For most clean spaces, in order to prevent the intrusion of external pollution, it is necessary to keep the internal pressure (static pressure) higher than the external pressure (static pressure).
The maintenance of the pressure difference should generally comply with the following principles:
1. The pressure of the clean space is higher than the pressure of the non-clean space.
2. The pressure of a space with a high level of cleanliness is higher than that of an adjacent space with a low level of cleanliness.
3. The door between the communicating clean rooms should be opened to a room with a high level of cleanliness.
The maintenance of the pressure difference depends on the fresh air volume, which must be able to compensate for the air volume leaking from the gap under this pressure difference. Therefore, the physical meaning of the pressure difference is the resistance when the leakage (or penetration) air volume passes through various gaps in the clean room.
Air velocity regulations in clean rooms
The airflow speed to be discussed here refers to the airflow speed in the clean room, and the airflow speed in other clean spaces will be explained when discussing specific equipment.
For the turbulent clean room, because the dilution effect of air is mainly used to reduce the degree of indoor pollution, the concept of the number of air changes is mainly used instead of the concept of speed. However, the indoor airflow speed also has the following requirements;
(1) The airflow velocity at the outlet of the air supply outlet should not be too high. Compared with a purely air-conditioned room, the velocity attenuation is required to be faster and the diffusion angle is larger.
(2) The air velocity blowing across the horizontal plane (such as the recirculation velocity during side feeding) should not be too high, so as to avoid blowing surface particles back into the airflow and causing re-pollution. Generally, this velocity should not be as high as 0.2m/s.
For the parallel flow clean room, "the laminar flow clean room is customarily called), the speed on the cross section is a very important indicator because it mainly relies on the "piston squeezing action of the airflow to eliminate dyeing. In the past, the US 20gB standard was used and 0.45 was adopted. m/s. However, people also know that the amount of ventilation required for such a large speed is extremely large. In order to save energy, they are also exploring the feasibility of reducing the speed-wind speed.
In our country, "Technical Measures for Air Cleanliness" and "Code for Design of Clean Plants)) are all stipulated as follows:
Vertical parallel flow (laminar flow) clean room ≥ 0.25m/s;
Horizontal parallel flow (laminar flow) clean room ≥0.35m/s.
Studies have shown that the above regulations basically meet the requirements for pollution control, but it is believed that different situations should be separated into different grades, which can better reflect the purpose of energy saving.
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