Heat Transfer - Conduction and Radiation

In summary, when an animal with a core body temperature of 37oC and a skin temperature of 34oC is in an environment with an air temperature of 25oC, a decrease in skin temperature will lead to an increase in the rate of heat transfer via conduction through body tissue, but a decrease in the rate of heat loss via radiation. This is due to the principle of energy conservation, where heat must be transferred away from the outer skin surface at the same rate as it arrives there. Therefore, changes in one form of heat transfer will affect the other in order to maintain a stable equilibrium skin temperature.
  • #1
sinthreck
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Homework Statement


An animal has a core body temperature of 37oC and a skin temperature of 34oC while in surrounding of an air temperature of 25oC. If the skin temperature fell, what would happen to:
(i) the rate of heat transfer via conduction through body tissue?
(ii) the rate of heat loss via radiation

Homework Equations



Q = h * A * [change in temp]

Qnet = e * (boltzsman) * (Tsurface4 - Tenvironment4)

The Attempt at a Solution



(i) the rate of transfer due to conduction will increase because the change in temperature has increased. e.g. (37 - 30) > (37 -34)

(ii) the rate of transfer due to radiation will decrease because the Tsurface4 has decreased.

Whilst my solution seems ok, doesn't the heat transfer need to be conserved?

ie. my textbook says the following:
" Heat must be transferred away from the outer surface at the same rate as it arrives there"

So I take this to mean, if one increases the other must increase and vice versa, If one decreases, the other must decrease.

With my solution, I have conduction increasing but radiation decreasing...
 
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  • #2
Solution looks good to me. And I agree with your argument about energy conservation; in fact, that's why skin temperature is maintained at an equilibrium level that remains stable unless one of the other parameters changes also.
 

1. What is heat transfer conduction and how does it work?

Conduction is the transfer of heat from one object to another through direct contact. It occurs when two objects with different temperatures are in contact with each other and the heat energy flows from the hotter object to the colder one until they reach thermal equilibrium.

2. What is the difference between conduction and radiation?

Conduction involves the transfer of heat through direct physical contact, while radiation is the transfer of heat through electromagnetic waves without the need for physical contact. Conduction is more efficient at transferring heat in solids, while radiation is more efficient in gases and vacuum.

3. How does the thermal conductivity of a material affect heat transfer by conduction?

The thermal conductivity of a material is a measure of how well it can conduct heat. Materials with high thermal conductivity, such as metals, are better at transferring heat by conduction compared to materials with low thermal conductivity, such as plastics. This is because the molecules in materials with high thermal conductivity are more closely packed, allowing for faster transfer of heat energy.

4. Can heat transfer by radiation occur in a vacuum?

Yes, heat transfer by radiation can occur in a vacuum. This is because radiation does not require a medium to transfer heat, unlike conduction and convection which require a solid, liquid, or gas. This is why the sun's heat can reach the Earth through the vacuum of space.

5. How does the color of an object affect heat transfer by radiation?

The color of an object affects heat transfer by radiation because different colors absorb and emit different amounts of heat. Darker colors, such as black, absorb more heat and are better at radiating heat compared to lighter colors, which reflect more heat. This is why black objects feel warmer in sunlight compared to white objects.

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