Influence of liquid receiver on the performance of reversible heat pumps using refrigerant mixtures

A liquid receiver is normally included in reversible vapour compression heat pumps (RHPs) to temporarily store the excess refrigerant charge occurring due to change of operation mode. The presence of a liquid receiver influences the total amount of refrigerant charged into a system, and particularly when using refrigerant mixtures, could affect the system circulation composition. Using a computer simulation, this paper compares the performance of RHPs designed with and without a liquid receiver, when using R407C. It was shown that the presence of a receiver caused an increase in the positive shift in the circulating composition, resulting in improved capacity while reducing the system COP in both heating and cooling modes when compared to a system without a receiver.     

非共沸混合工质自复叠热泵相积存实验研究

混合工质循环浓度是影响自复叠热泵循环性能的主要因素之一,而相积存导致工质循环浓度偏离充灌浓度,造成热泵性能变化.实验结果表明热泵中存在明显的相积存,最大可达充灌总量的50%以上;加热水温度对相积存的影响很大,每升高10℃,积存量减少10%～21%;工质充灌浓度一定时,积存量随充灌量的增大而增加,工质充灌量增加10%,其积存比例增加1%左右.相积存导致工质循环浓度高于充灌浓度1.6%～37%,由于工质积存量随加热水温度的升高不断降低,循环工质浓度受相积存的影响也不断减小而逐渐接近充灌浓度.     

天然气参数对混合制冷剂液化天然气流程性能的影响分析

在液化天然气流程中,影响流程性能的参数很多。文中分析天然气的入口压力、温度、各摩尔分率和各个换热器热端面的温差对流程制冷剂流量、压缩机耗功、冷却水的冷却量、丙烷预冷量的影响;并指出这些流程性能受哪些流程参数影响比较大。     

A method to estimate the circulated composition in refrigeration and heat pump systems using zeotropic refrigerant mixtures

In recent years a number of refrigerant mixtures have appeared on the market. Some of these refrigerant mixtures are zeotropic, e.g. R407C and R417A. When zeotropic refrigerant mixtures are used in a system, the circulated composition may change from the nominal to a different composition. The changes in composition may be due to leakage or hold-ups of liquid or vapour phase, different solubility in the oil by the different components, or the fact that the system has been charged in an incorrect way. For the understanding of performance measurements made on systems, it is important to know the composition of the circulated refrigerant mixture. A promising method to estimate the circulated composition has been developed. The method has been applied and evaluated on a well equipped lab rig at the Department of Energy Technology at the Royal Institute of Technology. The tests show that it is possible to estimate the composition of the circulated refrigerant mixture to within 2%, by measuring only two temperatures and pressures.     

Thermophysical Properties of Binary Mixtures of R125 + R143a in Comparison with a Simple Prediction Method

The thermal diffusivity and sound speed of binary refrigerant mixtures of R143a (1,1,1-trifluoroethane) and R125 (pentafluoroethane) have been determined for both the saturated liquid and vapor phase using dynamic light scattering (DLS). Measurements were performed for four quite different mixture compositions over a wide temperature range from 293 to 345 K approaching the vapor-liquid critical point. The results obtained corroborate the usefulness of a simple prediction method for the determination of different thermophysical properties of multicomponent mixtures in the two-phase region up to the critical point. Besides the information on the properties for the pure components, the successful application of the prediction method is also based on an exact knowledge of the critical temperature. The composition dependence of the critical temperature has been determined by observation of the vanishing meniscus between liquid and vapor phases. The mixture results are discussed in detail and compared with available literature data.     

