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Example 14: Natural Convection with Correction Coefficient Automatically Calculated

General

• The model consists of two heat sources and a substrate. The heat sources are placed on the substrate.
  The heat is released to the ambient by natural convection.
   

• The coefficient of natural convection is calculated automatically based on the model shape.
   

• The temperature distribution and the heat flux vectors are solved.
   

• Unless specified in the list below, the default conditions will be applied.
   

• Obtain this session's project file. (Right-click and choose 'Save link as')




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

 

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

 

Analysis Conditions

Item	Settings
Solver	Thermal Analysis [Watt]
Analysis Type	Steady-state Analysis
Options	N/A

Model

• To use the boundary condition of [Natural convection (automatic calculation)], the model must be directed so that the negative Z direction points to the ground.

 

Body Attributes and Materials

The finer mesh size is set for via holes (HOLE), where the heat flux is expected to change drastically.

Body Number/Type	Body Attribute Name	Material Name	Mesh Size
0/Solid	SUB	006_Glass_epoxy *
1/Solid	GND	008_Cu *
2/Solid	MAINCHIP	001_Alumina *
3/Solid	SUBCHIP	001_Alumina *
4/Solid	HOLE	008_Cu *	0.5
5/Solid	HOLE	008_Cu *	0.5
6/Solid	HOLE	008_Cu *	0.5
7/Solid	HOLE	008_Cu *	0.5
8/Solid	HOLE	008_Cu *	0.5
9/Solid	HOLE	008_Cu *	0.5
10/Solid	HOLE	008_Cu *	0.5
11/Solid	HOLE	008_Cu *	0.5

* Available from the material DB

 

The heat quantities of MAINCHIP and SUBCHIP are set up as follows.

Body Attribute Name	Tab	Settings
MAINCHIP	Heat Quantity	0.2 [W]
SUBCHIP	Heat Quantity	0.1 [W]

Boundary Conditions

Select "Natural convection (automatic calculation)" on the outer boundary condition.

 

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Outer Boundary Condition	Thermal	Heat Transfer/Convection	Natural Convection (Automatic Coefficient Calculation) Room Temperature: 25 [deg]

 

* The correction coefficient for the natural convection is calculated automatically. For the details, please refer to the Thermal tab.

 

Results

The temperature distribution is shown below.

The temperature of MAINCHIP is the highest.

 

The vectors of the heat flux are shown below.

The heat is well transfered through the via holes (HOLE).