Thermodynamics HW Solutions 771

Thermodynamics HW Solutions 771 - Chapter 9 Natural...

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Chapter 9 Natural Convection 9-102 A solar collector consists of a horizontal tube enclosed in a concentric thin glass tube is considered. The pump circulating the water fails. The temperature of the aluminum tube when equilibrium is established is to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. Properties The properties of air at 1 atm and the anticipated film temperature of ( T s + T )/2 = (33+30)/2 = 31.5 ° C are (Table A-15) D o =7 cm D i =4 cm, ε = 1 Air T = 30 ° C Air space ε = 1 20 W/m 1 - 2 5 K 003284 . 0 K ) 273 5 . 31 ( 1 1 7278 . 0 Pr /s m 10 622 . 1 C W/m. 02599 . 0 = + = = = × = ° = f T k β υ Analysis This problem involves heat transfer from the aluminum tube to the glass cover, and from the outer surface of the glass cover to the surrounding ambient air. When steady operation is reached, these two heat transfers will be equal to the rate of heat gain. That is, && & QQ Q tube glass glass ambient solar gain −− == = W (per meter length) 20
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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