Home / Examples / Thermal Analysis [Watt] / Example 9: Body-to-Body Heat Radiation (Transient Analysis)

Example 9: Body-to-Body Heat Radiation (Transient Analysis)

General

The two bodies with different initial temperatures are equalized by radiation.
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.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	m

Analysis Conditions

Item	Settings
Solver	Thermal Analysis [Watt]
Analysis Type	Transient Analysis
Options	N/A

The transient analysis tab is set up as follows. The number of calculation steps is 200. The timestep is 30 sec.

Therefore, the temperature distributions for 6000 sec are solved.

Tab

Setting Item

Settings

Transient analysis

Table

Number	Calculation Steps	Output Interval	Timestep [s]
1	200	10	30

Initial Temperature

25 [deg] *

* This setting is ignored because the initial temperature, which will be set later in each body attribute, is given priority over this setting.

Model

The surface-to-surface radiation analysis of symmetric model is supported in version 2020.0 and later.

The above is a model diagram of the full model. The project file contains three symmetric models (half, quarter, and 1/8 models) as well.

The symmetric models require less analysis time than the full model and produce results similar to the full model.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
1/Solid	VOL1	MAT1
4/Solid	VOL2	MAT1

The initial temperature of each body is set as follows.

Body Attribute Name

Tab

Properties

VOL1

Initial Temperature

Specify on Each Body Attribute

Initial Temperature: 100 [deg]

VOL2

Initial Temperature

Specify on Each Body Attribute

Initial Temperature: 0 [deg]

The material properties are set up as follows:

Material Name	Tab	Properties
MAT1	Specific Heat	0.8×103 [J/kg/deg]
	Density	1000 [kg/m3]
	Thermal Conductivity	8X101 [W/m/deg]

Boundary Conditions

The outer boundary condition is set as adiabatic. Therefore this model is isolated thermally from the outer world. The radiation between VOL1 and VOL2 are set in the boundary conditions as follows.

Boundary Condition Name/Topology

Tab

Radiation Setting

Settings

RadFace3/Face

Thermal

Surface-to-surface (Accuracy Prioritized)

Select Individual Setting

Emissivity: 0.7
Group Number: 1

RadFace4/Face

Thermal

Surface-to-surface (Accuracy Prioritized)

Select Individual Setting

Emissivity: 0.5
Group Number: 1

Results

The following graph shows the calculated time variation of the temperatures of VOL1 and VOL2.

The temperatures of the two bodies are converging gradually.