R404A在小管径管内流动沸腾换热特性研究

Study on Flow Boiling Heat Transfer Characteristics of R404A in Small-diameter Tubes

R404A在小管径管内的流动沸腾换热过程是一个极其复杂的物理现象。目前对R404A换热特性的研究大多集中在大管径上,对小管径换热特性的研究较少,且对不同实验现象的机理分析也不尽相同。因此R404A在小管径管内换热特性的理论研究仍需要大量具体的实验数据来支撑。本文通过搭建小管径内螺纹铜管蒸发实验台,研究R404A在小管径管内流动沸腾换热过程中不同热流密度、不同蒸发干度、不同质流密度、不同饱和温度对表面传热系数的影响,研究表明:热流密度、干度、质流密度、饱和温度均对R404A在小管径管内换热特性的影响较大,干涸现象发生前后这些因素产生的影响也不同。此外,这些因素对管内干涸现象发生的起始干度、沸腾主要换热形式以及干涸现象是否发生具有直接影响。

The flow boiling heat transfer process of R404A in small-diameter tubes is a very complex physical phenomenon. At present, research on the heat transfer characteristics of R404A is mostly focused on large-diameter tubes, and there has been little research on small-diameter tubes, despite the different mechanisms underlying the experimental phenomena. Therefore, there is a strong need for spe-cific experimental data to support the theoretical study of the heat transfer characteristics of R404A in small-diameter tubes. An experi-mental platform for evaporation in small-diameter micro-fin copper tubes was constructed, and the effects of heat flux, evaporation quality, mass flux, and saturation temperature on the heat transfer coefficient in the process of R404A flow boiling heat transfer was investigated. Each factor was studied independently, with all variables other than the particular one under consideration held constant throughout the a-nalysis. The research results shows that the heat flux, quality, mass flux, and saturation temperature all have a significant influence on the heat transfer characteristics of R404A in small-diameter tubes, with the effects of these factors varying before and after dryout. Furthermore, these factors have a direct influence on the initial quality of dryout, the main form of heat transfer, and the occurrence of dryout.