Corona Virus Patient steady Breathing in Clean Room, ANSYS Fluent Training
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The problem simulates the air conditioning system inside a patient’s room considering the CORONA virus.
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Description
Project Description
The problem simulates the flow of fresh air through the air conditioning system inside a patient’s room considering the CORONA virus by ANSYS Fluent software. We place the patient on a bed in a room with a high temperature on his body and constantly spreads the CORONA-virus particles by breathing through his mouth into the room’s interior.
In fact, the goal is to use an air conditioning system and keep the fresh air flowing continuously inside the room to remove contaminants from the patient’s mouth through the outlet vents, and the room environment should be purified in terms of pollution, and a balanced and pleasant temperature should be provided for the thermal comfort of the patient inside the room.
There are two main issues in this CFD simulation. The first issue is that the flow of the CORONA virus in the respiratory must be defined through the patient’s mouth, for which we use a Discrete Phase Model (DPM); Because in this model, we track the particles of the CORONA virus, we apply this type of view (Lagrangian view) in examining the behavior of particles.
Project Description
In fact, the difference between Lagrangian and Eulerian view is that we examine the fluid behavior in Lagrangian view on the basis of particle tracing. Whereas fluid behavior is considered in Eulerian view based on the assumption of a finite volume element in the fluid flow path.
Therefore, an injection process has been used in this model, in which these CORONA virus particles, called anthracite, are injected into the outer space as a surface inlet from the patient’s mouth. The second issue is that the patient’s comfort should be considered in terms of the temperature of the interior of the room and also the discussion of indoor air conditioning in the current model so that the indoor air of the room is ventilated for fresh air supply.
For this purpose, two specific parameters for describing thermal comfort conditions have been used, including PMV indicating the scale of thermal comfort and PPD indicating the percentage of dissatisfaction with the air, and also a scalar variable for the average air life, which indicates the persistence and age of the air available in the room.
In the present model, the fresh airflow from the upper vents of the room has a velocity equal to 0.58 ms-1 and a temperature of 294 K, the patient’s body surface temperature is equal to a constant value of 308 K. The virus particles are injected from the patient’s mouth at a rate of 0.05 m.s-1 and a temperature of 308 K with a diameter of 0.000001 m.
Geometry & Mesh
The present model is three-dimensional and is drawn using the Design Modeler software. The model consists of a cubic room with dimensions of 2.9 m ⨯ 2.23 m ⨯ 3.7 m; So that a hospital bed and a patient are designed on it. Also, six circular holes are considered as fresh air inlet flow and five rectangular holes are considered as flow outlet sections in the sidewalls of the room. The following figures show a view of the geometry.
The meshing is done using ANSYS Meshing software. The mesh type is unstructured and the element number is 5666870. Cells are smaller in the areas adjacent to the internal boundaries and have higher accuracy. The following figure shows a view of the mesh.
Air Conditioning of a patient’s room (CORONA virus) CFD Simulation
To simulate the present model, we consider several assumptions:
- The solver is pressure-base.
- The present simulation is steady in terms of time.
- The gravity effect is equivalent to -9.81 m.s-1.
Here is a summary of the steps for defining the problem and its solution in the following table:
Models (CORONA) | ||
Viscous model | k-epsilon | |
k-epsilon model | realizable | |
near-wall treatment | standard wall function | |
Discrete phase | on | |
particle treatment | steady particle tracking | |
material in injection | anthracite | |
particle type in injection | inert | |
injection type | surface | |
Energy | on | |
Boundary conditions (CORONA) | ||
Inlet | Velocity inlet | |
velocity magnitude | 0.58 m.s^{-1} | |
temperature | 294 K | |
discrete phase BC type | reflect | |
Outlet | Pressure outlet | |
gauge pressure | 0 Pascal | |
discrete phase BC type | escape | |
Inlet – mouth | Velocity inlet | |
velocity magnitude | 0.05 m.s^{-1} | |
temperature | 308 K | |
discrete phase BC type | escape | |
Patient | (CORONA-Virus) | Wall |
wall motion | stationary wall | |
temperature | 308 K | |
discrete phase BC type | trap | |
Bed & Walls | Wall | |
wall motion | stationary wall | |
heat flux | 0 W.m^{-2} | |
discrete phase BC type | trap | |
Solution Methods (CORONA) | ||
Pressure-velocity coupling | Coupled | |
Spatial discretization | pressure | second-order |
momentum | second-order upwind | |
turbulent kinetic energy | second-order upwind | |
turbulent dissipation rate | second-order upwind | |
energy | second-order upwind | |
CORONA | Initialization | |
Initialization method | Standard | |
gauge pressure | 0 pascal | |
y-velocity | -0.58 m.s^{-1} | |
x-velocity, z-velocity | 0 m.s^{-1} | |
temperature | 294 K |
Discrete Phase Model (DPM) for CORONA Virus
We use the discrete phase when the aim is to investigate the behavior of the particles from a Lagrangian and discrete perspective. In the present model, the CORONA virus flow in the patient’s respiratory air is transmitted from the patient’s mouth to the inner space of the hospital room. By selecting the unsteady particle tracking mode, the behavior of the discrete particles in the breathing air is steady and time-independent.
