Batteries and Fuel Cells Module
Improved Usability of Chemical Reactions in Porous Media
The Reactions source term in the Transport of Diluted Species in Porous Media interfaces now provides the following options to account for the reacting volume base for saturated and unsaturated porous media:
- Total volume
- Pore volume
- Liquid phase
- Gas phase
Using literature data for kinetic expressions is thereby simpler and less error prone, since they can be tabulated for different volume bases.
You can now select the proper reaction relation as the basis for the reaction rate expression. In this case, reaction per total pore volume is selected.
Hygroscopic swelling is an effect of internal material strain caused by changes in moisture content. The new Hygroscopic Swelling multiphysics coupling is used to couple moisture concentration between the Transport of Diluted Species or Transport of Diluted Species in Porous Media interfaces and the Solid Mechanics interface.
Dusty Gas Model
Knudsen diffusion is included as an additional transport mechanism in the Transport of Concentrated Species interface to enable Dusty Gas models. This mechanism is available for the Fick’s law and Mixture-averaged diffusion models. The Dusty Gas model is sometimes preferred to accurately predict mass transport accompanied by chemical reactions in porous media, for example in catalytic membranes and fuel cell applications.
In gases, this mechanism is important for the transport rate if the mean free path of transported molecules is in the same order of magnitude or larger than the length scale of the system. For example, in a long pore with a narrow diameter (2 to 50 nm), the molecules frequently collide with the pore wall and the diffusion needs to be adjusted accordingly.
Mass-Based Concentration Variables
The Transport of Concentrated Species interface now provides mass-based concentration variables (kg/m3) in addition to mass fractions. This can be used in postprocessing, reports, and visualization, adding the flexibility to present data in different units depending on the preferences of the person interpreting the results.
Improved Convergence and Stability Through Current Distribution Initialization Step and New Studies in Electrochemical Interfaces
Many electrochemical models require properly derived initial values to achieve convergence or even to get a time-dependent solver to work. The new Stationary with Initialization and Time-dependent with Initialization studies are now available for all electrochemistry interfaces, with the use of a Current Distribution Initialization study step. These new studies facilitate solving electrochemical models with nonlinear kinetics.
Cross Sectional Area
A new property, Cross Sectional Area, is now available in 1D models for the Electrochemistry interface. With this feature, the cell area can be specified and the total cell current can be calculated. Additionally, the boundary features Electrolyte Current and Electrode Current are now available in 1D.
Point and Line Current Sources for Efficient Electrode Modeling
For large problems with complex geometries, it is often not possible to geometrically resolve all parts of the geometry. If a small electrode is used to provide a current source, it may suffice to "inject" the current source at a point in the geometry, rather than to create the electrode boundary and provide the electrode current as a proper boundary condition. With the Point and Line Current Source features in the Primary and Secondary Current Distribution interfaces, it is possible to apply a current source at a point in 2D, 2D axisymmetric, and 3D geometries.
Initial Cell Charge Distribution
Providing proper initial values for battery simulations can be challenging, since the modeler has to "invert" global cell properties that are often used by battery engineers. New inputs, such as an overall state-of-charge or an initial battery open circuit voltage, have now been introduced to the battery-based interfaces.
With the use of a new Initial Cell Charge Distribution node in the Lithium-Ion Battery and Battery with Binary Electrolyte interfaces, it is now possible to set the initial cell voltage or cell state-of-charge (SOC), rather than the individual solid lithium concentrations in the porous electrodes. This feature also makes it possible to balance the amount of active materials available for intercalation in the electrodes by computing the electrode phase porosities automatically.
New Tutorial: Zinc-Silver Oxide Battery
Zinc-Silver oxide (Zn-AgO) batteries are used in different industries thanks to their high capacity per unit weight. They also have superior performance characteristics, such as long operating lifetimes and low self-discharges (long shelf life). Larger sized Zn-AgO batteries are used in critical applications, such as submarines, missiles, and aerospace applications. Smaller sized button cells are well suited for miniature power sources in hearing aids, electronic watches, and other low-power devices.
This new application simulates the discharge of a zinc-silver oxide battery. The electrochemical reactions in the positive and negative electrodes lead to changes in porosity and species concentration in the electrodes.
New Tutorial: Lithium-Air Battery
Rechargeable metal-air batteries have recently attracted great interest, mainly due to their high specific energy density. Lithium-air batteries have a theoretical energy density value of about 11400 Wh/kg, which is nearly 10 times greater than, for instance, the lithium-ion batteries used in today's mobile phones and electric cars.
This new application studies the discharge of a lithium-air battery, including the transport of oxygen in the porous positive electrode where the electrochemical reduction of oxygen leads to changes in concentration of the reaction product and electrode porosity.
Infinite Element Domains in Darcy's Law Interfaces
The Darcy's Law interfaces now supports infinite element domains and more advanced computations of boundary fluxes.