Hello dear friends
What is the conditions that we can assume that we have thermally fully developed flow for both laminar and turbulent flows? I mean can we assume that we have thermally fully developed flow in transient flow with boundary condition that wall temperature varies with time and the place? If not what is the boundary condition that we can assume thermally fully developed flow for a transient situation.
Just consider the internal energy equation. For turbulent flow you should reach a statistically steady internal energy level.
The answer would be that we can not have thermally fully developed flow with a transient boundary condition of flux. Thats what i make out from the document shared by @ Ali Benhmidene .
Please discuss if you figured it out.
Regards
In a thermally fully developed flow, the temperature profile will no longer change along the length of flow, Similarly the velocity profile.It means that there is no further growth of boundary layer.Hence , the heat transfer coefficient will become constant.
If the flow is fully developed (Hydrodynamic and thermal),it means that steady state is reached .There will be no variation of the temperature with respect to time for the given constant heat flux.
Hence, in my view , We can not link transient situation for fully developed case (flow and thermal).
Transient case shall be considered for a developing flow where flow and thermal behavior need to be captured.
Steady condition is correct in the sense that all the pointwise variables have zero time derivative, a fact that can happens in laminar flows.
In turbulence, a fully developed flow is such when we have still an unsteady flow due to the fluctuations but it is statistically steady if an energy equilibrium is possible.
The question is unclear and Masoud needs to rephrase it in a way to understand what is exact flow configuration. Anyhow, the transient flow is undetermined and has no unique solution since it is sensitive to the boundary conditions, flow geometry, surface roughness among other factors. Therefore, fully developed conditions for transition is null. Moreover with conditions, as Masoud claimed, the wall temperature changes with time and space no specific fully developed flow conditions can be set.
Thank you dear all friends
For thermally developed flow we consider a temperature profile that is not changed along the path. In which conditions we can assume this? Can we assume thermally developed flow in an internal fluid flow with the boundary condition that is changed with the time? With your answers I think it is NO.
regards
Dissipation of mechanical energy, that is conversion of mechanical energy into thermal energy by viscous action, increases the temperature of the fluid as we progress downstream, not talking about boundary conditions. The flow can not be thermally developed in the sens that the temperature keeps the same profile downstream,
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