# Heat Flow Rate

on . Posted in Thermodynamics

Heat flow rate, abbreviated as $$Q_f$$, is a measure of the amount of heat energy transferred or conducted through a material or system per unit of time.  It represents the rate at which thermal energy is moving from one region to another.  Heat flow rate can be important in various applications and fields, including physics, engineering, and environmental science.  It is used to quantify heat transfer in systems such as heat exchangers, buildings, electronic devices, and many other situations where understanding and controlling heat transfer is essential.

### Heat Flow Rate FORMULA

$$Q_f = -k \; ( A \;/\; l )\; \Delta T$$
Symbol English Metric
$$Q_f$$ = heat flow rate $$Btu\;/\;hr$$ $$W$$
$$k$$ or $$\lambda$$   (Greek symbol lambda) = thermal conductivity $$Btu-ft\;/\;hr-ft^2-F$$

$$W\;/\;m-K$$

$$A$$ = area of emitting body $$ft^2$$ $$m^2$$
$$l$$ = length of material $$ft$$ $$m$$
$$\Delta T$$ = temperature differential  ($$T_1 - T_2$$) $$F$$ $$K$$
$$T_1$$ = temperature of one surface of the wall $$F$$ $$K$$
$$T_2$$ = temperature of the other surface of the wall $$F$$ $$K$$