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-   -   Efficient thermal conductivity for horizontal layer cooled both from top and bottom (https://www.cfd-online.com/Forums/main/130623-efficient-thermal-conductivity-horizontal-layer-cooled-both-top-bottom.html)

nickvinn March 1, 2014 13:14

Efficient thermal conductivity for horizontal layer cooled both from top and bottom
 
I'm trying to simulate cooling of horizontal water layer with heat fluxes specified at top and bottom with a simple engineering model of 1D thermal conduction equation. So, I need an empirical expression for efficient thermal conductivity coefficient. I suppose, it is different for the upper sublayer with unsteady stratification (temperature has maximum at some depth) and for the lower stably-stratified sublayer. I tried using molecular heat conductivity for the lower sublayer and the standard Nusselt-Rayleigh relation for two horizontal plates for the upper one, but the result was unsatisfactory. I guess, this is because there is penetrative convection in the lower sublayer, since the bound between the sublayers is fluid, not a wall. Has anybody encountered relations for efficient thermal conductivity or Nusselt number in such configuration?


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