Home / Examples / Coupled Analysis / Electric-Thermal Analysis [Coulomb/Watt] / Example 2: Heating of Conductive Strip (Transient Analysis)

Example 2: Heating of Conductive Strip (Transient Analysis)

General

The model is a strip line having bend shapes. An electric potential is given across the strip line and the electric current is solved
in the electric analysis. Then the eventual joule loss and the resulting temperature rise are solved in the thermal analysis.
The model is similar to that of Example 1.
The temperature distribution is observed to vary over time in the transient analysis and the results are saved.
Unless specified in the list below, the default conditions will be applied.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

Select the transient analysis.

Item

Settings

Solver

Electric Analysis [Coulomb]

Thermal Analysis [Watt]

Analysis Type

Transient Analysis

Tab	Setting Items	Settings
Transient Analysis	Timestep	Manual
	Timestep	1.0-3 [s]
	Calculation Steps	10
	Initial Temperature	25 [deg]

Model

The conductive strip is a solid body in this example.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	Board	001_Alumina *
6/Solid	StripLine	008_Cu *

* Available from the material DB

It is assumed that there is no current flow in the alumina substrate.

Body Attribute Name	Thickness/Width	Analysis Domain
Board		Solver: Deselect Electric Analysis (Coulomb)

Resistivity/conductivity is required to be set to “Board” to run the Coulomb/Watt solver
even though it is not used in the electric analysis. As the resistivity in the database of the 001_Alumina is not defined by default,

the value is temporarily set to 1.0. (The result will not be affected)
In the thermal analysis, specific heat is required. It is not defined in the database of the 001_Alumina either.

Therefore the setting below is applied.

Material Name	Specific Heat	Resistivity
001_Alumina	1.0 [J/kg/deg]	1.0 [Ωm]

Boundary Conditions

The temperature of the bottom face of the substrate is set to 25 [deg] using the boundary condition of T0.
The [Adiabatic] boundary condition is set to a part of faces using the boundary condition of T_Wall.
This keeps the outer boundary condition from being applied on those faces.
Boundary conditions, V0 and V1, define the electric potential at each end of the microstrip line.
The heat transfer to the ambient is defined by the outer boundary condition.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
T_Wall/Face	Thermal	Adiabatic
T0/Face	Thermal	Temperature	25 [deg]
V0/Face	Electric	Electric Wall	Electric Potential Specified, Waveform: Constant, Electric Potential: 0.00 V
V1/Face	Electric	Electric Wall	Electric Potential Specified, Waveform: Constant, Electric Potential: 0.01 V
Outer Boundary Condition *	Thermal	Heat Transfer: Convection	Heat Transfer Coefficient: 10 [W/m2/deg] Ambient Temperature: 25 [deg]

To set Outer Boundary Condition, go to the [Model] tab

and click [Outer Boundary Condition] .

Results

The temperature distribution at elapsed time 0.002 [s] is shown below.

The temperature distribution at elapsed time 0.006 [s] is shown below.

The temperature distribution at elapsed time 0.010 [s] is shown below.

The temperature around the thin film conducting line increases as the time passes.