An engineer considers two designs for a boundary wall of a warehouse having an…
PHYSICS · Multi-part · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics
Problem
An engineer considers two designs for a boundary wall of a warehouse having an exposed area of 10m2.
Design A: A single uniform concrete slab of thickness 12cm with thermal conductivity 1.1W m−1K−1.
Design B: Two concrete slabs each 5cm thick, separated by a stagnant air gap of thickness 2cm(kair=0.026W m−1K−1).
The indoor air temperature must be held at 20∘C while the outdoor temperature may reach 40∘C. Assume steady one-dimensional conduction and neglect surface resistances.
(i) For each design, calculate the heat flow rate through the wall when the temperature difference mentioned above prevails.
(ii) Which design is thermally more effective? Quantify the percentage reduction in heat loss obtained by the better design compared with the other.