\(80^{\circ} \mathrm{C}\). Also, determine the convection heat transfer
coefficients at the beginning and at the end of the heating process.
1-133 It is well known that wind makes the cold air feel much colder as a
result of the wind chill effect that is due to the increase in the convection
heat transfer coefficient with increasing air velocity. The wind chill effect
is usually expressed in terms of the wind chill temperature (WCT), which is
the apparent temperature felt by exposed skin. For outdoor air temperature of
\(0^{\circ} \mathrm{C}\), for example, the wind chill temperature is \(-5^{\circ}
\mathrm{C}\) at \(20 \mathrm{~km} / \mathrm{h}\) winds and \(-9^{\circ}
\mathrm{C}\) at \(60 \mathrm{~km} / \mathrm{h}\) winds. That is, a person exposed
to \(0^{\circ} \mathrm{C}\) windy air at \(20 \mathrm{~km} / \mathrm{h}\) will
feel as cold as a person exposed to \(-5^{\circ} \mathrm{C}\) calm air (air
motion under \(5 \mathrm{~km} / \mathrm{h}\) ).
For heat transfer purposes, a standing man can be modeled as a 30 -cm-
diameter, 170-cm-long vertical cylinder with both the top and bottom surfaces
insulated and with the side surface at an average temperature of \(34^{\circ}
\mathrm{C}\). For a convection heat transfer coefficient of \(15 \mathrm{~W} /
\mathrm{m}^{2} \cdot \mathrm{K}\), determine the rate of heat loss from this
man by convection in still air at \(20^{\circ} \mathrm{C}\). What would your
answer be if the convection heat transfer coefficient is increased to \(30
\mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) as a result of winds? What is
the wind chill temperature in this case?
