Ultrasonic vibration and porous medium utilization are both proven to be beneficial techniques to im- prove cooling performance of heat sinks. Present work aims at exploring the impacts of using porous medium in heat sinks under ultrasonic vibration effect on the cooling performance and entropy genera- tion characteristics, hence, the interrelation of these two techniques is evaluated. Simulations are per- formed for a constant Reynolds number ( Re = 20 0 0) and ultrasonic vibration frequency ( f = 30 kHz), whereas five different porosities ( ε= 0.75 to 0.95) along with five different pore diameters ( d p = 1 to 17 mm) determining the permeability of the porous structure are considered. The results are compared to the non-porous case to determine the effects of porous medium on the ultrasonically vibrated heat sink. It is found that using porous medium increases convective heat transfer coefficient by up to 84.5% attaining a temperature reduction of 10.22 K. Low porosity along with high pore diameter attains an effective cooling, while high porosity with high pore diameter ensures lower pumping power require- ment, which is only 1.2-folds of the non-porous case. Frictional entropy generation rises by up to 23% due to porous structure restricting fluid flow depending on its porosity and permeability, while thermal entropy generation can be even decreased below that of non-porous case by 8% with appropriate choice of parameters. Yet, considering the total irreversibility, the frictional entropy generation is significantly dominant compared to the thermal entropy generation. Overall, using ε= 0.95 and d p = 17 mm along with 30 kHz of ultrasonic vibration is recommended for significantly enhanced heat transfer together with lowest possible pressure drop penalty and low thermal entropy generation.
