Boiler tubes exposed to the products of coal combustion in a power plant are subject to fouling by the ash (min- eral) content of the combustion gas. The ash forms a solid deposit on the tube outer surface, which reduces heat transfer to a pressurized water/steam mixture flowing through the tubes. Consider a thin-walled boiler tube (Dt = 0.05 m) whose surface is maintained at Tt = 600 K by the boiling process. Combustion gases flowing over the tube at Too = 1800 K provide a convection coefficient of h = 100 W/m2 · K, while radiation from the gas and boiler walls to the tube may be approximated as that originating from large surroundings at Tsur = 1500 K.
Explore the effect of variations in Dd and h on q', as well as on relative contributions of convection and radiation to the net heat transfer rate. Represent your results graphically.