Alternating airflow method

In the alternating airflow method, a piston is used to generate a low frequency alternating airflow through the test specimen and a condenser microphone is used to obtain the root mean square (rms) value of the pressure change in front of the porous material. Fig. 5.2 shows the basic principle of the experiment setup. 

In the alternating airflow method, a piston is used to generate a low frequency alternating airflow through the test specimen and a condenser microphone is used to obtain... 

The use of tracers for airflow measurement in ventilation ducts is not very common. There are several reasons for this. Compared to other flow measurement methods, tracers require more complicated equipment, skilled personnel, and are more expensive. There are, however, situations when conventional measurement methods are not applicable. For instance, if the space available is small, and hence the flow meter cannot be installed, or if no space is free to carry out traversing measurements, the use of a tracer might be an alternative. 

Airflow Technique An alternative method, the airflow technique, measures the flow of air passing through the membrane surface. Several variations of this test method are available from the various membrane suppliers, and the test is usually automated. This test may involve applying a constant feed-side gas pressure below the bubble point of the selected size hole. The operator then measures the diffused gas filtrate flow or the displaced water from the membrane. 

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