1. Consider the conditions of Example 9.3, including the effect of adding insulation of thickness t and thermal conductivity k = 0.035 W/m · K to the duct. We wish to now include the effect of radiation on the outer sur- face temperatures and the total heat loss per unit length of duct.
(a) If Ts,1 = 45°C, t = 25 mm, s = 1, and Tsur = 288 K, what are the temperatures of the side, top, and bot- tom surfaces? What are the corresponding heat losses per unit length of duct?
(b) For the top surface, compute and plot Ts,2 and q' as a function of insulation thickness for 0 t 50 mm. The exposed duct surface (t = 0) may also be assumed to have an emissivity of s = 1.
2. An electrical heater in the form of a horizontal disk of 400-mm diameter is used to heat the bottom of a tank filled with engine oil at a temperature of 5°C. Calculate the power required to maintain the heater surface tem- perature at 70°C.