# Heat Flow Rate

Written by Jerry Ratzlaff on . Posted in Thermodynamics

The rate at which heat moves from an area of higher temperature to an area of lower temperature.  Btu/hr (W/hr). Heat flow is generally used to quantify the rate of total heat gain or heat loss of a system.

## FORMULA

$$Q_t = -\lambda \left( \frac {A} {l} \right) { \left( \Delta T \right) }$$

Where:

$$Q_t$$ = heat transfer rate

$$\lambda$$ = thermal conductivity

$$A$$ = area of the emitting body

$$l$$ = length of the material

$$\Delta T$$ = temperature differential