Modeling Thermal Runaway

Simcenter STAR-CCM+ provides the Heat Release and Vent models to predict the heat and mass that are released by the solid parts of the battery cell during thermal runaway.

These models require experimental data input, namely the heat rate of the battery cell as a function of either temperature of the battery cell or time, and the vent rate, that is, mass flow rate and temperature of the venting gas as a function of time. In Simcenter STAR-CCM+, this data is imported in the form of tables. To use the Heat Release and Vent models in Simcenter STAR-CCM+, a 0D battery cell is created directly in Simcenter STAR-CCM+.

注	In Simcenter STAR-CCM+, the Circuit model is activated when the Battery model is selected. You do not need to create circuit elements to run thermal runaway models. Therefore, you can disable the Circuit model, if you prefer.

To model thermal runaway:

Right-click the Batteries > Battery Cells node and select Create User-Defined Battery Cell.
Right-click the Battery Cells > [User Defined Battery Cell] node and select Select Battery Cell Models….

To set up the Heat Release model:

In the Select Battery Cell Models dialog, activate Heat Release Model.
To import the heat rate table, right click the Tools > Tables node and select New Table > File Table.
The table format is two columns—one representing the heat rate in Watts, and the other representing either the corresponding temperature of the battery cell in Kelvin or the time in seconds, depending on the type of heat rate table imported.

Select the Battery Cells > [User Defined Battery Cell] > Models > Thermal Runaway Heat Release Model node and set the following properties:


Property	Setting
Maximum Releasable Energy	Set the chosen value for the maximum releasable energy of the battery.
Apply Model Constraints	When activated, enables the Model Activation Constraints node.

If the Apply Model Constraints property is activated, constraints that control the activation of the Heat Release model can be added.

Right-click the Thermal Runaway Heat Release Model > Model Activation Constraints node and select New to add a model activation constraint.

Select the new Thermal Runaway Heat Release Model > Model Activation Constraints > Model Constraint 1 node and set the following properties:


Property	Setting
Field Function	Select the field function to which the constraint applies.
Range Operation	Select one of two range operations to define at which point the thermal runaway heat release model is activated.
Value	Set a value for the constraint.
Evaluation Method	Select one of two methods to define how the field variable is evaluated over the core parts of the battery cell.

注	After setting up the constraint, the name of the Model Constraint 1 node changes to match the property selection.

Depending on how you want to specify the input for the heat source to the battery cell, do one of the following:


Method	Steps
Heat rate as a field function	Define a field function for the volumetric heat source to the battery. See 创建用户场函数. Select the Thermal Runaway Heat Release Model > Heat Rate node and set Method to Field Function. Expand the Heat Rate > Field Function node and select the field function for volumetric heat rate for Function.
Heat rate as a function of temperature	Select the Thermal Runaway Heat Release Model > Heat Rate node and set Method to Table(Temperature). Select the Table(Temperature) node and set the following properties: Table—Select the previously imported table that is stored within the Tools > Tables node and represents the heat rate of the battery. Temperature, K—Select the heading of the column in the table that represents the temperature of the battery. Heat Rate, W—Select the heading of the column in the table that represents the heat rate of the battery. Temperature Type—Select whether heat is applied to each cell of the battery cell mesh based on the local temperature inside the battery cell, or to the complete volume of the battery cell based on the maximum or volume-averaged temperature of the complete battery cell.
Heat rate as a function of time	Select the Thermal Runaway Heat Release Model > Heat Rate node and set Method to Table(Time) Select the Table(Time) node and set the following properties: Table—Select the previously imported table that is stored within the Tools > Tables node and represents the heat rate of the battery. Time, s—Select the heading of the column in the table that represents the time elapsed since initiation of the thermal runaway. Heat Rate, W—Select the heading of the column in the table that represents the heat rate of the battery.

See Battery Cells Reference: Thermal Runaway Heat Release Model.

