Molecular weight physical properties are used in vapor/liquid equilibrium (VLE) calculations when the Standard or Selective Speciation method applies to material mixtures. The Air module speciation logic calculates the Vapor Mixture MW by summing each component's Vapor Mole Fraction Yi multiplied by its molecular weight for mixtures where material components are known, or constant. For unknown, or varying, components with distinct liquid and vapor molecular weights, a primary molecular weight is used to determine the component's Vapor Mole Fraction Yi value, which is then used with a secondary molecular weight to calculate the Vapor Mixture MW. The Vapor Mixture MW results for all components that are part of the mixture are summed.
Material mixtures can be comprised of:
multiple known components only, or
one-to-many known components and one unknown component.
Configuration requirements are provided below.
Enter a typical result for your molecular weight physical property in the Physical Properties subsection of the Material Composition and Properties section on the Material form.
Select the Standard Speciation or Selective Speciation option for the Speciation Type field on the Process Unit Material Emission Calculations or Process Unit Material Group Emission Calculations form. Refer to Speciation Method Emission Rate Determination for additional information about speciation.
Select your MW Physical Property on the Process Unit Material Emission Calculations or Process Unit Material Group Emission Calculations form. The default is MOLECULAR WEIGHT.
Select the Requires two MW values option for the component in the Composition subsection of the Material Composition and Properties section on the Material form.
Enter a typical result for your primary and secondary molecular weight physical properties in the Physical Properties subsection of the Material Composition and Properties section on the Material form.
Select the Standard Speciation or Selective Speciation option for the Speciation Type field on the Process Unit Material Emission Calculations or Process Unit Material Group Emission Calculations form. Refer to Speciation Method Emission Rate Determination for additional information about speciation.
Select your primary molecular weight in the MW Physical Property field on the Process Unit Material Emission Calculations or Process Unit Material Group Emission Calculations form. The default is MOLECULAR WEIGHT.
Select the Second MW Phys. Prop. on the Process Unit Material Emission Calculations or Process Unit Material Group Emission Calculations form.
When a component is designated as requiring two MW values and a second one has not been identified, the option specified in the MW Physical Property field will be used for the entire calculation. If a result value has not been entered for any MW physical property selected, the property will be identified in calculation warning messages.
Note:
Both molecular weight values and physical properties are displayed
in the Calculation Log, separated by a backslash (/).
