Chapter 4, Problem 4.92P

Consider the system of Problem 4.54. The interior surface is exposed to hot gases at 3500C with a convection coefficient of $100{\text{W/m}}^{\text{2}}\cdot \text{K,}$ while the exterior surface experiences convection with air at 250C and a convection coefficient of $5{\text{W/m}}^{\text{2}}\cdot \text{K}\text{.}$

1. Using a grid spacing of 75 mm, calculate the temperature field within the system and determine the heat loss per unit length by convection from the outer surface of the flue to the air. Compare this result with the heat gained by convection from the hot gases to the air.
2. Determine the effect of grid spacing on the temperature field and heat loss per unit length to the air. Specifically. consider a grid spacing of 25 mm and plot appropriately spaced isotherms on a schematic of the system. Explore the effect of changes in the convection coefficients on the temperature field and heat loss.