Asolid plate, with a thickness of 15 cm and a thermal conductivity of 80 w/m·k, is being cooled at the upper surface by air. the air temperature is 10°c, while the temperatures at the upper and lower surfaces of the plate are 650 50 and 60°c, respectively. determine the convection heat transfer coefficient of air at the upper surface and discuss whether the value is reasonable or not for force convection of air.