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Q7. A spherical steel pressure vessel has an internal diameter of 1.5 m and a wall thickness of 20 mm. It is covered with two layers of insulation, each with 25 mm thick.

The inner surface temperature of the steel is 450℃ and the surrounding air temperature is 25℃.

Calculate EACH of the following:

(a) the heat loss from the pressure vessel per m² of surface area. (8)

(b) the temperature drops across EACH layer. (6)

(c) the outer surface temperature. (20)

Note :the heat transfer coefficient of the inner surface may be ignored.

the thermal conductivity of steel = 52  W⁄(m K)

the thermal conductivity of the inner insulation = 0.04  W⁄(m K)

the thermal conductivity of the outer insulation = 0.25  W⁄(m K)

the heat transfer coefficient of the outer surface = 2  W⁄(m²K)