Can heat transfer in air in a confined space be associated with conduction instead of convection if there is little movement of the fluid?

Simulation
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Hello

You should specify your request because you mention air and in the same sentence fluid movement.

So air as a gas  or as a fluid?

For convection, it is a transport of matter and it concerns fluids (liquid and gas) while for conduction it is a phenomenon called "from one step to the next". For example, the conduction takes place from a heating bar to a profile and then to a plate

For Flow simulation I let other people answer

Kind regards

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Unless we are in the case of an ultra-thin layer of air, I don't see how we could consider conduction instead of convection for a gas. And even in the case of the thin air layer, I'm not sure that the results can actually be comparable.

So I would tend to answer no to the question.

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Hello @loucas.iborra.22 ,

Even in a confined space, most heat transfer within an air volume is done by convection, static air being rather a good thermal insulator. Replacing convection with conduction will not give a satisfactory result, neither in the time domain with regard to the evolution of physical quantities, nor at the 3D level for the temperature or velocity fields within the fluid (especially since it would be considered static...).
The principle of heat exchange in the globalized form that you are considering is found in certain applications for estimating the performance of heating/insulation of buildings, and gives only a few average indications of temperature, or energy consumption. And such a "global" approach implies defining "equivalent" thermal coefficients, which can only be evaluated on the basis of an experiment or a simulation. And here we are back to square one.

There are a number of examples in flow and thermal with Flow Simulation on the web, but quite few in the particular case you are considering, of natural convection within an enclosed space. 3 relatively accessible links:
https://www.youtube.com/watch?v=d6T-dvi2znk
https://www.youtube.com/watch?v=1dfOOuwCDQQ
https://www.youtube.com/watch?v=hSEYBkgcmhA
The last one is quite brief and not very "industrial", but it describes the model of a heat transfer in natural convection in a closed domain...

It's hard to help you further without having more details about your study.

Kind regards.

 

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Thank you very much, you have already helped me a lot and put me on the track of what I can consider.