Question

Hot air at 80°C is blown over a 2-m by> on0 4-m flat surface at 30°C. If the average? convection heat transfer coefficient varies between 20 W/m2 °C and 100 W/m °C, draw a relation between the rate of heat transfer from the air to the 80°C Air 30°C plate.(nm kW) and the convection heat transfer coefficient

Answer 1

Explanation:

The given data is as follows.

       $T_{air} = 80 ^{o}C$,       $T_{surface} = 30 ^{o}C$

Area of the flat plate is 2 × 4 = 8 $m^{2}$.

Average convection heat transfer coefficient $(h_(avg))$ = $\frac{(20 + 100) W/m^{2} ^{o}C}{2}$ = $60 W/m^{2} ^{o}C}$.

Hence, formula to calculate heat transfer through convection from air to the water is given as follows.

                    q = $h_{avg} \times A_{surface} \times (T_{air} - T_{surface})$

                        = $60 W/m^{2} ^{o}C} \times 8 m^{2} \times [(80 - 30)]^{o}C$

                        = 24000 W

or,                     = 24 kW

Hence, the direction of heat flow is from air to the surface.

Thus, we can conclude that transfer of heat is 24 kW.