【作者】 王雁；

【导师】 杜垲；

【作者基本信息】 东南大学 ， 制冷及低温工程， 2005， 硕士

【摘要】 近年来,随着国际社会替代工质研究进程的加快和对能源利用效率的重视,混合工质制冷循环技术迅速发展起来。其中自然复叠式制冷循环充分利用混合工质的特性,在-50℃以下温度区间显现出了独特的优势。使用自然复叠制冷循环的低温产品,也已经逐步应用在低温箱保存、低温测量、低温材料制造以及工业天然气液化等一些商业或非商业领域。但是由于混合工质循环特性比较复杂,变化因素多,混合工质热物性数据不够完整和精确,因此针对自然复叠制冷的分析方法和理论研究还在进一步发展之中。本文选取R134a/R23作为自然复叠式制冷系统混合制冷剂,对R134a/R23热物性及其自然复叠循环进行了详细的计算,主要完成了以下一些内容:1)在R134a/R23的热物性研究中,针对传统状态方程不能同时精确描述气液两相P-V-T关系的问题,提出了修正状态方程法,并给出了该方法应用于混合工质物性计算时的逸度系数及焓熵表达式;2)编制了混合工质R134a/R23物性计算程序模块,可完成R134a/R23基本热物性和迁移性质的计算。在对比文献数据进行误差分析之后,绘制了工程上广泛应用的混合工质焓浓度图。将R134a/R23物性数据与理想混合工质物性进行比较,从而得到了实际混合工质的偏移特性;3)系统地提出了基于焓浓度图的混合工质循环分析方法,并由此初步确定了自然复叠循环的约束条件和影响因素;4)对自然复叠循环进行了热力学分析和计算,确定了设计工况下循环各状态点的参数,并得出了循环性能在冷凝温度、中间温度、压力工况和浓度配比改变时的变化情况;5)在自然复叠循环特性计算的基础上建立了循环优化模型和优化方法,找出了循环运行在不同环境温度和蒸发温度下的最优浓度配比,以及在压比不超过13时的极限蒸发温度;6)自然复叠制冷的回热循环可以有效的降低压比和蒸发温度,而对混合工质浓度配比的优化影响很小,因此在实际应用中应当使用带回热的循环形式。更多还原

【Abstract】 In recent years, reachers have paid more attention to usage of energy and environment protection. Consequently alternative refrigerants and their mixture, including HFCs, HCs or nature refrigerants are studied. Autocascade refrigeration (ACR) is a kind of typical refrigeration cycle, which uses mixed refrigerant and makes good use of the mixture’s characteristics. ACR takes advantage to apply in the area below -50℃.More products based on ACR have been put into market. They are deep freezer, cryopreservation, low-temperature treatment, cryogenic material and so on. But the ACR system is relatively complex, having many restraints and influence factors, and even the thermophysical properties data of mixed refrigerant are not sufficient and precise .So anlysis and research on ACR needs to be further developed.In this thesis, mixed-refrigerant HFC134a/R23 is choosed as ACR’s working fluid. The thermophysical properties are calculated in detail and based on the mixture’s properties, performance of the ideal ACR cycle is simulated.The main content of this thesis is shown as follows:1) In calculation of R134a/R23 properties, the traditional equation of state is corrected. Using this corrected equation, we analyze R134a/R23 P-V-T-x and get new expression of fugucity, enthalphy and entropy. By theoretical calculation, data of the mixture’s VLE, enthalphy, entropy and transport properties are all obtained;2) Thermopropertes calculation is programmed and enthalphy-concentration diagram is plotted. Result data are compared with those obtained when R134a/R23 is assumed as ideal mixture. The difference from this comparison is the mixture’s deviation properties;3) An analysis method based on enthalphy-concentration diagram is systematicly put forward to explain the ACR cycle. Then we priliminarily decide the cycle’s constrait conditons and influence factors;4) Procedure of thermophysical calculation for ACR cycle is shown in this thesis. All state points’s parameters and coefficient of performance is decided under design condition and other conditions when condensation temperature, middle tempera -ture, pressure and mixture’s composition change;5) Optimization model for ACR cycle is set up and from this model we get the optimized compositon of R134a/R23 in different condensation temperature and evaporation temperature. The ultimate evaporation temperature exists when the pressure ratio limited to 13;6) This thesis’s study shows that pressure ratio and evaporation temperature of ACR cycle can be decreased when internal heat exchangeris installed, however which has little influence to the optimized compositon. So ACR cycle with internal heat exchanger should be recommended.更多还原