润滑油循环率对活塞式制冷压缩机性能影响的实验研究

论文用实验的方法研究了润滑油循环率对活塞式制冷压缩机工作性能的影响。为了确保实验分析的准确性,测试系统采用了双油分的装置,使排气后的制冷剂和润滑油尽量完全分离,制冷剂以纯冷媒的形式再次进入压缩机的吸气。实验中采用Sanyo某型号压缩机进行测试,其结果表明润滑油循环率随着压缩机注油量的增加而增加,油循环率对压缩机的制冷量、功率、COP以及排气温度均有影响,较低的油循环率使得压缩机具有较高的制冷量和COP,同时排气温度也比较高,较高油循环率则使压缩机的制冷量和COP下降。因此一定要选择与压缩机相匹配的注油量,控制油循环率在一个合理的范围内,这样既能使润滑油起到有效的润滑作用,保证压缩机正常工作,又能使压缩机获得最佳的性能指标。     

制冷压缩机的润滑油选用分析

文章简述了制冷系统中润滑油的作用和一般理化性能要求,阐明制冷剂系统中各设备对润滑油的特殊要求;并分析了冷冻油对制冷系统制冷性能的影响.列举常用制冷剂所用的冷冻油,分析不同种类的冷冻油对制冷剂的适应性,并指出,选用冷冻油要根据其制冷压缩机的类型、工况和制冷剂的种类来综合考虑,并且需要通过压缩机相应的性能测试来判定选用的合理性.     

制冷剂压缩机润滑油监测装置的研究

为监测制冷剂压缩机润滑油的使用状况,即时了解润滑油各项理化数据,掌握最佳换油时机,本文对润滑油监测技术进行剖析,对制冷剂压缩机润滑油监测装置的工作原理进行阐述,并对该技术在制冷空调领域的应用进行展望。     

制冷剂混合物水平微翅管内流动沸腾研究综述

本文对目前国内外制冷剂混合物在水平微翅管内流动沸腾特性的实验研究进行了综述。讨论了混合物在微翅管内流动沸腾的强化特性、替代制冷剂换热性能的比较和润滑油对换热的影响。同时,对进一步的研究提出了一些建议。     

R717在小管径水平光管内流动沸腾换热及压降特性

氨制冷剂存在可燃性和毒性,因此减少其在制冷系统中的充注量极为重要。小管径换热管通常可以提供更高的表面传热系数,这可以作为提升换热器紧凑性同时减少系统中充注量的有效方法。本文搭建了氨制冷剂管内流动沸腾换热及压降测试实验装置,测试了氨制冷剂在4 mm水平光管内的流动沸腾换热及压降,并分析了干度、质量流速及热流密度对换热及压降特性的影响。结果表明:流动沸腾换热表面传热系数随着干度的增加而增大,同时质量流速和热流密度越高,流动沸腾换热表面传热系数越大。此外,氨制冷剂在管内的两相摩擦压降也随着干度的增加而增大,在固定干度下,质量流速的升高导致压降增大。     

船用制冷剂泵供液制冷系统低压侧回油控制研究

介绍一种全新的船用制冷剂泵供液制冷系统回油方法,并将其与传统的回油方法进行比较,据此设计一种全新回油控制装置。重点介绍该装置的设计方法及设计要点、采用该回油方法的特点及其对整个制冷系统的影响。试验结果表明,该回油控制装置可实现连续地将低压侧液态制冷剂中溶解的润滑油返回至压缩机吸气口并进入油分离器,且能够有效地控制并将低压侧液态制冷剂中溶解的润滑油量稳定维持在制冷系统可接受的范围内。试验结果与理论计算结果基本吻合。     

