eq. (8.1)
SuperPro Designer offers a set of customizable options for the calculation of the liquid and vapor density.
● Liquid/Solid Phase Density Calculation Options
● Vapor Phase Density Calculation Options
● Customizing the Density Calculation Options
● Ideal-Mixture Model. In the ideal mixture model, the density of the liquid phase, ρL, is calculated by the ratio of the total volume to the total mass:
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eq. (8.1) |
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where mL is the total liquid mass flowrate
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eq. (8.2) |
and VL is the total liquid volumetric flowrate, calculated by:
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In eq. (8.3) above, mi is the mass flowrate of the component i and λi are weight factors called Volumetric Contribution Coefficients (VCCs). It is possible to shift the calculated liquid density values to reflect ones needs by appropriate adjustment of the VCCs. In general, the following guidelines should be applied:
1. Full volume additivity (i.e., λi=1) leads to an overestimation of the volumetric flowrate and consequently, of the equipment size.
2. Values of λi lower than unity will reduce the contribution of component i to the overall liquid volumetric flowrate.
3. For solid components that fully dissolve into a solvent mixture, λi should be equal to zero.
4. For solid components that form a slurry with the solvent, λi should be equal to 0.2-0.3.
● User-Defined Density Value
When this option is selected, the density of the liquid phase is set to a fixed value, regardless its composition and the operating conditions.
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Liquid density options have a direct impact on the calculation of the liquid volume accumulated inside vessels, and consequently, on the sizing of equipment (in design mode) or the triggering of liquid-level constraint violations (in rating mode). Liquid density calculation options also affect the volumetric flow of streams and procedure states. |
The program offers the following options for the calculation of the vapor phase density:
● Ideal Gas Model. The density (molar volume) of the vapor phase is calculated under the assumption of the ideal gas law:
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eq. (8.4) |
User-Defined Density Value.The density of the vapor phase is set to a fixed value, regardless its composition and the operating conditions.
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Modifying the density calculation options for the vapor phase impacts the volumetric flowrate of streams and procedure states but not the calculated equipment size. |
In the case that material in a stream or procedure state exists in two phases, an overall (mixed) stream density is calculated by the following equation:
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eq. (8.5) |
where mL, VL, ρL and mV, VV, ρV are the mass flowrate, the volumetric flowrate and density of the liquid and vapor phase, respectively.
Each process file keeps a set of default options for the calculation of the vapor and liquid/solid phase density. These options are automatically propagated to all of the streams and procedure states unless the Overwrite option has been enabled for any of them. You can shift the density values to more realistic bound by:
1. Changing the density calculation options at the process level or,
2. Overwriting the density calculation options for specific streams and/or procedure states.
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In the current version of SuperPro, you do not have the option to modify the density calculation options at the unit procedure level. |
Changing The Default Density Calculation Options at the Process Level
To set your own process-level preferences for the calculation of density, select Edit }Process Options }Density Calculation Options from the main menu or by selecting Density Calculation Options from the command menu of the process file. See also The Density Calculation Options Dialog.
To change the density calculation options of a stream, select the stream by left-clicking on it and pick Edit }Stream Options }Simulation Data or alternatively, double-click on it. In the dialog that appears, visit the Physical State tab, check the Overwrite options of either the liquid/solid or the vapor phase density and proceed in making the desired modifications. For more information see Stream Density Calculation Options.
Customizing The Density Calculation Options of Procedure States
To change the physical state calculation options of a procedure state, select its associated unit procedure by left-clicking on it and pick Edit }Unit Procedure Options}Procedure State Options. Alternatively, you can right-click on the associated unit procedure and select Procedure State Options. In the dialog that appears, visit the corresponding procedure state tab, check the Overwrite option of either the liquid/solid or the vapor phase density and proceed in making the desired modifications. For more information see Procedure State Density Calculation Options.
