Thermodynamics HW Solutions 678

Thermodynamics HW Solutions 678 - Chapter 8 Internal Forced...

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Chapter 8 Internal Forced Convection Properties The properties of water at the bulk mean fluid temperature of F 100 F 97 2 / ) 140 54 ( , ° ° = + = ave b T are (Table A-9E) 54 . 4 Pr F Btu/lbm. 999 . 0 /s ft 10 738 . 0 F Btu/h.ft. 363 . 0 lbm/ft 0 . 62 2 5 - 3 = ° = × = ° = = p C k υ ρ Analysis ( a ) The mass flow rate and the Reynolds number are ft/s 68 . 3 /4] ft) (0.75/12 )[ lbm/ft (62 lbm/s 7 . 0 2 3 = = = = π c m m c A m V V A m Water 54 ° F 0.7 lbm/s 140 ° F 250 ° F L D = 0.75 in 165 , 31 /s ft 10 738 . 0 ft) /12 ft/s)(0.75 (3.68 Re 2 5 = × = = h m D V which is greater than 4000. Therefore, the flow is turbulent and the entry lengths in this case are roughly in 5 . 7 in) 75 . 0 ( 10 10 = = D L L t h which is probably shorter than the total length of the pipe we will determine. Therefore, we can assume fully developed turbulent flow in the entire duct, and determine the Nusselt number from 8 . 165 ) 54 . 4 ( ) 165 , 31 ( 023 . 0 Pr Re 023 . 0 4
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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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