As shown in Fig. P2.45, an oven wall consists of a 0.25-in-thick layer of steel (ks = 8.7Btu/h ∙ft∙ oR) and a layer of thick (kb = 0.42Btu/h ∙ ft ∙ oR). At steady state, a temperature decrease of 1.2oF occurs over the steel layer. The inner temperature of the steel layer is 540oF occurs over the steel layer. The inner temperature of the steel layer is 540°F. If the temperature of the outer surface of the brick must be no greater than 105°F, determine the minimum thickness of brick, in that ensures this limit is met.

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Steel Brick 1, = 540 F T,s 105 F AT = -1.2°F L=0.25 im-