Like many kinds of homespun advice, this is bad advice. Alltypesof heat transfer;conductio4 convection, and radiation vary directlywith area. The surface area of thehead is much less than that ofthe other portion of the body and thus will lose less heat.This maybe shown experimentally by comparing expozure in cold weatherwearingheavy clothing and no hat, to that wearing a heavy hat andonly undergarments!
heat transfer solutions manual j.p.holman 9th edition.35
2-764 = total efficiency A/ = surface area of all fins 4f =ftnefficiencyA = total heat transfer area including fins andexposed tube or other surface.7O = base temp L = environmenttempQact = h(A- Ay)Qo - ?i) + rUAyhQs - T*){idear = lxAQo-L)a, = P-
Tube surface area = (t05.3)z(0.025x9.5 - 0.8)(10-3) = 0.0719m2Tube heat transfer = (l10X0.0719)(20O- 93) = 846.6 W-!l- =1o.aT(2)z(1 10X o.o2542 - o.onsz )e00 - 93) = 3 1 .46 *finTotal finheat transfer = (31.46)(105.3) = 3312 WTotal heat transfer=846.6+3312 = 4159 W2-79r t= l .0cm Z=5mm t=2 .5mm h=25 TO=26O"CT*=93oC k = 43 Lc = 5+1.25 = 6.25 mm e,c =1.625 cmfu-=1.62s A, =(0.0025X0.m625) = 1.56x10-5 m211
" \k4' )4,r = o.g5A - 4*r4S.4.*a(triang) = 2(4.32 + 0.1521rt2 =8.6 = 0.086 m2Aud4(triangle) = (0.086X0.85) = 0.073 1.4.u64(rect) =(0.043X0.96) = 0.04 I 3Triangle fin produces morc heat transfer forgiven weight.
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