This article investigates liquid micro-jet array impingement cooling of a micro-structured surface. An array of 16 free-surface DI water jets, each 125 μm in diameter, and jet Reynolds number ranging between 816 and 2124, is used. A parametric study is carried out with micro-studs of varying size and spacing, implemented on a 1 cm2 base area surface. Based on the decades of research on heat transfer enhancement by surface modification, one would intuitively think that impingement cooling of a micro-structured surface will always be better than that of a plain surface. The current results are in contrary. The micro-structures actually degrade single-phase impingement heat transfer, compared to a plain surface. On the other hand, in the phase change regime they significantly enhance heat transfer, leading to a clear choice of optimal structure. The results are explained in the light of thin film dynamics, heat transfer surface area enhancement and nucleation site density.

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