制冷系统水平管降膜蒸发理论分析和实验研究

发布时间：2018-08-07 22:01

【摘要】：在当前严峻的环境压力下，制冷剂的替代和新型制冷剂的开发已经刻不容缓，而减量延续技术可以作为当前形式下对制冷剂替代工质的补充与过渡。通过统计和调查发现，在相同制冷量前提下，降膜蒸发所消耗的制冷工质要低于满液式蒸发器的四分之一。本文以制冷剂的减量替代作为研究背景，针对水平管降膜蒸发的流动机理、传热特性、强化方式进行了深入的分析和总结，并对制冷系统中降膜蒸发技术的应用以及系统含油对传热系数的影响等几个方面逐一进行总结和说明。在不同的运行工况下，降膜蒸发的传热特征具有不同的变化规律，同时系统所含润滑油会对其传热特性产生一定影响，发现润滑油的存在会明显降低了换热系数。通过搭建R134a的制冷循环系统，将水平管降膜蒸发器应用于系统的蒸发器中，从而进行水平管降膜蒸发的实验研究，以制冷剂的喷淋量、热流密度、蒸发温度作为研究变量进行实验对比分析，总结实验规律。此外，根据水平管降膜蒸发的传热机理，改变管外表面结构可以不同程度提高管外对流换热系数，因此在实验过程中加入了机械加工的TJX管、EX管、测试1管、测试2管进行实验研究。分析表明，强化管的降膜蒸发传热特性主要与热流密度、工质喷淋量以及管型的不同强化特征有关，而随着热流密度的增加，管外传热系数均出现升高趋势，但经过临界热流密度后，强化管的传热系数均呈现出不同程度的下降趋势，同时强化表面的传热系数要明显优于光滑管，不同强化管的传热系数也不尽相同，说明强化表面结构对实验结果也具有一定影响。最后，利用光滑管变工质喷淋量的实验数据与Ribatski和Thome预测的传热模型进行对比计算，并在此基础上进行公式拟合，拟合结果与实验数据之间的误差在±20%以内，并在此基础上提出了适用于强化管的强化系数，，为强化管的传热特性研究提供参考。
[Abstract]:Under the severe environmental pressure, the replacement of refrigerant and the development of new refrigerant are urgent, and the technology of deweighting continuation can be used as the supplement and transition of refrigerant substitute in the current situation. Through statistics and investigation, it is found that the refrigerant consumption of falling film evaporation is lower than 1/4 of the full liquid evaporator under the same refrigerating capacity. Based on the research background of refrigerant reduction substitution, the flow mechanism, heat transfer characteristics and strengthening methods of falling film evaporation in horizontal tube are analyzed and summarized in this paper. The application of falling film evaporation technology in refrigeration system and the influence of oil content on heat transfer coefficient are summarized and explained one by one. Under different operating conditions, the heat transfer characteristics of falling film evaporation have different laws, and the lubricating oil contained in the system will have a certain influence on its heat transfer characteristics. It is found that the existence of lubricating oil will obviously reduce the heat transfer coefficient. By setting up the refrigeration cycle system of R134a, the horizontal tube falling film evaporator is applied to the evaporator of the system, and the experimental study of the horizontal tube falling film evaporation is carried out. The evaporation temperature is used as the research variable to carry on the experiment contrast analysis, summarizes the experimental rule. In addition, according to the heat transfer mechanism of falling film evaporation in horizontal tube, the convection heat transfer coefficient can be improved in varying degrees by changing the outer surface structure of the tube. Therefore, the machined TJX tube ex tube is added in the experiment, and the 1 tube is tested. Test 2 tubes for experimental study. The analysis shows that the heat transfer characteristics of falling film evaporation of the enhanced tube are mainly related to the heat flux density, the amount of liquid spray and the different strengthening characteristics of the tube type, but the heat transfer coefficient outside the tube increases with the increase of the heat flux density. However, after the critical heat flux, the heat transfer coefficient of the strengthened tube is decreased in different degrees, and the heat transfer coefficient of the strengthened surface is obviously better than that of the smooth tube, and the heat transfer coefficient of the different strengthened tubes is also different. It shows that the strengthened surface structure also has a certain influence on the experimental results. Finally, the experimental data of variable working fluid spray quantity in smooth tube are compared with the heat transfer model predicted by Ribatski and Thome, and the formula fitting is carried out on the basis of which, the error between the fitting result and the experimental data is less than 卤20%. On this basis, the enhancement coefficient suitable for the enhanced tube is put forward, which provides a reference for the study of the heat transfer characteristics of the enhanced tube.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657;TB611

【参考文献】