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Cleanroom principles and features

| 2006-09-28

Clean room classification


1, one-way flow clean room principle and characteristics


⑴ definition


A unidirectional flow cleanroom is a clean room through which airflow flows at a uniform cross-sectional velocity across a section of the chamber in a single direction along parallel flow lines.


⑵ principle


Unidirectional flow clean room by the air flow "piston" -like extrusion, the rapid discharge of indoor pollution.


To ensure the realization of the role of the piston, the most important point is that high efficiency filters must be covered. Of course, the filter has a border, the ceiling also has a border, it is impossible to 100% to filter.


Under normal circumstances covered cloth up to 80%. Vertical unidirectional flow should not be less than 60% of the cloth, horizontal unidirectional flow should be less than 40%, otherwise it is a local unidirectional flow.


⑶ characteristics of indicators


① streamline parallelism (streamline parallelism)


The parallel effect of flow lines is to ensure that the dust particles emitted by the dust source do not propagate perpendicular to the flow direction. It is required that the flow lines should be parallel (the angle between the inner lines can not be less than 15 ° at a distance of 0.5m) and the flow lines should be as perpendicular as possible to the air supply surface (the inclination angle can not be less than 65 °).


② turbulence (speed unevenness)


The effect of uniform speed is to ensure the lateral exchange of particles between the streamline minimum. Turbulence is defined as the concentration or dispersion of the velocity field.


③ lower limit wind speed


This is to ensure that the cleanroom can control the minimum wind speed for the following four types of pollution:


a. When the polluting air flow is distributed in different directions, the air flow should be able to effectively control the pollution range;


b. When the polluted air flow and air flow in the same direction, the air flow to be able to effectively control the flow of pollutants to reach the downstream diffusion range;


c. When the polluted air flow and the supply air flow reverse, the supply air flow can inhibit the pollution flow within the necessary distance;


d. In the case of contaminated rooms, sufficient room to quickly self-clean the indoor air at the right time.


Lower limit Wind speed Recommended value


Clean room lower limit wind speed (m / s) conditions


Vertical unidirectional flow 0.12--0.3


≯0.5 Usually no one or very few people out, no obvious heat (only general equipment)


No obvious heat of the general situation


Some people, there are obvious heat source, such as 0.5 is not enough, then it is appropriate to control the heat source size and to be insulated.


Horizontal unidirectional flow 0.3--0.35


≯0.5 usually no one or very few people out


generally


Higher requirements or frequent entry of personnel


2, turbulent clean room principle and characteristics


⑴ definition


Turbulent clean room is: air flow at a non-uniform velocity was non-parallel flow, with a clean room or backflow eddy current.


⑵ principle


Turbulent clean room by the air flow constantly dilute the indoor air, the indoor pollution gradually discharged, to achieve balance. To ensure that the dilution effect is well achieved, the most important point is that the indoor air flow spread as quickly as possible.


The role of ventilation is to ensure that there is sufficient dilution of clean air.


The number of ventilation should be based on calculations and experience to determine.


② air flow organization


The role of air flow organization is to ensure uniform supply air and return air, give full play to the dilution effect of clean air. Therefore, a single outlet requires a sufficient diffusion effect, uniform return air room layout, the number of more good, to minimize turbulence and air maneuvering.


③ self-purification time


Self-purification time is a reflection of the ability of the clean room to recover from a contaminated state to a steady state. The shorter the better. It can also be specified as the time from a contaminated state to a clean state.


Turbidity clean room self-purification time is generally not more than 30min.



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