Fire and Smoke in a Factory Building, CFD Simulation Tutorial

Description

Fire & Smoke in a Factory Building, CFD Simulation Tutorial

Description

The present problem simulates the combustion reaction (Fire & Smoke) of a pressure tank in a factory via ANSYS Fluent software. A factory is modeled as a computational zone. Several elements have been modeled within this space, including tanks, plates, boxes, etc. A cylindrical pressurized tank leaks, and flammable methane gas leaks into the tank’s outer environment. At this time, the contact of free ambient airflow with methane leads to reaction.

This project aims to investigate the behavior of the combustion flame and the path of smoke emission from combustion over time. So this simulation is done in a time-dependent manner.

This simulation is done in two steps. The first step only investigated methane leakage from inside the tank to the outside environment.

In this case, methane is released into the interior space over time. In the second step, this leaked gas reacts with air and ignites. As a result of the combustion reaction, flame and smoke or carbon dioxide gas are produced.

In the first step, there is no need to define the chemical reaction; only air and methane are defined without the reaction occurring.

The air inside the factory and the methane inside the tank is under pressure. The groove at the top of the tank is modeled as the leakage center, and defining a higher initial pressure for methane inside the tank under pressure leads to the release of methane to the outside environment.

After the release has fully occurred, it is time to define the combustion reaction between methane and free air. So with stoichiometric coefficients, a chemical reaction including methane and oxygen as reactants and carbon dioxide and vapor as products are defined.

Also, a spark is defined in the groove section of the tank to help the combustion occur.

The present geometry is designed in a 3D model via Design Modeler, and the mesh has been done via ANSYS Meshing software. Mesh is done unstructured, and the number of production cells equals 124,162.

Methodology: Fire & Smoke in a Factory Building

The viscous model used in the solution is RNG k-epsilon with a standard wall function. The solver is Transient, and the Energy equation is enabled to capture the temperature. Also Species Transport model simulates the combustion reaction.

Conclusion

After simulation, the behavior of the reactants and reaction products has been investigated. To study the behavior of the flame, the iso-surface has been used at a constant temperature. The flame temperature is determined as a measure to represent the level of the flame.

In investigating the smoke resulting from combustion, the behavior of carbon dioxide gas has been examined; Because this gas is defined as a product of the combustion reaction. Carbon dioxide gas mass fraction is determined as a measure representing the iso-surface.

To investigate the behavior of methane caused by leakage, its mass fraction has been determined as a measure of the iso-surface display. Investigation of methane leakage before combustion and combustion flame and carbon dioxide emission after combustion has been done.

This review has been done at different times and presented by animation. In the first step of the simulation, the results show the tank leakage process well. First, methane fills the pressure tank; But when a leak occurs, methane is released into the outside environment at high pressure. In the second step of the simulation, the results are presented as the occurrence of the combustion reaction.

The temperature rises significantly, which is caused by the explosion. The flame grows at the beginning of combustion and begins to fade over time. Carbon dioxide gas is also produced in space. This indicates the combustion incidence; this gas is considered the product of this chemical reaction. Carbon dioxide gas also erupts at the beginning of ignition, and its volume decreases with time.