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Thermodynamics HW Solutions 756

Thermodynamics HW Solutions 756 - = − = A A A Center of...

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Chapter 9 Natural Convection 9-89 The overall U-factor for a double-door type window is to be determined, and the result is to be compared to the value listed in Table 9-6. Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the window is one-dimensional. Properties The U-factors for the various sections of windows are given in Table 9-6. Analysis The areas of the window, the glazing, and the frame are 2 glazing window frame 2 glazing 2 window m 42 . 0 38 . 4 80 . 4 m 4.38 = m) m)(1.14 (1.92 2 width) Height ( 2 m 4.80 = m) m)(2.4 (2 width Height = = = = × × = = × = A A A A A The edge-of-glass region consists of a 6.5-cm wide band around the perimeter of the glazings, and the areas of the center and edge sections of the glazing are determined to be 2 center m .62 3 m) 13 . 0 14 . m)(1 13 . 0 92 . 1 ( 2 Width) Height ( 2 = = × = A 2 center glazing edge m .76 0 62 . 3 38 . 4 =
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Unformatted text preview: = − = A A A Center of glass Edge of glass Frame 2 m 1.92m 2.4 m 1.14 m 1.14 m The U-factor for the frame section is determined from Table 9-4 to be U frame = 2.8 W/m 2 . ° C. The U-factor for the center and edge sections are determined from Table 9-6 to be U center = 2.78 W/m 2 . ° C and U edge =3.40 W/m 2 . ° C. Then the overall U-factor of the entire window becomes C . W/m 2.88 2 ° = × + × + × = + + = 80 . 4 / ) 42 . 8 . 2 76 . 40 . 3 62 . 3 78 . 2 ( / ) ( window frame frame edge edge center center window A A U A U A U U Discussion The overall U-factor listed in Table 9-6 for the specified type of window is 2.86 W/m 2 . ° C, which is sufficiently close to the value obtained above. 9-79...
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