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Old   April 8, 2020, 14:44
Default Evaporation
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Ileayo
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Dear all,


PLEASE I NEED HELP!!!


I am simulation evaporation in horizontal pipe.


Theoretically, the temperature difference (Twall - Tsat) should become constant after the flow attains steadiness.


In my own case, I could not get a stable constant temperature difference, the temperature difference keeps increasing as the simulation continues. This I experience with both the UDF and the inbuilt Evaporation-Condensation (Lee) model.



Surprisingly, I got a constant temperature difference after some time when the simulation attains steadiness with a reduced length (about x 0.1) the original length.


My boundary conditions are mass flow inlet, pressure outlet, heat flux wall boundary condition using SST k-w and VOF model.


Please kindly advise me sir and ma.


I will indeed appreciate your expert advice.


Thank you in anticipation.
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Old   April 9, 2020, 05:14
Default Constancy
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What is the reason for assuming that the temperature difference becomes constant. T_{wall} - T_{sat} can always be constant if user applies temperature at the wall and keep the pressure constant. However, if heat flux is applied at the wall, which is the case for you, it will keep on supplying heat to the system, i.e., system will keep on gaining the heat. If the pressure is constant and consequently the saturation temperature is constant, the wall temperature will keep on increasing in line with increase of fluid temperature. The profile may become constant but not the value.
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Old   April 12, 2020, 06:52
Default Temperature or heat flux wall boundary condition
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Hi Vinem,
Thank you for your reply. I am grateful. I actually thought that both temperature or heat flux wall boundary condition should give constant temperature difference after the flow attains steadiness.
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