空调用滚动转子式压缩机内制冷剂泄漏的研究

滚动转子式压缩机内制冷剂泄漏，主要是以溶于润滑油的形式来进行的，通过润滑油流动模型来模拟计算制冷剂的泄漏量。计算结果表明：径向间隙的泄漏量最大，其次是转子通向吸气腔的轴向端面间隙的泄漏量。通过变间隙的性能试验来间接验证泄漏对滚动转子式压缩机的影响。因此合理地设计泄漏间隙值，可以有效地降低滚动转子式压缩机的泄漏损失。     

多台全封闭制冷压缩机串联运行系统中的润滑油路新结构

全封闭压缩机曲轴通常以约3500r.p.m的速度回转。对曲轴轴承和其它运运部件供给适量的润滑油是非常重要的。冷冻润滑油贮存在压缩机壳体下面的油池里,通常是用离心泵将油压送到压缩机,润滑各部件。在制冷循环过程中,因为润滑油与制冷剂蒸汽的亲和特性,有部份油与制冷剂一起运行。制冷系统仅配置一台压缩机,同行的润滑油最终会回到压缩机壳体内。但在配置二     

含油制冷剂在泡沫金属圆管内流动沸腾的换热特性

实验研究了填充泡沫金属的圆管内制冷剂与润滑油混合物流动沸腾换热特性。实验对象为两根分别填充5PPI、90%孔隙率与10PPI、90%孔隙率泡沫铜的圆管,以及相同管径的光管。实验工况为蒸发压力995kPa,质流密度为10~30 kg/(m2.s),热流密度为3.1~9.3kW/m2,入口干度0.175~0.775,油浓度为0~5%。实验结果表明:纯制冷剂工况下,泡沫金属的存在强化流动沸腾换热,换热系数最多提高185%;含油工况下,泡沫金属强化换热的效果弱化;相同工况下,更小的孔径可以提高流动沸腾换热系数,相比5PPI泡沫金属的实验数据,10PPI的泡沫金属可以使换热系数最多提高0.6倍。基于流型建立了填充泡沫金属的圆管内制冷剂与润滑油流动沸腾换热系数的预测模型,预测模型与98%的实验数据误差在±30%以内。     

制冷技术问答

三十六:氟里昂制冷压缩机的曲轴箱为什么要安装油加热器?压缩机润滑油与氟里昂制冷剂可以相互溶解,其中 R22、R114、R152、R502等制冷剂稍溶解于润滑油,属微溶型,而R11、R12、R21、R113、R500等对润滑油的溶解度很大,属完全互溶型。氟里昂制冷剂在润滑油中的溶解量与油温有关。压缩机运转时,曲轴箱中的油温较高,约在50℃或更高一些,这时氟里昂制冷剂     

Flow boiling characteristics and flow pattern visualization of refrigerant/lubricant oil mixtures

A comprehensive review of flow boiling characteristics and flow pattern visualization of refrigerant/lubricant oil mixtures is presented in this paper. First, various parameters influenced by the lubricant oil in convective boiling of refrigerants, such as mass velocity, vapor quality, oil concentration and geometric characteristics of the heat transfer tube are discussed. The effects of the unavoidable introduction of the lubricant oil on the thermodynamics properties of a refrigerant are described. Then, a review of the main experimental studies of flow boiling of refrigerant/lubricant oil mixtures is presented and also describes research with halocarbons, carbon dioxide, hydrocarbons and ammonia. There is no agreement among these studies regarding the effect of the oil in the evaporator, with studies showing an increase or decrease in the heat transfer coefficient. However, in relation to pressure drop, all the results presented the same trend, increasing the pressure drop with increasing oil concentration. Next, the flow patterns of refrigerant/oil mixtures are illustrated together with a selection of video images. It is possible to notice the difference in frothing formation with respect to the particular refrigerant and tube geometry. Some predictions of oil effects on the heat transfer coefficient and pressure drops based on the mixture physical properties are then presented and the trends compared to data. Finally, some suggestions for future work are given.     

