纯工质R245fa水平管内凝结换热实验研究及工况优化

发布时间：2018-07-11 10:13

  本文选题：R245fa + 水平圆管　； 参考：《天津商业大学》2016年硕士论文

【摘要】：科学技术的发展,在给人类带来益处的同时,也严重污染着环境,其中臭氧层破坏与温室效应尤为突出。能源的浪费与不环保制冷剂的应用造成大量碳氧化物与氟氯烃物质的排放。随着R245fa(五氟丙烷)的性质被发现以来,越来越多的学者对其蒸发及凝结换热进行研究与关注。R245fa具有零臭氧消耗潜能值(ODP)和较低的全球变暖潜势(GWP),已经被提出替代R11,R114和R141b等中高温制冷剂。并且R245fa在低压冷水机组、高温热泵和聚氨酯泡沫行业的应用具有良好前景,实验证明该制冷剂不可燃并具有良好的毒理学特性。本文研究纯工质R245fa在水平圆管内凝结换热的实验特性并对工况进行优化分析。本文研究了R245fa在内径为4.38mm水平铜管内凝结换热过程,实验工况为:工质冷凝温度30℃-55℃,工质质量流速92(kg/m2s)-276(kg/m2s),换热温差20℃,冷却水质量流速1056(kg/m2s)-1752(kg/m2s)。得出不同质量流速下换热系数随干度的变化规律与不同冷凝温度下换热系数随干度的变化规律。以工质进口温度与冷却水温度作为边界条件,质量流速、冷凝温度以及干度作为相关变量,对目标函数h寻找区域最大值,并引入熵分析法对流动性能与传热性能进行评价。得出以下相关结论:(1)验证了纯工质R245fa在单管凝结换热过程中换热系数由冷凝温度、工质质量流速以及干度共同影响。(2)干度在0.7-0.9之间R245fa单管凝结换热系数达到最大值,并且两相流型均为环状流。(3)通过熵分析法分析得出,在冷凝温度30℃-45℃,工质流量184(kg/m2s)-276(kg/m2s)工况下,其ΔQ/ΔP最大,在此范围内,既保持了较高的换热系数并有优良的流动性能,同时最大换热系数出现在冷凝温度30℃-40℃。R245fa在4.38mm单管凝结换热实验中冷凝温度对换热性能的影响大于对流动性能的影响。(4)R245fa冷凝换热系数在干度为0.1-0.7,变化率基本相同,在质量流速较大情况下,干度达到0.7-0.8时,变化率变小。在工质质量流速较小时,换热系数随干度近似线性增加。(5)实验数据对比Kim关联式,R245fa冷凝换热实验值与Kim关联式误差在15%以内。本文针对纯工质R245fa水平圆管内凝结换热的特性开展研究,研究不同工况下的分段以及整体换热系数,并分析换热规律,这对R245fa高效冷凝器的设计提供了理论依据并有一定的实践指导意义。
[Abstract]:The development of science and technology not only brings benefits to human beings, but also pollutes the environment seriously, especially ozone layer destruction and Greenhouse Effect. The waste of energy and the application of non-environmental refrigerants cause a large amount of carbon oxides and HCFCs emissions. Since the discovery of the properties of R245fa (pentafluoropropane), More and more scholars have studied the evaporation and condensation heat transfer. R245fa has zero ozone depletion potential (ODP) and low global warming potential (GWP) and has been proposed to replace the R11R114 and R141b refrigerants. The application of R245fa in low pressure chiller, high temperature heat pump and polyurethane foam industry has a good prospect. The experiment shows that the refrigerant is not combustible and has good toxicological properties. In this paper, the experimental characteristics of condensation heat transfer of pure working fluid R245fa in a horizontal circular tube are studied and the working conditions are optimized. The condensation heat transfer process of R245fa in 4.38mm horizontal copper tube is studied in this paper. The experimental conditions are as follows: refrigerant condensation temperature 30 鈩，

本文编号：2114784