Comparison of 2D and 3D unsteady effects of a pair of opposed confined impinging jets

The unsteady laminar flow and heat transfer characteristics for a pair of opposed confined impinging air jets in 2D and 3D were studied numerically. The present study continues the authors\´ earlier work [1] and identifies the main similarities and differences arising from the expansion to the third dimension. For comparison purposes, the space and time-averaged heat transfer coefficients for a pair of heat sources arranged at different locations on opposite target walls were determined together with the oscillating jet frequency. The authors\´ previous investigation found that opposite confined jets remain steady at Reynolds numbers that make the parallel (side-by-side) jets highly unsteady. The nature of the unsteadiness depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region, causing the jets to "wash" a larger surface area on the target wall. Depending on the proximity of the jet inlets, a fixed stagnation "bubble" is formed between the two jets, leading to a quasi-independence of the local heat transfer on flow conditions. The study focuses on the flow field unsteadiness and associated heat transfer coefficients when varying the distance between the chips placed on the target walls for a flow at Re = 750. The relevant trends for the 2D and 3D jet hydrodynamic and thermal fields are documented. Although similar in nature, the unsteady 3D opposite jets produce results that deviate from the 2D unsteady opposite jets. The complex vortex patterns resulting from the jet interaction at the higher Reynolds number is investigated and its impact on electronics component cooling are documented.