【作者】 曲晓萍；

【导师】 沈胜强；

【作者基本信息】 大连理工大学 ， 热能工程， 2005， 硕士

【摘要】 随着人们生活水平的提高,空调的使用日益广泛,然而大量使用机械压缩制冷系统带来电能消耗、环境污染问题也向人类可持续发展提出了挑战。利用太阳能等可再生资源来满足人们的需求是众多可供选择方案中较为直接的解决办法。由于可以利用低温热源驱动,并且本身结构简单、运行可靠,因而国际上很多学者开始关注喷射式制冷系统的研究。 在单喷射制冷系统基础上提出双喷射式制冷系统,以气-液喷射器替代原系统中的液体泵,将冷凝器中的部分冷凝液送回发生器,完成工作循环。在稳定运行情况下,双喷射式制冷系统不消耗任何电能,这是研究这一新型制冷系统的着眼点。 (1) 本文着重对双喷射式制冷系统中的新增部件—气-液喷射器进行了分析研究,建立针对气-液喷射器内流动过程的物理模型、数学模型,编制气-液喷射器性能分析与结构设计软件。可计算的工质包括R11、R12、R13、R14、R134a、R22、R114、R500、R502、R717(氨)、R123和R718(水)等。讨论了不同制冷剂和不同工况对性能参数和结构设计的影响。在以水为工质时,利用数值模拟方法编制了汽-水喷射器数值模拟程序,用于分析轴向压力场。结果表明,当气-液喷射器用于提升液体压力的场合时(出口压力大于等于工作压力),喷射系数随着工作温度(压力)的提高而降低。 (2) 推导了气-液喷射器结构设计和可达工作状态数学表达式,编制程序进行计算研究。引射流体的工作条件一定时,要满足某极限喷射系数的要求,工作压力越大,喷射器出口压力就越大。随着工作压力升高到一定值以上时,再增加工作压力,出口压力增加不多。在工作蒸汽压力和引射流体压力不变时,喷射器出口压力越高,极限喷射系数就越小。 (3) 在研究气-液喷射器的基础上,建立了分析太阳能双喷射式制冷系统的模块化分析模型,编制了针对喷射式制冷系统的运行软件。对应用各种制冷剂时、不同工况下系统的性能进行了分析。提出了一个系统性能分析模型,为选择适合工作条件提供了依据。结果表明,对于各种制冷剂,发生温度升高时,系统COP增大;冷凝温度降低时,系统COP增大;蒸发温度升高时,系统COP增大。对于R134a来说,系统工况最佳为冷凝温度低于32℃,蒸发温度高于8℃,发生温度则在允许的范围内,尽量提高。研究了双喷射式制冷系统与单喷射式制冷系统的对比情况。结果表明,在低温位热源方面,这是一种很值得推广和进一步改进的制冷装置。更多还原

【Abstract】 With the improvement of people’s living standard, air-conditioner has been more and more popularized. However, mechanical compression refrigerators consume a big quantity of electric power and indirectly make the problem severe, which brings forward a great challenge to the human’s sustainable development. Among the various solutions, the utilization of solar energy and other regenerative energy for refrigeration is one of the promising choices. Because of its ability to utilize the low-temperature thermal energy resources, and its simple structure and reliable operation, the ejector refrigeration system has gained much attention.Based on single ejector refrigeration system, a bi-ejector refrigeration system was presented, in which the mechanical pump is replaced by a gas-liquid ejector to bring part of the condensate back to generator. During ideal operation state, the system will not consume electricity absolutely, which is the reason why to study this new-style refrigeration system.(1) In this paper, the study of the performance and characteristics of the gas-liquid ejector, which is a new-added part, is carried out. Physical model and mathematical model for gas-liquid ejector are established, and a soft ware is exploited to analyze the performance and design the structure of gas-liquid ejector using various refrigerants including R11 R12 R13 R14 R134a R22, R114, R500, R502 R717 R123 and R718 etc. The effect of different refrigerant and operating condition is discussed considering entrained ratio and structure design. When water is used as refrigerant, with numerical computation, the numerical result of pressure distribution along axle direction is given. The result shows that entrained ratio is decreased with the increasing of working temperature when gas-liquid ejector is used to lift the pressui’e of liquid.(2) Mathematical expression is induced to explain the utmost working state of gas-liquid ejector. When induced liquid’s pressure is known, in order to reach the utmost entrained ratio, the higher the discharged pressure is, the higher the working pressure is needed. As the working pressure is up to some numerical value, lifting working pressure further makes less contribution to the discharged pressure. Thus the utmost entrained ratio decreases with the increasing of the discharged pressure while working pressure and induced liquid’s pressure remains unchanged.(3) A design of bi-ejector refrigeration system is presented and analysis model for bi-ejector refrigeration system is established. Based on the study of gas -liquid ejector, a package of software for the performance predicting and structure designing is made. The performances of ejectors and system depend a great deal on the refrigerants as well as operation conditions, which presents reference to choose appropriate refrigerant and working condition for the system. The results show that the COP rises with the increasing generator and evaporator temperature and decreasing of condensate temperature. For R134a, the better operating condition is a condenser temperature lower than 32 and a evaporator temperature higher than 8. The utility effect of solar energy and waste heat by different systems is also discussed, which indicates that bi-ejector refrigeration system is worth to recommend and improve further in utilizing low-staged energy.更多还原