Vapour-liquid equilibrium of ternary mixtures of the refrigerants R125, R143a and R134a

Apart from ternary mixtures of R32 with R125 and R134a, similar mixtures with R143a instead of R32 are discussed as alternatives to the widely used refrigerants R22 and R502. In the present work, the phase equilibrium of such ternary mixtures is described by simple cubic equations of state which are based only on experimental data for the pure substances and for a nearly equimolar mixture of every binary system.In addition to previous experimental investigations the critical properties and the saturation pressure were measured for pure R143a and for nearly equimolar mixtures of the binary systems and . The temperature ranged from −70°C up to the respective critical point. The validity of the resulting equations of state for ternary mixtures of R125, R143a and R134a is confirmed by comparison with experimental results of the vapour-liquid equilibrium for a mixture with about 17mol% of R125 and R143a, respectively, and about 66mol% of R134a.     

HFC-161混合物替代R502的理论研究

提出一种新型制冷剂HFC-161/125/143a(质量百分比10/45/45)用于替代制冷剂R502.新制冷剂环境性能良好,ODP值为0,GWP值为3466,GWP值小于R502及其常用替代制冷剂R404A和R507.采用Refprop软件计算了HFC-161混合物的基本热物理性质,以及低温工况和变工况下的理论循环性能,并与制冷剂R502、R404A、R507的相关数据进行对比.结果表明:新制冷剂的运行压力、压比、COP值、单位容积制冷量与R502相当,温度滑移小于R502常用替代物R404A,是一种性能优良的制冷剂R502的替代物.     

Experimental study on HFC-161 mixture as an alternative refrigerant to R502

Ternary near-azeotropic mixture of HFC-161 as an alternative refrigerant to R502 is firstly presented in this paper. The physical characteristics of this new refrigerant are similar to those of R502. Its environment performance is friendly. It has an ODP of zero and a GWP smaller than those of R502, R404A and R507. Without any modification to system components, drop-in experimental tests are performed on a vapor compression refrigeration plant with a reciprocating compressor, which was originally designed to use R404A, a major substitute for R502. Experimental results under two different rated working conditions indicate that the pressure ratios of this new refrigerant are nearly equal to those of R404A. Under lower evaporative temperature, its COP is almost equal to that of R404A and its discharge temperature is slightly higher than that of R404A, while under higher evaporative temperature, its COP is greater than that of R404A and its discharge temperature is lower than that of the latter. This new refrigerant can achieve a high level of COP and can be considered as a promising retrofit refrigerant to R502.     

Role of microstructures on the growth of long fatigue cracks

An analysis is presented to understand the role of microstructures on the two crack growth driving force parameters, and , without invoking the extrinsic crack closure concepts. Microstructural variables considered are: grain size, precipitates and stacking fault energy. It is shown that is strongly affected by the scale of the microstructure, such as grain size or precipitate spacing. For each case, the mode of slip deformation and environment affects the fatigue resistance as represented by . However, the microstructures seem to have a smaller effect on . Also, the enhanced planarity of slip from the reduction in stacking fault energy has a pronounced effect on when compared with the materials deforming under homogeneous slip.     

Refrigeration system performance using liquid-suction heat exchangersPerformance d''un système frigorifique utilisant des échangeurs liquide-vapeur à l''aspiration

Heat transfer devices are provided in many refrigeration systems to exchange energy between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant exiting the condenser. These liquid-suction or suction-line heat exchangers can, in some cases, yield improved system performance while in other cases they degrade system performance. Although previous researchers have investigated performance of liquid-suction heat exchangers, this study can be distinguished from the previous studies in three ways. First, this paper identifies a new dimensionless group to correlate performance impacts attributable to liquid-suction heat exchangers. Second, the paper extends previous analyses to include new refrigerants. Third, the analysis includes the impact of pressure drops through the liquid-suction heat exchanger on system performance. It is shown that reliance on simplified analysis techniques can lead to inaccurate conclusions regarding the impact of liquid-suction heat exchangers on refrigeration system performance. From detailed analyses, it can be concluded that liquid-suction heat exchangers that have a minimal pressure loss on the low pressure side are useful for systems using R507A, R134a, R12, R404A, R290, R407C, R600, and R410A. The liquid-suction heat exchanger is detrimental to system performance in systems using R22, R32, and R717.     

Selective adsorption of cations on single-walled carbon nanotubes: A density functional theory study

The selective adsorption of cation on single-walled carbon nanotubes (SWNTs) is systemically studied by using density functional theory calculations. It is found that the adsorption energy of cations on SWNTs depends on the concentration of cations and the diameter and the electronic structure of SWNTs. The binding strength of on each SWNT increases monotonically as the concentration of decreases, undergoing a change from endothermic to exothermic reaction. Generally speaking, the binding of on SWNTs becomes weaker as the diameter increases. In the medium-diameter region (9 < d < 11 Å), prefers to interact with metallic SWNTs (m-SWNTs) rather than semiconducting SWNTs (s-SWNTs) at the same concentration of . In the small-diameter region (d < 9 Å), the binding of is nearly independent of metallicity, but it is stronger than that of on the medium-diameter s-SWNTs. In the large-diameter region (d > 11 Å), the dependence of adsorption on the electronic structure is complicated, but the binding of is weaker than that on the medium-diameter s-SWNTs. Our results are in agreement with the experimental report that the small-diameter m- and s-SWNTs and the medium-diameter m-SWNTs are etched away by while the medium-diameter s-SWNTs and the large-diameter m- and s-SWNTs are intact.     

