Passive Ventilation by PCM, ANSYS Fluent CFD Simulation Tutorial
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- The present CFD Project simulates PCM for Passive Ventilation via ANSYS Fluent software.
- We modeled the geometry using ANSYS Design modeler software and created the mesh using ANSYS meshing software.
- The meshing is structured, and the number of cells for the first and second models is 228448 and 241560, respectively.
- The solidification and Melting Model has been used to define PCMs.
- Incompressible Ideal Gas has been used to define density changes.
- The problem is dependent on time and unsteady.
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This project is related to a simulation of PCM for passive ventilation using ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.
Phase change materials can store energy and give it back to the environment when necessary.
So, PCMs can cause cooling and heating and also thermal storage in the environment by changing the phase between solid and liquid.
If the ambient temperature is high, the phase change from solid to liquid occurs. The resulting liquid stores the latent energy of melting.
Meanwhile, the phase change from liquid to solid happens if the ambient temperature decreases. The resulting solid releases the latent energy of solidification.
So PCMs cause heat transfer without using any mechanical device. Therefore, these systems are included in the passive ventilation group.
This passive ventilation system works based on the buoyancy effect. The difference in density caused by temperature changes leads to natural convection.
In this project, we have modeled a passive ventilation system. We performed this project in two steps.
- We only investigated a room’s natural convection heat transfer in the first step. We assumed that one of the walls had a constant heat flux. This heat is derived from the warm air of the surrounding environment and the radiation of solar rays.
2. We used a PCM panel for the same heated wall in the second step. Our goal was to investigate the effect of PCMs on heat transfer.
We designed the geometry of the model using Design Modeler software. We modeled a simple room for the first step, and in the next step, we also applied a PCM panel.
Then we meshed the model using ANSYS Meshing software. The meshing is structured, and the number of cells for the first and second models is 228448 and 241560, respectively.
Passive Ventilation Methodology
Using ANSYS Fluent software, we numerically simulated this model according to computational fluid dynamics (CFD). This problem is dependent on time and unsteady state, and the solution is based on the pressure-based solver.
In this project, we need to define the phase change process between solid and liquid. The operating mechanism of phase change materials is based on continuous phase changes.
Then we use the solidification and melting model. When we use this model, we need to determine three parameters for our PCM.
The maximum temperature at which the solid phase prevails is equivalent to the solidus temperature. The minimum temperature at which the liquid phase prevails is equivalent to the liquidus temperature. Another parameter is equivalent to pure solvent melting heat.
As we said, natural convection heat transfer also happens in this problem. Natural convection is created based on the buoyancy effect. This means that changes in temperature cause changes in density.
Therefore, we do not consider the air density constant to apply the buoyancy effect. Then we use the incompressible ideal gas option to change the air density.
The relation between density, pressure, and temperature according to the ideal gas law is used in the incompressible ideal gas model. Note that the density is dependent on the operating pressure and is independent of the local relative pressure. So assuming constant pressure, density becomes a function of temperature.
Passive Ventilation Conclusion
After the simulation, we obtained the plot of the average temperature inside the room over time. This plot compares two modes (with PCM and without PCM).
Also, we obtained 2D and 3D temperature contours and velocity vectors.
We want to analyze the effect of using PCM in passive ventilation.
The results show that the temperature increases over time in the first simulation. The heat flux of the wall and heat transfer inside the room lead to an increase in temperature.
Meanwhile, the temperature increases with the minimum slope in the second simulation.
Although the heat flux is applied, the presence of the PCM layer between the heat flux and the room space is effective. So these phase change materials receive heat in the form of latent heat. As a result, low heat penetrates the room.