The airflow organization of the clean room system
is different from that of a general air-conditioned room. It requires that the cleanest air be sent to the operating site first. Its function is to limit and reduce the pollution of the workpiece. To this end, these principles should be considered when designing airflow organization: minimize eddy currents, avoid contamination outside the work area into the work area; try to prevent secondary dust from flying to reduce the chance of dust contamination of the workpiece; airflow in the work area As uniform as possible, and the wind speed should meet the requirements of process and hygiene. When the airflow flows to the return air, the dust in the air can be effectively carried away. According to different cleanliness requirements, choose different delivery and return air modes.
Different airflow organizations have their own characteristics and scope:
1) Vertical unidirectional flow: It can obtain uniform downward airflow, which is convenient for process equipment layout, strong self-cleaning ability, and can simplify common facilities such as personal purification facilities. The four air supply modes have their own advantages and disadvantages: full The cloth high-efficiency filter has the advantages of low resistance, long filter replacement period, and the like, but the ceiling structure is complicated and the cost is high; the side cloth high-efficiency filter top feed, the full-hole plate top feed and the high-efficiency filter top feed are opposite to the advantages and disadvantages. When the whole hole plate is sent in the system for non-continuous operation, the inner surface of the orifice plate is easy to accumulate dust, and the maintenance is not good, which has some influence on the cleanliness; the dense diffuser is sent overhead, because it needs a mixed layer, so it is only suitable for 4m or more. The tall clean room has the same characteristics as the full-hole plate top-loading; the return air mode for the plate on the opposite sides and the lower side of the opposite side wall is only applicable to the clean room with a net spacing of less than 6m on both sides; The return air outlet of the lower wall of the wall is only suitable for clean rooms with small wall spacing (such as ≤<2~3m).
2) Horizontal unidirectional flow: only achieves 100 cleanliness in the first working area, and the dust concentration gradually increases during the flow of air to the other side, so it is only suitable for the cleanliness of different cleanliness requirements in the same room process. Room; Partially-supplied high-efficiency filter of the air supply wall can reduce the amount of high-efficiency filter and save the initial investment, but there is eddy current in the local area.
3) turbulent flow: the characteristics of the orifice feeding and dense diffuser top feeding are the same as the above: the advantages of side feeding are easy to arrange the pipeline, no technical interlayer is required, and the cost is low, which is beneficial to the transformation of the old factory building. The disadvantage is the wind speed in the working area. Larger, the leeward side has higher dust concentration than the upwind side; the high-efficiency filter tuyere has the advantages of simple system, high efficiency filter without pipeline, and clean airflow directly to the working area, but the clean airflow spreads slowly, and the working area airflow is slower. Uniform; however, when a plurality of tuyères are evenly arranged or a high-efficiency filter tuyere with a diffusing plate is used, the airflow in the working area can be made uniform; however, in the case of non-continuous operation of the system, the diffusing plate is easy to accumulate dust.
The above discussion is all in an ideal state and is also recommended by the relevant national standards, standards or design manuals. In the actual project, it may be limited by objective conditions, or the airflow organization is not designed due to the subjective reasons of the designer. Commonly, the vertical unidirectional flow adopts the return air from the lower side of the adjacent side walls, and the local 100-level adopts the upper air return. (ie, there is no drooping curtain under the local air supply port), the turbulent flow type clean room adopts high-efficiency filter air outlet top to send back or one side to the next (larger spacing to the wall), etc. These airflow organization methods are measured and cleaned. Most of the degrees do not meet the design requirements. Due to the empty state or static acceptance specified in the current specification, individual clean rooms of this type barely reach the design cleanliness level in the open state or static state, but the anti-pollution interference ability is very low, once the clean room enters the working state, it will not reach To the request. The correct area of the airflow organization should be set to droop to the height of the work area, and the 100,000 class should not be used to send the upper back. There are also high-efficiency air supply ports with diffuser plates produced by most factories at present. The diffuser plates are only decorative orifice plates and do not act as a diffusion airflow. Please pay special attention to designers and users.