One wall of a refrigerated warehouse is 10.0-m-high and 5.0-m-wide. The wall is made of three layers: 1.0-cm-thick aluminum (k 5 200 W/m·K), 8.0-cm-thick fibreglass (k = 0.038 W/m·K), and 3.0-cm thick gypsum board (k = 0.48 W/m·K). The warehouse inside and outside temperatures are 210°C and 20°C, respectively, and the average value of both inside and outside heat transfer coefficients is 40 W/m2 ·K. (a) Calculate the rate of heat transfer across the warehouse wall in steady operation.
(b) Suppose that 400 metal bolts (k = 43 W/m·K), each 2.0 cm in diameter and 12.0 cm long, are used to fasten (i.e., hold together) the three wall layers. Calculate the rate of heat transfer for the “bolted” wall.
(c) What is the percent change in the rate of heat transfer across the wall due to metal bolts?