Use of fluorescence to measure the lubricant excess surface density during pool boiling

This paper presents what are believed to be the first measurements of the non-adiabatic lubricant excess surface density on a roughened, flat, plain horizontal pool-boiling surface. Pool boiling heat transfer data is given for pure R123 and a R123/lubricant mixture. Lubricant excess surface density data are given for the boiling R123/lubricant mixture. A spectrofluorometer was used to measure the lubricant excess density that was established by the boiling of a R123/lubricant mixture on a test surface. The fluorescent measurement technique was used to confirm the existence of the lubricant excess layer during refrigerant/lubricant mixture boiling. The refrigerant preferentially boils, thus, concentrating and accumulating the lubricant on the surface in excess of the bulk concentration. The excess lubricant resides in a very thin layer on the surface and influences the boiling performance. Accordingly, the ability to measure the lubricant excess density on the heat transfer surface would lead to a fundamental understanding of the mechanism by which lubricants can degrade or improve boiling performance. In support of this effort, heat transfer data are provided for both pure R123 and an R123/lubricant (1.8% lubricant mass fraction) mixture at 277.6 K. The heat transfer data shows that the lubricant excess causes an average degradation of 12% in the heat flux for a given superheat.

Résumé

This paper presents what are believed to be the first measurements of the non-adiabatic lubricant excess surface density on a roughened, flat, plain horizontal pool-boiling surface. Pool boiling heat transfer data is given for pure R123 and a R123/lubricant mixture. Lubricant excess surface density data are given for the boiling R123/lubricant mixture. A spectrofluorometer was used to measure the lubricant excess density that was established by the boiling of a R123/lubricant mixture on a test surface. The fluorescent measurement technique was used to confirm the existence of the lubricant excess layer during refrigerant/lubricant mixture boiling. The refrigerant preferentially boils, thus, concentrating and accumulating the lubricant on the surface in excess of the bulk concentration. The excess lubricant resides in a very thin layer on the surface and influences the boiling performance. Accordingly, the ability to measure the lubricant excess density on the heat transfer surface would lead to a fundamental understanding of the mechanism by which lubricants can degrade or improve boiling performance. In support of this effort, heat transfer data are provided for both pure R123 and an R123/lubricant (1.8% lubricant mass fraction) mixture at 277.6 K. The heat transfer data shows that the lubricant excess causes an average degradation of 12% in the heat flux for a given superheat.     

Effect of bulk lubricant concentration on the excess surface density during R123 pool boiling

This paper investigates the effect that bulk lubricant concentration has on the non-adiabatic lubricant excess surface density on a roughened, horizontal flat (plain) pool-boiling surface. Both pool boiling heat transfer data and lubricant excess surface density data are given for pure R123 and three different mixtures of R123 and a naphthenic mineral oil. A spectrofluorometer was used to measure the lubricant excess density that was established by the boiling of a R123/lubricant mixture on a test surface. The fluorescent technique was used to measure the effect of bulk lubricant concentration on the lubricant excess layer during refrigerant/lubricant mixture boiling. The refrigerant preferentially boils, thus, concentrating and accumulating the lubricant on the surface in excess of the bulk concentration. The excess lubricant resides in a very thin layer on the surface and influences the boiling performance. Accordingly, the ability to measure the effect of bulk lubricant composition on the lubricant excess density and in turn the effect on the heat transfer would lead to a fundamental understanding of the mechanism by which lubricants can degrade or improve boiling performance. In support of this effort, heat transfer data are provided for pure R123 and three R123/lubricant mixtures at 277.6 K. For heat fluxes between approximately 25 to 45 kW/m², an average enhancement of the heat flux of 9 and 5% was achieved for the 0.5 and 1% lubricant mass fractions, respectively, and an average degradation of 5% in the heat flux was obtained for the 1.8% lubricant mass fraction mixture.

