R717在小管径水平光管内流动沸腾换热及压降特性

Heat Transfer and Pressure Drop Characteristics of R717 Flow Boiling inside a Horizontal Small Diameter Plain Tube

氨制冷剂存在可燃性和毒性,因此减少其在制冷系统中的充注量极为重要。小管径换热管通常可以提供更高的表面传热系数,这可以作为提升换热器紧凑性同时减少系统中充注量的有效方法。本文搭建了氨制冷剂管内流动沸腾换热及压降测试实验装置,测试了氨制冷剂在4 mm水平光管内的流动沸腾换热及压降,并分析了干度、质量流速及热流密度对换热及压降特性的影响。结果表明:流动沸腾换热表面传热系数随着干度的增加而增大,同时质量流速和热流密度越高,流动沸腾换热表面传热系数越大。此外,氨制冷剂在管内的两相摩擦压降也随着干度的增加而增大,在固定干度下,质量流速的升高导致压降增大。

Ammonia has drawbacks associated with combustibility and toxicity,and therefore,reducing the charge in ammonia refrigeration systems is of great importance. The application of small diameter tubes offer a higher surface coefficient of heat transfer,which has the potential to improve the compactness of the heat exchanger and reduce refrigerant charge. This study conducted experiments to investigate the characteristics of heat transfer and pressure drop for ammonia flow boiling in a horizontal plain tube with an inner diameter of 4 mm.The dependencies of the heat transfer and frictional pressure drop on vapor quality,mass flux,and heat flux are analyzed in detail. The experimental results show that the surface coefficient of heat transfer increases with vapor quality. In addition,an increase in the mass flux and heat flux can lead to a higher surface coefficient of heat transfer. In addition,the two-phase frictional pressure gradient also increases with increasing vapor quality. Further,at a certain vapor quality,the two-phase frictional pressure gradient increases with an increase in mass flux.