Abstract
A series of experimental and numerical studies on the heat transfer behavior for unconfined/confined heat spreaders having a uniform or an asymmetric discrete heating load with different cooling methods have been performed. Two types of cooling method such as natural cooling and fan jet impingement cooling are employed in the present study. The relevant parameters influencing heat transfer performance on the studies with natural cooling and fan jet impingement cooling are: (1) natural cooling －Grashof number(GrT or GrH), ratio of confinement spacing to characteristic length (S/LH), ratio of heater area to spreader area (r), heater installation location and type of spreader material. The ranges of these parameters studied are GrH = 8.15×106 – 3.75×107; S/LH=0.077 and ; and r=0.217-1. (2) fan jet impingement cooling － Grashof number (GrT or GrH), Reynolds number (Re), ratio of heater area to spreader area (r), heater installation location and type of spreader material. The ranges of these parameters explored are GrH = 1.39×108 – 3.42×108, Re = 4344-7125 and r = 0.217-1. Their effects on heat transfer behavior with natural cooling and with fan jet impingement cooling have been systematically explored.For precisely evaluating the effective thermal conductivities of various types of heat spreader, an effective and time-saving semi-empirical method, by using both a numerical thermal-network method and an experimental measurement together with a statistical least-square technique, has been proposed. Three new correlations of effective thermal conductivity in terms of temperature for eleven types of heat spreader have been presented.For investigating the local and average thermal behavior of heat spreaders having a uniform or an asymmetric discrete heating load with natural cooling or with fan jet impingement cooling, an effective semi-empirical method integrated by the experimental measurement and thermal network analysis has been successfully developed. The parametric studies on relevant thermal performances are conducted; and the results and conclusions are also verified by a statistical sensitivity analysis of ANOVA F-test. In addition, five new generalized correlations of average Nusselt numbers for heat spreaders having a uniform or an asymmetric discrete heating load with natural cooling or with fan jet impingement cooling are presented with satisfactory agreements. Furthermore, two new composite correlations of average Nusselt number for a confined heat spreader having an asymmetric discrete heating load in mixed convection due to fan jet impingement and buoyancy in terms of r and GrT/Re2 (or GrH/Re2.5) have been proposed; and another new correlations for evaluating external and total thermal resistances for all the cases have also been presented.Finally, the empirical response formulas with a quadratic RSM model for evaluating all relevant thermal performances such as average Nusselt number and total thermal resistance for various types of heat spreader having a uniform or an asymmetric heating load with either natural cooling or fan jet impingement cooling have been presented. Comparisons of the predictions with such empirical response formulas with the experimental data and relevant experimental correlations are made. The maximum and average deviations compared with the experimental data are less than 10.84% and 5.89%, respectively; those compared with the experimental correlations are less than 9.98% and 5.73%, respectively.