Abstract

Boiling utilizes latent heat of vaporization of the fluid to dissipate large amount of heat at small temperature budgets. Surfaces with micro−/nano-scale wettability patterns have been shown to improve the heat transfer coefficient during pool boiling. In this work, we propose a simple and cost-effective technique to fabricate heterogenous surfaces with macroscale wettability patterns comparable to the capillary length of the boiling fluid. We demonstrate that such surfaces can enhance boiling heat transfer coefficient significantly. Four configurations (two samples of hydrophobic dots and lines each) of heterogeneous surfaces are investigated to understand the influence of the diameter, pitch and arrangement of hydrophobic regions on the hydrophilic background surface on the heat transfer coefficient. Results indicate that up to ≈66% enhancement in the heat transfer coefficient can be achieved in comparison to the bare surface. If the hydrophobic dots are spaced out sufficiently, number of dots on the surface controls the heat transfer coefficient at low heat fluxes. However, nucleation is initiated even on the hydrophilic background surface at high heat fluxes and smaller diameter dots start performing better than the larger diameter dots. Smaller pitch (< bubble departure diameter) leads to lateral coalescence among the departing bubbles in case of lined pattern configuration, thereby lowering the heat transfer coefficient. The study demonstrates that simple and cost-effective macroscale wettability patterns can separate liquid supply and vapor removal pathways to enable comparable heat transfer coefficients enhancements otherwise achieved through sophisticated and costly surface patterning techniques discussed in literature.

中文翻译：

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可扩展的宏观润湿性模式，可增强池沸腾换热

摘要

沸腾利用流体汽化的潜热以较小的温度预算消散大量的热量。具有微米/纳米级可湿性模式的表面已显示出可改善池沸腾过程中的传热系数。在这项工作中，我们提出了一种简单且具有成本效益的技术来制造具有与沸腾流体的毛细管长度相当的宏观润湿性图案的异质表面。我们证明了这种表面可以显着提高沸腾传热系数。研究了异质表面的四种结构（每个疏水点和线的两个样本），以了解亲水背景表面上疏水区域的直径，间距和排列方式对传热系数的影响。结果表明，与裸露表面相比，传热系数最多可提高约66％。如果疏水点充分隔开，则表面上的点数可控制低热通量下的传热系数。但是，即使在高热通量下，即使在亲水性本底表面上也会开始成核，并且直径较小的点开始比直径较大的点表现更好。在具有线型图案构造的情况下，较小的节距（＜气泡离开直径）导致离开的气泡之间的横向合并，从而降低了热传递系数。