A building wall 25 cm thick is built of bricks (thermal conductivity 0.90 W m⁻¹ K⁻¹)…
PHYSICS · Multi-part · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics
Problem
A building wall 25 cm thick is built of bricks (thermal conductivity 0.90 W m⁻¹ K⁻¹) but contains vertical wooden studs (thermal conductivity 0.12 W m⁻¹ K⁻¹) that extend from the inner to the outer surface. The studs occupy 15 % of the total cross-sectional area of the wall, the remainder being brick. The inner surface of the wall is at 35 °C and the outer surface is at 5 °C. Steady conditions prevail.
(i) Treating the bricks and studs as parallel paths for heat flow, compute the effective thermal conductivity of the wall.
(ii) Hence determine the heat loss per square metre of wall area.
(iii) Rank the brick and the wood in order of their insulating efficiency for this situation and justify your answer numerically.