School for Engineering of Matter, Transport and Energy, Arizona State University , Tempe, Arizona 85287, United States.
Langmuir. 2017 Oct 31;33(43):12095-12101. doi: 10.1021/acs.langmuir.7b03141. Epub 2017 Oct 10.
Promoting dropwise condensation (DWC) could improve the efficiency of many industrial systems. Consequently, a lot of effort has been dedicated to finding durable materials that could sustainably promote DWC as well as finding routes to enhance the heat transfer rate during this phase change process. Motivated by previous reports of substrate softening increasing droplet nucleation rate, here we investigated how mechanical properties of a substrate impact relevant droplet-surface interactions and DWC heat transfer rate. Specifically, we experimentally quantified the effect of hydrophobic elastomer's shear modulus on droplet nucleation density and shedding radius. To quantify the impact of substrate softening on heat transfer through individual droplets, we combined analytical solution of elastomer deformation induced by droplets with finite element modeling of the heat transfer process. By substituting these experimentally and theoretically derived values into DWC heat transfer model, we quantified the compounding effect of the substrate's mechanical properties on the overall heat transfer rate. Our results show that softening of the substrates below a shear modulus of 500 kPa results in a significant reduction in the condensation heat transfer rate. This trend is primarily driven by additional thermal resistance of the liquid posed by depression of the soft substrate.
促进滴状冷凝（DWC）可以提高许多工业系统的效率。因此，人们投入了大量的精力来寻找能够可持续地促进 DWC 的耐用材料，以及寻找在相变过程中提高传热速率的途径。受先前关于基底软化会增加液滴成核速率的报道的启发，我们在这里研究了基底的机械性能如何影响相关的液滴-表面相互作用和 DWC 传热速率。具体来说，我们通过实验定量研究了疏水性弹性体的剪切模量对液滴成核密度和脱落半径的影响。为了量化基底软化对单个液滴传热的影响，我们结合了液滴引起的弹性体变形的解析解和传热过程的有限元建模。通过将这些通过实验和理论推导得出的值代入 DWC 传热模型，我们量化了基底机械性能对总传热速率的复合影响。我们的结果表明，基底的软化会导致剪切模量低于 500 kPa 的情况下冷凝传热速率显著降低。这种趋势主要是由软基底的凹陷导致液体产生额外的热阻引起的。
