assume that a man can be represented by a cylinder 350mm in diameter and 1.65 m in height with the surface temperature of 28 degrees c calculate the heat loss from the human body whicle standing in the wind at a velocity of 30 km/hr. and a temperature of 12 degrees c. take thermophysical properties of air at mean film temp

 To calculate the heat loss from a human body modeled as a cylinder under forced convection, we follow these steps:

1. Determine the mean film temperature:

   $$T_{\text{film}}=\frac{T_s+T_{\mathrm{\infty }}}{2}=\frac{28+12}{2}=20$$

2. Thermophysical properties of air at 20°C:

   • Thermal conductivity,

   • Kinematic viscosity, $\nu =1.516\times 10^{-5}{\text{m}}^2\mathrm{/}\text{s}$

   • Prandtl number, $Pr=0.713$

3. Convert wind speed to m/s:

   $$V=\frac{30\text{km/hr}\times 1000}{3600}=8.333\text{m/s}$$

4. Calculate Reynolds number (Re):

   $$Re=\frac{V\cdot D}{\nu }=\frac{8.333\times 0.35}{1.516\times 10^{-5}}\approx 192,385$$

5. Calculate Nusselt number using Churchill-Bernstein correlation:

   $$Nu=0.3+\frac{0.62\cdot R{e}^{1\mathrm{/}2}\cdot P{r}^{1\mathrm{/}3}}{{[1+{\left(\frac{0.4}{Pr}\right)}^{2\mathrm{/}3}]}^{1\mathrm{/}4}}\cdot {[1+{\left(\frac{Re}{282000}\right)}^{5\mathrm{/}8}]}^{4\mathrm{/}5}$$

   Substituting values:

   $$Nu\approx 340$$

6. Calculate convective heat transfer coefficient (h):

   $$h=\frac{Nu\cdot k}{D}$$

7. Calculate surface area (A) of the cylinder:

   $$A=2\pi rL=2\pi \cdot 0.175\cdot 1.65\approx 1.815{\text{m}}^2$$

8. Calculate heat loss (Q):

   $$Q=h\cdot A\cdot (T_s-T_{\mathrm{\infty }})=25\cdot 1.815\cdot 16\approx 726\text{W}$$

Final Answer

The heat loss from the human body is \boxed{726} watts.