A novel concept of rapid cooling method of refrigeration system

This paper describes a novel cooling method of enhancing refrigeration capacity during short time (order of 1 min) by storing low-temperature liquid refrigerant. This method actively controls the refrigerant mass flow rate for the evaporator. The compressor of the refrigerator, therefore, does not have to be oversized to cope with intermittent large cooling load of the system. During a short period of time, a higher cooling capacity than that of the steady operation is achieved by the increased mass flow rate of liquid refrigerant. An experimental apparatus was designed and fabricated to validate the proposed cooling methodology. Two reservoirs as temporary sequential storages of the refrigerant were set up before and after the evaporator. Several on/off solenoid valves were installed to control the refrigerant flow. From the experimental results, we confirmed a successful operation of rapid cooling process as designed. This rapid cooling methodology shall be useful for temporarily enhancing the refrigeration capacity in other low-capacity refrigeration systems. The practical system must optimize the design of refrigerant reservoirs to reduce the whole system size.     

重力供液蒸发器的实验研究

采用R404A作为制冷剂对重力供液蒸发器在低温工况下的特性进行实验研究,建立重力供液蒸发器的传热模型,搭建重力供液蒸发器的实验装置,用热平衡法测试重力供液蒸发器在不同蒸发器供液高度下的运行特性.研究表明:供液压头在h1=1200mm时比供液压头在h1=800mm、h1=1000mm时的传热温差明显下降,且随着室内温度的下降,传热温差随之变小;在同一供液高度下,重力供液蒸发器的循环倍率n随蒸发温度的降低而增大,而在不同供液高度下,循环倍率n随供液高度的升高而增大;重力供液蒸发器在供液高度h_1=1000mm时的制冷量明显高于h_1=800mm时的制冷量,其最大增幅为16.9%;而h_1=1200mm时其制冷量与h_1=1000mm很接近,甚至会有所下降;与h1=800mm相比,h_1=1000mm时重力供液制冷系统COP大幅度增加,最大增幅为17%,h_1=1200mm时系统COP介于前两者之间,重力供液制冷系统存在最佳的蒸发器供液高度.     

小型MRC天然气液化装置中板翅式换热器动态特性仿真研究

针对采用混合制冷剂液化流程(MRC)的小型天然气液化装置(LNG)中的板翅式换热器建立了动态特性仿真数学模型,基于气液两相流理论及气液相平衡理论,对多股流、多组分、有相变的板翅式换热器进行了动态仿真研究,并对该MRC-LNG装置中某换热器在非稳态工况下进行了仿真分析.结果表明:在小型MRC液化天然气装置设计和调试过程中,该模型对提高换热器设计效率、降低运行成本有指导意义.     

A proposed combination model for predicting surface tension and surface properties of binary refrigerant mixtures

A combination model is proposed to describe the surface tension and surface properties of binary refrigerant mixtures combining the Laaksonen and Kulmala equation with the phase equilibrium between the bulk liquid and surface phases to predict the surface tension, surface composition and surface mole density of the binary refrigerant mixtures. Also, the present model is combined with the volume-translated Peng–Robinson (VTPR) equation of state to describe the fugacity coefficients of the components and molar volumes of the bulk and surface phases. This proposed combination model is subsequently applied for 13 binary refrigerant mixtures and compared with the gradient theory. The results of this model show that the surface tensions predicted by this model agree well with experimental data for these mixtures (overall AAD ∼4.35). Compared with the gradient theory (overall AAD ∼5.67 and 3.94 for density and temperature dependant influence parameter), the proposed combination model performs well.     

Thermophysical Properties of a Quaternary Refrigerant Mixture: Comparison of Dynamic Light Scattering Measurements with a Simple Prediction Method

Dynamic light scattering (DLS) has been used for the measurement of several thermophysical properties of a quaternary refrigerant mixture R-125/143a/32/134a in its liquid phase under saturation conditions. The thermal diffusivity and sound speed have been obtained by light scattering from bulk fluids over a temperature range from about 293 K up to the liquid–vapor critical point. By applying the method of DLS to a liquid–vapor interface, also called surface light scattering (SLS), the saturated liquid kinematic viscosity and surface tension can be determined simultaneously. These properties have been measured from about 243 to 343 K. The results are discussed in comparison with literature data and with a simple prediction method based on the mass-weighted properties of the pure components, expressed as functions of the reduced temperature. Once again, the simple prediction method was shown to be applicable for the calculation of different transport and other thermophysical properties of multicomponent refrigerant mixtures and this with sufficiently high accuracy for technical practice. Moreover, the input data for the simple prediction scheme can be reduced without loss of accuracy by treating binary or ternary mixtures as a subset of the multicomponent mixture.     

