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Thermosyphon not condensating

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Old   May 17, 2017, 05:50
Question Thermosyphon not condensating
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Robert Vizitiu
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Hello! I'm trying to simulate evaporation and condensation inside a closed cooper pipe using this tutorial :

The pipe is 50cm long with the external diameter of 1cm and internal 0.9cm. Inside I have 1/3 water and 2/3 air at 4000Pa, pressure wich I'm defining in the Initial conditions. The exterior of the pipe has 3 zones 1/3 evaporator, 1/3 adiabatic zone, 1/3 condenser.

I'm using the transient state, VOF model with 3 phases (implicit body forces checked), laminar turbulence with viscous heating.
The primary phase is vapour,secondary liquid, third air. For the phases interactions I'm using the evaporate-condensate model with a saturation temperature of 308K, and for the surface tension I've checked wall adhesion with a constante value of 0.07N/m.

For the boundry conditions I have used 1000W/m2 heat flux on the evaporator, 0 heat flux on the adiabatic zone and Convection with a heat transfer coefficient of 500w/m2-k with 293.15K as free stream temperature for the Condenser zone.

I have initialized the simulation, patched the volumes inside , (water-liquid and air) and used a variable time step so the Global courant number doesn't get ove 250.

I have run the simulation for about 12 hours and 22000 iterations and then I stopped it to check the results. A phase change occurs inside, the vapour and liquid mix in the bottom area, but the vapours doesn't seem to be rising. The maximum temperature inside the tube is about 303K.
I've also tried with higher heat fluxes, like 10000W/m2 applied to the evaporator, still the same temeperatures and results.

Does anyone know why does the temperature inside the tube does not get higher values?

P.S. I'm using Ansys 18 education software.

Last edited by robertvizitiu; May 17, 2017 at 07:23.
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evaporation condensation, vof phase change

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