Thermodynamics HW Solutions 656

# Thermodynamics HW Solutions 656 - Chapter 8 Internal Forced...

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Chapter 8 Internal Forced Convection 8-44 Oil flows through a pipeline that passes through icy waters of a lake. The exit temperature of the oil and the rate of heat loss are to be determined. Assumptions 1 Steady operating conditions exist. 2 The surface temperature of the pipe is very nearly 0 ° C. 3 The thermal resistance of the pipe is negligible. 4 The inner surfaces of the pipeline are smooth. 5 The flow is hydrodynamically developed when the pipeline reaches the lake. Oil 10 ° C 0.5 m/s T e (Icy lake, 0 ° C) L = 300 m D = 0.4 m Properties The properties of oil at 10 ° C are (Table A-13) 28750 Pr C, J/kg. 1838 /s m 10 2591 kg/m.s, 325 . 2 C W/m. 146 . 0 , kg/m 5 . 893 2 6 - 3 = ° = × = υ = μ ° = = ρ p C k Analysis (a) The Reynolds number in this case is 19 . 77 /s m 10 2591 m) m/s)(0.4 (0.5 Re 2 6 = × = = υ h m D V which is less than 2300. Therefore, the flow is laminar, and the thermal entry length is roughly m 384 , 44 ) m 4 . 0 )( 28750 )( 19 . 77 ( 05 . 0 Pr Re 05 . 0 = = = D
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