Home / Examples / Fluid Analysis [Bernoulli] / Example 20: Room Ventilation (Air of Humidity)

Example 20: Room Ventilation (Air of Humidity)

General

The case where the air of 60% humidity flows into the room of air of 30% humidity through its window is analyzed.
The case where the air of 30% humidity flows into the room of air of 30% humidity from the door is analyzed.
A comparison has been made between two cases: one taking into account the weight of water vapor, and the other not.
See [Diffusion Analysis] for setting 30% and 60% humidity.
Unless specified in the list below, the default conditions are applied.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	m

Analysis Condition

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	180	5	1

Diffusion Analysis

Fluid Analysis

Diffusion Analysis Setting

Select Execute diffusion analysis

Analysis type: Transient Analysis

Type and Unit of Diffusion Quantity: Molar Concentration

Ambient Value (Default Value): 0.3834 [mol/m3]

See [Diffusion Analysis] for setting 30% humidity.

Initial Value: Use ambient value

Take into account buoyancy:

Analysis Model

Settings

Buoyant

(Take into account buoyancy)

Select Take into account weight of diffusing materials..

Select [300_Water Vapor H2O] in the material DB and click [Input].

No_Buoyant

Do not take into account buoyancy.

Deselect Take into account weight of diffusing materials..

Meshing Setup

Mesh

General Mesh Size: 0.3 [m]

Model

The air domain is shown as below. The model represents a room with a ventilator, a door, and a window. The door and the window are assumed to be opened.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
5/Solid	Room	000_Air *

* Available from the material DB

Boundary Condition

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Door/Face	Fluid	Inlet/Outlet	Natural Inflow/Outflow Diffusion Analysis Setting Select Use Ambient Value.
Window/Face	Fluid	Inlet/Outlet	Natural Inflow/Outflow Select [Direct Entry]. 0.7668 [mol/m3] See [Diffusion Analysis] for setting 60% humidity.
Fan/Face	Fluid	Outlet	45 [m3/min]

Results

The streamlines of the flow coming from the window at 180 [s] is shown below.

If buoyancy is not taken into account, a direct flow toward the ventilator is observed, and if buoyancy taken into account, a flow circulating around the top of the room toward the ventilator is observed.

Take into account buoyancy	Do not take into account buoyancy

The contours of molar concentration after 180 [s] are shown below.

If buoyancy is taken into account, the area of high humidity spreads around the top of the room.

Take into account buoyancy	Do not take into account buoyancy