The Lumped Thermal System Interface
The Lumped Thermal System (lts) interface () is used to model heat transfer in a system using a thermal network representation.
By analogy with electrical circuits, it provides a lumped element model that idealizes the domain and boundary conditions for heat transfer into components such as thermal resistors, thermal capacitors, and heat rate sources, joined by a network of perfectly thermally conductive wires.
Components representing heat pipes, thermoelectric modules, or user defined thermal subsystems are also available, and the temperatures and heat rates on boundaries can be defined in terminal nodes, including connections to distributed finite element models.
The physics interface supports stationary and time-domain analysis, and solves an energy conservation equation using global variables (space-independent) for the temperatures and heat rates at elements. It is available in all space dimensions.
Settings
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is lts.
System Settings
Specify the following in this section:
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 Create unique nodes for new components
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 Check for hanging nodes before solving
When Create unique nodes for new components is selected, newly added components will be assigned unused node names. The components will be disconnected from the rest of the system and the nodes should be updated to reflect the actual system connections. When this setting is deselected, new components will be connected to the lowest-numbered nodes, starting from 0.
When Check for hanging nodes before solving is selected, a check for hanging (not connected) nodes is performed before solving the equations. An error message is displayed if one or more hanging nodes are present in the system.
Dependent Variables
Every feature of the physics interface adds certain ODE dependent variables in the form of temperatures, heat rates, and others. All the ODE dependent variables are grouped in the following ODE fields:
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Temperatures (default field name: temperatures)
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Heat Rates (default field name: heatRates)
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Other (default field name: other)
Discretization
All the dependent variables in this physics interface are global (space-independent) and do not need any spatial discretization.