Re: How does heat gain in animals by convection work (or is it possible)?

Thanks for the question, Peter.

It sounds like you've been misled a little bit by the dictionary's 
definition of "convection" and the instructor's lack of detail about the 
entire mechanism in this case.

Generally speaking, convection is heat transfer through the motion of a 
fluid. The heat can be transferred to or from anything, as long as the 
means of transport is some kind of fluid. By extension of this, anything 
could be heated or cooled by heat moving into or from that fluid.

As an example, let's look at the animal your professor mentioned. Let's 
say it's winter, and the air is very cold. If you look at the air 
immediately against the animal's body, the air molecules will come in 
contact with it and pick up some heat. As the air heats up the molecules 
move farther apart, making the air less dense. The less dense air rises 
away from the body, allowing cooler air to move in to pick up some more 
body heat and rise. The animal will become cooler because of the heat lost 
to the surrounding air. If the air did not move away continuously, the air 
and the animal's body would eventually reach an equilibrium and no more 
heat transfer would occur. As you can see, the heat in the animal's solid 
body warms the fluid it is in contact with, and then the fluid's motion 
carries the heat away through convective means.

Heat transfer can also go the other direction. If our animal is now out in 
the intense summer heat there's a good chance that the air is warmer than 
its body. As this warm air comes in contact with the surface of the 
animal's body it transfers the heat to the animal. The animal's body 
temperature will rise, and the temperature of the air immediately against 
the body will drop. As the air temperature goes down the molecules move 
closer together, the density of the air increases, and it sinks down and 
away from the animal. This will allow warmer air to move in from above and 
deposit its heat to the animal, as well. Again, though the animal's solid 
body is transferring heat from the air through direct contact, the heat is 
being carried to the body by the convective motion of the air.

The most accurate way for the professor to state what is happening would 
be "Heat is transferred between a solid body and a fluid through 
conduction, and the heat is then dispersed through the fluid by 
convection"; but since the fluid convection is the controlling mechanism 
in the whole process, it is simply treated as the sole action of 
convection.

I hope this is helpful!