Defining Phases

The second step in defining a property package using the Generic Property Package Framework is to define the phases of interest in the system. Due to the equation-oriented nature of the IDAES modeling framework, it is necessary to define any phases the user believes may be important a priori as it is not possible to determine what phases should be included on-the-fly. Phases are defined using IDAES Phase objects<core/phase:Phase Objects>, and are automatically constructed using the phases configuration argument from the GenericParameterBlock.

The phases Argument

Each GenericParameterBlock has a configuration argument named phases which is used to construct the Phase objects and populate them with instructions on how to calculate thermophysical properties for that phase. The phases configuration argument is expected to be a dict where the keys are the names for the phases of interest and the values are a configuration arguments for the named phase (which are passed to the Phase object as it is instantiated).

"phases": {
    "phase_1": {
        "type": Phase,
        "equation_of_state": EoS,
        "equation_of_state_options": {},
        "parameter_data": {}},
    "phase_2": {
        "type": Phase,
        "equation_of_state": EoS,
        "equation_of_state_options": {},
        "parameter_data": {}}}

Type Argument

Each phase in the phases argument must be assigned a valid phase type from those supported by the IDAES Framework (e.g. LiquidPhase, SolidPhase, VaporPhase). This should be provided using the type argument.

Equations of State

Equations of state (or equivalent methods) describe the relationship between different thermophysical properties within a mixture and ensure that the behavior of these are thermodynamically consistent. Each phase must be assigned an Equation of State (or equivalent method) in the form of a Python module which will assemble the necessary variables, constraints and expressions associated with the desired approach.

A wide range of equations of states are available in literature for different applications and levels of rigor, and the IDAES Generic Property Package Framework provides a number of prebuilt modules for users, which are listed below.

Equation of state packages may allow for user options (e.g. choosing a specific type of cubic equation of state). The options are set using the equation_of_state_options argument, and the options available are described in the documentation of each equation of state module.

Equation of State Libraries

• Ideal Gases and Liquids
• Cubic Equations of State

Phase-Specific Parameter

In some cases, a property package may include parameters which are specific to a given phase. In these cases, these parameters are stored as part of the associated Phase object and the values of these set using the parameter_data argument when declaring the phase.

Phases with Partial Component Lists

In many applications a mixture will contain species that only appear in a single phase (either by nature or assumption). Common examples include crystalline solids and non-condensable gases. The IDAES Generic Property Package Framework provides support for these behaviors and allows users to specify phase-specific component lists (i.e. a list of components which appear in a given phase).

This is done by providing a phase with a component_list argument, which provides a list of component names which appear in the phase. The framework automatically validates the component_list argument to ensure that it is a sub-set of the master component list for the property package, and will inform the user if an unrecognized component is included. If a phase is not provided with a component_list argument it is assumed that all components defined in the master component list may be present in the phase.