Visualizing and disrupting liquid films for filmwise flow condensation in horizontal minichannels

G. A. Riley, C. Méndez, Munonyedi Egbo, G. Hwang, M. Derby
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引用次数: 1

Abstract

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.
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水平小通道中膜状流动冷凝的液体膜的可视化和破坏
本文研究了半球形土墩对微通道膜状冷凝换热的影响。还研究了三面冷凝表面的空间取向(即引力效应)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表面),要么是上表面(即重力将液体拉离冷凝表面)。两个试验片使用1.9毫米的液压直径和一个普通的铜表面或铜表面修改2毫米直径的半球形土墩。在质量通量为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。在所有测试条件下,发现土墩增加冷凝传热系数最少13%,最多79%。当试验截面倒置(即流动蒸汽顶部的冷凝面)时,土墩性能差异最小,而平原板可降低传热系数达14%。流动可视化表明,由于薄膜的破坏以及通过减少薄膜的热阻,土丘增强了传热。压降随质量呈抛物线型变化,丘陵区压降高于平原区压降。在倒置方向上没有观察到明显的压降差异。
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