Chapter 8, Problem 8.42P

Atmospheric air enters a $\text{1}0-\text{m}$ -long. $\text{15}0-\text{mm}$ -diameter uninsulated heating duct at $\text{6}0°\text{C}$ and $0.0\text{4 kg}/\text{s}$ . The duct surface temperature is approximately constant at $T_s=15$ °C.

(a) What are the outlet air temperature, the heat rate q. and pressure drop $\Delta p$ for these conditions?

(b) To illustrate the tradeoff between heat transfer rate and pressure drop considerations, calculate q and $\Delta p$ for diameters in the range from 0.1 to 0.2 m. In your analysis, maintain the total surface area, $A_s=\pi DL$ , at the value computed for pan (a). Plot q. p. and L as a function of the duct diameter.