General
Home / Examples / Thermal Analysis [Watt] / Example 10: Natural Convection with Correction Coefficient Manually Calculated
Two heat sources are placed on a substrate. Some heat is conducted to the bottom copper sheet of the substrate through via holes.
The heat is released to the ambient from the substrate by natural convection.
The temperature distribution and the heat flux vectors are solved.
Unless specified in the list below, the default conditions will be applied.
Results will vary depending on Femtet version and the PC environment.
Item |
Settings |
Analysis Space |
3D |
Model Unit |
mm |
Item |
Settings |
Solver |
Thermal Analysis [Watt] |
Analysis Type |
Steady-state Analysis |
Options |
N/A |
The finer mesh size is set to 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 sources of MAINCHIP and SUBCHIP are set up as follows.
Body Attribute Name |
Tab |
Settings |
MAINCHIP |
Heat Source |
0.2 [W] |
SUBCHIP |
Heat Source |
0.1 [W] |
It is assumed that the heat is released to the ambient only from the top and bottom faces of the model. The heat released from the side faces is ignored because the total area of the side faces is much smaller than that of the top and bottom faces.
Boundary Condition Name/Topology |
Tab |
Boundary Condition Type |
Settings |
Bottom/Face |
Thermal |
Heat Transfer/Convection |
Natural Convection *1: 1.39 [W/m2/deg5/4] Room Temperature: 25 [deg] |
TOP/Face |
Thermal |
Heat Transfer: Convection |
Natural Convection *2: 2.78 [W/m2/deg5/4] Room Temperature: 25 [deg] |
MAINCHIPUPPER/Face |
Thermal |
Heat Transfer: Convection |
Natural Convection *3: 6.41 [W/m2/deg5/4] Room Temperature: 25 [deg] |
SUBCHIPUPPER/Face |
Thermal |
Heat Transfer: Convection |
Natural Convection *4: 7.62 [W/m2/deg5/4] Room Temperature: 25 [deg] |
(*1) BOTTOM
2.51×C×（1/L)＾（1/4） = 1.39 [W/m2/deg5/4]
where
C = 0.26
Size of the substrate : 0.06x0.04
L (Typical Length) = (0.06 x 0.04 x 2) / (0.06 + 0.04) = 0.048
(*2) TOP
2.51×C×（1/L)＾（1/4） = 2.78 [W/m2/deg5/4]
where
C = 0.52
Size of the substrate : 0.06x0.04
L (Typical Length) = (0.06 x 0.04 x 2) / (0.06 + 0.04) = 0.048
(*3) MAINCHIPUPPER
2.51×C×（1/L)＾（1/4） = 6.41 [W/m2/deg5/4]
where
C = 0.96
Size of the chip : 0.02x0.02
L (Typical Length) = (0.02 x 0.02 x 2) / (0.02 + 0.02) = 0.02
(*4) SUBCHIPUPPER
2.51×C×（1/L)＾（1/4） = 7.62 [W/m2/deg5/4]
where
C = 0.96
Size of the chip : 0.01x0.01
L (Typical Length) = (0.01 x 0.01 x 2) / (0.01 + 0.01) = 0.01
The temperature distribution is shown below.
Even though the absolute value of the temperature difference is about as low as 1.5 deg, the temperature of MAINCHIP is highest.
The vectors of the heat flux are shown below.
The heat is well transferred from each heat source through the via holes.