Chapter 9, Problem 9.88P

To reduce heat losses, a horizontal rectangular duct that is $W=0.80\text{m}$ wide and $H=0.3\text{m}$ in high is encased in a metal radiation shield. The duct wall and shield are separated by an air gap of thickness $t=0.06\text{m}$ . For a duct wall temperature of $T_d=40°C$ and a shield temperature of $T_{\text{sh}}=20°C$ , determine the convection heat loss per unit length from the duct.