Abstract:

In the present study, the effects of wettability, surface topography and surfactant on the growth of bubbles and pool boiling heat transfer of straight and gradient square copper pillar arrays with partially-modified surface were investigated. The experimental medium was deionized water, 100, 200, 400, 800 mg·L^-1 in isopropanol solution and n-heptanol solution. The results showed that silver deposition on square copper pillar decreases the wettability, and increases bubble number. Addition of isopropanol or n-heptanol into deionized water decreases the number and departure diameter of bubbles in the heat flux range of 66.1—202 kW·m^-2. However, when the heat flux increases to 413 kW·m^-2, the surfactant can effectively prevent bubbles from merging, so the boiling heat transfer coefficient of the pool boiling decreases first and then increases with the increase of the concentration. The gradient square pillar structure with upper and lower layers of 0.5 mm and 1mm and a spacing of 2 mm promotes the coalescence of bubbles and formation of a gas film on the heating surface, and then worsens pool boiling heat transfer.

Key words: partially-modified surface, square copper pillar array, wettability, pool boiling, surfactant

摘要：

以局部表面改性的紫铜直方柱和梯度方柱阵列为研究对象，实验研究了表面润湿性、表面形貌和表面活性剂对池沸腾换热性能和气泡生长特性的影响。实验工质为去离子水，浓度分别为100、200、400、800 mg·L^-1的异丙醇溶液和正庚醇溶液。实验结果表明：方柱阵列表面镀银之后润湿性变差，表面产生的气泡数量减少。向去离子水中添加异丙醇或正庚醇后，在热通量为66.1～202 kW·m^-2时，气泡脱离直径变小、数目减少，而当热通量增至413 kW·m^-2时，活性剂能够有效阻碍气泡合并，故池沸腾传热系数随着浓度增加先减小后增大。上下层宽分别0.5 mm和1 mm、间距为2 mm的梯度方柱阵列结构有助于气泡的合并，但由于促进了固体表面气膜的形成，从而降低了沸腾换热性能。

关键词: 局部表面改性, 紫铜方柱阵列, 润湿性, 池沸腾, 表面活性剂