Question

The metabolic energy generated in the person is 3.8x10⁶ J in a 6 hour period, and this is balanced by cooling of the body by 2.6 L of perspiration and radiative cooling (you can neglect conductive and convection cooling). What is the effective surface area of the person?

Answer 1

The cooling in our body is mainly due to four processes. precipitation, conduction, convection and radiations .

If we neglect conduction and convection we are left with precipitation and radiation

Due to precipation :Evaporation of sweat from skin surface has a cooling effect due to latent heat of vaporisation .  

Given that precipitation in form if sweat is 2.6L. So heat absorbed = 2.6* latent heat of vaporisation per kg

= 2 *2260 kiilo joule= 4520 KJ

Note for the student:: Which is clearly more than the heat absorbed by the body by the metabolism . ( i think u have mistakenly written 2.6 l in place of 2.6 ml or mistyped the unit of heat aborbed so i m neglection the effect of perspiration.. As in actual radiation alone is sufficient in the heat loss and contribution of perspiration is small.

solution of question taking only radiative cooling

using the basic principle of calorimetry:

Heat absorbed= heat loss by radiation