12.6-1. Insulation Needed for Food Cold Storage Room. A food cold storage room is to be constructed of an inner layer of 19.1 mm of pine, a middle layer of cork board, and an outer layer of 50.8 mm of concrete. The inside wall surface temperature is -178°C and the outside surface temperature is 29.4°C at the outer concrete surface. The mean conductivities are for pine, 0.151; cork, 0.0433; and concrete, 0.762 W/m K. The total inside surface area of the room to use in the calculation is approximately 39 m2 (neglecting corner and end effects). What thickness of cork board is needed to keen the heat loss to 586 W?
Write the expression of heat loss.
dT RR,R dT q dx dx dx, Ak, Ak, Ak dT 1 d,dx,dxe A k A (T-T) dx2 ds dd kg ky
Substitute the known value...
39 m2[29.4°C-(7.8°C)] 586 W 0.0191 m 0.0508 m 0.151 W/m K 0.0433 W/m K 0.762 W/m -K 1840.8 586 dx 0.1265 0.0667 0.0433 dx 0.1932 3.1413 0.0433 dx2 = 2.9481 0.0433 dx, = 0.128 m
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