sun absorption, radiative transfer, and conve zain or loss from thermal radiation each hour ing to the equation 6.51 in Herman and an er skin)Eskin Askin (Tskin – Troom)
sun absorption, radiative transfer, and conve zain or loss from thermal radiation each hour ing to the equation 6.51 in Herman and an er skin)Eskin Askin (Tskin – Troom)
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Heat loss
Transcribed Image Text:Give step-by-step calculation and explanation
Consider a person sitting nude on a beach in Florida. On a sunny day, visible radiation energy from the
sun is absorbed by the person at a rate of 30 kcal/h or 34.9 W. The air temperature is a warm 30 °C and
the individual’s skin temperature is 32 °C. The effective body surface exposed to the sun is 0.9 m².
(Assume this same area for sun absorption, radiative transfer, and convective loss. Is this a good
assumption?)
a. Find the net energy gain or loss from thermal radiation each hour. (Assume thermal radiative
gain and loss according to the equation 6.51 in Herman and an emissivity of 1.)
-(4).
Equalion
(6.51)
- (40Tin)Eskin Aşkin (Tskin – Troom)
dt
= (4 x 5.67 x 10¬8 w/m²–K*
x (307 K)')€skin Askin (Tskin – Troom).
(6.52)
b. If there is a 4 m/s breeze, find the energy lost by convection each hour. (Use Eq. 6.61 with eq.
6.63.)
1
Equation
he(Tskin – Tair),
(6.61)
A
dt
he
10.45 – w + 10w0.5
(6.63)
-
c. If the individual’s metabolic rate is 80 kcal/h (93.0 W) and breathing accounts for a loss of 10
kcal/h (11.6 W), how much additional heat must be lost by evaporation to keep the body core
temperature constant?
d. How would you suggest that he loses this energy? Explain your answer clearly and convincingly.
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