两种双侧强化管管外R245fa降膜蒸发的实验对比

Experimental Comparison of R245fa Falling Film Evaporation in Two Doubly-enhanced Tubes

本文搭建了水平单管降膜蒸发实验台,以R245fa为工质实验研究两种三维翅双侧强化管降膜蒸发的换热特性。提出了新型Wilson-Gnielinski图解法,用于从实验的总传热系数中获得管内外表面传热系数。分析强化管表面结构对换热性能的影响,拟合出管内外换热关联式并提出强化换热方案。结果表明,与光滑管理论表面传热系数相比,Y型管的管内、管外换热强化倍率分别为2.12~2.94和2.27~5.54,T型管的管内、管外强化倍率分别为2.48~2.98和2.58~3.00。Y型管管外换热性能较好,T型管管内换热性能较好。Y型管的最佳喷淋密度(0.14~0.18 kg/(m·s))比T型管的最佳喷淋密度(约0.10 kg/(m·s))大;两种强化管表面传热系数均随热流密度的增加先上升后下降,但Y型管表面传热系数的变化速率较快;两种管子的换热效果均随蒸发温度的升高而增强。

The heat transfer performance of two types of doubly enhanced tubes was experimentally studied using R245 fa after the horizontal single-tube falling film evaporating test bench no built. The Wilson-Gnielinski graphic method was proposed to obtain the surface heat transfer coefficient of the tubes. The effect of the wall structure on the heat transfer performance was analyzed. The heat transfer correlations inside and outside the tubes were provided, and a fitting optimization scheme was proposed. The results showed that the enhancement rates of in-tube and out-tube heat transfer of the Y tube were 2.12-2.94 and 2.27-5.54, respectively. The internal and external enhancement rates of the T tube were 2.48-2.98 and 2.58-3.00, respectively. The out-tube heat transfer performance of the Y tube and the in-tube heat transfer performance of T tube were better. The heat transfer performance of the Y tube can be reinforced by optimizing its in-tube structure. The best spraying density of the Y tube [0.14-0.18 kg/(m·s)] was higher than that of the T tube [approximately 0.10 kg/(m·s)]. The surface heat transfer coefficient of the two tubes first increased and then decreased with the increase in the heat flux. However, the surface heat transfer coefficient of the Y tube changed more rapidly, which indicated that the thermosyphon boiling phenomenon caused by the smaller fin pitch of the Y tube accelerated the evaporation of refrigerant. The surface heat transfer coefficient of the two tubes increased with the increase in the evaporation temperature.