Issue with Intro to heat transfer course

Hi Sir,

I was doing an Intro heat transfer course, I found some issues with an example which I am expanding below,

In video number 01 of the Intro heat transfer course the instructor explaining the conduction with the below example,

I think the example shown in the above image (highlighted in red box) for conduction is not correct because the fluid which is near to the bottom plate will move upward as it's having a high temperature the fluid which is near to the top plate will move downward as it's having low temperature and because of this thing fluid circulation begins and this type of heat transfer we referred as Natural convection right?

I request you to please check on this.


Thank you,

Abubakar khan

Comments

  • KremellaKremella Posts: 3,123Admin

    Hello,

    You are right about natural convection if the density of the gas is a function of temperature and if the gravitational vector is in the favorable direction (downward-pointing). We don't mention any of these details here and are simply assuming that there is no gravity and the density of the gas is constant. Under these conditions, conduction is the primary mode of heat transfer. I hope this helps.

    Karthik

  • AbubakarAbubakar Posts: 140Member

    Hi Sir,

    Just one follow-up question "As we have a temperature gradient the density can't be constant, right?"

  • KremellaKremella Posts: 3,123Admin

    Not necessarily. Density is a property of the material. Whether it is a strong or weak function of temperature depends on the fluid or solid material. Again, this is just to simplify and help understand the concept. But, I can see your point if the material were air and we had a favorable gravity vector for causing natural convection.

    Karthik

  • AbubakarAbubakar Posts: 140Member

    Understood @Kremella sir. Thanks for helping me.

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