The application of splitters has been proven to be useful to control the separated wake downstream of the pinfins. This paper aims to evaluate the thermal (S˙th) and frictional (S˙f ) irreversibility rates in the fluid flow inside the plate-pin-fin heatsinks (PPFHSs). To this end, the numerical analysis of forward and backward water flow inside the PPFHS with three different attached splitters was performed considering Re of between 50 and 250. The main objective was to determine the locations with intense thermal and frictional entropy generation rates inside the fluid flow geometry. Based on the results, the frictional entropy generation rate is significantly lower than that the thermal term. Also, the pin-fin with arched splitter has the minimum thermal irreversibilities as compared to straight and wavy splitters. Furthermore, the major irreversibilities are associated with the locations near the pin-fin lateral and frontal surfaces as well as the plate fin walls and heatsink upper case and lower base. Moreover, it was shown that for all considered cases and two flow directions, the increasing of the Re results in decreasing and increasing the thermal and frictional entropy generation rates, respectively.
