共查询到20条相似文献,搜索用时 140 毫秒
1.
2.
《工程热物理学报》2020,(7)
CO_2/DME(Dimethyl ether二甲醚)混合工质作为制冷剂既可以降低CO_2单独使用时过高的工作压力,又可抑制二甲醚的可燃性。针对跨临界热泵系统中制冷剂在超临界压力下放热时复杂的传热性能,本文对超临界CO_2/DME混合工质和超临界CO_2在螺旋管内流动冷却的换热过程进行了数值模拟研究。结果表明,与纯CO_2相比,在高温区CO_2/DME混合工质的换热性能更优;通过比较不同配比的CO_2/DME混合工质的换热特性,得到了不同温度范围对应的换热性能最优的CO_2/DME混合工质配比。此外,对固定质量比的CO_2/DME混合工质,分别分析了不同质量流速和热流密度下的流体温度、壁面温度及传热系数的变化规律,并与纯CO_2传热系数的变化进行了对比。该研究为制冷剂选取及热泵系统中气冷器的优化设计提供了理论依据。 相似文献
3.
4.
5.
6.
7.
多元混合工质筛选及配比原则的研究 总被引:10,自引:0,他引:10
1前言目前,混合工质组元的筛选及配比的优化问题一直困绕着人们。对于如何通过筛选合理的组元及配比,国内外学者对此问题进行了初步的研究。这些文献大都从物性着手,把注意力集中在物性、循环特性的理论和简单匹配上,往往忽略系统设备和实际应用中存在的问题对混合工质组元的筛选及配比的影响。本文从循环本身出发,探讨混合工质组元的筛选及配比的优化问题。2混合工质组元筛选的分析从理论上讲,几种优势互补的纯工质经合理配比,总可望得到与被替代物性能相当的混合物。但如何通过筛选合理的组元以保证因泄漏而再补充新混合工质后系统… 相似文献
8.
通过美国标准和技术研究所开发的软件程序计算出了混合工质在不同配比下的物理性质;最终以要求的制冷量为标准,确定了混合工质的最佳配比;并通过分析计算,得出了一个三级自动复叠系统中各测点的状态参数;最后分析了压缩机高、低压对系统性能的影响。 相似文献
9.
10.
本根据在给定工质相变温度与热源温度最小温差点(献称Pinch-point)温差数值的前提下,通过选择工质组成,使单位传热量所引起的不可逆熵增最小,提出了一个基于最小传热熵增为目标的混合工质最佳组成的确定方法,并分析计算比较了二元混合工质和多元混合工质在减少传热熵增的不同效果,结果表明,多元混合工质比二元混合工质在减少不可逆熵增方面具有更大的优越性。 相似文献
11.
12.
13.
14.
S. V. Kidalov F. M. Shakhov V. M. Davidenko V. A. Yashin I. E. Bogomazov A. Ya. Vul’ 《Physics of the Solid State》2008,50(5):981-985
Experimental data are used in an attempt to unravel the mechanism underlying the effect of modification of a graphite blend by fullerenes on the diamond synthesis at high pressures and temperatures in the presence of metal catalysts. Diamonds have been synthesized under different conditions in a wide range of temperatures and at different pressures, and the effects of blend modification by fullerenes and by addition of natural microcrystalline diamonds to a blend on the diamond synthesis at high pressures and temperatures have been compared. 相似文献
15.
An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m2s) and heat fluxes of 3–12 kW/m2. The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed. 相似文献
16.
17.
制冷空调系统替代工质的发展现状及方向 总被引:3,自引:0,他引:3
本文主要针对CFC11、CFC12以及HCFC22介绍了目前替代工质的发展现状,阐述了混合工质以及氨、二氧化碳、碳氢化合物等自然工质作为替代工质的特点以及其发展现状,总结了制冷空调系统替代工质的发展方向。 相似文献
18.
Highly oriented self-reinforced 80/20 blends of polylactide (PLA)/thermoplastic polyurethane elastomer (TPU) were successfully fabricated through solid hot stretching technology. Different from the isotropic sample, stress rose rapidly in a low strain region, and exhibited strain hardening for the drawn samples of the PLA/TPU blend. Superior mechanical properties of the blend, with the notched Charpy impact strength 150 KJ/m2, and tensile strength 197 MPa, were achieved. With increasing hot stretch ratio, the storage modulus increased, the glass transition temperatures of the PLA-rich phase and TPU-rich phase in the blends moved to higher temperatures, and the melting temperature and crystallinity of the blend increased, indicating the stress-induced crystallization of the blend during drawing. The longitudinal fracture surfaces of the blends at different stretch ratios exhibited orderly arranged fibrillar bundle structure, which contributed to the significantly higher strength and toughness of the blend. 相似文献
19.
阐述了目前HCFCs替代的形势、替代制冷剂和替代技术路线。从各个方面介绍了几种有潜力的单一替代制冷剂R32、R161、R1234yf和R1234ze等。并对将来替代制冷剂的发展进行分析,认为混合制冷剂是大势所趋。 相似文献
20.
Large magnetic entropy change and magnetic properties in La (Fel-xMnx)ll.TSil.3Hy compounds 下载免费PDF全文
Magnetic properties and magnetic entropy change in La(Fe_{1-x}Mn_x)_{11.7}Si_{1.3}H_y compounds have been investigated. A significant increase of the Curie temperature T_C and a small increase of the saturation magnetizations μ_S have been observed after the introduction of interstitial H, which caused a slight volume expansion. The first-order field-induced itinerant-electron metamagnetic (IEM) transition remains and brings about a large magnetic entropy change around room temperatures for the compounds. The maximal magnetic entropy change is about 23.4, 17.7 and 15.9J/kg·K under a magnetic field change from 0 to 5T for x=0.01, 0.02 and 0.03, respectively. Therefore, the compounds appear to be potential candidates for magnetic refrigerants around room temperatures. 相似文献