= 2.45 As shown in Fig. P2.45, an oven wall consists of a 0.25- in.-thick layer of steel (KS 8.7 Btu/h ft R) and a layer of brick (kb = 0.42 Btu/h ft R). At steady state, a temperature decrease of 1.2F occurs over the steel layer. The inner temperature of the steel layer is 540F If the temperature of the outer surface of the brick must be no greater than 105F determine the minimum thickness of brick, in in., that ensures this limit is met. T = 540F AT=-1.2F Steel- Brick Ls = 0.25 in.k Lb Fig. P2.45 To 105F