Question

A runner moves along the road at $2m{s}^{-1}$ in still air that is at a temperature of ${29}^{\circ }C$. His surface area is $1.4m^2$, of which approximately $85\%$ is exposed to the air. Coefficient of convection for dry air and bare skin at wind speed $2m{s}^{-1}$ is $22W{m}^{-2}{}^{\circ }{C}^{-1}$. The rate of convective heat loss from his skin at a temperature ${35}^{0}C$ to the outside air is :

• A. $10W$
• B. $20W$
• C. $30W$
• D. $160W$

Answer 1

The correct option is D $160W$

Area exposed $=85\%$ of $1.4$ $=1.19m^2$
Power $=$ coefficient of convection $\times$ area $\times$ temperature difference
$=22\times 1.19\times 6=157$