Thermal Coupling

Use a Thermal Coupling simulation object to:

• Model conduction between the surfaces that are physically in contact without implicitly modeling the geometry of the interface.

• Model generalized conductances defined by a coefficient.

• Create additional conductances between selected elements.

• Create perfect contact between two surfaces in contact with each other.

In general, you create a thermal coupling between parallel surfaces. While there is no prohibition against creating thermal couplings between non-parallel surfaces and edges, non-parallel arrangements introduce inaccuracy; the farther from parallel, the greater the inaccuracy.

Types of thermal coupling simulation objects

Thermal Coupling type

Lets you create a thermal coupling of a specified type between each primary region and each secondary region. For more information, see Thermal Coupling magnitude types.

Perfect Contact type

Lets you create conductances between model object in perfect contact with each other. With this option, the software performs element merging based on proximity. It creates a very large conductance between each of the primary elements and the nearest of the secondary elements. This produces inaccuracies in the conductance matrix, especially when the primary and secondary element meshes are very different. Use this type only when the meshes are nearly aligned or when the in-plane temperature gradients are insignificant.

To model thermal cyclic symmetry, the thermal solver revolves all secondary elements around the specified axis of revolution, such that the secondary elements are in contact with the primary elements.

Additional Conductance type

Lets you create a conductance of the specified type between each primary region and each secondary region. When you select m elements in the primary region and n elements in the secondary region, m x n additional conductances are created. For more information, see Additional Conductance types.

Selecting geometry or elements

Typically, you define a thermal coupling on faces of bodies meshed with 3D elements, faces meshed with 2D elements, edges of meshed entities or edges meshed with 1D elements. Other geometry/mesh combinations are also supported.

You define an additional conductance on different element types, such as, 3D, 2D, 1D, axisymmetric, non-axisymmetric, and non-geometric elements.

When you define a thermal coupling, you can choose which projected area is used to calculate the magnitude of the thermal coupling. Use the projection of the primary to the secondary, or the secondary to the primary areas.

For 2D elements, you can specify which side of the primary region is connected to which side of the secondary region: top or bottom.

When you define a simulation object of additional conductance type, the software does not support multi-layer shell uniform elements with side specification.

Note:

You can only create a thermal coupling or additional conductance on elements that have thermal material properties defined.

Selected entity	Heat transfer calculation
Face of body meshed with 3D elements	Area = Face surface area
Face meshed with 2D elements	Area = Face surface area
Edge of face meshed with 2D elements	Area = length of the edge × the thickness of 2D elements
Curve or edge meshed with 1D elements	Area = length of the edge × perimeter of the associated beam cross section
Mesh point meshed with 0D element	Area = Surface of a sphere of the 0D element's diameter

Creating thermal couplings between geometry or elements and a non-geometric element

You create a thermal coupling to a non-geometric element to model conduction between the primary areas and an entity that is not represented geometrically. You must select the non-geometric element as the secondary region.

The thermal solver uses a one-to-one coupling resolution to calculate a single conductance from each primary element to the non-geometric element. Thermal coupling with a non-geometric element does not support spatial distribution.

Supported variables and functions

The following table lists the independent variables and auto-generated expressions for the Thermal Coupling type quantities that you can define using fields and expressions.

Quantity	Variables	Auto-generated expressions*
Total ConductanceTotal ResistanceHeat Transfer CoefficientConductance per LengthGap Thermal Conductivity	TimeTemperatureHeat flow rateTemperature differenceThermal capacitanceSpatial variablesTime, spatial variablesTemperature, spatial variablesHeat flow rate, spatial variablesTemperature difference, spatial variablesThermal capacitance, spatial variables	fluid_temperature heat_flow_rate mass_flow_rate nx ny nz pressure radius rotational_speed temperature temperature_difference thermal_capacitance thickness time volume_flow_rate x y z

Note:

*The auto-generated expressions are not available if Secondary Override Region is selected, when you define the Thermal Coupling.

In expressions, you can also use all built-in functions that are listed in Mathematical functions in expressions and most built-in functions that are listed in Thermal-flow functions in expressions.

Where do I find it?

Application	Pre/Post
Command Finder	Thermal Coupling
Simulation Navigator	Right-click the Simulation Objects node→New Simulation Object→Thermal Coupling

How do I

Create a thermal coupling

Model conduction in a bonded joint

Model conduction across a card edge guide

Model a BGA contact using a Thermal Coupling

Model additional thermal resistance in a bolted joint

Create a perfect contact thermal coupling

Learn more

Thermal Coupling magnitude types

Additional Conductance types

Specifying a Coupling Resolution

Using the Only Connect Overlapping Elements option

Using the Overlap Projection Direction option

Temperature dependency for thermal and electrical couplings

Inputs to expressions

Look up more details

Thermal cyclic symmetry using perfect contact thermal coupling

Perfect Contact options

Auto-generated expressions

Quick links

Simcenter 3D Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal boundary conditions

Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Thermal Coupling, Simcenter 3D 2021.1 Series

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