Convection is transfer of heat between a solid and a moving fluid. Boiling or condensing processes are example for convection processes.
The formula for convection is:
q = hc A dT
where
hc is convective heat transfer coefficient of the process (W/(m2K) or W/(m2oC q
A is the heat transfer area of the surface (m2, ft2)
hc = convective heat transfer coefficient of the process (W/(m2K) or W/(m2oC), Btu/(ft2 h oF))q is heat transferred per unit time (W, Btu/hr)dT is the temperature difference between the surface and the bulk fluid (K or oC, F)