采用R22、R134a两种制冷剂的毛细管特性对比研究

建立单相区和两相区毛细管模型,模型计算的毛细管质量流量与实验测量的质量流量差别小于(10%.研究了R134a代替R22后毛细管的质量流量随冷凝温度、过冷度、毛细管内直径和毛细管长度的变化规律,结果表明,两种制冷剂有相同的变化规律,但是在相同的条件下,R22的质量流量比R134a大,比如冷凝温度为45℃时,R22的质量流量比R134a高31.1%.     

采用制冷剂R410A的绝热毛细管特性仿真

基于能量守恒、动量守恒、质量守恒方程,建立描述绝热毛细管特性的数学模型.毛细管内制冷剂流量的模型仿真结果与实测数据的差别小于5%,说明仿真结果具有可信度.用模型研究了通过毛细管的制冷剂质量流量随毛细管的内直径、长度、冷凝温度和蒸发温度的变化关系.仿真结果可以用于指导采用R410A的空调系统的设计和实验,具有很好实际应用价值.     

R290/R134a用于家用空调器的性能匹配分析

对具有低可燃性的R290/R134a空调器样机与原R290空调器进行性能对比试验,并改变制冷剂充注量、毛细管长度、电子膨胀阀步数、换热器管径等对系统进行优化设计,使系统达到最佳匹配效果。试验结果表明：优化后的R290/R134a空调器样机的制冷能力最高达2 786 W,能效比为3.41,符合国家标准GB12021.3—2010的2级能效的要求。     

考虑亚稳态的绝热毛细管模型与计算

制冷剂在通过毛细管过程中,存在一个不稳定的亚稳态流动阶段.在考虑亚稳态现象的基础上,基于两相流动的漂移流模型,建立了绝热毛细管内制冷剂流动特性的数学模型.针对工质为R134a的制冷系统开发了绝热毛细管数值模拟程序,并对漂移流模型中的3个重要参数:空隙率、漂移速度和干度进行了计算和分析.该程序在制冷系统毛细管的匹配中具有一定实用价值.     

R32毛细管流量特性模型计算和诺模图建立

毛细管是一种重要的节流元件，广泛应用于各种小型制冷制热装置中，R32作为环境友好型制冷剂，在家用空调领域应用愈发广泛。本文首先基于均相流假设及能量守恒、动量守恒、质量守恒方程，建立绝热毛细管的数学模型，并经适量简化，分别从过冷区和两相区对毛细管模型进行分析求解，得到毛细管长度的计算公式。同时，在该模型中引入了壅塞流概念，采用临界流量作为壅塞流是否出现的判断依据，有效提高了算法精度和稳定性。其次，搭建了针对R32的毛细管测试平台，通过实验获得了内径为1 mm,长度为0.5 m和1 m的两根毛细管在冷凝压力为2.4～3.2 MPa、过冷度为5～20℃下的质量流量数据，验证了该仿真模型的精度。最后，基于仿真模型得到的大量数据点，绘制了R32毛细管的诺模图。     

新型混合制冷剂R1270/R152a/R13I1的理论研究

针对制冷剂R22的替代问题,提出了一种适用于空调等制冷设备的环保型混合制冷剂R1270/R152a/R13I1。基于Refprop8.0,对R1270/R152a/R13I1的基本热物理性质和制冷系统循环性能进行了分析,研究表明:在标准工况下,R1270/R152a/R13I1混合制冷剂的COP和单位容积制冷量均与R22相当,非常有利于直接灌注式替代;在变工况下,R1270/R152a/R13I1的滑移温度较小,性能优于R407C,单位容积制冷量与R407C和R22相当,是一种优良的R22替代物。     

混合制冷剂R134a/R600a应用于冰箱的研究

对于R134a/R600a组成的混合制冷剂,当R134a的质量百分比在75%～95%之间时,可以形成一种近共沸混合物.本文介绍了这种近共沸混合制冷剂的性质,理论分析并实验验证了它作为R12的替代制冷剂的循环性能,并对它采用烷基苯或者矿物油作为润滑油时的制冷系统回油性能进行了实验研究.     

R32/R134a混合制冷剂扩散吸收制冷系统实验研究

在国内外扩散吸收制冷研究现状的基础上,分别采用R32、R134a和R32/R134a混合物为制冷剂,DMF(N,N-二甲基甲酰胺)为吸收剂,Ar为扩散气体,对扩散吸收制冷系统进行了性能研究,探究了混合制冷剂配比以及加热功率对系统制冷效果的影响。实验结果显示,R32/R134a混合制冷剂的制冷效果要优于R32或R134a纯制冷剂,且在不同的组分浓度和不同的加热量下,制冷效果不同,存在较好的R32浓度范围。     

R134a与R410A在空调工况下的性能比较

传统制冷剂R22的替代已是大势所趋.本文着重对R22的替代制冷剂R134a与R410A的传热、阻力压降特性进行实验比较研究,认为R410A在传热、阻力压降特性方面比R134a优良,作为R22的替代制冷剂,R410A应比R134a更有竞争力.     

近共沸混合制冷剂R134a／R600a／R600的应用研究

对于制冷剂R134a／R600a／R600组成的混合制冷剂，当其成分满足一定的要求时，可以形成一种近共沸混合物。本文介绍了这种近共沸混合制冷剂的性质，理论分析并实验验证了它作为R12的替代制冷剂的循环性能，并对它采用烷基苯或者矿物油作为润滑油时的制冷系统回油性能进行了实验研究。     

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.     

