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The main features of the cleanroom air supply outlet, return air outlet, and high-efficiency filter
The main features of the cleanroom air supply outlet, return air outlet, and high-efficiency filterThe main characteristics of a clean room air supply outlet, air return outlet, and high-efficiency filter are that the main feature of turbulent clean room is that the cross-section of the airflow changes from the incoming flow to the outgoing flow (from the air supply outlet to the air return outlet), and the cross-section of the clean room is much larger than that of the air supply outlet, which can't form a uniform airflow in the whole room cross-section or the cross-section of the whole room working area.Therefore, the air supply after the flow lines with each other has a large or growing angle, the radius of curvature is very small, the airflow in the room can not be a single direction of flow, will hit each other, there will be reflux, vortex generation. This determines the flow of a turbulent clean room is the essence of the flow: mutation flow; and non-uniform flow. This is more accurate and comprehensive than the turbulent flow to describe the turbulent clean room. Turbulent flow is mainly determined by the Reynolds number, that is, mainly affected by the flow velocity, but if a high-efficiency filter top-feeding air supply form, even if the flow velocity is very low, but also produces the above results, because it is a mutant flow and non-uniform flow. Therefore, in this case, there is not only the flow layer due to turbulent flow and mixing but also the whole room-wide large backflow, vortex mixing. Unidirectional flow cleanroom: There are two general types of unidirectional flow cleanrooms, horizontal flow and vertical flow. In a horizontal flow system, the airflow is from one wall to the other. In a vertical flow system, the airflow is from the ceiling to the floor. Unidirectional airflow is used where the cleanroom is required to have a lower concentration of suspended particles or microorganisms. This type of cleanroom was previously referred to as a "laminar flow" cleanroom. The names unidirectional and laminar both describe the condition of the airflow: the air flows in one direction (either vertically or horizontally) and passes through the space at an even velocity, typically 0.3 m/s to 0.5 m/s (60 ft/min to 100 ft/min). The air is supplied to the room by high-efficiency filters that line the ceiling of the cleanroom. The airflow acts as an air piston, flowing down through the room, picking up contaminants, and then exiting through the floor. After mixing with some fresh air from outside, the air is recirculated to the high-efficiency filters. Suspended contaminants from people and processes are immediately removed by this air, whereas turbulent flow ventilation systems use the mixing and dilution principle. In an empty room without any obstructions, unidirectional flow removes contaminants very quickly with a much lower air velocity than previously mentioned. However, in an operating room, machines and people walking around the machines can create obstacles to the airflow. Obstructions can turn unidirectional flow into turbulence, which creates air masses around the obstruction. The movement of people can also cause unidirectional flow to become turbulent. In these turbulent flows, there is less dilution of air due to lower wind speeds, resulting in higher pollution concentrations. It is therefore important to maintain wind speeds in the range of 0.3 m/s to 0.5 m/s (60 ft/min to 100 ft/min) so that interrupted unidirectional flow can be restored quickly enough to adequately dilute the pollution in the turbulent zone around the obstacle. Unidirectional flow can be correctly expressed in terms of air velocity, since the higher the air velocity the cleaner the room will be. The number of air changes per hour is related to the volume of the room, such as the height of the ceiling, so it is not suitable to express unidirectional flow. The volume of air supplied in a unidirectional flow room is many times (10 to 100 times) higher than in a turbulent flow room. |
