Description
What is the visualization of air flow in clean rooms?
GOST R ISO 14644-3-2007 defines the purpose of the visualization of air flow:
The purpose of this test is to confirm that the direction of flow, the pattern of flow distribution, or both, are in accordance with the design or the corresponding specification.
During the initial certification of clean rooms in the equipped state, the question may arise, what effect does the technological equipment installed in the room have on air movement?
The answer to this question and gives the visualization of air flow. The visualization of flows near the process equipment also makes it possible to detect stagnant zones in which air movement is obstructed or absent, which can lead to an increase in the concentration of particles and non-compliance of the room with the requirements for cleanliness class.
In rooms with unidirectional air flow (highly aseptic operating rooms, critical areas of pharmaceutical production), visualization of the flows, along with the measurement of the flow velocity, makes it possible to evaluate how effectively the laminar air flow performs its protective function.
Air flow visualization is also often required when testing laminar boxes (biosafety cabinets, clean air shelters) to check the degree of particle retention inside the box.
Other useful data on clean zones obtained by the visualization method:
flow behavior in supply and exhaust air zones
zones of influence of waste process air
wrap around workplace personnel
wrapping around equipment parts (conveyor belts, etc.)
For each separate clean room, a visualization plan should be developed taking into account the characteristics of the clean room, its purpose, installed equipment and technological equipment.
Flow visualization methods
GOST R ISO 14644-3-2007 defines several possible methods for visualizing airflows, among which are the visualization of air flow using filaments, by introducing aerosol particles into the air flow, photo and video filming of the visualization process, as well as mathematical modeling of air flows in pure indoors.
Visualization with threads
The method consists in observing the threads (silk threads, individual nylon fibers, flags or thin ribbons) that are attached to the pins or intersection points of the wire mesh in the air stream. This gives a visible picture of the direction of air flow and their change due to turbulence. It is advisable to use effective lighting and video recording or photograph of the resulting pattern of air flow. To determine the angle of deviation of the flow, measurements should be made at two points (for example, at a distance of 0.5 to 2 m).
Visualization using an aerosol generator or particle generator (particle injection method)
The method consists in observing the behavior of particles that are introduced into the air stream. The use of light sources with a high intensity of luminous flux allows to determine the direction and uniformity of air flow. Tracing particles can be obtained from sprayed deionized water, alcohol, etc. The source of particles should be chosen so as to eliminate air pollution and surfaces of the clean room.
When choosing a method of spraying should take into account the requirements for the size of particles (droplets). It should be sufficient to visualize the flow of air by the chosen method, but not so large that gravity or some other effect could affect their movement and distortion of the resulting picture.
Visualize airflow with video
Video recording of the visualization of air flow allows you to obtain quantitative characteristics of the flow (velocity vectors) in a two-dimensional image. It uses digital cameras that transmit images to computers with the necessary interfaces and software. To achieve greater spatial resolution, laser light sources, etc. can be used.
Visualization of air flow by building velocity distribution (mathematical modeling and calculation of air flow)
The distribution of air flow velocities can be constructed at several points where the velocity is determined by a hot-wire anemometer, an ultrasonic anemometer, or another device. Subsequent modeling of air flow makes it possible to assess the effect of changes in the parameters of the operation of HVAC systems on the air flow in the room.
How is the visualization of air flow
In accordance with the methodology described in GOST R ISO 14644-3-2007, visualization can be performed in various ways suitable for achieving the objectives of the test:
The purpose of checking the air flow direction and visualizing the flow is to confirm that the direction and uniformity of the flow comply with the established requirements and, if necessary, the spatial and temperature characteristics.
Our laboratory has a variety of equipment for imaging
in the air - a fog generator, aerosol particle generator, high-speed digital camera and auxiliary equipment.
The most convenient and least expensive visualization method used by our laboratory specialists is stream visualization using an aerosol particle generator. In this method, a DEHS fluid and an aerosol generator are used to create a visible flow of particles — the same equipment that is used when testing filters for leakage and determining recovery time.
In cases where the use of DEHS aerosol is undesirable due to the high demands on the cleanliness of air and surfaces, for example, in the operating state, the flow can be visualized using an ultrasonic mist generator, where deionized (ultrapure) water is used as the source of aerosols. With this method of visualization the risk of contamination of surfaces is completely absent.
Air flow modeling for visualization
If the configuration of the room is relatively simple, and the purpose of visualization is to obtain information about the speed and direction of air movement in the room, you can perform mathematical modeling of a clean room, calculate the distribution of air velocity and build a visual representation of air flow in any plane or in 3D.
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Air visualization report
The report on the conducted visualization includes photographs showing the movement of air flows, and information on the compliance of the obtained picture with the requirements of the regulatory and design documentation.
When carrying out visualization by the method of mathematical modeling and building the distribution of velocities of air flow in some cases, the report may include a video clearly demonstrating the movement of air and aerodynamic processes.
