How does supply air vortex affect open workstations?

There are no enclosures in the open workstation, and people and materials can enter and exit freely. This openness makes operation easier, but also makes airflow boundaries more susceptible to disturbance. Air supply vortex is one of the common phenomena: the air flow forms a loop or entrainment near the work station, bringing background air into the protected area, or allowing particles to pass through the product repeatedly.

The eddy current is not necessarily large or persistent, but it may weaken the protective effect during critical operating periods. The following will start with the sources of eddy currents, their impact on open workstations, identification methods and adjustment directions.

Eddy currents can come from a variety of conditions, both internal and external

The formation of supply air vortex is usually related to the following factors:

• Outlet surface structure: filter frame, diffuser plate or protective net may change the direction of local airflow;

• Material placement: High boxes, vertical boards, and fixtures may block the air supply and form eddy currents on the back;

• Lateral airflow: Air conditioning vents, exhaust air from adjacent workstations, and personnel movement may meet the supply air and form a vortex;

• Heat source: The heating of the equipment or the heating of lamps produces a thermal plume, which changes direction after meeting the supply air;

• Return air conditions: The position of the return air outlet or the suction direction is unreasonable, which may cause the air flow to circulate near the work station.

These factors may exist individually or simultaneously. Because there are no enclosures in an open workstation, the boundaries are weaker and more susceptible to external conditions. For partial protection methods of open workstations, please refer to How to establish a local clean area in an open workstation? , first confirm the basic ideas of border protection.

Eddy currents entrain background air

After the supply air blows out from the outlet surface, if there is a vortex nearby, the airflow boundary may be broken. Pressure changes in the vortex area draw surrounding background air into the protected area. Background air, if it contains particles, will enter directly into the vicinity of the product.

This entrainment is more obvious in open workstations because there is no physical isolation around the workstation and background air can enter at any time. When the lateral airflow meets the supply air, it is also easy to form entrainment at the edge of the workstation. For the lateral interference identification method in the unidirectional flow area, please refer to How to identify lateral interference in unidirectional flow areas?。

Particles may pass through the product repeatedly

Another effect of vortices is to cause particles to circulate repeatedly in local areas. When air swirls around workstations, particles can be repeatedly carried into the product area instead of being effectively removed. This will cause the particle concentration at the workstation to remain high and recover slowly.

If it is found that the particles at the workstation do not fall for a long time and are not obviously related to personnel activities, check whether there is eddy current. The difference between airflow short circuit and reflow area can be referred to What particle problems can airflow short circuits cause? and Why is it easy for contamination to accumulate in the return flow area? , to understand the performance of different path problems.

The protective boundaries of open workstations are more easily weakened

The protective boundary of the open workstation is virtual and depends on the supply air flow. Eddy flow will change the boundary shape of the airflow, causing gaps or deviations in the originally stable protection zone. Products may be affected by particles if they are located in a weak protection zone after migration.

To judge whether the protective boundary has been weakened, you cannot just look at the average wind speed. A qualified average wind speed does not mean that every location is stable. For details, please refer to Why does the measured average wind speed not mean that the air flow is uniform? , avoid judging the overall effect by just looking at an average value.

How to identify supply air vortices

To identify eddy currents, you can combine the following methods:

• Airflow visualization : use smoke or silk thread to observe the direction of airflow near the work station and look for vortex or circulation areas;

• Local wind speed and direction measurement : measure wind speed and direction at suspected vortex locations and compare differences at different locations;

• Particle trend recording : observe whether the particle concentration continues to be high at a specific location or recovers slowly;

• Operation status correlation : record the time relationship between the occurrence of eddy currents and human actions, equipment operation or door opening.

Air flow visualization should be performed under actual operating conditions rather than just measuring the air condition. Typical operating actions should be covered during verification, and static data cannot be used for judgment. The impact of the height of the front window of the workbench on airflow can also be referred to Will the height of the workbench front window affect the clean airflow?。

Orientation: Start with airflow paths and layout

After discovering the supply air vortex, priority should be given to adjusting the airflow path and layout rather than simply increasing the wind speed. Common adjustment directions include:

• Adjust the position or direction of the air outlet surface to make the air flow cover the product more stably;

• Remove or lower obstructions to reduce airflow shadows;

• Adjust the source of lateral airflow, such as changing the direction of the air conditioning outlet or adding baffles;

• Adjust the position or air volume of the return air outlet to improve local circulation;

• Optimize the workstation layout to make the air supply path more direct.

Increasing wind speed may increase disturbance and energy consumption and may not necessarily eliminate eddies. If the eddy current is related to the air supply distance, please refer to How will the airflow change when the air supply distance increases? , to understand the effect of distance on airflow stability.

Dynamic verification is more important than static testing

The effects of eddy currents tend to be more pronounced under dynamic conditions. The approach of people, the penetration of tools, product removal and mechanical movements can trigger or change eddy currents. Verification should cover these states rather than just emptying the deck.

If multiple devices require partition duty and troubleshooting, they can be combined FFU group control system provides unified management. Please refer to the room background air supply FFU clean air supply products , please refer to the local protection of the equipment side. EFU equipment side fan filter unit . The logic of division of labor between the two lies in The division of labor between device-side EFU and room FFU is explained in detail.

Filter selection should correspond to target particle size and actual resistance.The HEPA and ULPA filter pages have parameters for different levels of products. When selecting, check the efficiency of the specific model at the target air volume. If you are still unclear about the difference between space rating and filter efficiency, you can read What is the difference between cleanliness level and filtration efficiency?。

Project judgment example

The particles at an open station are occasionally high, but the static wind speed is normal. Air flow visualization revealed that there were vortices at the edge of the workstation, which pulled particles in the adjacent channels into the vicinity of the product. Adjustment method: adjust the direction of the air outlet, add transparent baffles on the sides, and change the walking route of people. After adjustment, the eddy current was significantly weakened and the station particles returned to stability.

There is an air-conditioning vent above another project work station, and the supply air and air-conditioning air meet to form a vortex. Adjustment method: adjust the direction of the air conditioning outlet and add a diversion structure above the work station. After adjustment, the eddy current disappears and the protective boundary is restored.

These two situations illustrate that the air supply vortex will weaken the protective boundary of the open workstation, and a comprehensive judgment needs to be combined with air flow visualization, local measurement and dynamic verification.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Air supply vortices are more likely to occur in open workstations and are easier to ignore. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly links. It can combine the project air flow visualization results, work station layout and external interference conditions to check the equipment air supply direction, operation settings and filter configuration, helping to judge whether to adjust the air outlet surface, change the work station layout or increase local diversion, rather than just adjusting based on the wind speed value. Specific models can be viewed FFU clean air supply products , supporting equipment can be viewed EFU equipment end fan filter unit , please refer to the filter package. HEPA and ULPA filters。