Based on the Second Law of Thermodynamics

the entropy generation is studied for laminar forced convection flow of different nanoparticles (Al

2

O

3

CuO and SiO

2

) mixed with water through a hexagon microchannel heat sink (HMCHS). The effects of different heat fluxes and Reynolds numbers on the entropy generation for different nanofluids

volume fractions and nanoparticles diameter are investigated. The heat flux is in the range of 125 to 500 kW·m

-2

and the Reynolds numbers vary between 200 and 1500. The thermal

frictional and total entropy generations are calculated by integrating the volumetric rate components over the entire HMCHS. The results clearly show that the rise in the heat flux leads to an increase in the thermal entropy generation for nanofluids and pure water but they don't have any influence on the frictional entropy generation. Moreover

when the Reynolds number increases

the frictional entropy generation increases while the thermal entropy generation decreases. The results revealed that at low heat fluxes and high Reynolds numbers

pure water gives the lowest entropy generation

while

at high heat flux the nanofluid has to be used in order to lower the overall irreversibility.