Heat transfer between resistance and water

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Discussion Overview

The discussion revolves around the mechanisms of heat transfer between a thermal resistance made of copper and water, specifically addressing whether the primary mechanism is conduction or convection. The context includes a problem from a high school national test involving heating water from 20ºC to 90ºC using a 500 W thermal resistance.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that heat transfer should primarily occur by convection due to the presence of water as a fluid, despite copper being a good thermal conductor.
  • Another participant challenges this view, stating that convection cannot occur without mass transport and questions the reasoning behind considering convection in this scenario.
  • A third participant expresses confusion about the possibility of mass transport in water, affirming that it is indeed a fluid.
  • Further clarification is provided that while heat transfer in water typically involves convection, the specific question pertains to the transfer mechanism between the solid copper resistance and the liquid water.
  • A participant acknowledges the confusion stemming from different definitions of convection found in various textbooks, highlighting a discrepancy in understanding the concept.

Areas of Agreement / Disagreement

Participants express differing views on whether conduction or convection is the primary mechanism of heat transfer in this scenario, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations regarding the definitions of convection and conduction as presented in different sources, which may affect participants' understanding of the mechanisms involved in heat transfer.

Carcul
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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.
 
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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.
 

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