Hello, I'm currently researching the phase change of water as heat is applied to a surface. My work is comparable to the wallboiling tutorial (\multiphase\reactingTwoPhaseEulerFoam\RAS\wallBoiling). I understood we had to create separate thermophysical properties for water and steam, and that the phasepropeties file was used to describe the phase change, while Tsat in the phasepropeties file denoted the temperature at which the phase change occurred?
I have two doubts
1)Why is the velocity of steam defined in the same way as the velocity of liquid at the inlet? If I'm not mistaken, water enters at the inlet and is converted to steam once the temperature hits the saturation. This means that steam only emerges in the middle, where a significant temperature is reached, so why does the velocity have to be defined at the inlet?
2)Is it necessary to use 'mapped' patch at the inlet if the velocity has to be defined for both steam and water?
Dr. Ijaz Fazil
Dear Dr. Fazil,
The case that the tutorial is trying to validate is the DEBORA wall boiing experiments or a modified version of it. In the experiments you will see that it is the liquid phase enters the inlet and the flow is allowed to develop for some distance before the wall heat flux is applied. Now to answer your questions,
- Even though the inlet velcoity for the gaseous phase is specified, it wouldn't affect the simulation as at the inlet, the phase fraction of gas is set to 0. This would result in the actual flow rate of the gaseous phase to be 0 at all times at the inlet.
- The mapped patch is used to mimic the flow in the initial length of the geometry where the flow is allowed to develop over adiabatic walls. You can see from the blockMeshDict file that the inlet field is mapped from a distance 0.1 m axially away from the inlet. You can also check the allRun script which would say that the mapped condition is switched to fixedValue after 0.5 seconds. I'm assuming that's the time taken for the flow at the inlet in a mappedPatch geometry to match the flow at the start of the heated wall section in the full geometry.