Heat Flow

heat flow

[′hēt ‚flō] (thermodynamics) Heat thought of as energy flowing from one substance to another; quantitatively, the amount of heat transferred in a unit time. Also known as heat transmission.

Heat Flow

 

the amount of heat transferred across an isothermal surface in a unit time. Heat flow has the same dimensions as power and is measured in watts (W) or kilocalories per hour (kcal/hr); 1 W = 0.86 kcal/hr.

The amount of heat transferred across an isothermal surface of unit area in a unit time is called the heat flux. It is usually designated

Figure 1. Designs of recuperative heat exchangers: (a) coiled tubular heat exchanger, (b) double-pipe heat exchanger, (c) shell-and-tube heat exchanger, (d) tubular air heater, (e) plate-fin heat exchanger

by q and is measured in W/m2 or kcal/(m2·hr). Heat flux is a vector. The magnitude of any component of this vector is equal to the amount of heat transferred in a unit time across a surface of unit area perpendicular to the direction of the component. In English, the term “heat flux” is sometimes used in the sense of “heat flow.”

heat transfer

The flow of heat from one body at higher temperature to another body at a lower temperature, until the two temperatures are equal.