Numerical investigation into the thermo-fluid performance of wavy microchannels with superhydrophobic walls

As an efficient cooling method, wavy microchannel heat sink (W-MCHS) with superhydrophobic walls is suggested as an alternative to a straight microchannel heat sink (S-MCHS) with conventional walls. Navier-Stokes and Energy equations with slip boundary conditions (velocity slip and temperature jump) are solved to study the hydraulic and thermal performances of the microchannels. It is observed that based on the "goodness factor" criterion, the overall performance of the new heat sink design is improved by 47.3%. In fact, the pressure drop reduction accompanying the use of superhydrophobic walls outweighs the thermal performance degradation due to the presence of trapped layers of air. It is also observed that with an increase in the waviness of the channel (either by an increase in the wave amplitude or a decrease in the wavelength), the pressure drop reduction by the use of superhydrophobic walls intensifies as the maximum velocity shifts from the centre of the channel towards the crest regions. This, in turn, increases the velocity gradient at the wall which excites the velocity slip and results in a better hydraulic performance. On the other hand, the thermal performance is deteriorated to a greater extent (compared to the hydraulic improvement) when the channel waviness increases, due to the elongated flow path and the related increase in the trapped layers of air. As a result, as long as the cooling performance of the heat sink with superhydrophobic walls is concerned, microchannels with lower waviness are desirable.