Home / Examples / Fluid Analysis [Bernoulli] / Example 19: Convection Caused by Generation of Impurity Substance

Example 19: Convection Caused by Generation of Impurity Substance

The diffusion analysis with the weight of the diffusing materials taken into account is applied for the convection caused by an impurity substance generated in a closed space.
The resulting convection and concentration distribution are compared between cases where the diffusing material is water vapor (H2O), which is lighter than air, and cases where it is sulfur dioxide (SO2), which is heavier.
The flow velocity distribution, the flow velocity vectors, and the impurity substance concentration distribution are solved.
Unless specified in the list below, the default conditions are applied.

Item

Tab

Settings

Solver

Fluid Analysis [Bernoulli]

Analysis Type

Fluid Analysis

Transient Analysis

Timestep

Transient Analysis

Timestep: Specify

No.	Calculation Steps	Output Interval	Timestep [s]
1	20	1	1

Diffusion Analysis

Fluid Analysis

Diffusion Analysis Setting

Select Execute diffusion analysis

Analysis Type: Transient Analysis

Type and Unit of Diffusion Quantity: Molar Concentration [mol/m3]
Select [Take into account weight of diffusing materials].

Diffusing Material Setting:

Analysis Model	Settings
H2O-Wall	Select [300_Water Vapor H2O] from the material DB and click [Input].
SO2-Wall	Select [314_Sulfur Dioxide SO2] from the material DB and click [Input].

Meshing Setup

Mesh

General Mesh Size: 10 [mm]

* Available from the material DB

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Ground/Face	Fluid	Solid Wall
Source/Face	Fluid	Solid Wall	Diffusion Analysis Setting Select Flux Molar Concentration Flux: 0.01 [mol/m2/s]
Outer Boundary Condition	Fluid	Solid Wall

The flow velocity vectors on the section at y=0 at 20 [s] are shown below.

When water vapor, which is lighter than air, is generated on the top of Plate, an upward flow occurs.

When sulfur dioxide, which is heavier than air, is generated on the top of Plate, a downward flow occurs.

H2O-Wall	SO2-Wall

The contours of molar concentration on the section at y=2 at 5 [s], 10 [s] , and 20 [s] are shown below.

If the impurity substance is water vapor, the substance stays at the top of the closed space, and if sulfur dioxide, stays at the bottom.