Flow of clean room air

The cleanliness of clean rooms is often affected by airflow. In other words, the movement and diffusion of dust generated by people, machine compartments, building structures, etc. are governed by airflow.

 

The clean room uses HEPA and ULPA to filter the air. The dust collection rate is as high as 99.97~99.99995%, so the air filtered through this filter can be said to be very clean. However, in addition to people, there are still dust sources such as organic devices in the clean room. Once the dust generated is diffused, the clean space cannot be maintained. Therefore, it is necessary to use the air current to quickly discharge the generated dust.

 

The airflow in the clean room is an important factor in the performance of the clean room. Generally, the airflow speed of the clean room is between 0.25 and 0.5 m/s. This airflow is a breeze area, which is susceptible to movements by people and machines. Although increasing the wind speed can suppress the influence of this disturbance and maintain the cleanliness, the increase of the wind speed will affect the increase of the running cost. Therefore, when the required cleanliness level is met, the wind speed can be supplied at the appropriate wind speed. Achieve an appropriate wind speed supply to achieve economical results.

 

On the other hand, in order to achieve the stability of clean room cleanliness, the maintenance of uniform airflow is also an important factor. If the uniform airflow cannot be maintained, it means that the wind speed is different, especially on the wall surface, and the airflow will vortex on the wall surface. Achieving high cleanliness is actually very difficult.

 

To maintain a uniform airflow in the vertical laminar flow direction, (a) there must be no difference in speed between the wind speeds on the blowout surface; (b) There must be no difference in speed between the wind speeds on the suction surface of the floor return air panel. If the speed is too low or too high (0.2m/s, 0.7m/s), there will be eddy current phenomenon, and at 0.5m/s, the airflow will be more uniform. At present, the general clean room has a wind speed of 0.25~0.5. Between m/s.

 

There are many factors affecting the airflow in the clean room, such as process equipment, personnel, clean room assembly materials, lighting fixtures, etc., and the diversion point of the airflow above the production equipment should also be considered.

 

The airflow diversion point on the surface of the general operation console or production equipment should be set at 2/3 of the distance between the clean room space and the partition wall. This allows the airflow from the inside of the process area to the work area when the operator is working. If the diversion point is placed in front of the process area, it will become an improper airflow diversion. At this time, most of the airflow will flow to the process area, and the dust caused by the operator's operation will be brought to the back of the equipment. The station will therefore be polluted and the yield will be reduced.

 

Obstructions such as work tables in clean rooms will have eddy currents at the junctions, and the cleanliness will be relatively poor in the vicinity. The return air holes on the working table will reduce the eddy current phenomenon. Whether the choice of assembly materials is appropriate and whether the equipment layout is perfect is also an important factor in whether the airflow becomes a vortex phenomenon.