Thermodynamics HW Solutions 43

Thermodynamics HW Solutions 43 - Chapter 1 Basics of Heat...

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Chapter 1 Basics of Heat Transfer 1-87E A 200-ft long section of a steam pipe passes through an open space at a specified temperature. The rate of heat loss from the steam pipe and the annual cost of this energy lost are to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer by radiation is disregarded. 3 The convection heat transfer coefficient is constant and uniform over the surface. Analysis ( a ) The rate of heat loss from the steam pipe is D =4 in 280 ° F L=200 ft Q Air,50 ° F 2 ft 4 . 209 ft) 200 ( ft) 12 / 4 ( = = = ππ DL A s Btu/h 289,000 = F ) 50 280 )( ft 4 . 209 ( F) . Btu/h.ft 6 ( ) ( 2 2 pipe ° ° = = air s s T T hA Q & ( b ) The amount of heat loss per year is QQ t == × = × & (, . Δ 289 000 2532 10 9 Btu / h)(365 24 h / yr) Btu / yr The amount of gas consumption per year in the furnace that has an efficiency of 86% is therms/yr 438 , 29 Btu 100,000 therm 1 86 . 0 Btu/yr 10 532 . 2 Loss Energy Annual 9 = × = Then the annual cost of the energy lost becomes Energy cost Annual energy loss)(Unit cost of energy) = (29,438 therms / yr) therm) = = ( ($0. / 58 $17,074 / yr 1-88 A 4-m diameter spherical tank filled with liquid nitrogen at 1 atm and -196 ° C is exposed to
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This note was uploaded on 01/14/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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