Jet impingement flow is known to generate some of the highest single-phase heat transfer, with strong potential for micro-electronics cooling applications. However, this flow generates strong thermal non-uniformity, which is still not clearly understood. At micro-scales flow is predominantly laminar, which greatly simplifies analysis and prediction. Thereby, great progress has recently been made by the authors, in clarification of the involved physical mechanisms and modelling of the heat transfer.
Firstly, for a single-jet it is recognized that the emerging velocity profile shape, at the nozzle, and its evolution during flight (dependent on external forces and boundary conditions – free-surface or submerged) are crucial to heat transfer distribution. Free-surface jet simulations show that velocity-profile relaxation occurs, whereas under submerged conditions, shear can lead to vortices. Horizontal free-jet experiments show that gravity (body force) causes stronger asymmetry in heat transfer than predicted. In these studies, the age-old heat transfer peaks under a jet have been experimentally observed in liquids and explained through subsequent numerical analysis, for the first time. Farther downstream, in the wall-jet region, similarity solutions have been identified for free-jets, while analysis of experimental observations has allowed prediction of the hydraulic jump location as a function of downstream depth (back-pressure). Thereby, a complete description is obtained for free-jets, while submerged ones are seen to be too complex for such modelling.
Arrays of impinging jets obtain better thermal uniformity and coverage than a single-jet, but due to spent liquid cross-flow and adjacent jet interference, much cooling potential is lost. Experiments of mini/micro free-jet arrays show that spent-liquid evacuation reduces these effects and provides a higher level of symmetry, for modular description and easier simulation. Finally, the hydraulic jump prediction is shown to hold under array conditions and inter-jet low-cooling zone reduction is demonstrated.
