## 2 Materials and Methods
### CFD Simulation
#### 2.1.1 Model  
The geometry of the model was developed in real dimensions, exactly preserving the dimensions of the interior equipment, such as the operating table, instrument tables, and the operating lamp. The model also includes six people as a source of heat and particles. The positions of the luminaire and the humans in the CFD simulation model is shown in Figure 1. The dimensions of the operating room model are 5.76 \(\times\) 6.05 \(\times\) 2.70 m. The dimensions of the model and interior equipment copy the actual dimensions of the experimental laboratory in Figure 2.  
The total air volume in the CFD model is divided into four parts. The first is VOT, which presents the volume of air above the operating table, where the floor plan dimensions copy the dimensions of the operating table, 2000 \(\times\) 500 mm, with a height of 500 mm. The patient is included in this volume. The other two volumes, named VIT 1 and VIT 2, copy the floor plan dimensions of the instrument tables, 600 \(\times\) 450 mm, and the height is 300 mm. These reference volumes are used to compare the number of particles inside the clean zone. They are proportional to the total amount of particles that are in the volume around the reference volumes. The resulting ratio of particles within the control volume and all particles in the room illustrates the improvement or deterioration of the environment's  
Several parameters affect the character of the particle flow in the operating room. The different states in the operating room can be projected by setting the simulation boundary conditions correctly. The mesh of the CFD model was densified around obstacles to filtered airflow trajectory in the room to capture unwanted turbulence and to faithful represent the Coanda effect as air flows around the objects. The greatest influence on airflow is the ceiling lamp located above the operating table. In addition to disturbing the directed flow, the air velocity profile may be affected by the higher surface temperature of the light source. The element type was subsequently modified using Ansys Fluent solution software to a polyhedra type in order to improve the quality of the network and reduce the number of elements. The simulation was performed in transient mode, so it was time dependent. The time step of one iteration was chosen to be 0.05 s and the total simulated time was 5 min. The gravity and energy model makes it possible to simulate buoyancy forces and the effect of natural convection caused by different temperature gradients. In this work, an energy-neutral environment without external heat loads or losses through the perimeter structures of the operating room is considered. Heat gains are only considered from the staff and the operating light. The temperature of structures, equipment, and air supply is 24 \({}^{\circ}\)C. The surface temperature of the operating LED lamp was set to 40 \({}^{\circ}\)C. A higher temperature, in combination with the Coanda effect, results in a change in the airflow velocity profile. The surface temperatures of the human body were set at 30 \({}^{\circ}\)C. Humans are the majority source of particles, as the natural convection caused by the temperature gradient from peoples' bodies can affect their distribution throughout the operating room. The multi-phase model ensures the emission of a given number of particles from each of the selected areas. According to measurements, one person in an ISO EN 7 cleanroom produces approximately 30,000 particles per minute up to 0.5 \(\upmu\)m in size [44]. This value is calculated based upon the emission of particles from the surface of the body, clothing, talking, breathing, coughing, and other activities. The ventilation system is a mechanism for cleaning the building, but its filtering ability is not perfect. Although the (HEPA) filters serve to eliminate the measurement error by the primary particles [45], filters will miss a certain amount of particles, which was considered in the simulation at 25 min\({}^{-1}\) in one cubic meter of supply air.