3.1.3.5 Role of surface temperature
HTC data were evaluated for any dependence of the heat transfer coefficient upon the roll surface
temperature. The results plotted in Figure 3.1.11 show that heat transfer is not significantly dependent
upon surface temperatures over the range of temperatures encountered in rolling mills. Vapour
formation at the hot surface causes better separation of the coolant from the roll surface than the
nucleation of vapour bubbles and is further assisted by centrifugal forces that accelerate the residual
water away form the roll surface. Cooling is less intensive at the hot surface in the areas outside of the
spray impact region, owing to the lack of momentum of the water to break through the vapour layer.