Your task Is to evaluate the effects of hair and hats on the rate of heat loss f
ID: 1717750 • Letter: Y
Question
Your task Is to evaluate the effects of hair and hats on the rate of heat loss from a persons head. Model the head as a hemisphere with D=9inches. Model hair as a covering of thickness between zero and 2 inches with thermal conductivity between 0.02 and 0.2W/mK. Model a hat as a covering of thickness varying between zero and 1 inch with thermal conductivity varying between 0.01 and 0.1W/mK. Make the appropriate comparisons and plot your results. It the convective heat transfer cofficient vary between 5 and 50 w/m^2 degree K Let the skin temperature be 35 degree C and the surrounding air temperature be 10 degree CExplanation / Answer
Given : Thickness of hat = 1 inch
thermal conductivity between hat = 0.55
radius of head r =4.5"
radius of hat r1 =6"
radius of outer hat r2= 7"
R =RESISTANCE =1/2xpiexL [1/K1 ln(r1/r0 )+1/k2ln(r2/r1)+1/hr2}
=1/2x3.14x1(1/0.11ln(6/4.5)+1/0.55ln(7/6)+1/27.5x7)
heat loss=Q= T1 - T2 /R
Q= 35-10 / 0.75
= 25 / 0.75
= 33.33 KW
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