Optimization design of a novel closed-loop spray cooling system
Due to the superiority of spray cooling system in removing high waste heat flux generated by the electronics, a novel spray cooling system combined with ejective condenser is proposed and its work procedure is introduced. Most previous relevant studies are only focus on the influences of parameters on the spray cooling performance. In the present paper, a multi-objective optimization function on the overall system is provided through the analysis of fluid flow and heat transfer characteristics, and the Particle Swarm Optimization (PSO) is applied to solve this problem. The optimized results of the total mass, the total pump power consumption and the heat surface temperature are obtained at different heat power. The optimal system structure parameters of the sprayer, the ejective condenser, the radiator are obtained. The work conditions of the sprayer mass flow and the heat surface temperature are also got under the performance of minimum power consumption, minimum system mass and the lowest heat source temperature at heat source power 500 W (heat flux 500 W/cm2).
Theoretical and experimental study of the effects of spray inclination on two-phase spray cooling and critical heat flux
Abstract Experiments were conducted with PF-5052 liquid sprays impacting a 1.0 × 1.0 cm 2 heated test surface at different inclination angles, flow rates, and subcoolings. Inclination angle had no noticeable effect on the single-phase or two-phase regions of the boiling curve. Maximum CHF was always achieved with the spray impinging normal to the test surface; increasing angle of inclination away from the normal decreased CHF appreciably. Video analysis showed inclined sprays produced lateral liquid film flow towards the farthest downstream region of the test surface. The film liquid provided partial resistance to dryout despite the weak volumetric spray flux in the downstream region. A new theoretical model of the spray’s impact area and volumetric flux proves this decrease is the result of a sharp reduction in the fraction of the test surface area that is directly impacted by the spray. Combining the model and video results with a previous point-based CHF correlation for normal sprays is shown to accurately predict the effects of orientation angle on CHF for different nozzles and operating conditions.
On the use of flat heat pipes as thermal spreaders in power electronics cooling
Power devices such as IGBTs dissipate very large heat flux densities. Therefore the thermal environment is a main issue in their performance and reliability. In order to improve heat transfer, materials with high thermal conductivity seem to be very useful. Because of their high cost, we suggest replacing them with a groove wick and sintered metal powder wick heat pipes. Thermal simulations are provided to show the interest of these structures in power electronics. Heat spreaders composed of heat pipe or plain material are compared. A 40% decrease of the thermal resistance between the heat source and the ambient is expected. Then an experimental study on a brass-water heat pipe is described. Results are compared with thermal simulations.