Thermodynamics HW Solutions 654

Thermodynamics HW - Chapter 8 Internal Forced Convection 8-43 Air enters the constant spacing between the glass cover and the plate of a solar

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Chapter 8 Internal Forced Convection 8-43 Air enters the constant spacing between the glass cover and the plate of a solar collector. The net rate of heat transfer and the temperature rise of air are to be determined. Assumptions 1 Steady operating conditions exist. 2 The inner surfaces of the spacing are smooth. 3 Air is an ideal gas with constant properties. 4 The local atmospheric pressure is 1 atm. Properties The properties of air at 1 atm and estimated average temperature of 35 ° C are (Table A-15) /s m 10 655 . 1 C W/m. 02625 . 0 kg/m 146 . 1 2 5 - 3 × = υ ° = = ρ k 7268 . 0 Pr C J/kg. 1007 = ° = p C Analysis Mass flow rate, cross sectional area, hydraulic diameter, mean velocity of air and the Reynolds number are Air 30 ° C 0.15 m 3 /min 60 ° C Collector plate (insulated) Glass cover 20 ° C kg/s 1719 . 0 ) /s m 15 . 0 )( kg/m 146 . 1 ( 3 3 = = = V m & & ρ A c == (1 m)(0.03 m) m 2 003 . D A P h c + = 4 4003 21 0 05825 (. . m) m m ) m 2 V V A m c = & . 015 5 m/ s 0.03 m m/s 3 2 606 , 17 /s m 10 655 . 1 m) 25 m/s)(0.058 (5 Re 2 5 = × = = υ h m D V which is greater than 10,000. Therefore, the flow is turbulent and the entry lengths in this case are roughly
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This note was uploaded on 01/22/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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