When we accidentally burn our hand in the kitchen, a common way to soothe the burn is to put our hand under running water from the faucet. Compared to a fan blowing on the hand or putting the hand into a bowl of room temperature water, it seems that running water indeed eases the pain more effectively. Why is this? The effectiveness of convection varies based on many different factors, including the type of fluid, the speed of the fluid moving over a hot surface, the smoothness of the surface, etc.
These differences in convection are accounted by film coefficient when using a conduction-based solver.