The thermal resistance or R-factor of a material is the ratio of the thickness of the material to its thermal conductivity. Forced convection increases heat transfer by convection. The rate of transfer of heat by convection is directly proportional to the difference in temperature between a hot body and its surroundings. This is known as Newton's Law of Cooling . Radiation is the transfer of heat energy by electromagnetic radiation.
Radiation takes place through a medium or in a vacuum.
The rate of emission of heat energy by radiation from a black body varies as the fourth power of thee absolute temperature . A black body is a perfect radiator. Real bodies emit a fraction of the black body radiation called its emissivity . The wavelength for which a body radiated the maximum amount of energy depends on its temperature. Evaporation is the transfer of heat energy by vaporization.