IDAES Modeling Standards

Model Formatting and General Standards

The section describes the recommended formatting used within the IDAES framework. Users are strongly encouraged to follow these standards in developing their models in order to improve readability of their code.

Headers and Meta-data

Model developers are encouraged to include some documentation in the header of their model files which provides a brief description of the purpose of the model and how it was developed. Some suggested information to include is:

  • Model name,
  • Model publication date,
  • Model author
  • Any necessary licensing and disclaimer information (see below).
  • Any additional information the modeler feels should be included.

Coding Standard

All code developed as part of IDAES should conform to the PEP-8 standard.

Model Organization

Whilst the overall IDAES modeling framework enforces a hierarchical structure on models, model developers are still encouraged to arrange their models in a logical fashion to aid other users in understanding the model. Model constraints should be grouped with similar constraints, and each grouping of constraints should be clearly commented.

For property packages, it is recommended that all the equations necessary for calculating a given property be grouped together, clearly separated and identified by using comments.

Additionally, model developers are encouraged to consider breaking their model up into a number of smaller methods where this makes sense. This can facilitate modification of the code by allowing future users to inherit from the base model and selectively overload sub-methods where desired.


To help other modelers and users understand the how a model works, model builders are strongly encouraged to comment their code. It is suggested that every constraint should be commented with a description of the purpose of the constraint, and if possible/necessary a reference to a source or more detailed explanation. Any deviations from standard units or formatting should be clearly identified here. Any initialization procedures, or other procedures required to get the model to converge should be clearly commented and explained where they appear in the code. Additionally, modelers are strongly encouraged to add additional comments explaining how their model works to aid others in understanding the model.

Units of Measurement and Reference States

Due to the flexibility provided by the IDAES modeling framework, there is no standard set of units of measurement or standard reference state that should be used in models. This places the onus on the user to understand the units of measurement being used within their models and to ensure that they are consistent.

The IDAES developers have generally used SI units without prefixes (i.e. Pa, not kPa) within models developed by the institute, with a default thermodynamic reference state of 298.15 K and 101325 Pa. Supercritical fluids have been consider to be part of the liquid phase, as they will be handled via pumps rather than compressors.

Standard Variable Names

In order for different models to communicate information effectively, it is necessary to have a standard naming convention for any variable that may need to be shared between different models. Within the IDAES modeling framework, this occurs most frequently with information regarding the state and properties of the material within the system, which is calculated in specialized property blocks, and then used in others parts of the model. This section of the documentation discusses the standard naming conventions used within the IDAES modeling framework.

Standard Naming Format

There are a wide range of different variables which may be of interest to modelers, and a number of different ways in which these quantities can be expressed. In order to facilitate communication between different parts of models, a naming convention has been established to standardize the naming of variables across models. Variable names within IDAES follow to the format below:


Here, property_name is the name of the quantity in question, and should be drawn from the list of standard variable names given later in this document. If a particular quantity is not included in the list of standard names, users are encouraged to contact the IDAES developers so that it can be included in a future release. This is followed by a number of qualifiers which further indicate the specific conditions under which the quantity is being calculated. These qualifiers are described below, and some examples are given at the end of this document.

Basis Qualifier

Many properties of interest to modelers are most conveniently represented on an intensive basis, that is quantity per unit amount of material. There are a number of different bases that can be used when expressing intensive quantities, and a list of standard basis qualifiers are given below.

Basis Standard Name
Mass Basis mass
Molar Basis mol
Volume Basis vol

State Qualifier

Many quantities can be calculated either for the whole or a part of a mixture. In these cases, a qualifier is added to the quantity to indicate which part of the mixture the quantity applies to. In these cases, quantities may also be indexed by a Pyomo Set.

Basis Standard Name Comments
Component comp Indexed by component list
Phase phase Indexed by phase list
Phase & Component phase_comp Indexed by phase and component list
Total Mixture   No state qualifier
Phase Standard Name
Supercritical Fluid liq
Ionic Species ion
Liquid Phase liq
Solid Phase sol
Vapor Phase vap
Multiple Phases e.g. liq1

Condition Qualifier

There are also cases where a modeler may want to calculate a quantity at some state other than the actual state of the system (e.g. at the critical point, or at equilibrium).

Basis Standard Name
Critical Point crit
Equilibrium State equil
Ideal Gas ideal
Reduced Properties red
Reference State ref


Constant Standard Name
Gas Constant gas_const

Thermophysical and Transport Properties

Below is a list of all the thermophysical properties which currently have a standard name associated with them in the IDAES framework.

Variable Standard Name
Activity act
Activity Coefficient act_coeff
Bubble Pressure pressure_bubble
Bubble Temperature temperature_bubble
Compressibility Factor compress_fact
Concentration conc
Density dens
Dew Pressure pressure_dew
Dew Temperature temperature_dew
Diffusivity diffus
Diffusion Coefficient (binary) diffus_binary
Enthalpy enth
Entropy entr
Fugacity fug
Fugacity Coefficient fug_coeff
Gibbs Energy energy_gibbs
Heat Capacity (const. P) cp
Heat Capacity (const. V) cv
Heat Capacity Ratio heat_capacity_ratio
Helmholtz Energy energy_helmholtz
Henry’s Constant henry
Internal Energy energy_internal
Mass Fraction mass_frac
Material Flow flow
Molecular Weight mw
Mole Fraction mole_frac
pH pH
Pressure pressure
Speed of Sound speed_sound
Surface Tension surf_tens
Temperature temperature
Thermal Conductivity therm_cond
Vapor Pressure pressure_sat
Viscosity (dynamic) visc_d
Viscosity (kinematic) visc_k
Vapor Fraction vap_frac
Volume Fraction vol_frac

Reaction Properties

Below is a list of all the reaction properties which currently have a standard name associated with them in the IDAES framework.

Variable Standard Name
Activation Energy energy_activation
Arrhenius Coefficient arrhenius
Heat of Reaction dh_rxn
Entropy of Reaction ds_rxn
Equilibrium Constant k_eq
Reaction Rate reaction_rate
Rate constant k_rxn
Solubility Constant k_sol

Solid Properties

Below is a list of all the properties of solid materials which currently have a standard name associated with them in the IDAES framework.

Variable Standard Name
Min. Fluidization Velocity velocity_mf
Min. Fluidization Voidage voidage_mf
Particle Size particle_dia
Pore Size pore_dia
Porosity particle_porosity
Specific Surface Area area_{basis}
Sphericity sphericity
Tortuosity tort
Voidage bulk_voidage

Naming Examples

Below are some examples of the IDAES naming convention in use.

Variable Name Meaning
enth Specific enthalpy of the entire mixture (across all phases)
flow_comp[“H2O”] Total flow of H2O (across all phases)
entr_phase[“liq”] Specific entropy of the liquid phase mixture
conc_phase_comp[“liq”, “H2O”] Concentration of H2O in the liquid phase
temperature_red Reduced temperature
pressure_crit Critical pressure