A thin electrical heating element provides a uniform heat flux q;' to the outer surface of a duct through which air flows. The duct wall has a thickness of 10 mm and a thermal conductivity of 20 W/m . K.

(a) At a particular location, the air temperature is 30°C and the convection heat transfer coefficient between the air and inner surface of the duct is 100 W/m2 ∙ K. What heat flux q: is required to maintain the inner surface of the duct at Ti = 85°C?

(b) For the conditions of part (a), what is the temperature (To) of the duct surface next to the heater? With Ti = 85°C, compute and plot q"o and To as a function of the air-side convection coefficient h for the range 10 ≤ h ≤ 200 W/m2 ∙ K. Briefly discuss your results.

Transcribed Image Text:

Dụct Air Air T, Duct wall To Electrical heater Insulation