Home / Examples / Thermal Analysis [Watt] / Example 7: Heat Radiation by Forced Convection (Steady-State Analysis)

Example 7: Cooling by Forced Convection (Steady-State Analysis)

General

• A heat source is placed on a substrate, and there is a forced air flow for cooling in parallel to the substrate. The heat radiation is analyzed under the steady-state condition.
   

• The coefficient of heat transfer is acquired manually.
  To acquire it automatically, see "Ex.1 of Simple Fluid-Thermal Analysis".
   

• 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

The substrate (VOL1) and the heat source (VOL2) are created as solid bodies, and the heat amount is defined in the body attribute of VOL2.

The coefficient of heat transfer for the top and bottom faces of the substrate and the top face of the heat source are calculated by the simplified equation and set to them.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	VOL1	006_Glass_epoxy *
1/Solid	VOL2	001_Alumina *

* Available from the material DB

 

The heat quantity of VOL2 is set up as follows.

Body Attribute Name	Tab	Settings
VOL2	Heat Quantity	1 [W]

Boundary Conditions

The coefficient of heat transfer for the forced convection are calculated as follows. See [Heat Transfer Coefficient for Forced Convection] for more information.

To acquire it automatically, see [Ex.1 of Simple Fluid-Thermal Analysis].
 

h = 3.86 x (V/L)0.5 x C [W/m2/deg]

 

where

Air flow V=1 [m/s]

Top and Bottom Faces of Substrate (VOL1): Typical length L=0.05, C=1 -> h=17.26
Top Face of Heat Source (VOL2): Typical length L=0.02, L'=0.015, C=1 * -> h=27.3

 

*

The thickness (d) of the speed boundary layer at the edges of the heat source is calculated as follows

 

δ=0.0182 x (L’/V)0.5= 2.3 [mm]

 

This is close enough to the thickness of heat source, so we set C=1.

 

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
BC1/Face	Thermal	Heat Transfer/Convection	Coefficient of Heat Transfer: 27.3 [W/m2/deg] Ambient Temperature: 25 [deg]
BC2/Face	Thermal	Heat Transfer/Convection	Coefficient of Heat Transfer: 17.26 [W/m2/deg] Ambient Temperature: 25 [deg]

Results

The temperature distribution is shown below.

 

A cross section's temperature distribution is shown below.