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Why does Conval require %vapour content and mol. wt of gas phase in liquid flashing valve to calculate Cv

Allgemeine Diskussion » Why does Conval require %vapour content and mol. wt of gas phase in liquid flashing valve to calculate Cv Posted: 26. Mai 2020 - 9:19

Whenever we do liquid sizing in conval and if flashing occurs, the software asks to enter %vapor content and molecular weight and the softwared does not calculates any Cv unless we provide this data. Why is it so? Is there no other way the software can calculate the flashing Cv on its own? The sizing softwares from other vendor does not asks for any such data and calculates the Cv. 

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Tim Steinbach

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Why does Conval require %vapour content and mol. wt of gas phase

Posted: 26.05.2020 - 11:08

Many thanks for your support request. To calculate the CV-value, the input of steam fraction and molar mass of the steam is not necessary. However, the critical pressure must be known because of choked flow during flashing. Steam fraction and molar mass of the steam are used to calculate the outlet velocity of the medium behind the valve. In case of high outlet velocities it may be necessary to adjust the nominal outlet diameter after the valve.