Chapter 8, Problem 8.84P

A device that recovers heat from high-temperature combustion products involves passing the combustion gas between parallel plates, each of which is maintained at $\text{35}0\text{ K}$ by water flow on the opposite surface. The plate separation is $\text{4}0\text{ mm}$ , and the gas flow is fully developed. The gas may be assumed to have the properties of atmospheric air, and its mean temperature and velocity are $\text{1}000\text{ K}$ and $\text{6}0\text{ m}/\text{s}$ . respectively.

(a) What is the heat flux at the plate surface?

(b) If a third plate, $\text{2}0\text{ mm}$ thick, is suspended midway between the original plates, what is the surface heat flux for the original plates? Assume the temperature and flow rate of the gas w be unchanged and radiation effects to be negligible.