COVID-19 Transient Breathing in the Operating Room

COVID-19 Patient Transient Breathing in the Operating Room CFD Simulation, ANSYS Fluent Training

The problem simulates the COVID-19 Transient Breathing in the Operating Room airflow from a patient’s mouth by ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

In fact, in the present case, a particular operating room has been designed that is equipped with ventilation and air conditioning systems. On the other hand, the patient receives oxygen and exhales carbon dioxide every time he inhales and exhales.

The main purpose of this simulation process is to allow fresh air (oxygen-carrying) to flow continuously into the room’s interior rather than expel polluted air from the patient’s mouth to the environment.

Ventilation systems and air conditioners designed on the room’s ceiling and floor are responsible for circulating fresh air inside the room and directing it from the side pores to the outside environment.

The model consists of a cubic room with dimensions of 2.9 m ⨯ and 2.23 m ⨯ , 3.7 m, so a hospital bed and a patient are designed on it. Also, six circular holes are considered fresh air inlet flow, and five rectangular holes are considered to flow outlet sections in the room’s sidewalls.

The current model is three-dimensional and is drawn using Design Modeler software. Because the main purpose of the problem is to focus on the exhaled airflow from the patient’s mouth, the patient’s oral surface is considered the inlet boundary.

The meshing is done using ANSYS Meshing software. The mesh type is unstructured, and the element number is 4354238. Meshing is smaller in the areas adjacent to the internal borders and has higher accuracy.

Due to the dependence on respiration over time, the present problem is unsteady and has a time step of 0.01 s.

COVID-19 Methodology

The fresh air flow entering the room’s interior is composed of a combination of oxygen and nitrogen with a ratio of 3.76. Exhaust air from the patient’s mouth also contains carbon dioxide.

Therefore, the Species Transport model has been used in the present simulation. Thus, the airflow with an oxygen mass fraction of 0.23 and nitrogen with a mass fraction of 0.77 and without any percentage of carbon dioxide from the room’s air conditioners enters the room’s interior space.

This fresh airflow has a speed of 1 m/s and a temperature of 293.15 K.

Also, because the flow of air consisting of oxygen, nitrogen, and carbon dioxide in the form of exhaled air comes out of the patient’s mouth as a source, a Discrete Phase Model (DPM) has been used; Because in this model, the particles that make up the flow of the exhaled gaseous species are tracked, this type of view is called Lagrangian view in examining the fluid behavior of the particles.

In this model, it is assumed that the exhaled air from the patient’s mouth has oxygen with a mass fraction of 0.16, carbon dioxide with a mass fraction of 0.04, and a temperature of 310.15 K.

Also, the input flow rate from the oral area is defined as the UDF. In reality, when breathing, the mouth constantly inhales, and the nose exhales; But in the present model, only the mouth is assumed to be a constant source for both inhaling and exhaling.

Therefore, both inhalation and exhalation should be defined for the oral area. So to determine the velocity of the incoming airflow from the mouth to the interior of the room, a UDF is used.

The magnitude of the airflow velocity is 0.25 m/s; So, in each 2.5 s interval, the value becomes negative or positive, depending on whether the action is inhaled or exhaled. So the input velocity in the mouth area has a positive value at the exhalation time because it rejects the air.

At the time of the inhalation, it has a negative value because it receives air.

COVID-19 Conclusion

We use the DPM when the aim is to investigate the behavior of the particles from a Lagrangian and discrete perspective.

In the present model, the exhaled airflow, including oxygen, nitrogen, and carbon oxide, is transmitted from the patient’s mouth as a particle to the inner space of the operating room. By selecting the unsteady particle tracking mode, the behavior of the discrete airborne particles is affected over time.

So, we can quickly analyze the CORONAvirus particle in the operation room in the presence of air conditioning and ventilation systems in terms of time.