CHEN 3005 Lecture 1: Recitation 10232014.pdf
25 Dec 2014
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Q = qa = ua(ta - tb) for a slab. Cylinder: as you move out, the area gets bigger and bigger. -> the u will become smaller and smaller constant just outside thingdoesn"t have to do with stuff in sum inner radius outer radius. Ex: a pipe containing steam @ 110 oc has inner diameter of 50 mm, outer diameter of 90 mm ksteel = 45 w/(mk) (better conductor) Insulation layer surrounding outside of pipe, thickness of insulation layer = 76 mm the insulation layer has thermal conductivity of kin = 0. 043 w/(mk) (worse conductor. Need heat transfer coefficient @ steam-steel interface h0 = 40 w/(m2k) (heat transfer coefficient is differenet from thermal conductivity --> different units) @ insulation-air interface h2 = 35 w/(m2k) What"s the heat loss rate per unit length? first, draw diagram h2 = 35 w/(m2k) kst = 45 w/(mk) h0 = 40 w/(m2k)
