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-   -   total enthalpy variation in nonequilibrium steam (https://www.cfd-online.com/Forums/cfx/24434-total-enthalpy-variation-nonequilibrium-steam.html)

 Tim August 22, 2007 09:08

total enthalpy variation in nonequilibrium steam

Hi, I have to compute a steam flow through a nozzle using the nonequilibrium steam model (condensation occurs in the nozzle). The walls are adiabatic but the total enthalpy of the fluid varies on its way through the nozzle (h_tot,out is much higher than h_tot,in).

Is anyone familiar with this problem? Is there a physical explanation or does a numerical proplem occur?

p.s.: I'm sure that my mesh is accurate as I tested it with equilibrium steam.

 jakjak August 22, 2007 14:54

Re: total enthalpy variation in nonequilibrium ste

How much higher are we talking about here? Have you try running it in double precision? Also, I was just wondering what's the mass flux for each phase?

 Peter August 23, 2007 05:54

Re: total enthalpy variation in nonequilibrium ste

@ jakjak: thanks for your response

yes, I tried running double precision.

Total entahlpy remains constant in the convergent part of the nozzle. From the throat (nucleation zone) to the outlet (supersonic) total enthalpy increases (1,2%).

I used the method massFlowAve() to average h_tot at the inlet and the outlet.

Liquid mass fraction is zero at the inlet. The mass flow at the inlet is equal to the mass flow at the outlet (or did you mean interphase mass flux?).

 jakjak August 24, 2007 09:07

Re: total enthalpy variation in nonequilibrium ste

What you have described for the boundary conditions seem reasonable. As I understand, the total enthalpy includes static enthalpy and kinetic energy from the flow. Could the raises in total enthalpy be caused by flow acceleration?

What about the imbalance from the inlet to outlet ?

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