Defining Reaction Kinetics

The first step in modeling any system is establishing the material balances. Using the Reaction Engineering interface, you can enter chemical equations and automatically obtain the material balance equations for the chemical species in the system and the energy balance equations for the system. When you type in the reaction mechanism, the kinetic expressions as a function of the species concentrations are derived automatically from the mass action law for elementary steps. You can also type in your own analytical expressions for the reaction rate as a function of the species concentrations and temperature.

The material balances and the reaction kinetic expressions give the ordinary differential equations that are formulated automatically by the software. For a perfectly mixed batch reactor, the solution to the equations gives the composition of the reacting mixture with time.

Parameter Estimation

Studies of chemical reactions and reaction mechanisms usually rely on parameter estimation of frequency factors, activation energies, and other parameters that may quantitatively describe experimental observations. The Chemical Reaction Engineering Module can be combined with the Optimization Module in order to access a dedicated interface for chemical kinetics.

The typical workflow for the estimation of model parameters for a certain assumed reaction mechanism is as follows. You first select the model parameter to estimate, such as the rate constants, and enter initial values and scales for the parameters. Then, you can link to the file that contains the experimental data, matching up the data columns with the model variables. Once you have run the parameter estimation, you can compare the model results and the experimental measurements in postprocessing.

Chemical Species Transport

Modeling of transport phenomena in reacting systems involves the description of the chemical species in so-called multicomponent transport models. The Chemical Reaction Engineering Module contains sophisticated models for multicomponent transport in the Transport of Concentrated Species interface, where you can select between the Maxwell–Stefan formulation and the mixture-averaged models for multicomponent transport. For diluted solutions, you can also choose the Transport of Diluted Species interface, which treats cases where the interactions in the solution are dominated by solute–solvent interactions. The chemical species transport equations are also available for porous media, for example, to include Knudsen diffusion. The dusty gas diffusion model is also included. The formulation of the mass balance model as well as the transport properties can be obtained directly from chemical equations when generating a space-dependent model from the Reaction Engineering interface.

Heat Transfer

The heat transfer functionality included in the Chemical Reaction Engineering Module can account for heat transfer by conduction, convection, and radiation. The radiation term is given by surface-to-ambient radiation, while the Heat Transfer Module is required for surface-to-surface radiation and radiation in participating media. The heat transfer capabilities in the Chemical Reaction Engineering Module include heat transfer in fluids, solids, and porous media. The formulation of the heat transfer model, as well as the thermodynamic and transport properties, can be obtained directly from chemical equations when generating a space dependent model from the Reaction Engineering interface.

Thermodynamic Properties Database

The Chemical Reaction Engineering Module contains a thermodynamic properties database, which you can use to calculate properties for gas mixtures, liquid mixtures, gas–liquid systems at equilibrium (flash calculations), liquid–liquid systems, and gas–liquid–liquid systems at equilibrium. There is a variety of thermodynamic models that can be used to calculate density, heat capacity, enthalpy of formation, enthalpy of reaction, viscosity, thermal conductivity, binary diffusivity, activity, and fugacity. Read more about this functionality on the Liquid & Gas Properties Module page, all of which is included in the Chemical Reaction Engineering Module.

The thermodynamic properties database can be used to create a so-called property package for a specific reacting system by selecting the chemical species present in the system, the desired properties, and the thermodynamic model. When defining reaction mechanisms, the reactants and products can be matched with the chemical species in the property package defined by the thermodynamic properties database. This matching automatically links the functions and equations generated by the property package to the model of the reacting system.

Generating Space-Dependent Models

Once you have a working model for a perfectly mixed system, you can use this model to automatically define material, energy, and momentum balances for space-dependent systems. The transport properties calculated in the Reaction Engineering interface (for example, heat capacity, thermal conductivity, viscosity, and binary diffusivity) automatically transfer to the physics interfaces for chemical species transport, heat transfer, and fluid flow. This functionality allows you to refine and perfect your kinetics and thermodynamics expressions of the chemical reactions before moving to 2D, 2D axisymmetric, and 3D models.

Fluid Flow

The fluid flow functionality included the Chemical Reaction Engineering Module can handle laminar and porous media flow. Additionally, when combined with the CFD Module, there are ready-made couplings for the modeling of chemical species transfer in turbulent flow. The formulation of the fluid flow model as well as the viscosity and density can be obtained directly from chemical equations when generating a space-dependent model from the Reaction Engineering interface.

Electrokinetic Effects

When modeling the transport of diluted or concentrated species, you can include electric fields as driving forces for transport for the modeling of electrolytes and ions. The Nernst-Planck and Electrophoretic Transport interfaces are dedicated to the modeling of electrolytes and can include the formulations of Poisson’s equation or the electroneutrality condition for the charge balance in the electrolyte. Applications of this functionality include electrokinetic valves, electroosmotic flow, and electrophoresis.