Thermophysical properties of R143a (1,1,1-trifluoroethane)

Various thermophysical properties of refrigerant R143a (1,1,1-trifluoroethane) have been determined under saturation conditions using dynamic light scattering (DLS). Light scattering from bulk fluids was applied for measuring the thermal diffusivity and the sound velocity for both the saturated liquid and vapor phase over a wide temperature range of 273-346 K. The results were also used to obtain information on the specific heat at constant pressure and the isentropic compressibility. Furthermore, the surface tension and liquid kinematic viscosity were determined simultaneously in the temperature range 253-333 K from light scattering by surface waves on a horizontal liquid-vapor interface. All experiments are based on a heterodyne detection scheme and a signal analysis by photon correlation spectroscopy (PCS). The results for R143a are discussed in detail and compared to literature data available.     

The advantages non-azeotropic refrigerant mixtures for heat pump application

The advantages of using non-azeotropic refrigerant mixtures in heat pumps are discussed. In comparison with conventional refrigerants the appliance of refrigerant mixtures can result in energetic improvements, extension of the application limits and a continuous capacity control. In order to investigate the behaviour of refrigerant mixtures measurements were carried out, as well as a constant-volume-cell for investigating the thermodynamic behaviour as in a heat pump test arrangement for measuring the realistic performance and operating data of mixtures in a plant. The results of changing the mixture composition for a continuous capacity control are presented. It was shown that by using refrigerant mixtures in a heat pump, several improvements can be made.     

气体导流装置对微通道蒸发器性能的影响

针对微通道蒸发器制冷剂流量分配不均匀造成的换热性能恶化和干蒸现象,本文搭建了双流程微通道蒸发器性能测试实验台,研究导气装置对蒸发器换热性能及扁管中制冷剂分配均匀性的影响,并与常规的双流程微通道蒸发器进行对比。结果表明：由于入口制冷剂流量不变,液相制冷剂蒸发为气体的最大相变潜热不变,导致二者换热量和传热系数差值较小,最大值仅相差0.5%和6.9%。但加导气装置后流动阻力降低,两相段长度较常规结构增幅为87.3%,过热度显著降低,风速为3 m/s时两种结构的过热度降幅为44.4%。各扁管间制冷剂分布趋于一致,均匀性得到提升,干蒸现象得到缓解。     

Foaming of refrigerating oil in a rolling piston type rotary compressor

This paper is concerned with foaming of refrigerating oil in a rolling piston type rotary compressor for an air conditioner. Factors causing foaming during the starting operation were investigated experimentally. It was proved that foaming was caused by the stirring of the refrigerant-oil mixture with a motor rotor, a vane and a discharge refrigerant flow. The foaming was correlated with the solubility of refrigerant in oil and with the amount of refrigerant contained in the stirred region of the liquid mixture.     

Experimental study of the gravity effect on the distribution of refrigerant flow in a multi-pass condenser

Gravity in multi-pass condensers affects the refrigerant flow rate distribution, owing to the gravitational pressure drop that occurs mainly in the U-bend tubes in fin and tube condensers with horizontal tubes. This effect was studied using an experimental approach. A condenser with two ‘nU’ circuits was selected, and the temperature variation of the refrigerant side was measured and compared along each circuit. The critical air velocity, which indicated the initiation of the gravity effect, was found for a given refrigerant flow rate. As the air velocity increased beyond the critical air velocity, the gravity effect (or mal-distribution of the refrigerant flow) developed further. Similarly, the critical refrigerant flow rate was also determined for a given air velocity. As the refrigerant flow rate decreased below the critical refrigerant flow rate, the gravity effect also developed further. The gravity-affected region was shown in the table with rows of air velocities and columns of refrigerant flow rates, and expressed using a single parameter for a given refrigerant flow circuit.     

