Home / Examples / Thermal Analysis [Watt] / Example 6: Heat Radiation by Natural Convection (Transient Analysis)

Example 6: Heat Radiation by Natural Convection (Transient Analysis)

General

The model is the same as the example 5: The heat radiation from an aluminum plate with its bottom face fixed at a specified temperature is analyzed. This is a transient analysis.
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	mm

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 30. The timestep is 10 sec.

Therefore, the temperature distributions for 300 sec are solved.

Tab

Setting Item

Settings

Transient analysis

Table

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

Initial Temperature

25 [deg]

Model

The same as example 5. The body attributes, the material properties and the boundary conditions are the same as well.

Aluminum plate, defined by a rectangular solid body, is placed vertically. The bottom face is set with the Temperature boundary condition.

The other faces are set with the Heat transfer/Ambient radiation boundary condition.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	VOL1	404 Pure-Al1100 *

* Available from the material DB

Boundary Conditions

The coefficient for the natural convection is given by the formula below. For the details, please refer to the Thermal tab.

The coefficient can be calculated automatically by selecting [Heat transfer] > [Natural convection (automatic calculation)] for the boundary condition.

2.51×C×（1/L)＾（1/4） = 2.50 [W/m2/deg5/4]

where

C = 0.56

L = 0.1

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Settings

Temp/Face

Thermal

Temperature

80 [deg]

Outer Boundary Condition

Thermal

Heat Transfer: Convection

Natural Convection: 2.50 [W/m2/deg5/4]

Ambient Temperature: 25 [deg]

Results

The temperature distributions in 20 sec, 60 sec and 120 sec are shown below.

At Minimum/Maximum Value on the Contour tab of [Graphics Setup], deselect [Automatic] and set 25 => 80.

In 20 sec

In 60 sec

In 120 sec

The heat creeps up as the time goes by.

The chart below shows the temperature of the tip of the plate.

It stabilizes at around 200 sec.