PHYSICS

posted by .

a.A person with skin area of 3 m2 is nude in a room of still air at 22 C.
i.Calculate the rate of conduction of heat loss in watts if the skin temperature is 28 C at a distance of 5 cm.

• PHYSICS -

recall that the rate of energy being transferred is given by:
q = -kA(dT/dx)
where
q = energy per unit time (in Watts)
k = thermal conductivity (W/m-K)
T = temperature (in Kelvin)
x = distance (in meters)
assuming steady-state heat transfer (meaning, at a particular location, the variable does not vary with time), the formula becomes:
q = -kA(T2 - T1)/(x2 - x1)
where subscripts 2 and 1 refer to final and initial values, respectively.
for air, k = 0.025 W/(m-K)
substituting,
q = -0.025*3*(22-28)/(0.05)
q = 0.0225 W
..this is the amount of heat that is being transferred from the skin to air at a distance of 0.05 meters.

*note that for change in temp, you may not convert Celsius to Kelvin since the conversion factor (which is, + 273) will just cancel each other, and answers will be the same:
in Kelvin: (22+273) - (28+273) = 22-28

hope this helps~ :)

• PHYSICS -

I have no idea what the 5 cm "distance" represents. You cannot assume that the heat is conducted through a 5 cm layer of air, with a linear temperature gradient in between. That is not what happens. This is a natural convection problem. There is a dimensionless equation involving a parameter called the "Grashof Number" that will allow you to estimate the natural convection heat loss. It should be find a reference to it online.

• PHYSICS -

For a discussion of how to perform a natural convection problem correctly, see
http://en.wikipedia.org/wiki/Natural_convection#Natural_Convection_from_a_Vertical_Plate

What you want to calculate, to estimate the heat transfer, is a Newtonian "film coefficient" h or a "Nusselt number" Nu. To do this will require calculating the Grashof number first.

You may get about the same answer as you would get assuming heat is concucted through a 5 cm layer of still air, but this would be a lucky coincidence.

Similar Questions

1. Physics

A person's body is covered with 1.4 m2 of wool clothing. The thickness of the wool is 1.3 10-3 m. The temperature at the outside surface of the wool is 14°C, and the skin temperature is 36°C. How much heat per second does the person …
2. SCIENCE

a.A person with skin area of 3 m2 is nude in a room of still air at 22 C. i.Calculate the rate of conduction of heat loss in watts if the skin temperature is 28 C at a distance of 5 cm.
3. PHYSICS

A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C .Calculate the heat loss rate in watts
4. PHYSICS

A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C .Calculate the heat loss rate in watts
5. physics

A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C. Calculate the heat loss rate if the skin temperature is raised by 8 C by …
6. physics

a. A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C Calculate the heat loss rate in watts
7. physics

a. A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C Calculate the heat loss rate in watts
8. physics

A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C. Calculate the heat loss rate if the skin temperature is raised by 8 C by …
9. physics

A person with skin area 2 m2 and 0.97 radiation efficiency is at rest and has a skin temperature of 28 C in an environment with a uniform temperature of 22 C. Calculate the heat loss rate if the skin temperature is raised by 8 C by …
10. Physics

The surface area of an adult human is about 1.8m2 . Suppose a person with a skin temperature of 34 ∘C is standing nude in a room where the air is 25∘C but the walls are 17 ∘C. A) There is a "dead-air" layer next to …

More Similar Questions