The external wall of a small cabin consists of three layers in series per unit area…
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
The external wall of a small cabin consists of three layers in series per unit area as follows:
Layer 1: Brick, thickness 0.20m, thermal conductivity 0.80Wm−1K−1
Layer 2: Still air gap, thickness 0.020m, effective thermal conductivity 0.024Wm−1K−1
Layer 3: Wooden panel, thickness 0.015m, thermal conductivity 0.12Wm−1K−1
The inside surface of the wall is at 25∘C and the outside surface is at 5∘C.
(a) Derive an expression for the total thermal resistance per square metre of the three-layer wall.
(b) Using the data provided, calculate the heat current per square metre through the wall.
(c) If the air gap (Layer 2) were completely removed so that the brick is in direct contact with the wooden panel, calculate the new heat current per square metre and comment qualitatively on how the dominant heat transfer mechanism within the original air gap is affected.
(d) Suggest one practical modification of the wall that would further reduce heat loss, specifying which mode of heat transfer it is intended to suppress.