Modeling Phase Change During Adiabatic Expansion with ANSYS CFD Simulation

Modeling Phase Change During Adiabatic Expansion with ANSYS CFD Simulation Hello everyone, this is Mohsen Seraj. I'm a senior application engineer, and today I want to have another video about adiabatic expansion cooling processes. The focus of this part is on phase change using safety analysis.

Adiabatic expansion refers to the process where gas passing through an opening suddenly expands. If there is no heat transfer from the walls, this causes a temperature drop and pressure reduction of the gas. This is a cooling method that can be used efficiently, as it doesn't require energy input.

It can also save millions or even billions of water records, which is beneficial for the environment. Adiabatic expansion is not limited to industry; it also occurs in geology and nature. For example, when air expands as it goes up, the pressure and temperature drop.

This principle can be applied in air conditioning systems, data centers, adiabatic chillers, and cooling towers. In an adiabatic system, the flow of warm, usually dry air passing through a duct with sudden expansion can cause cooling and even droplet formation, indicating phase change.

The exit of the adiabatic system continues to show growth due to the lower temperature and increased humidity of the air. Importantly, there is no additional energy input required for cooling the air and increasing its humidity.

In the next section of this video, I will show you a CFD simulation using ANSYS Workbench. We will work on the same geometry as in the previous example. The thinner part has a radius of 40, while the larger part has a radius of 200 millimeters.

The ratio is 4 to 1. For the mesh, we will use a much smaller size, as we are working on phase change. We will have a very small radius for surface mesh sizing. The other steps will be the same as before.

For the inlet, we will consider a mass flow rate, and for the outlet, we will have an outlet pressure. The walls will be defined as inlet, outlet, and walls regions.

We will consider five layers for the boundary layer and create a volume machine with minimum orthogonality of 0.2, improved to 0. 3. For the model, we will use a multi-phase model with a mixture of two phases: water vapor as the primary phase and water liquid as the secondary phase.

For phase interaction, we will set heat and mass transfer between the phases using the evaporation-condensation mechanism. We will consider the saturation temperature of 95 degrees for this problem. For the inlet, we will consider a mass flow rate for vapor and 0 for liquid.

The temperature will be 100 degrees. For the outlet pressure, we will consider ambient pressure at 100 kilopascals. The walls will be insulated with zero heat flux. For the method, we will use a second-order field for the discretization of turbulent parameters.

Pressure will be set for monitoring or report definitions. We will set up reports for monitoring the maximum temperature or minimum temperature in the domain and maximum velocity. We will also define a plane symmetry for the outlet.

We will initialize the domain from the inlet with a temperature of 100 degrees and zero velocity everywhere. After initializing the domain, we will run the simulation and monitor the results. In the adiabatic expansion system, we expect to see phase change in addition to cooling.

This can be observed through the temperature, volume fraction of liquid, and mass flow rate between the phases. Negative mass transfer rate values indicate condensation, indicating phase change from vapor to liquid.

After running the model for further iterations, we will observe the minimum temperature, maximum temperature, maximum velocity, vertex minimum for temperature, and pressure at the outlet. We will also check the contours for temperature and mass transfer rate between the phases.

Thank you for being with me.