I found an online calculator relating to convective heat transfer, but the calculator's description says it's for heat transfer between a solid surface and a moving fluid. However, the definitions I've read for convection say convection also applies to heat transfer between fluids.

Could the method used by this calculator be applied to heat transfer between non-solids? For example, what if you had heat transfer between the surface of a liquid and the air?

  • $\begingroup$ Just how would you have heat transfer between two fluids without the fluids mixing? Air is not a fluid - it is a gas. $\endgroup$
    – paparazzo
    Feb 10, 2016 at 2:17
  • 1
    $\begingroup$ Air is a fluid. The confusion is that what that website really means by "solid" is "fixed surface at a fixed temperature." All the convection happens in the fluid part of the "solid-fluid" case anyway. $\endgroup$
    – user10851
    Feb 10, 2016 at 2:19
  • $\begingroup$ As Chris pointed out, convection requires rotation, thus this generally requires a fluid (Note: fluid includes liquids and gases), whereas advection requires bulk flow... $\endgroup$ Feb 10, 2016 at 13:46
  • $\begingroup$ see also physics.stackexchange.com/q/62423/226902 and physics.stackexchange.com/q/497923/226902 $\endgroup$
    – Quillo
    Mar 28 at 10:44

1 Answer 1


The phenomenon of convective heat transfer occurs as a result of a combination of fluid deformation (movement) and conduction within the moving fluid. The fluid deformation physically brings hotter fluid into contact with cooler fluid to enhance the rate of conductive heat transfer between these regions. In many cases, this occurs in close vicinity to a boundary, and is modeled using a convective heat transfer coefficient to calculate the heat flux at the boundary. If there is a boundary between two fluids, and both fluids are moving/deforming/shearing, then there can be convective heat transfer on both sides of the boundary, within each of the fluids. In this type of situation, these is a convective heat transfer coefficient applicable to each side of the interface.


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