Cleanrooms rely heavily on airflow to maintain their high levels of cleanliness. The movement and dispersion of dust generated by people, machinery, and building structures are all influenced by air currents. To ensure a controlled environment, cleanrooms use HEPA (High-Efficiency Particulate Air) and ULPA (Ultra-Low Penetration Air) filters, which can remove up to 99.97% to 99.99995% of airborne particles. This filtration process results in highly purified air, capable of achieving cleanliness levels ranging from 1 to 100 million particles per cubic foot. However, despite the effectiveness of these filters, dust sources still exist within the cleanroom—such as machinery, raw materials, and human activity. If not properly managed, this dust can compromise the entire space, making it essential to quickly exhaust contaminated air out of the room.
Airflow is one of the most critical factors in determining the performance of a cleanroom. Typically, the airflow speed is maintained between 0.25 and 0.5 meters per second. This gentle breeze is ideal for maintaining cleanliness but is easily disturbed by movement or equipment. Although increasing the airflow speed can help reduce turbulence and improve air quality, it also increases energy consumption and operational costs. Therefore, the optimal airflow speed should be determined based on the required cleanliness level, balancing efficiency with cost-effectiveness.
To maintain consistent air quality, uniform airflow distribution is crucial. If airflow becomes uneven, especially near walls, vortices may form, making it difficult to achieve and sustain high cleanliness standards. In vertical laminar flow systems, maintaining a consistent wind speed across both the supply and return surfaces is essential. For example, if the airflow speed is too low (e.g., 0.2 m/s) or too high (e.g., 0.7 m/s), eddies can develop, reducing effectiveness. At 0.5 m/s, the airflow tends to be more stable and uniform, which is why most cleanrooms operate within the range of 0.25 to 0.5 m/s.
Several factors can influence airflow in a cleanroom, including process equipment, personnel, construction materials, and lighting. It's important to consider where airflow might be diverted, particularly above production equipment. To prevent dust from spreading, an air shower or entryway is often used before entering the clean area. Additionally, the placement of airflow diversion points on workstations or equipment should be set at two-thirds of the distance from the wall to the center of the room. This ensures that air flows smoothly from the process area to the workspace, preventing contamination from operator activities.
Obstructions such as workbenches can create turbulence, leading to localized areas of poor air quality. Installing return air vents on the workbench can help minimize these eddies. The choice of materials and the design of equipment also play a key role in ensuring smooth airflow and avoiding vortex formation. By carefully planning the layout and airflow dynamics, cleanrooms can maintain optimal conditions for sensitive processes.
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