroll compressors

This paper presents simple and thermodynamically realistic models of two types of compressors widely used in domestic heat pumps (reciprocating and scroll compressors). These models calculate the mass flow rate of refrigerant and the power consumption from the knowledge of operating conditions and parameters. Some of these parameters may be found in the technical datasheets of compressors whereas others are determined in such a way that the calculated mass flow rate and electrical power match those given in these datasheets.The two models have been tested on five reciprocating compressors and five scroll compressors. This study has been limited to compressors with a maximum electrical power of 10 kW and for the following operating conditions: evaporating temperatures ranging from −20 to 15 °C and condensing temperatures ranging from 15 to 60 °C.The average discrepancies on mass flow rate and power for reciprocating compressors are 1.10 and 1.69% (for different refrigerants: R134a, R404A, R22, R12 and R407C). For scroll compressors, the average discrepancies on mass flow rate and power are 2.42 and 1.04% (for different refrigerants: R134a, R404A, R407C and R22).     

风冷螺杆热泵机组制冷剂替换试验研究

对R22、R407c、R134a三种制冷剂的基本物性及热力性能进行了分析比较，并在风冷螺杆热泵机组基础上进行了替换试验研究。结果表明：R407c为最佳替换R22的制冷剂；R134a替换后能效比较高，但制冷（热）量衰减过多，同时R134a的运行压力过低不太适合热泵工况。