Prediction of vapour-liquid and vapour-liquid-liquid equilibria of nitrogen-hydrocarbon mixtures used in J-T refrigerators

Nitrogen-hydrocarbon mixtures are widely used as refrigerants in J-T refrigerators operating with mixtures, as well as in natural gas liquefiers. The Peng-Robinson equation of state has traditionally been used to simulate the above cryogenic process. Multi parameter Helmholtz energy equations are now preferred for determining the properties of natural gas. They have, however, been used only to predict vapour-liquid equilibria, and not vapour-liquid-liquid equilibria that can occur in mixtures used in cryogenic mixed refrigerant processes. In this paper the vapour-liquid equilibrium of binary mixtures of nitrogen-methane, nitrogen-ethane, nitrogen-propane, nitrogen-isobutane and three component mixtures of nitrogen-methane-ethane and nitrogen-methane-propane have been studied with the Peng-Robinson and the Helmholtz energy equations of state of NIST REFPROP and compared with experimental data available in the literature.     

Novel top-loading 20 mK/15 T cryomagnetic system

A new type of dilution refrigerator is described with easy loading of the sample directly into the dilute phase in the mixing chamber. Electrical, optical and mechanical services to the sample are readily incorporated and electrically insulating tails allow the use of high and variable magnetic fields. A sample temperature of 20 mK in a field of 15 T has been achieved.     

气调冰箱对冷藏肉类的保鲜效果

为研究气调冰箱（氧分压为18.0%～18.5%）对冷藏肉类的保鲜效果,选取雪花牛肉、三文鱼和金枪鱼3种高价值肉类,置于气调冰箱中冷藏。以普通冰箱作为对照,对贮藏期间肉类表层细胞形态、汁液流失率、挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、硫代巴比妥酸反应物（thiobarbituric acid reactive substances,TBARs）值和菌落总数等指标进行定期监测。结果表明：相较于普通冰箱,气调冰箱显著降低了雪花牛肉、三文鱼和金枪鱼贮藏过程中的汁液流失率、TVB-N含量、TBARs值和菌落总数,延缓了3 种肉类贮藏过程中品质的降低,表明相较于普通冰箱,气调冰箱对冷藏雪花牛肉、三文鱼和金枪鱼具有更好的保鲜效果。综合分析各项评价指标发现,在使用气调冰箱冷藏肉类过程中,雪花牛肉应选用TVB-N含量作为判断保质期的指标,而三文鱼和金枪鱼应选用菌落总数作为判断保质期的指标。     

A model for exergy analysis and thermodynamic bounds of Stirling refrigerators

A thermodynamic model based on exergy flow through a Stirling Refrigerator is developed. Important irreversibilities of the refrigerator due to external heat transfer with the reservoirs, heat leak, flow and heat transfer in regenerator are included in the model. Expansion and compression efficiencies are introduced in the model to account for the losses in these processes. The effect of a control phase shift between the mass flow rate and pressure across regenerator on the performance of the refrigerator is presented. Analytical solutions representing important quantities in the design of Stirling refrigerators such as the load curve, cooling power and efficiency in terms of basic system input parameters are developed. Thermodynamic bounds for the performance of Stirling refrigerators are obtained. Results indicating a compromise between cooling power and efficiency that are dependent on the constraint of the system are presented and discussed.     

Experimental analysis of a pulse tube based new prototype for cells cryopreservation

Cells cryopreservation is crucial for the treatment of several diseases, but the survival rate of the cells is significantly affected by the cooling process. Currently, programmable freezers based on liquid nitrogen technology are usually adopted but these solutions may cause the death of the cells due to undesired crystallization, membrane damage or osmotic shock. In the recent years, pulse tube refrigerators have attracted a lot of interest in many applications because of their intrinsic characteristics. Despite more gradual, the cooling rate of a similar refrigerator needs to be carefully controlled to meet the desired requirements of cells cryopreservation. Therefore, at the premises of Sapienza University of Rome a pulse tube-based prototype has been designed for cells cryopreservation and an experimental tests campaign has been conducted to assess the performance of the system for the scope. A new control logic, able to adjust the supplied voltage to electric heaters for the conditioning of the temperature inside the stand tubes, has been implemented and different configurations evaluated with cooling rate varying in the range 0.5°C/min to 1.5°C/min. The analysis has shown that the proposed control logic is able to cool down the stem cells in all the investigated range with a maximum temperature difference between the mean temperature of the tubes and the theoretical temperature of −7.65°C for the configuration with copper plate and −4.09°C for the configuration with aluminium plate which represents a safe condition. On the contrary, the copper plate allows approximating better the real cooling curve with the theoretical one and achieving a lower temperature variance at cooling rates higher than 1.25°C/min. Although some further efforts are needed to tune the system up, the present work has demonstrated that a pulse tube refrigerator can be technically and commercially adopted as a viable solution for stem cells cryopreservation.     

冰箱沙特能效标准换版解析

文章对新版冰箱沙特能效标准的换版执行时间表和新旧版能效标准的差异进行了详细介绍。为冰箱产品出口沙特提供了重要信息支撑。     

Thermodynamic analysis of processes in refrigerators using superfluid helium (He II) by means of T − q diagram

A T − q diagram is presented for superfluid helium (He II) by means of which a technique for thermodynamic analysis of processes in refrigerators using He II is worked out. With large pressure drops it is necessary to use p, T, q diagrams, i.e. three-dimensional space. The mathematical basis for using either method is presented and explained.     

论果蔬冷库建筑的发展趋向

在分析国内果蔬冷库的发展概况并与国外对比的基础上,提出“果蔬冷库建筑发展趋向”的概念。     

Maximum exergy input rate from a hot stream in solar‐driven refrigerators

The authors believe that reducing the size of solar‐driven refrigerators and air conditioning systems will make them more attractive to potential users. This paper presents a contribution to understanding the behaviour of such systems with a view to determining the manner in which refrigeration rate, mass flows and heat transfer areas are related. The intention is to make possible the identification of preliminary design rules. The basic thermodynamic problem of how to obtain maximum exergy input rate in a solar‐driven refrigerator is considered. The existence of an optimal refrigerant flow rate for maximum refrigeration is investigated. The analysis proceeds by relating the entropy generation rate, the physical and operating parameters, and the constraints of the system, through well‐established heat transfer relationships. Finally, a thermodynamic analysis determines the optimal characteristics that lead to minimum entropy generation. The second law efficiency is identified as the appropriate figure of merit for the thermodynamic optimum. Copyright © 2001 John Wiley & Sons, Ltd.     

Virial equation of state of helium, xenon, and helium-xenon mixtures from speed-of-sound and burnettPρT measurements

The virial equation of state was determined for helium, xenon, and helium-xenon mixtures for the pressure and temperature ranges 0.5 to 5 MPa and 210 to 400 K. Two independent experimental techniques were employed: BurnettPρT measurements and speed-of-sound measurements. The temperature-dependent second and third density virial coefficients for pure xenon and the second and third interaction density virial coefficients for helium-xenon mixtures were determined. The present density virial equations of state for xenon and helium-xenon mixtures reproduce the speed-of-sound data within 0.01% and thePρT data within 0.02% of the pressures. All the results for helium are consistent, within experimental errors, with recent ab initio calculations, confirming the accuracy of the experimental techniques.