Heat Flow Rate

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Heat Flow Rate

Heat flow rate ( $$Q_f$$ ) is 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.

Heat Flow Rate FORMULA

$$heat \; flow \; rate \;=\; -\; thermal \; conductivity \;\; \left( \; \frac { area \; of \; body } { length \; of \; material } \; \right) \;\; temperature \; differential$$

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

Where:

$$Q_f$$ = heat flow rate

$$\lambda$$ (Greek symbol lambda) = thermal conductivity

$$A$$ = area of the emitting body

$$l$$ = length of the material

$$\Delta T$$ = temperature differential