Advanced XFlow file options

On the Settings tab, you can select which properties are to be saved to the XFlow file. On the Advanced tab, you can specify some further details on how to save the XFlow file.

If the Write Enthalpy box is checked, the overall enthalpy of the stream is saved in the XFlow file to allow the product stream of an XFlowLoader unit operation to be flashed at pressure and enthalpy. If enthalpy is saved, it is saved as a different with respect to a single phase enthalpy at mixture composition and a known pressure and temperature, so that the actual enthalpy state in the target stream can be reproduced irrespective of the enthalpy reference state of the source and target thermodynamic systems.

If the enthalpy reference state is set to Automatic, currently the only supported phase is the Vapor phase; the reference pressure is set to 1 atm; a pressure-vapor fraction flash is performed at a vapor fraction of 1, to determine a suitable temperature. Vapor is guaranteed to exist at this temperature.

The automatic reference state can be overridden by manually selecting a reference phase. The ideal vapor phase is not currently supported, as it is much less likely that the ideal gas enthalpy can be obtained at both the source and target thermodynamic system than it is to calculate enthalpy at both systems. If a custom reference state is selected, reference temperature and pressure must be specified.

Additional options

By default, the first entry in an XFlow file is a comment containing the time stamp, location, user name, computer name and executable name of the flowsheeting application that created the XFlow file. This can be suppressed by unticking the Write Creator Comment option.

Additional comments can also be suppressed, by unticking the Write Comments option.

By default, information about the present phases (name, aggregation state) is written to the XFlow file even if no properties are selected to store for the present phases. If you want all phase information to be suppressed in the XFlow file, make sure no phase properties are selected on the Settings tab, and untick the Write Phase Information box on the Advanced tab.

Recommended Auto Flash

As the XFlowSaver unit has access to all stream information, it is often better able to judge which properties are suitable for flashing the target stream than the XFlowLoader unit operation. To this end, by default, a flash recommendation will be written to the XFlow file. The flash recommendation is:

use a pressure-vapor fraction flash if there are multiple phases, a vapor phase is present and the vapor phase fraction is zero or unity. This indicates that the stream is at the phase boundary of the vapor phase, which is often the case for streams coming out of a unit operation that performs phase separations. Note that the pressure-vapor fraction flash recommendation will not be present if Vapor Fraction is not selected as an overall property and Phase Fraction is not selected as a phase property, as the XFlowLoader unit operation will be unable to determine the vapor fraction.
use a pressure-enthalpy flash if the number of phases is not known, or if the number of compounds is less than the number of phases (e.g. a single compound in the two-phase region). The number of present compounds is determined from the composition, and a compound with a composition of less than 10^-10 is considered absent.
by default, a pressure-temperature flash is recommended.

The flash recommendation can be suppressed by unticking the Write Recommended Auto Flash option.