To set up the Vent model:

Right-click the Battery Cells > [User Defined Battery Cell] node and choose Select Battery Cell Models….
In the Select Battery Cell Models dialog, activate Vent Model.
To import the vent rate table, right-click the Tools > Tables node and select New Table > File Table.
The table format is three columns—one representing the mass flow rate of the venting gas in kg/s, one representing the corresponding venting gas temperature in Kelvin, and one representing the corresponding time in seconds.

Select the Battery Cells > [User Defined Battery Cell] > Models > Thermal Runaway Battery Vent Model node and set the following properties:


Property	Setting
Table	Select the previously-imported table which represents the vent rate of the battery venting gas.
Time, s	Select the column for time.
Mass Flow Rate, kg/s	Select the column for mass flow rate of the venting gas.
Vent Temperature, K	Select the column for temperature of the venting gas.
Initial Core Part Density	Set the chosen value for the initial core part density of the battery.

If the Apply Model Constraints property is activated, constraints that control the activation of the Vent model can be added.

Right-click the Thermal Runaway Battery Vent Model > Model Activation Constraints node and select New to add a model activation constraint.

Select the Thermal Runaway Battery Vent Model > Model Activation Constraints > Model Constraint 1 node and set the following properties:


Property	Setting
Field Function	Select the field function to which the constraint applies.
Range Operation	Select one of two range operations to define at which point the thermal runaway vent model is activated.
Value	Set a value for the constraint.
Evaluation Method	Select one of two methods to define how the field variable is evaluated over the core parts of the battery cell.

注	After setting up the constraint, the name of the Model Constraint 1 node changes to match the property selection.

See Battery Cells Reference: Thermal Runaway Battery Vent Model.

Select the Regions > [fluid] > Boundaries > [venting inlets] > Physics Values node and set the following properties:


Node	Property	Setting
Mass Flow Rate	Method	Field Function
Mass Flow Rate	Scalar Function	Battery Vent Model Mass Flow Rate
Total Temperature	Method	Field Function
Total Temperature	Scalar Function	Battery Vent Model Total Temperature

Make these settings for all venting inlet boundaries.

Select the Continua > [battery stack physics continuum] > Models > Solid > [battery stack] > Material Properties > Density node and set the following properties:


Node	Property	Setting
Density	Method	Field Function
Field Function	Scalar Function	Battery Vent Model Core Part Density

During the simulation, the Thermal Runaway Heat Release model performs the following tasks:

If the Apply Model Constraints property is activated, the model checks if all the model constraints are met.
The model checks if the cumulative energy released by the core part is below the value set for Maximum Releasable Energy.
The model reads the heat rate from the imported heat rate table for the current temperature of the core part. If the temperature is beyond the table's range, then the heat rate is set to zero. The heat rate is also set to zero when the extrapolated heat rate is negative.
The model computes the energy released using the heat rate values and the corresponding time step.
The computed energy is fed back into the system.

During the simulation, the Thermal Runaway Vent model performs the following tasks:

If the Apply Model Constraints property is activated, the model checks if all the model constraints are met. Once the Vent model is activated, it cannot be deactivated.
The model starts accumulating vent time.
The model reads the venting gas mass flow rate and temperature from the imported vent rate table for the current vent time. If the vent time is beyond the range of the table, the venting gas mass flow rate is set to zero and the venting gas temperature is set to the battery core part temperature.
The model computes the battery cell mass loss using the mass flow rate value and the corresponding time step, and then evaluates the effective core part density. The model also computes energy loss of the cell as minimum of either venting gas enthalpy or the internal energy change of the cell due to mass loss. If the venting gas enthalpy is higher than the internal energy change of the cell due to mass loss, then the difference is treated as heat generation during thermal runaway. Instead, if the venting gas enthalpy is lower than the internal energy change of the cell due to mass loss, then the difference would contribute to the cell temperature increase.
The computed energy loss is fed back into the system.