Airflow direction and visualization test

 

1.1.        Airflow direction test and visualization

The purpose of this test is to confirm either the airflow direction or airflow pattern or both in regard to the design and performance specifications. If required, spatial characteristics of airflow in the installation may also be confirmed. Procedures for this test are given in ISO-14644.

1.1.1.  Testing schedule for optional tests

In addition to the normative tests specified in ISO-14644 , optional tests, such as those listed in Table A.1, may be included within the testing plan.

Table 1: Schedule of optional tests

 

Test parameter	Class	Suggested maximum time interval	Test procedure
Airflow visualization	All classes	24 months	ISO 14644-3:—, clause B.7

1.1.2.  Principle

The purpose of airflow direction test and visualization is to confirm that the airflow direction and its uniformity conform to the design and performance specifications and, if required, spatial and temporal characteristics of airflow in the installation.

1.1.3.  Methods

The airflow direction test and visualization can be performed by the following four methods:

a)        tracer thread method;

b)        tracer injection method;

c)        airflow visualization method by image processing techniques;

d)        airflow visualization method by the measurement of velocity distribution.

 

By methods a) and b), airflow in the installation is actually visualized by the use of fibre tracer thread, or tracer particulate matter. Storage devices such as a video camera, chemical films, disks or tapes record the profiles. The fibre tracer thread or tracer particulate should not be a source of contamination, and should follow the airflow profile accurately. Other apparatus such as a tracer particle generator, and high intensity light source may be used for these methods.

Method c) is used to demonstrate quantitatively the airflow velocity distributions in the installation. The technique is based on tracer particle image processing techniques using computers. Care should be taken to ensure that the operator(s) do not interfere with the airflow patterns being investigated.

NOTE The airflow is affected by other parameters such as air pressure difference, air velocity, and temperature.

1.1.4.  Tracer thread method

The test is carried out by observation of tufts, e.g. silk threads, single nylon fibres, flags or thin film tapes. These are set on the tip of support sticks or mounted on the crossing points of thin wire grids in the airflow. They provide visual indication of the airflow direction and fluctuations due to turbulence. Effective lighting will aid observation and recording on the indicated airflow. The airflow deflection is measured between two points (example 2 m to 0,5 m) to calculate the deviation angle.

1.1.5.  Tracer injection method

The test is carried out by observation or imaging of the behaviour of tracer particles illuminated by high- intensity light sources and provides information about the direction and uniformity of airflow in installations. The tracer particles can be generated from materials such as de-ionized (DI) water, sprayed or chemically generated alcohol/glycol etc. The source should be carefully selected to avoid contamination of surfaces. The desired size of droplets should be considered when selecting the droplet generation method. Droplets should be large enough to be detected with the available image processing techniques, but not so large that gravitational or other effects will result in their motion diverging from that of the airflow being observed.

1.1.6.  Apparatus airflow direction test and visualization

Apparatus, materials and accessories for airflow  direction  test  and  visualization,  see  Tables C.19 and C.20 of 14644.

Table 2: Materials or particles used in tracer thread or injection methods

Item						Description
Materials used in the tracer thread method						Silk thread, cloth, etc.
Particulate method	used	in	the	tracer	injection	DI water or other fluid mist of 0,5 µm to 50 µm in diameter. Bubbles of neutral density in the air at the measurement location. Organic or inorganic test fog.
Image recording devices for recording the visualized pictures or images of tracer particles						Various devices, such as photographic cameras, video cameras, including high-speed or strobe or synchronized functions and image recording devices, used in flow visualization procedures.

NOTE  After flow visualization, it is generally required to re-clean the installation.

Fog generator, used to generate aerosols (mist), utilizing phase transition between gas to liquid by cooling steam boiled DI water. The specifications for the fog generator are given in Table C.22 of 14644.

Table 3: Specifications for fog generator

Item	Specification
Particle size range of droplet	1 µm to 10 µm (MMD)
Particle generation rate	1 g/min to 25 g/min

This is the mandatory test at the time of validation. The photographs and videos are keep as a record and attach with the validation report as an annexure.