Résumé

This paper investigates the effect that bulk lubricant concentration has on the non-adiabatic lubricant excess surface density on a roughened, horizontal flat (plain) pool-boiling surface. Both pool boiling heat transfer data and lubricant excess surface density data are given for pure R123 and three different mixtures of R123 and a naphthenic mineral oil. A spectrofluorometer was used to measure the lubricant excess density that was established by the boiling of a R123/lubricant mixture on a test surface. The fluorescent technique was used to measure the effect of bulk lubricant concentration on the lubricant excess layer during refrigerant/lubricant mixture boiling. The refrigerant preferentially boils, thus, concentrating and accumulating the lubricant on the surface in excess of the bulk concentration. The excess lubricant resides in a very thin layer on the surface and influences the boiling performance. Accordingly, the ability to measure the effect of bulk lubricant composition on the lubricant excess density and in turn the effect on the heat transfer would lead to a fundamental understanding of the mechanism by which lubricants can degrade or improve boiling performance. In support of this effort, heat transfer data are provided for pure R123 and three R123/lubricant mixtures at 277.6 K. For heat fluxes between approximately 25 kW/m² to 45 kW/m², an average enhancement of the heat flux of 9% and 5% was achieved for the 0.5% and 1% lubricant mass fractions, respectively, and an average degradation of 5% in the heat flux was obtained for the 1.8% lubricant mass fraction mixture.     

An experimentally validated model for microchannel heat exchanger incorporating lubricant effect

This paper presents the further development of Li and Hrnjak's (2013) microchannel heat exchanger model which includes the thermodynamic and transport properties of refrigerant–oil mixture. Effect of lubricant is accounted in boiling heat transfer, pressure drop and refrigerant distribution. A newly proposed infrared thermography based method is implemented in the model to describe the liquid refrigerant distribution in the inlet header of the microchannel heat exchanger. The new model is validated against experimental results (R134a-PAG 46 oil) at various oil circulation ratios (0.1%–8.3%). Simulation results also indicate that lubricant addition improves refrigerant distribution which is in agreement with experiments and the infrared thermography based method enables the model capture lubricant effect on capacity more comprehensively.     

Boiling of ammonia/lubricant mixture on a horizontal enhanced tube in a flooded evaporator with inlet vapor quality

In a flooded evaporator of an ammonia vapor-compression refrigeration system, boiling commonly takes place with ammonia mixed with compressor lubricant and subjected to a vapor quality at the inlet of the evaporator. In the present study, flooded boiling tests of ammonia on an enhanced tube under simultaneous influence of a miscible lubricant and inlet quality were conducted. The results suggest that the boiling heat transfer coefficient increases with both saturation temperature and heat flux. The coefficient slightly increases or does not significantly vary with the inlet quality. The coefficient in general is decreased by adding lubricant to the refrigerant, but the coefficient does not necessarily decrease as the lubricant concentration increases. The lubricant effect is generally more significant than the inlet quality effect. A correlation was developed based on the present data for flooded boiling of lubricant/ammonia mixture on an enhanced horizontal tube under the influence of inlet quality.     

A semi-theoretical model for predicting refrigerant/lubricant mixture pool boiling heat transfer

This paper outlines the framework of a semi-theoretical model for predicting the pool boiling heat transfer of refrigerant/lubricant mixtures on a roughened, horizontal, flat pool-boiling surface. The predictive model is based on the mechanisms involved in the formation of the lubricant excess layer that exists on the heat transfer surface. The lubricant accumulates on the surface in excess of the bulk concentration via preferential evaporation of the refrigerant from the bulk refrigerant/lubricant mixture. As a result, excess lubricant resides in a thin layer on the surface and influences the boiling performance, giving either an enhancement or degradation in heat transfer. A dimensionless excess layer parameter and a thermal boundary layer constant were derived and fitted to data in an attempt to generalize the model to other refrigerant/lubricant mixtures. The model inputs include transport and thermodynamic refrigerant properties and the lubricant composition, viscosity, and critical solution temperature with the refrigerant. The model predicts the boiling heat transfer coefficient of three different mixtures of R123 and lubricant to within ±10%. Comparisons of heat transfer predictions to measurements for 13 different refrigerant/lubricant mixtures were made, including two different refrigerants and three different lubricants.     

