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ISSN Online: 2379-1748
ISBN Flash Drive: 978-1-56700-517-2
5-6th Thermal and Fluids Engineering Conference (TFEC)
HEAT TRANSFER INVESTIGATION OF SPRAY COOLING FOR THERMAL MANAGEMENT OF A HIGH POWER LED MODULE
Abstract
The cooling demand for contemporary high power LEDs is of the order of 200-250 W/cm2 at the chip-scale where junction temperature should be lower than 120°C for reliability. Special thermal management techniques are required to remove such high heat fluxes. In this study, single nozzle spray and jet impingement techniques are experimentally studied and compared, with water as the working fluid. Flow originates from a nozzle and impinges on the packaged LED module. Depending on the operating pressure and nozzle diameter, the resulting flow can be in the form of a jet or a spray. The parameters of interest are the fluid flow rate (flow Re varies from 2,000 up to 13,500) and its height of impingement from the substrate. Depending on the nozzle diameter, maintaining the flow parameters necessitates appropriate inlet
operating pressures, ranging up to 5 bar in the present case. High-speed videography and subsequent image analysis provide droplet size distribution and other parameters of interest. Heat flux is estimated by inverting the temperature distribution data obtained on the rear of the LED module by embedded thermocouples. Spray cooling using water shows that, for an electrical input power of 240 W, surface temperatures are well below 85°C when flow rate of the coolant exceeds 100 ml/min (corresponding Re = 3,000). Jet cooling
shows quite similar heat transfer performance, though the pressure penalty for creating a water jet is considerably smaller. However, the spatial distribution of heat transfer rates is much better in the case of sprays. Experimental results are additionally compared using numerical simulation (on COMSOL®) for various thermal boundary conditions. The experiments clearly establish the efficacy of spray and jet cooling for high power LED modules.
Video presentation
Video presentation