Q3. A furnace wall consists of firebrick 440 mm thick. The surface heat transfer coefficients on the hot side and the cold side are 10 W/m2 K and 5 W/m2 K respectively. The hot gas temperature is 1500°C and the surrounding air is at a temperature of 25°C. The thermal conductivity of firebrick is 1.6 W/m K. To reduce heat loss, it is proposed that an outer layer of insulating brick of thermal conductivity 0.45 W/m K be added, but the temperature of the insulating brick must not exceed 850°C.
Determine EACH of the following:
(a) the rate of heat loss (per m2) without insulation; (5)
(b) the outside surface temperature without insulation; (3)
(c) the maximum permissible thickness of insulating brick; (5)
(d) the corresponding percentage reduction in heat loss. (3)
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