Thermodynamics HW Solutions 284

Thermodynamics HW Solutions 284 - Chapter 3 Steady Heat...

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Chapter 3 Steady Heat Conduction ( b ) The thickness of the insulation needed that would maintain the outer surface of the insulation at a maximum temperature of 40°C can be determined from C/W 02274 . 0 C ) 20 40 ( C/W 02274 . 0 0.23876 ) 12 . 0 / ln( 03079 . 0 C ) 20 235 ( 3 3 3 insulation o, 2 2 insulation total, 2 1 insulation ° ° = ° + + ° = = D D D R T T R T T Q whose solution is cm 2.22 = = = ⎯→ = 2 12 - 16.44 2 - thickness m 1644 . 0 2 3 3 D D D 3-173 A 6-m-diameter spherical tank filled with liquefied natural gas (LNG) at -160°C is exposed to ambient air. The time for the LNG temperature to rise to -150°C is to be determined. Assumptions 1 Heat transfer can be considered to be steady since the specified thermal conditions at the boundaries do not change with time significantly. 2 Heat transfer is one-dimensional since there is thermal symmetry about the midpoint. 3 Radiation is accounted for in the combined heat transfer coefficient.
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