# Heat Flow Rate

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Heat flow rate, abbreviated as $$Q_f$$, 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

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

### Where:

$$\large{ Q_f }$$ = heat flow rate

$$\large{ A }$$ = area of emitting body

$$\large{ l }$$ = length of material

$$\large{ \Delta T }$$ = temperature differential

$$\large{ k }$$ or $$\large{ \lambda }$$   (Greek symbol lambda) = thermal conductivity