微米级余弦槽表面疏水性及冷凝传热实验研究
Experimental Study on the Hydrophobicity and Condensation Heat Transfer of Cosine Micro？？Grooved Surfaces

为了研究余弦微槽结构的疏水性和冷凝传热性能,首先制备了不同槽峰高度和槽距的微米级余弦槽结构表面,实验研究了不同结构微槽表面的静态接触角及其对滴状冷凝传热性能的影响,并对冷凝传热过程中液滴在微槽表面合并、脱落过程进行实验研究和热力学分析。结果表明,液滴在微槽表面的疏水性和传热性能都呈现明显的各向异性,横向静态接触角θ⊥明显高于纵向接触角θ∥。同时,冷凝传热过程中竖直纵槽阻碍液滴的横向合并,但其对液滴脱落过程起到极大促进作用,传热性能较光滑表面提高30％～50％,且峰距比越大液滴的脱落半径越小、脱落频率越高,表面传热效率也越高。水平横槽则相反,虽然增大峰距比促进了液滴合并,但却对其脱落过程产生不利影响,导致整体传热性能较纵向槽表面大幅下降,与光滑表面接近。引入表面润湿率对微槽表面的液滴脱落半径进行热力学计算,计算值与实验结果吻合较好,误差在20％以内。
In order to study the effects of cosine micro？？grooved structures on hydrophobicity and condensation heat transfer, the cosine micro？？grooved surfaces with depth of 12？？24 μm and width of 30？？60 μm were prepareed using dry etching. The wettability and heat transfer characteristics of these micro？？grooved surfaces were investigated experimentally, and the coalescence and sweeping processes of droplets on micro？？grooved surfaces were thermodynamically analyzed. The results showed that the wetting behavior and heat transfer characteristics of the micro？？grooved surfaces presented anisotropic characteristics, and the static contact angle in perpendicular direction θ⊥ was significantly larger than that in parallel direction θ∥. In heat transfer experiment, the plates were set vertically and the grooves were arranged in both vertical and horizontal positions. For the vertically grooved surface, the sweeping effect of falling drops was enhanced and the heat transfer in the dropwise condensation was increased to 30％？？50％, and a better heat transfer performance was achieved when the ratio of peak to interval increased. Different from vertical grooved surface, the experimental results obtained from horizontal grooved surface were similar to the results of smooth surface. This might be due to the dual effect of horizontal grooves, promoting droplet coalescence and hindering the departure process. The surface wetting rate was introduced in developing thermodynamic model to solve the departure radius of droplets, and the calculated values were in good agreement with the experimental results with a largest error less than 20％