Flow and thermal analysis of the transition scheme between micro-channel and micro-jet cooling solution

With the rapid development of high-power electronics, the thermal management of these emerging devices is challenging due to the danger of ultra high heat flux and uneven temperature distribution. In the past decade, certain heat-dissipation technologies based on micro-channel and micro-jet cooling have utilized geometrically identical heat sinks; however, their corresponding flow and thermal characteristics are quite dissimilar including temperature gradients, pressure drop and heat transfer coefficients only due to the different ways the coolant enters the test module. To characterize the enhanced heat-transfer mechanism driving this dissimilitude, a novel transition scheme between them was designed, featuring a gap on the channel fins top to provide extra flow area, and investigated experimentally and numerically. In this paper, by controlling the volumetric flow ratio of the channel and jet, including 1:1, 1:3 and 3:1, the flow and thermal characteristics of the transition scheme could be interchangeably transformed between the two schemes. Moreover, the effect of the vortex generated by the jet impingement was investigated, which was verified as an important factor causing the distinctions. The new results revealed that the vortex in the stagnation zone enhanced the local heat-transfer coefficient corresponding to the channel bottom and promoted temperature uniformity; however, it caused the thermal boundary layer on the fins top to thicken. Although the vortex was favorable for the forced convection in the acceleration zone, the vortex intersections formed by adjacent jets introduced a greater pressure-drop penalty and flow blockage, which were not conducive to enhancing the heat transfer. Subsequently, the Taguchi optimization method was employed to analyze effects of the aspect ratio, gap and jet diameters on flow and thermal characteristics. Accordingly, the optimal parameter combinations and contribution ratios were obtained. This paper systemat-ically shows how the micro-channel is transformed into a micro-jet cooling by adjusting the flow ratio and re-ports an intrinsic connection between them to promote a better understanding of cooling technologies used in electronic devices.