Numerical simulation of mixed convection heat transfer of galvanized steel sheets in the vertical alloying furnace

The local temperature in galvanized plates during heat treatment in vertical alloying furnaces is an important factor that influences the alloying quality. Herein we simulate the heat transfer of conjugate mixed convection and three-dimensional turbulence flow in the entire soaking zone and cooling tower of the vertical alloying furnace, using Reynolds-averaged Navier-Stokes and energy equations enclosed by k-ε two-equation turbulence model. The flow fields and temperature distribution were obtained, and the effect of the Grashof number (Gr) and Reynolds number (Re) on the air velocity and temperature distribution in the steel plate was analyzed. It was found that with increasing Gr, the buoyancy force, which induces natural convection, was enhanced and the steel plate temperature increased. With increasing Re, forced convection in the cooling zone increased and inhibited hot airflow going up. This led to a higher temperature of the steel plate in the soaking zone and a lower temperature in the cooling tower. When Gr/Re < 0.28, the flow direction reversed, opposing the direction of steel plate translation. This study demonstrates that the precise temperature requirements of the alloying process can be satisfied by regulating Gr and Re.