Single-Phase Self-Oscillating Jets for Enhanced Heat Transfer

In hybrid electric vehicles (HEVs), the inverter is a critical component in the power module, which conditions the flow of electric power between the AC motor and the DC battery pack. The inverter includes a number of insulated gate bipolar transistors (IGBTs), which are high frequency switches used in bi-directional DC-AC conversion. The heat generated in the IGBTs can result in degraded performance, reduced lifetime, and component failures. Heat fluxes as high as 250 W/cm² may occur, which makes the thermal management problem quite important. In this paper, the potential of self-oscillating jets to cool IGBTs in HEV power modules is investigated experimentally. A full factorial design of experiments was used to explore the impact of nozzle design, oscillation frequency, jet flow rate, nozzle-to-target distance, and jet configuration (free-surface or submerged) on heat transfer from a simulated electronic chip surface. In the free-surface configuration, self-oscillating jets yielded up to 18% enhancement in heat transfer over a steady jet with the same parasitic power consumption. An enhancement of up to 30% for the same flow rate (and velocity since all nozzles have the same exit area) was measured. However, in the submerged configuration, amongst the nozzle designs tested, the self- oscillating jets did not yield any enhancements in heat transfer over comparable steady jets. Results also suggest that oscillating jets provide a more uniform surface temperature distribution than steady jets.