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latent heat in vaporisation

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Old   March 28, 2011, 12:23
Default latent heat in vaporisation
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henry clarke
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I am trying to model flow boiling in liquid nitrogen using the eulerian model. I have defined a material for gaseous nirtogen (very similar to fluent database nitrogen properties) and a seperate one for liquid nitrogen (using temperature dependent polynomials to define most properties). I have been trying to model the phase change with the standard evaporation-condensation mass transfer model. I cannot see where the latent heat comes into this mass transfer, unless it is calculated from the difference between the standard state enthalpy of the two phases at the boiling point. This would be fine, except that when I change the standard state enthalpies, and the reference temperature in the fluid properties, fluent apparently takes no notice and continues to use some pre-defined values which result in a difference in enthalpy between phases of around 1200kJ/kg rather than 200kJ/kg. I know there are some oddities in the units to define these parameters (J/kgmol - very strange) but I have scaled accordingly, and even by changing these numbers randomly I cannot get the enthalpy shown on a contour plot post initialising (or running) to change.
Anybody else encountered this problem, or know where else latent heat is input into the evap-cond model?
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