Chapter 1 Basics of Heat Transfer1-87EA 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. Assumptions1Steady operating conditions exist.2Heat 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 ftQ Air,50°F2ft4.209ft)200(ft)12/4(===ππDLAsBtu/h289,000=F)50280)(ft4.209(F).Btu/h.ft6()(22pipe°−°=−=airssTThAQ&(b) The amount of heat loss per year is QQt==×=×&(,.Δ289 0002532 109Btu / h)(365 24 h / yr)Btu / yrThe amount of gas consumption per year in the furnace that has an efficiency of 86% is therms/yr438,29Btu100,000therm186.0Btu/yr10532.2LossEnergy Annual9=⎟⎟⎠⎞⎜⎜⎝⎛×=Then the annual cost of the energy lost becomes Energy costAnnual energy loss)(Unit cost of energy)= (29,438 therms / yr)therm)==(($0./58$17,074 / yr1-88 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.