A certain wall section is composed of a 12 in. by 12 in. brick area 4 in. thick. Surrounding the brick is a 36 in. by 36 in. concrete section, which is also 4 in. thick. The thermal conductivity of the brick is k = 0.086 lb/sec- F. For the concrete, k = 0.02 lb/sec-°F.
(a) Determine the thermal resistance of the wall section,
(b) Compute the heat flow rate through (1) the concrete, (2) the brick, and (3) the wall section if the temperature difference across the wall is 40°F.