Heat transfer between resistance and water

AI Thread Summary
The main mechanism of heat transfer between a thermal resistance and water is conduction, despite the presence of convection in the surrounding fluid. While copper is an excellent thermal conductor, the heat transfer from the solid surface of the resistance to the water occurs primarily through conduction at the interface. Convection plays a role in the overall heat transfer process, especially in the water, but it is not the primary mechanism between the solid and the liquid. The confusion arises from differing definitions of convection, which can include the effects of fluid motion and conduction together. Understanding this distinction clarifies why conduction is emphasized in the context of heat transfer from the resistance to the water.
Carcul
Messages
8
Reaction score
0
What is the *main* mechanism of heat transfer between a thermal resistance and water?

My doubt arose in the context of a problem (from a high school national test) dealing with the following situation: a 500 W thermal resistance made of copper is immersed in a jar containing 500 g of water at 20ºC, with the purpose of heating it to 90ºC, and then it is asked what is the principal mechanism of heat transfer between the resistance and the water.

Even being copper a very goog thermal conductor, we have here heat transfer between a fluid and a hot solid surface, so shouldn't it be mainly by convection? The correct answer is supposed to be "conduction", but I don't agree.
 
Physics news on Phys.org
Why do you say it is convection??

More importantly, why did you even consider convection? it never occurs in something where diffusion currents(of mass) cannot flow.
 
Now you have confused me. Why can't occur here mass transport of water? Isn't it a fluid??!
 
Carcul said:
Now you have confused me. Why can't occur here mass transport of water? Isn't it a fluid??!

Water is a fluid, and heat transfer in water takes place by convection, mostly.

But your question is, what is the method of heat transfer between a solid copper resistance and liquid water.. How can convection currents arise in solids and be transferred to liquids?? :wink:
 
Thank you very much for your help, I understand now what you meant. I guess my source of confusion is/was the way convection is defined in some books. For instance, in the book Thermodynamics, an engineering approach, from Çengel, we can read "Convection is the transfer of energy between a solid surface and the adjacent fluid that is in motion, and it involves the combined effects of conduction and fluid motion." This doesn't look like the explanation you have given, however.
 
Thread 'Motional EMF in Faraday disc, co-rotating magnet axial mean flux'
So here is the motional EMF formula. Now I understand the standard Faraday paradox that an axis symmetric field source (like a speaker motor ring magnet) has a magnetic field that is frame invariant under rotation around axis of symmetry. The field is static whether you rotate the magnet or not. So far so good. What puzzles me is this , there is a term average magnetic flux or "azimuthal mean" , this term describes the average magnetic field through the area swept by the rotating Faraday...
It may be shown from the equations of electromagnetism, by James Clerk Maxwell in the 1860’s, that the speed of light in the vacuum of free space is related to electric permittivity (ϵ) and magnetic permeability (μ) by the equation: c=1/√( μ ϵ ) . This value is a constant for the vacuum of free space and is independent of the motion of the observer. It was this fact, in part, that led Albert Einstein to Special Relativity.
Back
Top