Development and validation of a micro-fin tubes evaporator model using R134a and R1234yf as working fluids

This paper presents a model of shell and tube evaporator with micro-fin tubes using R1234yf and R134a. The model developed for this evaporator uses the ε-NTU method to predict the evaporating pressure, the refrigerant outlet enthalpy and the outlet temperature of the secondary fluid. The model accuracy is evaluated using different two-phase flow boiling correlations for micro-fin tubes and comparing predicted and experimental data. The experimental tests were carried out for a wide range of operating conditions using R134a and R1234yf as working fluids. The predicted parameter with maximum deviations, between the predicted and experimental data, is the evaporating pressure. The correlation of Akhavan– Behabadi et al. was used to predict flow boiling heat transfer, with an error on cooling capacity prediction below 5%. Simulations, carried out with this validated model, show that the overall heat transfer coefficient of R1234yf has a maximum decrease of 10% compared with R134a.     

Experimental study of an R1234ze(E)/R134a mixture (R450A) as R134a replacement

This work presents an experimental analysis of a non-flammable R1234ze(E)/R134a mixture (R450A) as R134a drop-in replacement. While R134a has a high GWP value (1430), the R450A GWP is only 547. The experimental tests are carried out in a vapour compression plant equipped with a variable-speed compressor. The replacement suitability has been studied combining different operating conditions: evaporation temperature, condensation temperature and the use of an internal heat exchanger (IHX). The drop-in cooling capacity of R450A compared with R134a is 6% lower as average. R450A COP is even higher to those resulting with R134a (approximately 1%). The discharge temperature of R450A is lower than that of R134a, 2K as average. The IHX has a similar positive influence on the energy performance of both fluids. In conclusion, R450A can be considered as a good candidate to replace R134a.     

改进的R23/R134a自复叠制冷系统实验研究

为了研究R23/R134a混合工质自复叠制冷系统在变工况下的运行性能,更深入地了解系统各部件对自复叠循环的影响,在已建成的自复叠循环系统实验台上进行实验研究.在冷凝温度较高的夏季,测试该自复叠实验装置所能达到的最低蒸发温度,并研究冷凝温度、工质充注质量分数及蒸发冷凝压力对该系统的影响.     

Liquid Thermal Conductivity of Binary Mixtures of Pentafluoroethane (R125) and 1,1,1,2-Tetrafluoroethane (R134a)

Thermal conductivities of zeotropic mixtures of R125 (CF₃CHF₂) and R134a (CF₃CH₂F) in the liquid phase are reported. Thermal conductivities have been measured by a transient hot-wire method with one bare platinum wire. Measurements have been carried out in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa. The dependence of thermal conductivity on temperature, pressure, and composition of the binary mixture is presented. Measured thermal conductivity data are correlated as a function of temperature, pressure, and overall composition of the mixture. The uncertainty of our measurements was estimated to be better than 2%.     

冷藏车层叠式蒸发器应用R404A与R22和R134a的比较

采用分布参数法对层叠式蒸发器建立数学模型，并对蒸发器采用R404A，R22和R134a时的换热和流动性能进行模拟比较。结果表明，在空调工况范围内，新型中低温混合制冷剂R404A具有R134a换热性能好和R22压降小的特点，能够很好地适用于冷藏车系统空调侧层叠式蒸发器。     

改进的R23/R134a自复叠制冷系统试验台设计

为了研究R23/R134a混合工质自复叠制冷系统在变工况下的运行性能,更深入地了解系统各部件对自复叠循环的影响,设计一套试验装置。该装置对现有循环流程进行改进,增加了电磁阀、膨胀容器等部件。对该系统的运行工况、参数范围以及系统的各部件进行设计或选型,并介绍所搭建的试验台。     

Composition shift in liquid-recirculation refrigerating systems: an experimental investigation for the pure fluid R134a and the mixture R32/134aChangement de composition dans les systèmes frigorifiques à recirculation de liquide : étude expérimentale du frigorigène pur R134a et d'un mélange de R32+R134a

The ability of zeotropic mixtures with a remarkable temperature glide to operate in liquid-recirculation systems is investigated and the results of an experimental comparison between the performances of the pure fluid R134a and the zeotropic mixture R32/134a (25/75% by mass) are presented. R134a performs slightly better in the liquid-recirculation mode than in the traditional dry-expansion mode; on the other hand, liquid-recirculation configuration has a detrimental effect on the zeotropic mixture's performance. The reason for this detrimental effect is the mixture component separation which occurs at the liquid/vapor separator. The effect of this separation is investigated using gas chromatograph analysis.     

R134a制冷剂在微通道中的相变传热特性实验

设计了一个可控制制冷剂流量、压力和温度等实验工况的微通道换热器相变流动与换热的可视化实验平台,对R134a制冷剂流经微通道换热器进行了冷凝换热实验研究.试验测量了小质量流率下的R134a制冷剂在多个饱和状态工况下的冷凝换热性能,涉及质量流量、进出口压力和温度等参数.实验分析了传热系数与雷诺数的关系,与Koyama的关联式预测比较接近.分析了摩擦系数随雷诺数的变化,与H L MO和Wu＆Little方程计算得到的数值相近.     

