低品位热源驱动的吸收式制冷循环特性分析及系统仿真

发布时间：2018-05-08 20:19

  本文选题：低品位热源 + 吸收式制冷　； 参考：《山东建筑大学》2014年硕士论文

【摘要】：吸收式制冷是一种可以利用余热、废热、太阳能等低品位热源作为驱动方式的制冷方式,其常用的工质对LiBr/H2O、NH3/H2O和R134a/DMF等都是环保制冷剂。对于在建筑能耗中占较大比重的中央空调系统来说,采用低品位热源驱动的吸收式制冷系统对节约常规能源、保护自然环境具有十分重要的意义。结合文献和手册数据,根据不同工质对二元溶液的物理性质,确定了利用Aspen Plus计算二元工质对溶液热力学性质的物性方法。溴化锂水溶液采用ELECNRTL物性方法,氨水溶液及R134a/DMF二元溶液均采用Peng-Rob物性方法,将采用相应物性方法计算的溶液热力学性质的结果同文献中实验数据进行了比较,最大误差分别为2.92%、2.91%和8.8%。 在确定物性方法的基础上对三种工质对的循环特性进行了分析,发现R134a/DMF工质对P-x-y曲线类似于NH3/H2O,在相图一个可辨别的DMF气相组成,需要在循环中假设精馏装置。 借助于Aspen Plus软件分别搭建了三种工质对循环的吸收式制冷系统,并对其进行了模拟分析。对溴化锂吸收式制冷系统,分析了发生温度、冷凝温度、稀溶液浓度的变化对系统的影响；计算及确定了不同冷凝温度下系统所需的最小冷却水量及串并联方式,当冷凝温度在42～45℃,冷却水采用串联形式,38-42℃时采用并联的形式：对氨水吸收式制冷系统,分析了回流比的变化及精馏塔塔底温度对系统性能的影响,综合考虑精馏效果以及系统的性能,回流比选择在0.4～0.6之间是比较合适,放气范围在0.065～0.15之间系统COP较高；对R134a/DMF吸收式制冷系统,分析了回流比、R134a在混合溶液的质量比及精馏塔底部温度的变化对系影响,合理的回流比范围为0.5～0.7,放气范围在0.17～0.39之间系统COP趋于稳定较优；吸收器中R134a被完全吸收,所需冷却源的温度较低,提高吸收器出口溶液的气相分率可以降低对冷却源温度的要求。 对比三种工质对的主要参数发现,对于发生温度可变化范围,LiBr/H2O工质对最小,仅为6.3℃,对于COP, NH3/H2O工质对最小；R134a/DlVIF的放气范围区间最大,发生温度可变化的范围最大,为31.36℃,发生温度最低为68.8℃,可以适用于一些低温且温度波动大的热源,有一定的发展应用前景。 在对我国太阳能资源及太阳能辐射强度与建筑负荷关系进行分析的基础上了,分析了太阳能集热器的类型与三种不同工质对所需驱动热源温度的匹配性。对于LiBr/H2O和NH3/H2O吸收式制冷系统采用真空管集热器比较适合,对于R134a/DMF吸收式制冷系统由于所需要的发生温度较低,大部分工况可以使用低温平板型集热器。
[Abstract]:Absorption refrigeration is a kind of refrigeration method which can be driven by low-grade heat sources such as waste heat, solar energy and so on. The commonly used refrigerants are environmental refrigerants such as LiBr-H _ 2O, NH _ 3 / H _ 2O and R134a/DMF. For the central air conditioning system which accounts for a large proportion of building energy consumption, it is very important to adopt absorption refrigeration system driven by low grade heat source to save conventional energy and protect the natural environment. According to the physical properties of binary solutions with different working fluids, a method of calculating the thermodynamic properties of binary solutions by Aspen Plus was established by combining the literature and manual data. The ELECNRTL physical property method is used in lithium bromide aqueous solution, and the Peng-Rob physical property method is used in ammonia water solution and R134a/DMF binary solution. The thermodynamic properties of the solution calculated by the corresponding physical property method are compared with the experimental data in the literature. The maximum error was 2.92% and 8.8%, respectively. Based on the determination of physical properties, the cyclic characteristics of three pairs of working fluids are analyzed. It is found that the P-x-y curve of R134a/DMF is similar to that of NH _ 3 / H _ 2O. In the phase diagram, a discernible DMF gas phase composition needs to be assumed in the cycle distillation unit. With the help of Aspen Plus software, three absorption refrigeration systems with working fluid pair cycle are built and simulated. For the libr absorption refrigeration system, the influence of the temperature, condensation temperature and dilute solution concentration on the system is analyzed, and the minimum cooling water quantity and the series-parallel connection mode are calculated and determined. When the condensing temperature is 42 ~ 45 鈩，

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