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Q2. An insulated container 3 m long, 2.4 m wide and 2.6 m high consists of an insulating layer of 200 mm thick cork placed between an inner layer of 5 mm thick aluminium and an outer layer of 5 mm thick steel.

The exposed surface of the aluminium is at -15ºC when the outside atmosphere is at +25ºC.

Calculate EACH of the following:

(a) The heat flow into the container per hour

(b) The interface temperatures between the cork and the steel

(c) the emissivity of the aluminium at -15ºC when the contents of the container are at -25ºC and the net emissive power from the aluminium is 15% of the value calculated in Q7(a).

Note: Thermal conductivity of aluminium = 205 W/mK

Thermal conductivity of cork = 0.04 W/mK

Thermal conductivity of steel = 54 W/mK

Outer surface heat transfer coefficient =13 W/m²K

Stefan-Boltzmann constant  = 56.7  kW/m²K⁴