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。     

Thermal conductivity of R32 and its mixture with R134a

The liquid thermal conductivity of R32 (CH₂F₂) and R134a (CF₃CH₂F) was measured in the range from 223 to 323 K and from 2 to 20 MPa by the transient hot-wire method. The thermal conductivity of the R32+R134a mixture was also measured in the same range by varying the mass fraction of R32. The measured data are analyzed to obtain a correlation in terms of temperature, pressure and composition of the mixture. The uncertainty of our measurements is estimated to be within ±2%.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

近共沸制冷剂R134a/R290的研究

当R134a的质量在55%～65%之间时,R134a/R290混合物是近共沸混合物.它可以作为R22的替代制冷剂,并具有优秀的循环性能.这种制冷剂用在空调器中是安全的,并有可能采用矿物油或者烷基苯作为润滑油.     

Measurements of the viscosity of R134a and R32 in the temperature range 270–340 K at pressures up to 20 MPa

This paper reports new measurements of the liquid viscosity of R134a and R32 in the temperature range 270 to 340 K and pressures up to 20 MPa. The measurements have been carried out in a vibrating-wire instrument calibrated with respect to the standard reference value of the viscosity of water. It is estimated that the uncertainty of the present viscosity data is one of 0.5%. The experimental data have been represented by polynomial functions of temperature and pressure for the purposes of interpolation.     

R134a/R600a混合制冷剂应用于大型空气源热泵的性能研究

R134a作为当前主要的R22替代制冷剂,在应用于空气源冷水(热泵)机组,尤其是在热泵运行时会出现能效降低、容易结霜等问题。本研究尝试在R134a的大型螺杆式空气源热泵机组中混合少量R600a来改善机组性能。通过对混合制冷剂物性计算、理论循环性能计算和机组试验,表明添加R600a后的混合制冷剂能显著改善热泵机组的运行性能,并有效提高机组运行可靠性。同时,虽然R600a具有可燃性,但是对于运行时置于室外,介质为水且添加比例不高的空气源热泵机组,这是一个简单、安全、可行的改进方案。     

Experiment and simulation on the performance of an autocascade refrigeration system using carbon dioxide as a refrigerant

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility of keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.

Résumé

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility in keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.     

近共沸制冷剂R290/R134a PVTx性质的实验研究

为了获得混合制冷剂R134a/R290的热物性数据,搭建了高精度PVTx实验系统。以Burnett法为基础,测定了R134a/R290质量分数为50%/50%、55%/45%和60%/40%在温度为252 K~320 K的PVT性质,并且拟合了三种不同配比的混合工质的气态维里方程。实验数据与方程的平均误差为1%左右,具有较好的重合度。     

The viscosity of liquid R134a

The paper reports new measurements of the viscosity of liquid R134a over the temperature range 235 to 343 K and pressures up to 50 MPa. The measurements have been carried out in a vibrating-wire viscometer calibrated with respect to the viscosity of several liquid hydrocarbons. It is estimated that the uncertainty in the viscosity data reported is ±0.6%. The data therefore have a lower uncertainty than that of earlier measurements of the viscosity of this environmentally acceptable regrigerant. The viscosity data have been represented as a function of density by means of a formulation based upon the rigid, hard-sphere theory of dense fluids with a maximum deviation of ±0.3%. This representation allows the present body of experimental data to be extended to regions of thermodynamic state not covered by the measurements.     

Performance of ejector cooling systems using low ecological impact refrigerants

The theoretical behaviour of an ejector cooling system, using as working fluids propane, butane, isobutane, R152a and R134a, is obtained. The ejector works as a thermo-compressor that is simulated with a validated one-dimensional mathematical model, whose errors are lower than 6%. For a system unitary cooling capacity, a parametric study is carried out varying the generation, condensation and evaporation temperatures. From the obtained data, a complete analysis of the system performance can be achieved when the ejector and system operation parameters are considered. The best performance corresponds to the system using propane, because has the highest system coefficient of performance and its ejector has the maximum entrainment ratio value, the least area ratio value and the highest efficiency value. The considered generation temperature ranging from 70 °C to 95 °C is appropriate for low-grade energy sources assisting thermal cooling systems. After this system performance, come those in which R152a and R134a are employed, with isobutane and butane at the end. The obtained results represent potential design points of an efficient ejector cooling system operation, because to each combination of the above mentioned temperatures corresponds one and only one ejector geometry.     

R134a单元式风冷冷风空调机蒸发器设计

以理论模型为基础，对R134a单元式风冷冷风机组翅片管式蒸发器进行设计。应用管内流动沸腾换热模型仿真分析R134a的质量流量对沸腾换热的影响，利用外掠翅片管束换热关联式计算管外翅片侧表面换热系数，进而得出翅片管蒸发器总传热系数，利用计算结果进行设计。     

Viscosity of R134a, R32, And R125 at Saturation

This paper reports the results of the measurement of the viscosity of R134a close to the saturation line in the vapor phase. The new measurements were carried out in a vibrating-wire viscometer specially constructed for the purpose, and the results have an accuracy of ±2%. In addition, the opportunity is taken to present a reevaluation of earlier measurements along the saturation line of the viscosity of R32 and R125. Improved equations of state for these fluids are now available and can be employed to generate improved values for the viscosity.     

二甲醚作为汽车空调制冷剂的性能研究

本文对二甲醚（DME）用作汽车空调制冷剂的性能与现有汽车空调制冷剂R134a进行了对比。首先比较了二甲醚和R134a的基础热力性质，然后对二甲醚和R134a的汽车空调标准工况和变工况下制冷循环性能进行了详细的理论计算及分析。分析表明：二甲醚的制冷性能与R134a基本相似，而性能系数（COP）却优于R134a。因此，更具环保优势的二甲醚是一种理想的潜在的汽车空调制冷剂。