Example15 Radiation and Cooling of IC inside a Case by Natural Convection (Closed Space and Open Space)

General

An IC is encased on a substrate. The heat dissipation of the IC by radiation and natural convection is solved by the steady-state analysis.
Natural convection in the closed space of the case and radiation and natural convection in the open space outside the case are solved at the same time.
In [Example 9: Cooling of IC inside the Case by Natural Convection (Closed Space and Open Space)], natural convection alone is taken into account but not radiation.
The temperature distribution and the heat flux vectors are solved.
Unless specified in the list below, the default conditions are applied.

Analysis Space

Item	Setting
Analysis Space	3D
Model Unit	mm

Analysis Condition

Item	Setting
Solver	Fluid analysis [Bernoulli] Thermal analysis [Watt]
Analysis Type	Fluid analysis: Steady-state analysis Thermal analysis: Steady-state analysis
Laminar Flow/Turbulent Flow	Select Turbulent Flow
Option	Select Take Buoyancy into Account (Natural Convection)
Layer Mesh Setting for Wall Surface (General Settings)	Parameters for Automatic Creation Expected Temperature Difference: 50[deg]
Meshing Setup	General Mesh size: 10 [mm]

Model

The model is a box solid body. The material is Air (000_Air).

Set natural inflow/outflow to the outer boundary condition of Inlet/Outlet.

The substrate (VOL1), the IC (VOL2), and the case (CASE) are solid bodies.

Setting of Body Attributes, Materials, and Mesh Sizes

Body Number/Type	Body Attribute Name	Material Name	Mesh Size
0/Solid	VOL1	006_Glass_epoxy *	2.0
1/Solid	VOL2	001_Alumina *	2.0
2/Solid	Air	000_Air *	–
3/Solid	CASE	001_Al *	4.0

* Available from the material DB

IC (VOL2) is set as follows on the Heat Source tab.

Body Attribute Name

Tab

Setting

VOL2

Heat Source

Thermal Surface

Emissivity:
Select Specify on each body attribute

0.85

Boundary Condition

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Setting

Outer Boundary Condition

Fluid-Thermal

Inlet/Outlet

Natural Inflow/Outflow

Inflow temperature: Use ambient temperature (25[deg])

Thermal

None

Radiation type: Surface-to-surface (accuracy prioritized)

Results

The radiation surface is automatically set to the case surface, the substrate surface, and the IC surface.

To check the setting, the emissivity of the case surface and the radiation rate of the substrate and the IC are shown.

From the diagram, it is confirmed that the emissivity is 0.8 and 0.85 respectively.

The temperature distribution is shown below. For comparison, the result of Example 9 (without radiation) is shown as well.

The cross section at x=0 is displayed.

It can be seen that the cooling effect is higher and the temperature of the IC is lower when the radiation is taken into account compared to the case where only natural convection is taken into account.

Example 9: Natural convection only	Example 15: Natural convection and radiation