Abstract This work experimentally studies the effects of single wall heating on laminar flow in a high-aspect ratio superhydrophobic microchannel. When water that is saturated with air is used as the working liquid, the non-wetted cavities on the superhydrophobic surfaces act as nucleation sites and allow air to effervesce out of the water and onto the surface when heated. Previous works in the literature have only considered the opposite case where the water is undersaturated and absorbs air out the cavities for a microchannel setting. The microchannel considered in this work consists of a rib/cavity structured superhydrophobic surface and a glass surface separated by spacers. The microchannel is 60 mm long by 14 mm wide and two channel heights of nominally 183 μm and 366 μm are explored. The superhydrophobic side is in contact with a heated aluminum block and a camera is used to visualize the flow through the glass side. Thermocouples are embedded in the aluminum to record the temperature profile along the length of the channel. Temperatures are maintained below the boiling temperature of the working liquid. The friction factor-Reynolds product (fRe) is obtained via pressure drop and volumetric flow-rate measurements. Five surface types/configurations are investigated: smooth hydrophilic, smooth hydrophobic, superhydrophobic with ribs perpendicular to the flow, superhydrophobic with ribs parallel to the flow, and superhydrophobic with ribs parallel to the flow with several breaker ridges perpendicular to the flow. The surface type/configuration has a significant impact on the mass transport dynamics. For surfaces with closed cell micro-structures, large bubbles eventually form and adversely affect fRe and lead to higher temperatures along the channel. When degassed water is used, no bubble nucleation is observed and the air initially trapped in the superhydrophobic cavities is quickly absorbed by the water.

中文翻译：

---

亚临界加热引起的超疏水微通道气泡成核

摘要 这项工作通过实验研究了单壁加热对高纵横比超疏水微通道中层流的影响。当用空气饱和的水作为工作液体时，超疏水表面上的非润湿空腔充当成核点，并允许空气在加热时从水中冒泡出来并到达表面。以前的文献工作只考虑了相反的情况，即水不饱和并从腔体中吸收空气以进行微通道设置。在这项工作中考虑的微通道由肋/腔结构的超疏水表面和由垫片隔开的玻璃表面组成。微通道长 60 毫米，宽 14 毫米，并探索了名义上 183 微米和 366 微米的两个通道高度。超疏水侧与加热的铝块接触，并使用相机观察通过玻璃侧的流动。热电偶嵌入铝中以记录沿通道长度的温度分布。温度保持在工作液体的沸点以下。摩擦因数-雷诺积 (fRe) 是通过压降和体积流量测量获得的。研究了五种表面类型/配置：光滑亲水、光滑疏水、具有垂直于流动的肋的超疏水、具有平行于流动的肋的超疏水以及具有平行于流动的肋且具有垂直于流动的多个断路器脊的超疏水。表面类型/配置对质量传输动力学有重大影响。对于具有闭孔微结构的表面，最终会形成大气泡并对 fRe 产生不利影响，并导致通道沿线温度升高。当使用脱气水时，没有观察到气泡成核，最初困在超疏水腔中的空气很快被水吸收。