The thermal conductivities of human tissues vary greatly. Fat and skin have cond

Question

The thermal conductivities of human tissues vary greatly. Fat and skin have conductivities of about 0.20 W/m · K and 0.020 W/m · K respectively, while other tissues inside the body have conductivities of about 0.50 W/m · K. Assume that between the core region of the body and the skin surface lies a skin layer of 1.0 mm, fat layer of 0.50 cm, and 3.2 cm of other tissues. (a) Find the R-factor for each of these layers, and the equivalent R-factor for all layers taken together, retaining two digits. Rskin m2 · K/W Rfat m2 · K/W Rtissue m2 · K/W R m2 · K/W (b) Find the rate of energy loss when the core temperature is 37°C and the exterior temperature is 0°C. Assume that both a protective layer of clothing and an insulating layer of unmoving air are absent, and a body area of 2.0 m2. W

Explanation / Answer

the equation to find R in L/K

so you have

Rskin=Lskin/Kskin

=0.001m/0.02W/MK

=0.05

Rfat=0.005m/0.2W/MK

=0.025

Rtissure=0.032m/0.5W/MK

=0.064

then R=Rtotal=Rskin+Rfat+Rtissure

=0.139.

(B) A(Thot-Tcold)/Rtotal

=2m^2(37 kelvin)/0.139

=532.37W.

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