1. A composite Ivan is formed of a 2.5-cm copper plate, a 3.2-mm laver of
asbestos, and a 5-an layer offiberglass. The wall is subjected to an overall
temperature difference of 560sc. Calculate the heat-flow per unit area
through the composite structure. The thermal conductivities of copper.
asbestos and fiberglass am 386. 0.16 and 0.038117m “c respectively.
2. A wall 2 cm thick is to be constructed from material. which has an average
thermal conductivic• of 1.3 117m “c. The wan is to be insulated with material
having an average thermal conductivity of 0.35 117m °c. so that the heat lost
per square meter will not exceed 1830 W Assuming that the inner and outer
surface temperature of the insulation wall are 1300 and 30°c. Calculate the
thickness of insulation required.
3. One side of copper block S cm thick maintained at 260°c. The other side is
covered with a layer offiberglass 2.5 cm thick. The outside of the fiberglass
is maintained at 38°r. and the total heat flow through the copper-fiberglass
combination is 44 k11: nut is the area of the slab? The thermal
conductivities of copper and fiberglass are 386 and 0.038 117m K
4. A fiancee wall consists of 250 mm firebrick. 125 mm insulating brick, mud 250
mm building brick. The inside wall is at a temperature of 600″c and the
atmospheric temperature is 20″c. Calculate the heat loss per tn1 of wall
area and the temperature of the outside wall surface of the furnace. The
heat transfer coefficient for the outside surface is 10 117a and the
thermal conductivities of the firebrick. insulating brick and the building
brick are 1.4. 0.2 and 0.711’/m K. respectively.