Capillary tube selection for HCFC22 alternativesSélection de capillaires pour les frigorigènes de remplacement du HCFC22

In this paper, pressure drop through a capillary tube is modeled in an attempt to predict the size of capillary tubes used in residential air conditioners and also to provide simple correlating equations for practicing engineers. Stoecker's basic model was modified with the consideration of various effects due to subcooling, area contraction, different equations for viscosity and friction factor, and finally mixture effect. McAdams' equation for the two-phase viscosity and Stoecker's equation for the friction factor yielded the best results among various equations. With these equations, the modified model yielded the performance data that are comparable to those in the ASHRAE handbook. After the model was validated with experimental data for CFC12, HFC134a, HCFC22, and R407C, performance data were generated for HCFC22 and its alternatives, HFC134a, R407C, and R410A under the following conditions: condensing temperature; 40, 45, 50, 55°C, subcooling; 0, 2.5, 5°C, capillary tube diameter; 1.2–2.4 mm, mass flow rate; 5–50 g/s. These data showed that the capillary tube length varies uniformly with the changes in condensing temperature and subcooling. Finally, a regression analysis was performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and subcooling. Thus determined simple practical equations yielded a mean deviation of 2.4% for 1488 data obtained for two pure and two mixed refrigerants examined in this study.     

Experimental investigation on diabatic flow of R-134a through spiral capillary tube

The present experimental investigation has been carried out to investigate the effects of various geometric parameters on the mass flow rate of R-134a through diabatic spiral capillary tube. In diabatic flow, the capillary tube is bonded with the compressor suction-line to form a counter-flow exchanger. The lateral type of diabatic capillary tube has been investigated in the present experimental study. The major geometric parameters investigated are capillary tube diameter, capillary tube length and coil pitch. In addition, effect of inlet subcooling on the mass flow rate through diabatic spiral capillary tube is also done. A comparison of the performance of diabatic spiral capillary tube has been made with adiabatic spiral capillary tube. Generalized empirical correlation for diabatic spiral capillary tube has also been proposed. It has been found that the predictions of the proposed correlation lie in the error band of ±7%.     

提高低温空气源热泵性能的研究

分析了热泵在低温环境工作时存在的问题。在热泵系统四通换向阀后的排气管上加旁通毛细管和在气液分离器中加过冷管。通过分析确定过冷管最小换热面积和旁通毛细管最佳长度范围。经实验证明在低温工况下时制热量提高显著。     

Ice crystal growth in supercooled solution

Study on the crystal growth of ice in water-ethyleneglycol solution was carried out, experimentally. The ice crystal, which was seeded on top of the capillary tube, propagated inside the tube slowly and began to grow freely at the tip of the tube in subcooled solution. The outer diameter of the tip of the capillary tube was less than 0.1 mm, which was much smaller than that of other researchers. Hence, considerable reduction of the influence of the existence of a capillary was accomplished and the initial growth of a single crystal was observed, precisely. Under the condition of subcooling of less than 8 K, the shape of the crystal was observed to be different from that of the one in pure water. The velocity of dendrite ice growth and the radius of the curvature of the tip were measured. It was found that after the dendrite ice developed to a certain size, the velocity of the dendritic growth and the radius of curvature were kept steady, and its values were dependent on the degree of subcooling and the concentration of the solution.     

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.     

A visual study of R-404A/oil flow through adiabatic capillary tubes

The present study explores the potential of using visualization techniques to investigate refrigerant/oil flow through adiabatic capillary tubes. A literature review shows that these techniques have been used before for capillary tube investigations, but none of these studies focused on the refrigerant/oil phenomena. Therefore, the main objective is to investigate the flow of a refrigerant/oil mixture through a glass capillary tube, with special emphasis on the behavior of the vaporization point. The test fluids are R-404A (a near azeotropic blend) and a polyolester-type oil. Experimental data cover oil concentrations ranging from 5.6 to 6.9% (by mass), degrees of subcooling ranging from 6.2 to 21.5 °C (11.2 F to 38.7 F), and a condensing pressure of 1825 kPa (250 psig). The results show trends of mass flow rate, and give some useful insights about the location of the vaporization point for various oil concentrations and operating conditions.     

Visualization of refrigerant flow at the capillary tube inlet of a high-efficiency household refrigerator

The subcooled condition at the condenser outlet ensures complete condensation, which is necessary in vapor compression systems to increase the cooling capacity and ensure the liquid conditions at the expansion device inlet. However, in household refrigerators, recent works indicate the presence of two-phase flow at the capillary tube inlet. These systems behave quite differently from other refrigeration systems due to the extremely low capacity. In the present work, a test bench was built to visualize the refrigerant flow at the condenser outlet and at the capillary tube inlet of a commercial household refrigerator. A transparent tube replaced the end of the condenser and three transparent filters were installed with different orientations. Different positions of the capillary tube within the filters were also tested. Despite measuring a certain subcooling, all the reported visualizations showed that the capillary tube was steadily drawing in two-phase flow.     

变径毛细管在R410A冷暖空调器中的流量特性

为减少变径毛细管在R410A冷暖空调器应用中的匹配实验工作量,利用节流元件制冷剂流量测试台对多个结构尺寸规格的变径毛细管进行了R410A制冷剂流量测试,建立了基于阻抗计算方法的流量特性经验模型。利用该模型计算出KFR-32GW冷暖空调器所需变径毛细管的初步结构尺寸,并在该冷暖型空调器上进行精确匹配实验,确定最佳变径毛细管结构尺寸。实验结果表明:采用变径毛细管节流的空调器相对采用毛细管组件节流的空调器,制冷量减少0.3%,制冷能效比不变,制热量增加0.5%,制热能效比减少0.3%,两者的性能指标基本相同。因此变径毛细管可以代替毛细管组件应用于R410A冷暖空调器,且通过实验方法建立的变径毛细管R410A制冷剂流量特性经验模型精度较高,可以满足实际工程应用。