Particle Emission from a Bursting Fire Extinguisher CFD Simulation, ANSYS Fluent

Description

Description

Fire extinguishers contains a variety of different materials. In this simulation, we will consider the powder fire extinguisher. The main material in these capsules is “ammonium dihydrogen phosphate” with a density of 1800 kg/m³. This material is stable until 200°C, and beyond that limit, it decomposes into NH₃ and H₃PO₄.  Also, this material is soluble in water, and when it dissolves, it imparts an acidic property to the water, so it can be dangerous to nature. In cylindrical capsules, the greatest tension is created in the vertical direction in their walls, so the capsules are almost always damaged in this direction.

In this simulation, the crack on the cylinder is modeled in the same direction. A capsule with a 40 cm diameter and 80 cm length is considered and simulated in a domain with dimensions of 200*200*50 meters to determine how far its content can disperse when the fire extinguisher is damaged, with a 15 m/s wind blowing in the area.
The fire extinguishers are usually pressurized to 50 atm, so the emitted substance’s velocity can be around 100 m/s.
The geometry is designed in SpaceClaim® and meshed using ANSYS Meshing®. The mesh is unstructured around the capsule and structured in most of the domain, with the 1,172,162 produced elements.

Methodology

In this simulation, the turbulence effect is modeled with the k-ε standard model, and emissions are simulated using the Discrete Phase Method (DPM) along with inert particle models of 0.7 mm diameter. In boundary condition section the wall DPM boundary is set to trap the particles.

Results

Contours of velocity and pressure around the capsule are presented in the cross section plane. Also, particle pathways are tracked, and the results show that emissions can travel between 67 to 126 meters downstream before settling on the ground.
Initially, the particles’ initial velocity causes them to elevate, and the force of gravity eventually pulls them back to the ground. However, this process takes time, and during this period, the drag force acting between the particles and the free-stream air pushes them downstream, away from the capsule.