Cross-sectional wind speed of clean room work area
Cross-sectional wind speed of clean room work area
The cross-sectional wind speed in the working area is the main parameter to ensure the cleanliness level of the unidirectional flow 5-level clean room.
Class 5 purification clean room must adopt unidirectional flow airflow organization.
The 5-level clean room relies on the action of the 'air flow piston' of the one-way flow, so that the clean air flow along the entire industrial...
Text label: clean room, clean room work area cross-sectional wind speed
Cross-sectional wind speed of clean room work area
The cross-sectional wind speed in the working area is the main parameter to ensure the cleanliness level of the unidirectional flow 5-level clean room.
Class 5 purification clean room must adopt unidirectional flow airflow organization.
The 5-level purification clean room relies on the action of the 'air flow piston' of the one-way flow, so that the clean air flow is advanced like a piston along the room section of the entire working area height, and the indoor pollution is completely pushed out, so this airflow organization can reach Ultra cleanliness from class 5 to class 4, class 3...even class 1. In order to achieve faster (generally within 2min) and complete removal of pollution, there is a requirement for the cross-sectional wind speed passing through the working area, which is 0.45m/s soil 20% adopted in the United States in the early years. That is, the regulations of China GMP and EU GMP on the 5-level unidirectional flow speed:
The one-way flow system must supply air evenly in its working position, and the wind speed is 0.36~0.54m/s (guidance value), but a lower wind speed can be used in a closed isolator or glove box.
For the one-way flow clean room, the wind speed requirements of the air supply surface are used in foreign countries, and the wind speed of the working surface (or working area section) has been used in China since the 'Technical Measures for Air Cleaning' in 1977. That is, the wind speed of the EU GMP working position. For the whole room unidirectional flow, the difference between the two is not much, generally not more than 20%, because the full coverage ratio of the unidirectional flow clean room filter (that is, the ratio of the net area of u200bu200bthe filtered air to the cross section of the entire room) generally reaches 80%, see Figure 4-6.
But it can be seen from Figure 4-6 that for the one-way flow in the whole room, as long as it is far away from the supply air (for example, about 1m), since the airflow has been completely overlapped, the average wind speed of the section measured at each height will be It should be basically the same (the space occupied by the object has some influence), so the difference between using the wind speed on the air supply surface or the cross-sectional wind speed on the working surface will not be very big.
However, the research practice in my country in the early years has proved that this wind speed is too large as the cross-sectional wind speed of T, and there should be a 'lower limit wind speed'. In general, the vertical one-way flow should be ≥0.3m/s, and the horizontal one-way flow should be ≥0.35m/s. It can also be as small as 0.12m/s (vertical).
The ISO14644 standard in 1999 began to reduce this wind speed, and its 14644-4 Appendix B specifically gave a table for the clean room for aseptic processing of products, as shown in the following table.
The table gives some notes. It mentions Uu003dunidirectional flow, Nu003dnon-unidirectional flow, Mu003dmixed flow (U and N exist at the same time). When the airflow speed is not clearly defined as the air supply surface or the working surface, as we have said earlier, the airflow speed is meaningful only if it is specified as the working surface. The so-called sterile core area is enclosed, so there is little difference between the air supply surface and the working surface. Otherwise, it is at least not rigorous without explanation. But judging from its annotations, it is pointed out that 'the average airflow velocity is the flow method of the unidirectional flow that is usually specifiedIt is even more pointless to specify the work surface. For such a local unidirectional flow (without enclosure), if the air supply speed is guaranteed to be 0.45m/s, the section of the work area with a height of 0.8m above the ground may be guaranteed to be ≥0.25
m/s. If the working area cross section is required to reach 0.45 under this condition
m/s, the air supply speed will be 0.7 ~ 0.8m/s, which is obviously unrealistic. However, it can be seen from Table 4-6 that the wind speed > 0.2m/s should be at the working face, which is much lower than the EU GMP, which is reasonable. Zhongjing Global Purification can provide supporting services such as consultation, planning, design, construction, installation and transformation of purification workshops and GMP workshops.
Same as the number of air changes, if the surface wind speed is much lower than the lower limit wind speed, even if it is only about 0.1m/s, the dust concentration can reach below 3.5 grains/L after a long period of self-cleaning in the absence of unmanned persons. That is, level 5, but this clean state cannot withstand external interference, including the influence of people's movement, equipment movement, door opening, etc., which can cause the concentration to rise immediately, and it will take a long time for self-cleaning up to tens of minutes to recover. , Such a clean room no longer has the characteristics of a 5-level one-way flow clean room, and it does not meet the purpose of GMP to control every factor in the process, especially the key factor. Therefore, as a standard, an important parameter that guarantees level 5 cleanliness and can powerfully remove pollution - the cross-sectional wind speed of the working area, gives a value that is relatively safe and can basically achieve the required value. This is the above mentioned value. Said lower wind speed. Wind speeds higher than the lower limit are of course less of a problem, but the energy consumption is greatly improved.
In view of the situation of arbitrarily increasing the safety factor and causing waste due to the unlimited number of air changes and cross-sectional wind speed in the past, GMP specifically stipulates that 'the number of air changes in the clean room and the surface wind speed in the working area should generally not exceed the level requirements. The number of air changes and 130% of the cross-sectional wind speed should be selected according to the design results under special circumstances.”
Obviously, if you increase the number of air changes and test in an empty or static state without people, after a long wait, you can also measure the level of 3.5 grains/L, but if there is pollution, the indoor dust concentration It will rise very quickly, it can reach 10 times, and it will take a long time to recover from the net. This is the reason why China's GMP and EUGMP have the background of A-level and B-level with non-unidirectional flow, although the static flow reaches the 5th level, but the dynamic level reaches the 7th level. According to the principle of air cleaning technology, even under dynamic conditions, the concentration of the one-way flow clean room generally only increases by about 2 times rather than 10 times or even 100 times, and the self-cleaning time is only within 2 minutes.
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