Chapter 3 Steady Heat Conduction 3-147 The U-value of a wall is given. A layer of face brick is added to the outside of a wall, leaving a 20-mm air space between the wall and the bricks. The new U-value of the wall and the rate of heat transfer through the wall is to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the wall is one-dimensional. 3 Thermal properties of the wall and the heat transfer coefficients are constant. Properties The U-value of a wall is given to be U = 2.25 W/m 2 . ° C. The R - values of 100-mm face brick and a 20-mm air space between the wall and the bricks various layers are 0.075 and 0.170 m 2 . ° C/W, respectively. Analysis The R-value of the existing wall for the winter conditions is RU existing wall existing wall 2 mC / W == = ⋅ ° 11 2 2 5 0 4 4 4//.. Noting that the added thermal resistances are in series, the overall R- value of the wall becomes C/W m 689. 0 170. 0 075. 0
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This note was uploaded on 01/19/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.