EFFECT OF SURFACE ROUGHNESS ON HYSTERESIS PHENOMENON OF CONDENSATION CURVE

本报告由三部分组成。摘要写在下面。[Part在较宽的过冷度Δ t范围内，对水平、倾斜和垂直粗糙表面上的滴状和膜状凝结换热进行了测量。结果表明，与光滑表面相比，在较高的过冷度Δ t范围内容易出现瞬态和膜状凝结。热通量值变得非常低，并且在DELTAt增大和减小的条件下显示出不同的值。人们可以很容易地在粗糙表面上再现这种滞后现象。[Part提出了两种估算粗糙表面滴状冷凝热流密度q_r的方法。即假定粗糙表面和光滑表面上的脱离液滴半径之比等于无凝结时的静力学半径之比（R_r/R_s），则q_r可表示为q_s、R_r/R_s和 ...更多信息 扫描周期比但该方法不能直接反映曲面的几何特征。在充分发展糙率区，用摩阻因子代替R_r/R_s和扫掠周期比，提出了另一种估算方法，结果表明，这两种估算的qr与实验值吻合较好。[Part在凝结曲线的过渡区，无论测量位置是被凝结液膜覆盖还是被液滴覆盖，计算DELTAt的表面温度都有较大幅度的变化。然后，利用膜状冷凝区的实测热流密度、冷凝膜覆盖率和滴状冷凝区的实测热流密度计算粗糙表面的平均表面温度，对粗糙表面上的冷凝曲线过渡区进行修正。结果表明，在较低的DELTAt区域，过渡凝结区的修正凝结曲线右移，而在较高的DELTAt区域，修正凝结曲线左移从之前的曲线中。少

This report is consist of three parts. The abstract is written in the next.[Part I] Dropwise and filmwise condensation heat transfer on vertical rough surfaces scratched horizontally, obliquely and vertically by various grades of sand paper was measured over a wide range of subcooled temperature DELTAt.By the results, the transient and filmwise condensation which appear in the higher range of DELTAt occurred easily compared with that on the smooth surface. The heat flux values became very much lower and showed different values under the condition that DELTAt was increased and decreased. One could easily reproduce this hysteresis phenomenon on the rough surface.[Part II] Two methods of estimating the heat flux (q_r) during dropwise condensation on rough surfaces is proposed. Namely, by assuming the ratio of the departure drop radius on the rough and smooth surfaces was equal to those of the statics (R_r/R_s) without condensation, q_r was formulated as a function of q_s, R_r/R_s and the … More ratio of sweeping cycle. But this method could not represent the geometical characterisities of the surfaces directly. Then, another estimation method was proposed by replacing R_r/R_s and the ratio of sweeping cycle with the friction factors in the region of fully developed roughness flow.As a result, these two kinds of estimated qr agreed well with experimental value.[Part III] In the transition regime of condensation curve, the surface temperature to calculate DELTAt changes of a large scale wheather it's measureing position is covered with condensate film or drop. Then, the transition regime of condensation curves on rough surfaces was modified by the average surface temperature of those which were calculated by using the measured heat flux in filmwise condensation area, the measured covering ratio of condensate film and the calculated heat flux in dropwise condensation area.By the results, it was found that the modified condensation curves in transition condensation regime shift to right side in the relatively lower DELTAt region and shift to left side in the higher DELTAt region out of the previous curves. Less