Liquid Micro-Jet Array Impingement Cooling for Large Area Systems

The necessity for high heat flux cooling over large areas is growing rapidly with the increasing push towards more electric systems. A significant amount of research over the past two decades has conclusively proved the suitability of impingement cooling, such as jet and droplet array, spray, etc. However all these works are focused on a small heat source area, typically about a few cm². Can a large array of impingement pattern covering a much wider area achieve similar heat flux levels? In pursuit of an answer, this article presents liquid micro-jet array impingement cooling of a heat source that is about two orders of magnitude larger in size compared to the previous works. Experiments are carried out with 441 jets of water and dielectric liquid HFE7200, each 200 μm diameter, impinging on a 189 cm² area surface, in free surface and confined jet configurations. The measured values of average heat transfer coefficient are compared with correlations from the literature. While some correlations show excellent agreement, others deviate significantly. The ensuing discussion suggests that the post impingement liquid dynamics, particularly the collision between the liquid fronts on the surface created from surrounding jets, is the most important criterion dictating the average heat transfer coefficient. Thus, similar thermal performance can be achieved irrespective of the length scale, as long as the flow dynamics are similar. These results decisively prove the scalability of the liquid micro-jet array impingement technique for cooling a few cm² area to 100s of cm² area.