Visualizing and disrupting liquid films for filmwise flow condensation in horizontal minichannels
Visualizing and disrupting liquid films for filmwise flow condensation in horizontal minichannels
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DOI：
10.3389/fther.2022.953051
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发表时间：
2022-09
期刊：
影响因子：
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通讯作者：
G. A. Riley;C. Méndez;Munonyedi Egbo;G. Hwang;M. Derby
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文献类型：
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作者：
G. A. Riley;C. Méndez;Munonyedi Egbo;G. Hwang;M. Derby
本文研究了半球形丘对微通道内膜状冷凝换热的影响。还研究了三面冷凝面的空间取向(即重力效应)对蒸汽冷凝的影响，其中冷却表面要么是下表面(即重力将液体拉向冷凝面)，要么是上表面(即重力将液体从冷凝面拉出)。使用了两个液压直径为1.9 mm的测试片，分别是普通铜表面或直径为2 mm的半球状土丘修饰的铜表面。在质量流量为50 kg/m2s和125 kg/m2s时，记录了两个方向上的传热系数、膜可视化和压降测量。在所有试验条件下，土丘的冷凝换热系数至少增加了13%，最大增加了79%。当试验段倒置(即在流动的蒸汽顶部冷凝面)时，堆性能的差异很小，而平板式换热器的换热系数降低了14%。流动可视化表明，由于薄膜的破坏以及通过降低薄膜的热阻，土丘增强了热传递。压降在质量上遵循抛物线行为，在丘状息票中高于普通息票。在倒置方向上没有观察到明显的压降差异。
This paper investigates the effects of hemispherical mounds on filmwise condensation heat transfer in micro-channels. Also investigated were the impacts that spatial orientation of the three-sided condensation surface (i.e., gravitational effects) on steam condensation, where the cooled surfaces were either the lower surface (i.e., gravity pulls liquid towards the condensing surfaces) or upper surface (i.e., gravity pulls liquid away from the condensing surfaces). Two test coupons were used with 1.9-mm hydraulic diameters and either a plain copper surface or a copper surface modified with 2-mm diameter hemispherical mounds. Heat transfer coefficients, film visualization, and pressure drop measurements were recorded for both coupons in both orientations at mass fluxes of 50 kg/m2s and 125 kg/m2s. For all test conditions, the mounds were found to increase condensation heat transfer coefficients by at minimum 13% and at maximum 79%. When the test section was inverted (i.e., condensing surface on the top of flowing steam), minimal differences were found in mound performance, while the plain coupon reduces heat transfer coefficients by as much as 14%. Flow visualization suggests that the mounds enhanced heat transfer due to the disruption of the film as well as by reducing the thermal resistance of the film. Pressure drops followed parabolic behavior with quality, being higher in the mound coupon than the plain coupon. No significant pressure drop differences in the inverted orientation were observed.