高取向锐钛矿TiO2薄膜的MOCVD法制备与表征

采用热壁低压ＭＯＣＶＤ方法，以Ｔｉ（ＯＣ４Ｈ９）４为源在ＳｉＯ２／Ｓｉ衬底上制备出高取向锐钛矿ＴｉＯ２薄膜。用Ｘ射线衍射技术研究了沉积温度和衬底对薄膜的结构和相组成的影响规律，采用ＸＰＳ和ＳＥＭ分别研究了薄膜的组成和形貌，结果表明，当沉积温度为５００＾０Ｃ和６００＾０Ｃ时，薄膜为锐钛矿结构，３００＾０Ｃ和４００＾０Ｃ地，薄膜以无定形结构为主，薄膜的组成为ＴｉＯ２，衬底影响薄膜的相组成，不同沉积温度     

Practical methods for measuring refrigerant mass distribution inside refrigeration system

The purpose of this paper is to present methods for measuring refrigerant mass distribution inside a refrigeration system conveniently and accurately. The quasi on-line measurement method (QOMM) was presented for measuring refrigerant mass inside heat exchangers. Compared with the existing liquid nitrogen method (LNM), QOMM can avoid the refrigerant waste and accelerate the measurement process. For measuring refrigerant mass inside the compressor, QOMM was used together with the oil level observation method. The liquid level method (LLM) was used to measure the refrigerant mass inside the accumulator and the receiver. In order to verify the accuracy of the measurement methods, not only the deviation of the measurement method for refrigerant in single component was analyzed, but also the prediction of the total refrigerant charge in an air conditioner was verified. The results showed that the maximal prediction deviation of the refrigerant charge in the whole refrigeration system is 1.7%.     

Low loss measurement of oil concentration in a refrigerant-oil mixture in a liquid line

A method of measuring the mass concentration of lubricating oil in a refrigerant-oil mixture in a liquid line within a refrigeration system is described. It is suitable for use where the oil and refrigerant are fully miscible in the liquid phase, e.g. for mineral oil and R12. The technique involves taking a small liquid sample, measuring its volume, venting the refrigerant back into the system and weighing the residual oil. Many measurements can be made, with negligible loss of refrigerant from the system. An application of the method to a split circuit bypass type compressor load stand is also described.     

Liquid Thermal Conductivity of Ternary Mixtures of Difluoromethane (R32), Pentafluoroethane (R125), and 1,1,1,2-Tetrafluoroethane (R134a)1

The thermal conductivities of ternary refrigerant mixtures of difluoromethane (R32), pentafluoroethane (R125), and 1,1,1,2-tetrafluoroethane (R134a) in the liquid phase have been measured by the transient hot-wire method with one bare platinum wire. The experiments were performed in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa at various compositions. The measured data are correlated as a function of temperature, pressure, and composition. From the correlation, we can calculate the thermal conductivity of pure refrigerants and their binary or ternary refrigerant mixtures. The uncertainty of the measurements is estimated to be ±2%.     

制冷剂回收再生的碳排放评估及经济性分析

我国已进入HCFCs制冷剂淘汰末期,并即将于2024年启动HFCs的产量和消费量削减。本文以制冷剂的回收再生过程为主要研究对象,基于LCCP气候性能模型,构建了制冷剂回收再生过程的碳排放量评估模型;分析了制冷剂回收再生的经济性;并对所构建模型,以汽车空调制冷剂R134a的回收再生为案例,计算其碳排放量及回收再生经济性。结果表明：本文案例中,对制冷剂进行回收再生处理可以减少当量CO2排放约42％,制冷剂回收再生的经济性能主要与再生后制冷剂单价及工人工资成本有关,工人工资按月最低工资标准时净化后制冷剂售价在11 元/kg（新制冷剂售价的50％）以上可在2年内开始盈利。