How to express FFU wind speed uniformity? How to distinguish average value from local deviation

Average wind speed is the same, uniformity may be different

In FFU performance comparisons, average wind speed is a commonly used metric. The average wind speed on the outlet surface of two FFUs may be the same, but the wind speed distribution may be completely different. One machine may be uniform overall, while another may have high center wind speed and low edge wind speed, or there may be significant local differences.

The average wind speed only reflects the overall level and cannot explain local deviations. For cleanroom applications, local air speed deviations may affect airflow coverage and particle control. Therefore, wind speed uniformity needs to be expressed and evaluated separately.

The expression of wind speed uniformity should be based on clear measuring points, measuring planes and calculation methods. Aili Industrial will explain the wind speed measurement conditions during the FFU complete machine testing and parameter compilation. For the basic structure of the FFU machine, please refer toAili Industrial FFU fan filter unit。

How to arrange measuring points

To evaluate wind speed uniformity, we must first unify the layout of measuring points. The number, location and distribution of measuring points will affect the results. A common practice is to arrange the measuring points in a grid on the wind outlet surface, for example, evenly divide them into several rows and columns, and measure the wind speed at the intersection points.

The greater the number of measuring points, the more local deviations can be reflected, but the measurement workload will also be greater. If the number of measuring points is too small, local high and low wind speeds may be missed. For conventional FFU, a certain number of grid measurement points can be used, such as several rows by several columns. For FFUs with larger sizes, the number of measuring points should be increased accordingly.

The measuring points should cover the entire area of ​​the air outlet surface, including the center and edges. If only the central area is measured, low wind speeds at the edges may be ignored.

How to determine the measuring plane

The measuring plane is where the wind speed is measured. The measurement plane can be near the FFU air outlet surface or at a certain distance from the air outlet surface. The wind speed distribution obtained from different measurement planes is different.

The measurement plane should be clearly defined and correspond to the purpose of the evaluation. If you evaluate the performance of the FFU air outlet surface, you can measure it close to the air outlet surface. If the effect of airflow reaching the process location is evaluated, it can be measured at a certain distance from the air outlet surface or at the process height.

After the measurement plane is determined, the measurement point layout and area diameter should correspond to it. When measuring changes in plane, the results are not directly comparable.

How to express average value and local deviation

The average value is the arithmetic mean of the wind speed at all measuring points. It reflects the overall air supply level. Average values ​​can be used to calculate air volume, but they do not account for uniformity.

Local deviations can be expressed in several ways. The difference between the maximum wind speed and the minimum wind speed reflects extreme deviations. The deviation of the maximum wind speed from the average value, or the deviation of the minimum wind speed from the average value, reflects the degree of local deviation. The standard deviation reflects the dispersion of all measurement points. Relative deviation can be expressed as the deviation divided by the mean.

When expressing, it is recommended to give both the average value and the deviation index, rather than just the average value. If the project requires uniformity, the allowable deviation range can be agreed upon.

How to save charts

Wind speed uniformity data can be saved via graphs. Common methods include wind speed distribution diagrams, bar graphs or tables. The wind speed distribution map can visually display the wind speed at various locations on the wind surface. The table can list the specific values ​​of each measuring point.

The chart should indicate the location of the measurement points, measurement plane, measurement conditions and measurement date. If the project requires multiple measurements, you can compare the distribution charts at different times to observe the changing trends.

For batch projects, sampling can be measured and records kept. If it is found that the wind speed of a certain FFU has a large deviation, you can further check the filter installation, fan status or sealing condition.

What factors are related to uniformity?

FFU wind speed uniformity is affected by multiple factors. The folding structure and installation status of the filter affect the wind speed distribution on the air outlet surface. The design of the fan and box air duct affects the uniformity of air flow. The wind outlet net or diversion structure may change the local wind speed. Installation seals and cabinet deformations may affect airflow.

If the wind speed deviation is large, you can check whether the filter is installed in place, whether the sealing is even, and whether the air outlet surface is blocked. For projects with higher design uniformity requirements, the FFU’s air duct design and test data can be confirmed during the selection stage.

Issues that should be confirmed in advance during project communication

During the FFU wind speed uniformity evaluation stage, it is recommended to confirm the following with the manufacturer: the number and arrangement of measuring points; the location of the measuring plane; the measuring method and instrument; the calculation method of the average and deviation indicators; uniformity requirements or allowable deviations; test data and chart format; whether on-site re-testing is required; whether the measurement conditions are uniform.

If you are doing FFU wind speed uniformity comparison, you can visitAili Industrial FFU fan filter unit to learn about the complete machine configuration, you can also contact Aili Industrial for wind speed testing and parameter description support.

in conclusion

FFU wind speed uniformity should be based on clear measurement points, measurement planes and calculation methods. Two devices with the same average wind speed may have different local high and low wind speed distributions. When expressing uniformity, the average value and local deviation indicators should be given simultaneously, and the measurement point layout and chart records should be retained.

Aili Industrial has complete production capabilities in FFU complete machine testing and parameter compilation, and can explain wind speed measurement conditions. If you need to know more about FFU wind speed parameters, you can visitAili Industrial FFU fan filter unit , you are also welcome to contact Aili Industrial for project support.