Thermodynamics HW Solutions 660

Thermodynamics HW Solutions 660 - A m& V 5 2 5 10 397...

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Chapter 8 Internal Forced Convection 8-47E Water is heated in a parabolic solar collector. The required length of parabolic collector and the surface temperature of the collector tube are to be determined. Assumptions 1 Steady operating conditions exist. 2 The thermal resistance of the tube is negligible. 3 The inner surfaces of the tube are smooth. Properties The properties of water at the average temperature of (55+200)/2 = 127.5 ° F are (Table A-9E) 368 . 3 Pr F Btu/lbm. 999 . 0 /s ft 10 5683 . 0 / F Btu/ft. 374 . 0 lbm/ft 59 . 61 2 5 - 3 = ° = × = ρ μ = υ ° = = ρ p C k Analysis The total rate of heat transfer is Btu/h 10 2.086 = Btu/s 4 . 579 F ) 55 200 )( F Btu/lbm. 999 . 0 )( lbm/s 4 ( ) ( 6 × = ° ° = = i e p T T C m Q Water 55 ° F 4 lbm/s 200 ° F (Inside glass tube) Solar absorption, 350 Btu/h.ft L D = 1.25 in The length of the tube required is ft 5960 = × = = Btu/h.ft 350 Btu/h 10 086 . 2 4 Q Q L total The velocity of water and the Reynolds number are ft/s 621 . 7 4 ) ft 12 / 25 . 1 ( ) lbm/m 59 . 61 ( lbm/s 4 2 3 = π = ρ = c m
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Unformatted text preview: A m & V 5 2 5 10 397 . 1 /s ft 10 5683 . ft) 12 m/s)(1.25/ (7.621 Re × = × = υ = − h m D V which is greater than 10,000. Therefore, we can assume fully developed turbulent flow in the entire tube, and determine the Nusselt number from 4 . 488 ) 368 . 3 ( ) 10 397 . 1 ( 023 . Pr Re 023 . 4 . 8 . 4 4 . 8 . = × = = = k hD Nu h The heat transfer coefficient is F . Btu/h.ft 1754 ) 4 . 488 ( ft 12 / 25 . 1 F Btu/h.ft. 374 . 2 ° = ° = = Nu D k h h The heat flux on the tube is 2 4 Btu/h.ft 1070 ) ft 5960 )( ft 12 / 25 . 1 ( Btu/h 10 086 . 2 = × = = π s A Q q & & Then the surface temperature of the tube at the exit becomes F 200.6 ° = ° ° = + = ⎯→ ⎯ − = F . Btu/h.ft 1754 Btu/h.ft 1070 + F 200 ) ( 2 2 h q T T T T h q e s e s & & 8-22...
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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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