[Rabin]

A horizontal cylinder of length 4 m and diameter 1.5 m is half-filled with water. Water temperature is 45°C. The cylinder rotates at 1 rpm. Hot air with temperature of 60°C is blown at a velocity of 1.5 m/s through the cylinder. Assume the system to be isothermal. Both air and water are continuous fluids.



Water evaporates and the air carries the evaporated water with it. The task is to determine the amount of evaporated water.



How to set this system up in CFX? "Multiphase Flow in a Mixing Vessel" tutorial is similar, however some details are lacking.



While performing the transient simulation with homogeneous multiphase model and standard free surface model, mass imbalances occur and the simulation does not converge.



Is there any other better tutorial for this problem? How can this be solved?

[ghorrocks]

Your initial sentence is not consistent. You say there is water at 45C, air at 60C and the water will evaporate. But you say the system is isothermal. This is inconsistent, the process has temperature variations and evaporation is an inherently temperature varying process so you cannot model this isothermal.

Before you model this you need to have a good knowledge of the physics. The key issue here is the physics of the water evaporating. Do you know all the physical processes which are going to take place there? How do you intend to model it?

Please note that any multiphase model which involves phase change is not a simple model, and not for beginners. I don't know what your CFD experience level is, but modelling this will be challenging. If you are a beginner you should choose a more realistic simulation.

Finally - why model this with CFD? Why can't hand calculations of the evaporation rate based on the temperature difference be close enough? What will CFD tell you which a hand calculation won't?