Thermal Head

(or temperature head), the difference in the characteristic temperatures of a medium and a wall (or phase boundary) or of two media, between which heat transfer is occurring. The local thermal head is the difference between the temperature of the medium and the local temperature of the wall (or phase boundary) or the temperature difference between two media in a given cross section of a heat-exchange system. The mean thermal head is the difference averaged over a heat-transfer surface. The product of the thermal head and the heat transfer coefficient represents the heat flux, that is, the amount of heat transferred from one medium to the other across a heating surface of unit area in a unit time.