heat loss insulated cylinder - Chemical Engineering...

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Chemical Engineering Problems October 29, 2016 1 Heat loss from an insulated pipe A standard schedule 40,2-in. steel pipe (inside diameter 2.067 in. and wall thickness 0.154 in.) carrying steam is insulated with 2 in. of 85% magnesia covered in turn with 2 in. of cork. Estimate the heat loss per hour per foot of pipe if the inner surface of the pipe is at 250 F and the outer surface of the cork is at 90 F. The thermal conductivities (in Btu/hr ft F) of the substances concerned are: steel, 26.1; 85% magnesia, 0.04; cork, 0.03. 2 Answer This is a very nice application of the problem of heat conduction through a composite wall, located between two fluid streams at temperatures T a , and T b . In this case T a = 250 F and T b = 90 F , the conductivity coefficients are K steel = K 01 = 26 . 1 Btu ft h F , K magnesia = K 12 = 0 . 04 Btu ft h F , K cork = K 23 = 0 . 03 Btu ft h F (1) and r steel = r 0 = 1 . 033 in = 0 . 086 ft, r 1 = 1 . 187 in = 0 . 099 ft, (2) r 2 = 3 . 187 in = 0 . 266 ft, r 3 = 5 . 187 in = 0 . 43 ft (3) we should apply Eq. (10.6-29) 1
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Q 0 = 2 π r 0 L q 0 = 2 π L ( T a - T b ) 1 r 0 h 0 + ln ( r 1 r 0 ) K 01 + ln ( r 2 r 1 ) K
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