【作者】 彭勃；

【导师】 徐士鸣；

【作者基本信息】 大连理工大学 ， 制冷与低温工程， 2008， 硕士

【摘要】 随着人们对臭氧层破坏和全球变暖问题的日益关注，在制冷行业中使用低ODP(Ozone Depletion Potential，臭氧消耗潜能)和GWP(Global Warming Potential，全球变暖潜能)的制冷剂已经成为不可逆转的趋势。其中自然工质因其对环境没有影响而受到广泛重视。R744、R290、R600a都是性能优良的自然工质，将它们混合后应用于自复叠制冷系统，可以扬长避短，达到理想的效果，成为制冷剂替代关注的对象。本文基于热力学定义，对R744／R290、R744／R600a两种混合自然工质的热力性质进行计算，比较各种计算方法的准确性，确定合适的理论公式，并将这两种混合工质应用于自复叠制冷系统，提出混合工质摩尔分数选择的方法，计算自复叠制冷系统的循环特性及其影响因素。结果表明：R744／R600a比R744／R290更容易分凝，且适用于较低压力或较高温度；分凝后R744的摩尔分数在气体中高于总体水平，在液体中低于总体水平；泡点露点温度随压力的升高而升高；将两种混合工质应用于自复叠系统中，在选择混合工质摩尔分数时要同时考虑制冷温度、冷凝器压力、蒸发冷凝器压力等因素；分凝后制冷剂的干度存在最佳值，使低温流在蒸发冷凝器中充分冷凝，同时使高温流在蒸发冷凝器中充分蒸发，这时系统性能达到最佳值；适当提高回热器换热系数有助于减少蒸发冷凝器的换热负荷，有助于提高压缩机入口处制冷剂的过热度，有助于提高系统性能。本文用数值模拟的方法计算出以上结论，为采用R744／R290和R744／R600a的自复叠制冷系统的深入研究和实际应用提供了理论依据，并对其它混合工质和采用其它混合工质的自复叠系统的研究提供了一些参考。更多还原

【Abstract】 Nowadays, people pay more and more attentions on ozone depletion and global warming, so it’s an unreversed trend to use low ODP and GWP refrigerant in refrigeration industry. Natural mixtures have broad regard because of their friendly properties to entironment. R744, R290 and R600a have nice properties, the auto-cascade refrigeration system using their mixtures also can cancel their disadvantage, so this method becomes an important one in the area of refrigerant substitute.In this paper, proceeding from the actual thermodynamic definition, the calculation of R744/R290 and R744/R600a’s thermodynamic properties are taken. The veracity and reliability of each calculation method and result are analyzed, appropriate equations are chosen, and the thermodyanamic properties of an auto-cascade refrigeration system and the factors which impact them are taken, a method how to choose the mole fraction of the mixture is taken. Results indicate that: R744/R600a is easier to separate phases than R744/R290, and adapt to work under lower pressure or higher temperature; after phases separated, the mole fraction of R744 is higher in gas and lower in liquid; the temperatures of bubble point and dew point become higher with higher pressure; in auto-cascade refrigeration system using natural binary mixture, it’s necessary to consider refrigeration temperature, the pressure of condenser and evaporative condenser at the same time when choose the mole fraction of mixture; there is a optimal mole proportion between the gas and liquid at the exit of the condenser, which can make the low temperature branch condense adequately and make the high temperature branch vaporize adequately; appropriately higher heat exchanger coefficient can be helpful to lighten the heat load of evaporative condenser, enhance system capability.The presented conclusions which are obtained from numerical simulation provide theoretic gist for the study and application of the auto-cascade refrigeration system using R744/R290 and R744/600a. Furthermore, it’s effective and useful for the studies of other mixtures and auto-cascade refrigeration system using other mixtures.更多还原