Reference no: EM13320901

A cold room has walls constructed of 0.24 m brick on the outside, 0.15 m foam insulation in the middle and 1.6 cm of wood on the inside. The air temperature on the outside is constant at 20?C, and the room is to be maintained at a temperature of -6?C (minus 6?C). The convection heat transfer coefficient for air to brick is 15 W/m2 K, and for wood to air is 30 W/m2 K. The thermal conductivities of wood, foam insulation and brick are 0.15, 0.025, and 1 W/m K respectively.

(a) Determine the overall thermal resistance of the composite wall by the summation of the individual resistances and hence verify the overall heat transfer coefficient U = 0.155 W/m2 K completed to get final answer.

(b) Calculate the heat transfer rate per unit area of the wall surface.

(c) Calculate the outside and inside surface temperature of the composite wall.

(d) Calculate the interface temperatures, of (i) the wood and the foam insulation, and (ii) the insulation foam and the brick.

(e) Calculate the amount of energy (MJ) to be removed by refrigeration in a 24 hour period if the total wall area is 80 m2.

(f) Calculate the thickness of the foam layer required to maintain the inside and outside air temperatures given in the question if the thickness of the brick was reduced to 0.12 m and the heat transfer rate is unchanged.