Flow Field Characteristics of Multiple Impinging Tapered Nozzles in Confined Channels for High Heat Flux Applications

Abstract

Impingement cooling with different tested fluids has been widely accepted and used to dissipate high transient and steady state localized heat loads. There are a plethora of advantages of direct impingement cooling over traditional cooling methods but till date the most alluring advantage is that of the boundary layer thickness proximity to the stagnation region being very small and consequentially leads to very high heat transfer rates. A numerical parametric setup involving 60 differing CFD simulations for a direct on-die multiple jet impingement in confined channels in the absence of phase change has been modeled for removing high heat fluxes emanating from the surface of die. The varying parameters for impingement setup includes Reynolds number (8000 ≤ Re ≤ 20000) based on the main inlet nozzle diameter, the nozzle jet orifice plate to the die (z/d) standoff (up to sixteen nozzle jet diameters distance), nozzle type, number of nozzles and aspect ratio. It is found for the higher aspect ratio tapered nozzle, the junction temperature of the silicon decreases 10° C - 20° C depending on the Reynolds number regime of the flow. Surface Nusselt number, a dimensionless heat transfer ratio is investigated on the surface of the die along with heat transfer coefficient (h) and it is shown that h increases with aspect ratio increase in the tapered nozzle and/or Reynolds number increase, and decreases with the tapered jet-to-target standoff distance. The fluid flow pattern reveals interesting features including a boundary layer separation point. The variation of secondary re-circulation zone downstream of the stagnation point with a Reynolds number increase is being investigated in Ansys Icepak, the commercial CFD package. A k-∈ model was used to predict the turbulent flow and associated characteristics. The findings from this investigation can improve the jet impingement design factors and performance of direct on-die impingement for high power density packages. The main objective of the present research is to gain insights computationally into the design and analysis of tapered micro nozzled jet impingement cooling for high power density packages so that robust and efficient impingement systems can be built for prototyping.