A numerical study was conducted to model the transient thermal behavior of a complex testing system including multiple fans, a mixing enclosure, copper inserts and a leaded package dissipating large amounts of power over short time durations. The system is optimized by choosing appropriate heat sink/fan structure for the efficient operation of the device under constant powering. The intent of the study is to provide a better understanding and prediction of a transient powering scenario at high powering levels, while evaluating the impact of alternative cooling fan/heat pipe designs on the thermal performance of the testing system. One design is chosen due to its effective thermal performance and assembly simplicity, with the package embedded in heat sink base with multiple (5) heat pipes. The peak temperature reached by the modified design with 4 cooling fans is similar to 95 degrees C, with the corresponding Rja thermal resistance similar to 0.58 degrees C/W. For the transient study (with embedded heat pipes and 4 fans), after one cycle, both peak temperature (at 45 s) and the end temperature (at 49 s) decrease as compared to the previous no heat pipe/single fan case (the end temperature reduces by similar to 16%). The temperature drop between peak and end for each cycle is similar to 80.2 degrees C, while the average power per transient cycle is similar to 31.27W. With this power, the design with 5 perpendicular heat pipes, 4 fans and insert reaches a steady state peak temperature of similar to 98 degrees C. Applying the superposition principle to the steady state value and 40.1 degrees C fluctuation, the maximum transient temperature after a large number of cycles will not exceed similar to 138. 1 degrees C, satisfying the thermal budget under the current operating conditions. The benefit of the study is related to the possibility to extract the maximum and minimum temperatures for a real test involving a large number of heating-cooling cycles, yet maintaining the initial and peak temperatures within a certain range for the optimal operation of the device. The flow and heat transfer fields are investigated; using a combination of numerical and analytical methods, the thermal performance of the device undergoing large number of periodic thermal cycles is predicted. The comparison between measurement and simulation shows good agreement.