Also, we define the injection process for the discrete phase. The material of the injected particles in this model is defined by the same anthracite and with properties including density equal to 1000 kg.m-3 and specific heat capacity equal to 1680 j.kg-1.K-1. It is injected into the inner space of the hospital room from the patient’s mouth. The type of injection process is SURFACE and the type of CORONA virus particles is INERT.
The inert mode is an element of the discrete phase (particle, droplet, or bubble) that follows the balance of forces. Particle properties for each particle of the CORONA virus in the respiratory air, including a diameter of 0.000001 m, a velocity of 0.05 ms-1, a mass flow rate of 5 * 10-7 kg.s-1, and the temperature is 308 K.
Discrete Phase Model (DPM) for CORONA Virus
Also, to define the boundary conditions related to the discrete phase model, three types of discrete particle behavior are used with respect to boundary areas; In this case, the Escape mode is used when the discrete phase, only crosses the desired boundary, and the Trap mode is used when the discrete phase is trapped adjacent to the desired boundary.
The Reflection mode is used when the discrete phase is reflected from the boundary after reaching the desired boundary. In the present model, the input section for air conditioners uses the reflect mode and the input section for the mouth area and the outputs from the escape mode, and in the walls of the room and bed and patient surfaces, the trap mode is used.
Thermal Comfort (Air Conditioning)
Thermal comfort is a state of mind, separate from the equations of heat transfer and mass and energy balance. But it comes from the concept of thermal comfort, which is one of the variables that affect the mass and heat transfer in the energy balance model. The most common perspective used to describe thermal comfort for estimating and designing buildings has linked the results of psychological experiments and variables to thermal analysis.
In fact, a lot of experiments have been done on humans at universities, and these people have different clothes or are doing different things in different situations. Also, the environment in which the experiments are performed has different air temperatures, different surface temperatures, different humidity levels, different airflow velocities, and different airflow patterns.
Then, the level of comfort of human beings was measured in different states and the response of their average thermal sensation was examined. As a result, the predicted mean vote (PMV) for thermal measurement was obtained in the form of the ASHRAE thermal scale. The values for this criterion vary between -3 and +3, and according to the following table, the different states of heat sensation range from very cold to very hot.
(CORONA-Virus)
sensation | value |
hot | +3 |
warm | +2 |
slightly warm | +1 |
neutral | 0 |
slightly cool | -1 |
cool | -2 |
cold | -3 |
(CORONA-Virus)
Relationships for PMV are derived as a function of six variables including air temperature, average radiant temperature, air velocity, air humidity, wear resistance of clothing, and type of physical activity.
Finally, the PMV relationship is obtained as follows, as a function of the thermal charge (L) on the body, which is the difference between the rate of metabolic heat production (M) and the calculated heat loss from the body to the real environment condition is defined:
There is also a fundamental relationship between the Predicted Percentage Dissatisfied (PPD) and a thermal environment as a function of PMV; As the PMV goes to +3 (very hot) and -3 (very cold), the PPD increases, meaning dissatisfaction increases; While moving to zero, the PPD decreases, i.e. dissatisfaction decreases.
Air Conditioning of a patient’s room (CORONA virus) Results
At the end of the solution process, we obtain two-dimensional and three-dimensional contours of pressure, temperature, velocity, PMV, PPD, and scalar parameters of air life. Also, we present the particle tracking in three dimensions based on the residence time or stability. Also, the path lines and velocity vectors are obtained in three dimensions. The two-dimensional contours are drawn on the XY section.
You can obtain Geometry & Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.
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