Enhancement of heat and mass transfer by herringbone microstructures in a simple shear flow
The heat and mass transfer characteristics in a simple shear flow over staggered herringbone structures are numerically investigated with the lattice Boltzmann method. Two flow motions are identified. The first is a spiral flow oscillation above the herringbone structures that advects heat and mass from the top plane to herringbone structures. The second is a flow recirculation in the grooves between herringbone ridges that advects heat and mass from the area around herringbone tips to the side walls of herringbone ridges and the bottom surfaces. These two basic flow motions couple together to form complex transport mechanisms. The results show that when advective heat and mass transfer takes effect at relatively larger Reynolds and Schmidt numbers, the dependence of the total transfer rate on the Schmidt number follows a power law, with the power being the same as that in the Dittus-Boelter equation for turbulent heat transfer. As Reynolds number increases, the dependence of the total transfer rate on Reynolds number also approaches a power law, and the power is close to that in the Dittus-Boelter equation.