How could we calculate the "X" thermodynamic quality, In order to make a comparison of critical heat flux correlation results with those mentioned in the 2006 CHF look up table .
The thermodynamic quality is defined by the enthalpy from the following expression:
x=(h - h_l,sat)/(h_v,sat - h_l,sat)
where h [J/kg] is the vapor/liquid mixture enthalpy, h_l,sat is the liquid enthalpy at saturation temperature, and h_v,sat is the vapor enthalpy at saturation tempreature. x is the thermodynamic quality, and can in principle be negative and larger than unity. However, for an equilibrion two-phase mixture x will be between zero and unity.
https://www.sciencedirect.com/search?qs=thermodynamic%20quality%20in%20the%20Look%20Up%20Table&show=25&sortBy=relevance
https://www.sciencedirect.com/science/article/pii/S0029549317301371
To complement Erling answer which is the right answer, the evaluation of 'local' enthalpy (noted 'h' in Erling's answer) is required. This enthalpy is calculated using the'enthalpy balance' as
h= he+P/m with he the inlet enthalpy (calculated with the temperature and pressure at inlet), P is the power provided to the system (W) and m is the flow rate (kg/s).
As the LUT values are relative to tubes of diameter D, you can calculate m using the mass velocity G (in kg/m² s) which is also one of the variable in the LUT (m=G*pi*D²/4).
LUT is not the easiest way to evaluate CHF, main interest is its very large range of parameters (PGX). For use in not 'extended' range, some general correlations (e.g. Biasi) may be used.
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