This paper presents a study regarding the thermal plumes generated by two thermal manikins in different positions, both numerically and experimentally. The numerical model represents an operating room with two surgeons, a patient, and a ventilation system with a unidirectional airflow diffuser, also called a laminar airflow diffuser, and outlets placed in the corners. The experimental study was made in a climatic chamber, similar with the numerical model, using particle image velocimetry and infrared thermography measurements. The thermal plumes of the two manikins were obtained by numerical and experimental studies. Another purpose of the study was to see how these thermal plumes will interfere with a low velocity ventilation system, like a unidirectional airflow system. The studies showed thermal plume velocities up to 0.35-0.4 m/s for a human subject that is standing and up to 0.2 m/s for a human subject that is lying on a bed. Analyzing the interaction of the thermal plumes with a diffuser that has low airflow velocities, like a laminar airflow system, one can observe that velocities !0.2 m/s will have difficulties in overcoming the thermal plumes generated by human subjects that have a sedentary to moderate activity.
The aim of this study is to determine how the air flow from a unidirectional air flow (UAF) system and a local ventilation system will interact with each other. The study analyzes the air circulation near the operating table at different air flow velocities from both systems. The air flow velocities correspond to the usual range of velocities that are recommended by norms and guidelines. The research was approached by numerical and experimental studies. The thermal plume of the patient was measured by Particle Image Velocimetry (PIV) and thermography (IR) and compared with the results from the numerical case. A mesh independency study was made for the numerical case. The study showed that velocities ≥0.2 m/s from the UAF, depending on the height of the room, can overcome the thermal plume generated by a human subject with a moderate activity (100÷120W). The velocities from the local ventilation system need to be higher with at least one step, in accordance with the distance from the ventilation system to the operating wound, in order to avoid disturbances generated from the UAF system.
In order to achieve more realistic boundary conditions on the inlet of a ventilation system it is necessary to study the influences of the air diffuser orifices geometry on the airflow distribution in the enclosure. Integrating these orifices directly in a real scale air diffuser for a numerical study will result in a huge computational grid which will translate in huge computational resources and a much larger calculation time. The solution, in this case, was the numerical simulation of the airflow through small parts of the studied air diffuser. Later, the numerical results will be implemented as boundary conditions in the unidirectional diffuser of a numerical simulation that represents a real scale operating room (OR). In the current study two diffusers with different orifices were studied, one having circular („O”) and the other one lobbed („+”) orifices. The initial numerical model had 25 orifices on the diffuser, but because of the very large numerical grid resulted for the initial meshes (>35 million tetrahedral cells), a solution with only 4 orifices was chosen for this study. A mesh independency study was made for these two types of air diffusers. The numerical studies were made using RANS method, with SST k-ω turbulence model in steady state conditions. The numerical results obtained with the first step models showed very good agreement with the PIV stereoscopic experimental measurements.
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