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Corona Virus Dispersion in an Elevator Cabin due to a Sneeze

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an attempt has been made to simulate the dispersion of corona virus particles due to cough from the mouth of a corona virus carrier patient inside the interior of an elevator cabin.

This ANSYS Fluent project includes CFD simulation files and a training movie.

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Description

Corona Virus Dispersion in an Elevator Cabin due to a Cough Project Description

Corona virus (COVID-19) is currently recognized as the greatest human challenge in the world; Because this disease, in addition to being dangerous to human health, has a high transmission power between a sick person and healthy people. Coughing or sneezing of a sick person without mask in a space causes the spread of corona viruses. One of the important recommendations of physicians in preventing the transmission of disease between people is to care about social distance between people in society.

The elevator cabin is one of the most important spaces in the discussion of corona virus disease; Because usually a number of people with the shortest possible distance are placed in a small space with a not very strong ventilation system. In this project, based on the CFD method and using ANSYS Fluent software, an attempt has been made to simulate the corona virus particles dispersion from the carrier patient cough inside an elevator cabin.

This model includes a computational domain in the form of an elevator cabin in which two humans are modeled; One of them is considered as a corona virus patient who coughs or sneezes and the other person is considered as a person who is at a certain distance from the patient and is exposed to the corona virus particles. The purpose of this work is to investigate the ability of virus particles to spread inside the elevator interior and the possibility of transmitting it to another person.

Project Description

For the present simulation, the discrete phase model (DPM) is used; Because this model allows us to study a mass of particles discretely in a continuous fluid space. Due to the choice of this model, the wet particles of the corona virus secreted from the patient’s mouth are considered as a discrete phase and the air flow transmitted through the elevator ventilation valves is considered as a continuous phase inside the interior of the elevator cabin.

The physical models of discrete particles defined in this simulation include two-way turbulence coupling meaning the two-way interaction between continuous and discrete phase (in addition to the discrete phase is affected by the continuous phase, by activating the interaction with continuous phase mode, discrete phase also affects the continuous phase), stochastic collision means irregular droplets collide with each other, coalescence means droplets merge with each other, and breakup means The collapse of the droplets.

Also, the type of discrete phase behavior will be time dependent and with a time step of 0.001 s (by activating the unsteady particle tracking mode). After activating the discrete phase model, the injection process must be defined, which determines the type and quality of discrete particles injected into the model. In this model, injection particles are defined as droplet; Thus, water is defined as droplets and water vapor is defined as an evaporating gas species. The injection is performed superficially and through the inner SURFACE of the patient’s mouth (inlet-mouth).

Project Description

According to this definition of injection, human cough virus virus particles are physically expelled from the patient’s mouth by water droplets that are evaporating in space. These virus droplets have a temperature of 310 K, a velocity of 31.85 m.s-1, and a mass flow of 0.018 kg.s-1, which are emitted at intervals of 0s to 0.1s. The particle diameter of the virus is not constant during propagation and the rosin-rammler-logamethric distribution method is considered for the size of the diameters.

Following this method and the relevant formulation, the values related to the minimum, maximum and average diameter size determine the exponential parameter of the spread and the number of diameters per injection. It should be noted that the drop mode is applied when the species transport model is also activated.

The boundary conditions of the discrete phase model are defined as particles at the boundaries of the patient’s mouth and the inlet and outlet of the elevator airflow with Escape mode, meaning that the particles pass through these boundaries, and at the boundary of the human body the Reflect mode is applied. It means the reflection of particles that collide with this boundary, and at the boundary of the side walls of the elevator cabin, the Trap mode is used, which means that particles are trapped and accumulate in this boundary.

Project Description

Also, the ventilation and air conditioning system of this elevator is such that fresh air flow enters the elevator cabin as a continuous fluid from the parts installed on the ceiling of the elevator with a speed equal to 2 ms-1 and a temperature equal to 291 K. The air flow exits from the outlet at the bottom of the cabin to the outside environment at a pressure equivalent to atmospheric pressure. It should be noted that the fresh air entering the elevator has oxygen with a mass fraction equal to 0.18. The present simulation process is performed in a time interval for 5.25s with a time step size equal to 0.0025 s.

corona virus

 

Elevator Geometry & Mesh

The present model is designed in three dimensions using SOLIDWORKS and Design Modeler software. The geometry of the model includes an elevator cabin with dimensions of 2 m * 2 m * 2.8 m, inside which two people are modeled. One of the two people is patient and should be identified as the source of the cough. Hence, the inner surface of the patient’s human mouth is differentiated by the inlet-mouth boundary condition; Because this surface is assumed as the reference boundary of discrete phase corona virus release.

corona virus

We carried out the meshing of the model using ANSYS Meshing software and the mesh type is unstructured. The element number is 454433. The following figure shows the mesh.

corona virus

Corona Virus Dispersion CFD Simulation

To simulate the present model, we consider several assumptions:

  • We perform a pressure-based solver.
  • The simulation is transient. Because the purpose of the problem is particle tracking related to the discrete phase over time.
  • The gravity effect on the fluid is equal to -9.81 m.s-2 along the Z-axis.

A summary of the defining steps of the problem and its solution is given in the following table:

Models
Viscous k-epsilon
k-epsilon model RNG
near-wall treatment standard wall function
Species model Species Transport
number of volumetric species 3 (H2O,O2,N2)
Discrete phase model On
interaction interaction with continuous phase
particle treatment unsteady particle tracking
physical models two-way turbulence coupling
stochastic collision
coalescence
breakup
Injection active
injection type droplet
release from surfaces inlet-mouth
material water-liquid
evaporating species H2O
diameter distribution rosin-rommler-logarithmic
point properties temperature 310 K
velocity 31.85 m.s-1
total flow rate 0.018 kg.s-1
Energy On
Boundary conditions
Floor Wall
wall motion stationary wall
heat flux 0 W.m-2
discrete phase conditions reflect
Walls of Elevator Wall
wall motion stationary wall
heat flux 0 W.m-2
discrete phase conditions trap
Inlet-Air Velocity Inlet
velocity magnitude 2 m.s-1
temperature 291 K
discrete phase conditions escape
H2O mass fraction 0
O2 mass fraction 0.18
Outlet-Air Pressure Outlet
gauge pressure 0 Pascal
discrete phase conditions escape
Inlet-mouth Wall
wall motion stationary wall
heat flux 0 W.m-2
discrete phase conditions escape
Two Men Body Wall
wall motion stationary wall
heat flux 0 W.m-2
discrete phase conditions reflect
Methods
Pressure-velocity coupling Coupled
pressure second oedre
momentum first order upwind
H2O first order upwind
O2 first order upwind
energy first order upwind
Initialization
Initialization methods Hybrid

Results

At the end of the solution process, we obtain the virus particle tracking at the last second of the simulation process. This particle tracking is based on residence time and particle diameter size. We also export the animation of the virus dispersion and its disappearance over time and attached to the project report file. Finally, we obtain three-dimensional contours related to the temperature and mass fraction of oxygen released from the ventilation system and water droplets secreted from the cough.

All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.

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