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/W02274.0C)2040(C/W02274.00.23876)12.0/ln(03079.0C)20235(333insulationo,22insulationtotal,21insulation°°−=°⎟⎟⎠⎞⎜⎜⎝⎛++°−→−=−=∞∞∞DDDRTTRTTQ&whose solution is cm2.22===⎯→⎯=212-16.442-thicknessm1644.0233DDD3-173 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. Assumptions1Heat 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. 3The combined heat transfer coefficient is constant and uniform over the entire surface.
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