A 10-in-thick, 30-ft-long, and 10-ft-high wall is to be constructed using 9-in-long solid bricks (k = 0.40 Btu/h·ft·°F) of cross section 7 in × 7 in, or identical size bricks with nine square air holes (k = 0.015 Btu/h·ft·°F) that are 9 in long and have a cross section of 1.5 in × 1.5 in. There is a 0.5-in-thick plaster layer (k = 0.10 Btu/h·ft·°F) between two adjacent bricks on all four sides and on both sides of the wall. The house is maintained at 80°F and the ambient temperature outside is 30°F. Taking the heat transfer coefficients at the inner and outer surfaces of the wall to be 1.5 and 4 Btu/h·ft²·°F, respectively, determine the rate of heat transfer through the wall constructed of

(a) Solid bricks

(b) Bricks with air holes.

Transcribed Image Text:

0.5 in 7 in 0.5 in Brick Air channels 1.5 in x 1.5 in x 9 in Plaster 0.5 in in9 in 0.5 i in - →