Flow and heat transfer analysis of hybrid cooling schemes: Adding micro-jets to a micro-gap

An extensive, combined experimental and numerical analysis is presented as a method for physically-driven, systematic improvement of heat transfer, applied to a single-phase hybrid quasi-2D cooling scheme, merging impinging flow with that parallel to a heated plate. Thereby cooling fluid is introduced into a micro-gap in a gradual way, through a succession of impinging micro-slot jets. Both the distributed inflow and impinging flows improve heat transfer and especially wall temperature uniformity. For a specific micro-fabricated system, the influence of flow rate is examined in an experimental study employing wall-side infrared thermography and flow visualization by micro-PIV. The measurements reveal the location of standing vortices and jet's deflection of the main flow towards the wall, and the characteristics of these flow patterns, associated with around 20% heat transfer enhancement. These flow patterns and wall heat transfer are quantitatively reproduced by numerical simulation spanning the transitional flow regime. From insights gained, the base configuration is varied numerically in terms of jet array location and pitch, micro-jet slot hydraulic diameter and initial flow distribution. As a result, a much improved configuration is identified, yielding a total heat transfer enhancement of almost 60%, as compared to a plain gap at the same overall flow rate, while attaining even more significant improvement in wall temperature uniformity. The systematic method followed to obtain such improvement is described in detail to facilitate future studies.