A numerical investigation of flow boiling of non-azeotropic and near-azeotropic binary mixtures

The flow and heat transfer characteristics of binary refrigerant mixtures in a heated horizontal tube were investigated numerically. The pressure drop, temperature profile, and heat transfer coefficient for non-azeotropic and near-azeotropic mixtures of different bulk compositions were obtained. It is found that the non-linear physical properties of the mixtures strongly affect the pressure drop characteristics. Both the fluid properties and mass transfer resistance are responsible for the heat transfer characteristics. The mass transfer resistance has a more significant influence on the nucleate boiling than the convective evaporation for non-azeotropic mixtures, while the resistance can be neglected for near-azeotropic mixtures.     

可燃制冷剂标准修订进展

阐述了全球各主要地区制冷剂及系统关于可燃性的安全标准的修订情况,并介绍了各国对于HCs类易可燃性制冷剂的应用态度。各国对弱可燃制冷剂的态度有所松动,但对于HCs类易燃制冷剂的应用仍有较大分歧。     

氨制冷剂应用的安全技术

讨论了氨的基本物理性质、相对安全性以及氨毒害、灼伤和冻伤等伤害作用.在此基础上对设计与制造安全措施和作业安全技术进行了探讨.     

非共沸混合工质沸腾换热系数实验关联式比较

利用从文献中收集到的局部沸腾换热系数的实验数据,对混合制冷剂水平管内局部沸腾和管外池沸腾换热系数的计算方法及计算公式进行了分析比较,筛选出了与实验数据吻合较好的计算公式,从而为其进一步的研究提供了理论基础。     

Experimental investigation of the effect of condenser subcooling in R134a and R1234yf air-conditioning systems with and without internal heat exchanger

This paper presents an experimental study about the effect of condenser subcooling on the performance of an air conditioning system operating with R134a and R1234yf, under the same operating conditions. For both refrigerants, it has been shown that the COP undergoes a maximum as a consequence of the trade-off between increasing refrigerating effect and increasing specific compression work. At a given operating condition, the system COP increased up to 18% for R1234yf and 9% for R134a. These results confirmed the trends obtained from a previous theoretical analysis, demonstrating that a system operating with R1234yf can benefit more from the condenser subcooling than that with R134a. The experimental results also showed that the presence of an internal heat exchanger significantly reduces the COP increase due to condenser subcooling, since both improvements compete towards reducing the throttling losses. Besides the interference between IHX and condenser subcooling, the use of both simultaneously still yields a more efficient air conditioning system, especially for R1234yf.     

CO2减排率Y——制冷工质的一种环保指标

围绕制冷空调行业加速淘汰HCFCs和逐步削减HFCs使用量的复杂局面,本文在文献的基础上,进一步分析新环保性能评价指标——CO2减排率Y,阐明它的必要性,探讨它的几种计算方法,并应用它界定长期替代工质的范围,从环保性能方面为筛选替代工质提供理论依据和实用判据。     

河南省民政厅综合办公楼数码多联空调工程设计

本文着重介绍了数码涡旋技术在商用办公楼的设计及应用,该工程能在一年四季提供稳定的制冷和制热,充分体现数码涡旋技术的广泛适用性、节能可靠性、控制便利及精确性,具有安装和后期维护简单方便等突出优点。     

室温磁制冷材料的研究进展

室温磁制冷材料的研究是室温磁制冷的关键因素,本文简述了磁制冷技术的发展前景以及基本原理,重点介绍了近年来室温磁制冷材料的研究进展。     

商用制冷设备在用制冷剂现状及未来趋势

随着生活水平的提高,制冷技术带给人们舒适的生活条件,但它也给人们造成一些负面影响。在环境问题尤其是臭氧层破坏和温室效应问题日益加剧的形势下,制冷剂的发展及替代越来越受到世界各国的关注。本文介绍了制冷剂发展历程及世界各国商用制冷设备常用制冷剂的现状,以此为基础,总结了制冷剂未来发展趋势。     

THERMODYNAMIC PROPERTY VARIATION OF NONAZEOTROPIC REFRIGERANT MIXTURES (NARMs) IN THE TEMPERATURE GLIDING ZONE

The relations among enthalpy, temperature and quality of nonazeotropic refrigerant mixtures (NARMs) in the phase change region (temperature gliding region) are investigated to seek a possibility for linear approximations. Using REFPROP, a refrigerant property calculation package developed by NIST, temperature-enthalpy, temperature-quality, quality-enthalpy relations are investigated for 4 binary and 15 ternary NARMs. Those 19 NARMs tested are the most promising alternative refrigerants for conventional CFC and HCFC refrigerants. A normalized enthalpy. which is a pseudo-quality in a sense, is defined based on the dew and bubble point enthalpies to compare with the conventional quality. The results show that the pseudo-quality and the conventional quality are almost identical independent of system pressure for all the NARMs tested while enthalpy-temperature and quality-temperature relations are diverse and highly pressure dependent depending on mixture combinations. The significance of the near-identical relation between the two qualities is that the easy-to-calculate pseudo-quality can replace quality in convective heat transfer coefficient representations.