Nozzle geometry effects in liquid jet array impingement

The use of impinging liquid jets in electronics thermal management is attracting some consideration due to their very high heat transfer coefficients, hot spot targeting capabilities and moderate hydraulic power requirements. In this investigation an experimental study of the cooling capabilities of impinging water jet arrays is presented. Of particular interest here is the influence that the inlet and outlet geometries have on the thermal-hydraulics of jet impingement heat transfer with the aim of determining practical configurations in which heat transfer to the impinging jets is increased and/or the hydraulic pumping power is decreased. For a square array of 45 jets of fixed 1.0mm diameter and fixed interjet spacing of 5mm, six different nozzle geometries were investigated. The arrays impinged normally upon a heated circular copper surface of 31.5mm diameter for a nominal heat flux of 25.66W/cm2. Each array was tested under confined-submerged flow conditions with a constant jet-to-target spacing of 2.0mm as well as free-surface conditions with a constant jet-to-target spacing of 20mm. All nozzles were tested for a Reynolds number range of approximately 800≤Redn≤10,000. It has been found that the confined-submerged tests yield greater heat transfer coefficients compared with their free jet counterparts. Chamfering and contouring the nozzle inlets showed significant decrease in the pressure drop across the nozzle plate whilst chamfering and contouring the exit showed moderate gains in the surface averaged heat transfer coefficient. Nozzles that provide the highest heat transfer for a given hydraulic pumping power are identified for each free-surface and confined-submerged scenarios.