超市展示柜中应用R404A/R744复叠制冷系统的理论分析

提出了一种可以应用于超市展示柜中的R404A/R744复叠制冷系统,该系统以R404A作为高温级制冷剂,以R744作为低温及制冷剂.并通过对该系统和R22制冷系统进行热力学性能和压缩机输气系数的计算和比较.研究表明:在蒸发温度和冷凝温度固定的情况下,存在一个最佳中间温度使系统的性能系数最大:R404A/R744复叠制冷系统的性能系数和R22制冷系统基本相当,而复叠系统的压缩机输气系数明显高于单级制冷系统.     

Explicit solutions to the one-phase Stefan problem with temperature-dependent thermal conductivity and a convective term

A one-phase Stefan problem for a semi-infinite material with temperature-dependent thermal conductivity and convective term with a constant temperature or a heat flux condition of the type (q₀>0) at the fixed face x=0 is studied. For both cases a parametric representation of the solution of the similarity type is also obtained.     

On deconvolution methods

Several methods for solving efficiently the one-dimensional deconvolution problem are proposed. The problem is to solve the

     

Thermophysical Properties of Binary and Ternary Fluid Mixtures from Dynamic Light Scattering

Several thermophysical properties of R507, a binary refrigerant mixture, and R404A, a ternary mixture, have been determined by dynamic light scattering (DLS), in both the liquid and the vapor states, along the saturation line approaching the vapor–liquid critical point. Data for the thermal diffusivitya and sound speed c _S cover a range of temperatures down to 270K, and data for the surface tension and kinematic viscosity down to 230K. For both mixtures the behavior of all properties determined can be correlated well by the mass-weighted sum of the respective pure component data, when all data are represented as a function of the reduced temperature.     

Development of thick-foil and fine-pitch GEMs with a laser etching technique

We have produced thick-foil and fine-pitch gas electron multipliers (GEMs) using a laser etching technique. To improve production yield we have employed a new material, liquid crystal polymer, instead of polyimide as an insulator layer. The effective gain of the thick-foil GEM with a hole pitch of , a hole diameter of , and a thickness of reached a value of 10⁴ at an applied voltage of 720 V. The measured effective gain of the thick-foil and fine-pitch GEM ( pitch, diameter, and thick) was similar to that of the thick-foil GEM. The gain stability was measured for the thick-foil and fine-pitch GEM, showing no significant increase or decrease as a function of elapsed time from applying the high voltage. The gain stability over 3 h of operation was about 0.5%. Gain mapping across the GEM showed a good uniformity with a standard deviation of about 4%. The distribution of hole diameters across the GEM was homogeneous with a standard deviation of about 3%. There was no clear correlation between the gain and hole diameter maps.     

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.     

Theoretical and experimental research on the working process of screw refrigeration compressor under superfeed condition

In order to increase the refrigeration capacity and improve the coefficient of performance (COP), an economizer arrangement is used in the refrigeration system with screw refrigeration compressor. In this system, the mid-pressure refrigerant gas from the economizer is injected in the screw refrigeration compressor. So it affects the performance of the compressor. In this paper, the working process of a twin screw refrigeration compressor with economizer under different superfeed pressures is studied. A mathematical model for simulating the working process of screw refrigeration compressor under superfeed condition with the economizer is presented; especially the flow coefficient of superfeed is obtained by the experimental research. To verify the model, the p–V diagrams (pressure–volume diagrams) of screw refrigeration compressor under different superfeed pressures with the economizer are recorded successfully by making use of a micro-type pressure sensor that embedded into the groove at the root of the female rotor on the discharge side. The p–V diagrams of theoretical calculation are in good agreement with the results of experimental recorded, which lead to conclusion that the model can be used as a powerful tool for performance prediction of screw refrigeration compressor, also, it is very helpful for refrigeration system design.     

Ion-molecule reactions in mixtures of methane with carbon tetrafluoride

Ion-molecule reactions have been measured for methane-carbon tetrafluoride mixtures of different composition using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment). Primary ions , , F⁺, CF⁺ and were produced by electrons with energy of 300 eV. Secondary ions , , , , and were observed as the result of ion-molecule reactions. Relative current intensities for primary and secondary ions are presented as a function of both total mixture pressure and concentration of methane in the mixture. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. Total mixture pressure was changed from 0.7 to 33.3 Pa. Schemes of ion-molecule reactions were proposed.     

环保制冷剂R1270/RE170/R13I1的热力学性能分析

针对制冷剂R22的替代问题,提出一种适用于空调等制冷设备的环保型混合制冷剂R1270/RE170/R13I1。基于Refprop8.0,对R1270/RE170/R13I1的基本热物理性质和制冷系统循环性能进行分析,研究表明:在标准工况下,R1270/RE170/R13I1混合制冷剂的COP和单位容积制冷量均与R22相当,非常有利于直接充注式替代;在变工况下,R1270/RE170/R13I1的滑移温度较小,性能优于R407C,单位容积制冷量与R407C和R22基本相当,排气温度和压比均低于R22和R407C,是一种优良的R22和R407C制冷设备的替代物,具有充注式替代的潜力。