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Example 1.14: Conduction and convection through a furnace wall The inner surface of a 23 cm brick furnace wall is kept at 820C, while the temperature of the outer surface is 180C a) Calculate the heat loss from the furnace, given a thermal conductivity of the brick of 0.865 W.m'.K. b) A further 23 cm is added to the furnace wall, consisting of insulating brick with a thermal conductivity of 0.26W.m'.K! Calculate the reduction in the heat loss, and the maximum temperature to which the insulating brick is exposed. Assume that the inner temperature remains at 820C. The temperature of the surrounding air is 20C. c) Re-calculate the heat loss and the maximum temperature to which the insulating is exposed, but allow for a convective heat transfer coefficient on the outer surface of 11.9 W.mK! Assume that the inner temperature remains at 820C, and the temperature of the surrounding air is 20C. d) How do the answers compare when convection is included? Solution