Effects of synthetic oil in a compression refrigeration system using R410A. Part II: quality of heat transfer and pressure losses within the heat exchangers

The consequences of the oil rejected by the compressor of a vapour-compression refrigeration system on the operation of the evaporator and condenser are analysed. The modelled prototype uses the mixture of HFC R410A and a synthetic polyolester (POE) oil. The rise of the amount of lubricant circulating in the system leads to a progressive change in the behaviour of the mixture of refrigerant and oil that, for the higher oil mass fraction, evolves like a zeotropic mixture. One also observes that the presence of lubricant is generally associated with a fall of the performances of the heat exchangers, except however in the evaporator where an optimum is observed when the quantity of oil is equal to 0.1% of the total mass of the mixture. Some conclusions are drawn about the choice of correlations for the calculation of the refrigerant side heat transfer coefficient in a plate evaporator.     

Influence of oil on nucleate pool boiling heat transfer of refrigerant on metal foam covers

Nucleate pool boiling heat transfer characteristics of refrigerant/oil mixture on metal foam covers were experimentally investigated. The refrigerant is R113, and the oil is VG68. The copper foams, having ppi (pores per inch) of 10 and 20, porosity from 90% to 98%, and thickness of 5 mm, are selected in this study. Experimental conditions include a saturation pressure of 101 kPa, oil concentrations from 0 to 5%, and heat fluxes from 0 to 80 kW m⁻². The experimental results indicate that the nucleate pool boiling heat transfer coefficient on copper foam covers is larger than that on flat heated surface by a maximum of 160% under the present experimental conditions; the presence of oil deteriorates the nucleate pool boiling heat transfer on copper foam covers by a maximum of 15% under the present experimental conditions, and the deterioration of oil on nucleate pool boiling heat transfer on copper foam covers is lower than that on a flat heated surface. A correlation for predicting the nucleate pool boiling heat transfer coefficient of refrigerant/oil mixture on copper foam cover is developed, and it agrees with 95% of the experimental data within a deviation of ±20%.     

Effect of bulk lubricant concentration on the excess surface density during R134a pool boiling

This paper investigates the effect that the bulk lubricant concentration has on the non-adiabatic lubricant excess surface density on a roughened, horizontal flat pool-boiling surface. Both pool boiling heat transfer data and lubricant excess surface density data are given for pure R134a and three different mixtures of R134a and a polyolester lubricant (POE). A spectrofluorometer was used to measure the lubricant excess density that was established by the boiling of an R134a/POE lubricant mixture on a test surface. The lubricant is preferentially drawn out of the bulk refrigerant/lubricant mixture by the boiling process and accumulates on the surface in excess of the bulk concentration. The excess lubricant resides in an approximately 40 μm layer on the surface and influences the boiling performance. The lubricant excess surface density measurements were used to modify an existing dimensionless excess surface density parameter so that it is valid for different reduced pressures. The dimensionless parameter is a key component for a refrigerant/lubricant pool-boiling model given in the literature. In support of improving the boiling model, both the excess measurements and heat transfer data are provided for pure R134a and three R134a/lubricant mixtures at 277.6 K. The heat transfer data show that the lubricant excess layer causes an average enhancement of the heat flux of approximately 24% for the 0.5% lubricant mass fraction mixture relative to pure R134a heat fluxes between 5 and 20 kW/m². Conversely, both 1 and 2% lubricant mass fraction mixtures experienced an average degradation of approximately 60% in the heat flux relative to pure R134a heat fluxes between approximately 4 and 20 kW/m². This study is an effort toward generating data to support a boiling model to predict whether lubricants degrade or improve boiling performance.