[oldisbest]

Hi, every one,

I have to simulate a gas-liquid flow in multi-port evaporator used for automotive HVAC system.

AS I found the latest ansys Fluent 12.1 has introduced a new mass transfer model named "Evaporation/condensation model", I set up my problem as follow:

Viscous model - Mixture, with consideration on slip velocity.
Bubble diameter - for Refrigerant 134a, about 0.1mm
Surface tension effect - constant, 0.01 N/m
Drag function - Default, S-N model
Mass transfer effect - liquid to gas, saturation temperature =8 deg C ,Frequence of Evaporation = 0.1(default)

Boundaries:
Inlet - velocity (Mass fraction of gas phase is about 10%)
Wall in Core area - Constant heat flux
Outlet - Pressure
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As I read the User guide, I found the new evaporation model is theoretically the same to UDF for mass transfer, while the default coefficient is still 0.1.

But the energy conservation is not considered in the new model.
That's because when evaporation happened, the quantity of latent heat needed is not known.

How can input heat be balanced by the evaporation?

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Since there is no heat transfer in the head pipes(tanks), I decide to set the inlet flow temperature to 7.99 deg C, which ensure no evaporation happened there.

Then I run the simulation, and get solution converged.
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In my results, the volume fraction seems ok, what most confused me is that inlet mass flow rate not equal to outlet one (a big difference, about 50%).

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So, what's my question are:
1. when use the new evaparation model in Ansys FLUENT 12.1, how to consider the energy conservation.
2. Why the mass not balanced between inlet and outlet while continuity equation is converged well? Where does the over mass come from?
3. Why the default coeff. is 0.1?
That mean when local temp. is higher than saturation temp., only 10% liquid flow will evaporate, is it true?

Your comments and advices are welcomed.
Thanks in advance.