Heat transfer between resistance and water

1. May 31, 2012

Carcul

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.

2. May 31, 2012

Infinitum

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.

3. May 31, 2012

Carcul

Now you have confused me. Why can't occur here mass transport of water? Isn't it a fluid??!

4. May 31, 2012

Infinitum

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??

5. Jun 9, 2012

Carcul

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.

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