Mode of heat transfer when there is fluid flow. As in conduction, a temperature gradient must be present, but convection is influenced by fluid flow, which alters the temperature gradient. Ratio of the actual energy emitted by a real body to that emitted by a blackbody. Emissivity can be considered equal to absorptivity for a graybody, i.e., an object whose emissivity is independent of wavelength and that reflects radiation in a diffuse manner. Most objects can be reasonably approximated as graybodies.
Heat flux can be positive or negative, depending on the direction of heat transfer.
Fundamental property that indicates the internal energy of matter. Consists of a pair of junctions between two different metals that will produce a voltage proportional to the temperature difference between the junctions of the wires due to the Seebeck effect. For a thermocouple to give an accurate reading, the second junction must be at a reference temperature, frequently taken to be room temperature. For more accurate measurements, the second junction is lowered to a known temperature, such as the ice point. Array of thermocouples.