Influence of micro-scale aspects and jet-to-jet interaction on free-surface liquid jet impingement for micro-jet array cooling

Arrays of impinging jets can cool large areas with good thermal uniformity and are often used in industrial processes, such as drying and electronics cooling. However, due to cross-flow of the spent liquid and interference between adjacent jets, a significant amount of the available cooling performance is lost. Under free-surface jet impingement the area beyond the hydraulic jump is associated with significantly reduced heat transfer, and locally increased temperatures, therefore the hydrodynamics in this area must be better understood. Specifically, the interaction of jets in the vicinity of this location is expected to shed light on improving multi-jet array cooling uniformity and performance. Beyond this, it has been shown that micro-scale (sub-millimeter) jets tend to behave somewhat differently from larger jets, due to the increased significance of surface tension, pumping noise and edge-effects (such as small recirculation zones, and jet widening due to contact-angle at the nozzle exit, noise and nozzle imperfections due to manufacturing). These become much more dominant at the micro-scale. These effects cannot usually be accounted for by traditional scaling laws or numerical simulations, and are preferably investigated experimentally. Moreover, at these scales a micro-machined fixed-geometry array of jets is typically used, leaving no possibility for geometric variation, optimization and limited observation.