Thermal management of ultra-high heat flux surfaces using controlled cooling

There is an ever increasing need to attain and maintain thermal devices at low, uniform and acceptable operating temperatures. Among the four main features involved in any heat transfer three of them -- namely heat absorption, transport and removal - were studied in detail for optimized cooling. First, thermal mass and characteristics of heat transfer surfaces were investigated. Comparisons between traditional flat surface, structured rough surface and porous media show that porous media exhibit superior performance. Ensuing, five different sintered filters with 2mum, 5mum, 10mum, 20mum, and 40mum porosity values were explored. Experimental findings show an inverse relationship of pore diameter on percolation rate; where surface tension and capillary pressure battle to affect Leidenfrost effect.;The present study uses fine wire Type-E thermocouples, high-speed camera and FLIR thermal imaging to capture evolution of droplet on heated porous surfaces. It is evident that droplet spread diameter and residence time highly depend on surface superheat and porosity. Interaction time, spread diameter, maximum temperature drop, and percentage increase of cooling enhancement are the main features used to seek effective cooling zone. The substrate with smallest porosity demonstrates swift coolant imbibing rate and larger wetting diameter. Temperature range between 130°C -- 210°C are found to offer a favorable spray cooling zone.;Second, heat spike analysis and control mechanisms were analyzed. High-density thermal loads and sudden heat spikes are attributed to not only limiting the overall efficiency of mechanical and electrical modules but also failing sensitive components. Temperature distribution and response of components were studied analytically, experimentally and numerically. All results confirm effect of thermal spike produced time lags propagating from the source. Thus instead of replicating the traditional thermostatic controller, two other techniques, for example, pressure control and rate of temperature control were examined. Pressure control does not show encouraging results because of the design of the current experimental setup. However, rate of temperature change controller works better detecting heat jump and thus managing heat much better. The results serve to show how misleading surface temperature monitor would be in predicting rate of temperature change.