Which of the following is the method of heat transfer that occurs mainly in liquids? Convection, Conduction, Infrared radiation, Diffusion, Advection.
We see that there’re two conditions to this question. One is that this method has to do with heat transfer and second that it occurs mainly in liquids. We can use these two conditions as filters for these five different terms to see which one is the best fit.
First, let’s consider heat transfer. Which of these five terms has to do with or involves heat transfer? When we look at the term diffusion, we know that it involves the general spreading out and mixing of substances. It doesn’t necessarily involve heat transfer. And so we’ll cancel that out as an option for our choice.
A similar thing happens with the term advection. Advection has to do with the transport of a substance by a large-scale motion. For example, imagine you had a number of particles of material submerged in water. If the water moved, say, by way of a large ocean current, then that motion of the surrounding medium would help to carry along these particles that are suspended in the water. This process involves motion. But it doesn’t involve the transfer of heat necessarily. So that’s not the method we want.
The three methods remaining all do involve heat transfer. So now we’ll apply our second condition that this method occurs mainly in liquids. When we consider heat transfer by conduction, this is when heat is transmitted by contact. It doesn’t involve the motion of any material. For example, if a hot object were in contact with a cold object, then heat would transfer from the hot to the cold. This transfer happens, though, between solid materials, not liquids. So conduction isn’t exactly the right term for this method.
Next, we can consider infrared radiation, the transfer of heat by electromagnetic means. An example of this would be some light moving through space and reaching Earth, transferring infrared energy that way. Note that this process need not involve liquids and generally does not. So that term also isn’t the method that we’re looking for.
This leaves us with one last option, convection. Convection describes the process where hot or less dense fluids rise up and cold or more dense fluids descend. This is a process that takes place in fluids, in the gases of the atmosphere, as well as the liquids of the ocean. This then is the term that describes heat transfer that occurs mainly in liquids.