Bubble point test wetting fluid

When the wetting fluid is expelled from the largest pore, a bulk gas flow will be detected on the downstream side of the filter system (Fig. 7). The bubble point measurement determines the pore size of the filter membrane, i.e., the larger the pore the lower the bubble point pressure. Therefore, filter manufacturers specify the bubble point limits as the minimum allowable bubble point. During an integrity test, the bubble point test has to exceed the set minimum bubble point. 

Bubble Point Test Theoretical aspects of the bubble point lest have been addressed in Section 1 above. The bubble point test predicts the performance of a filter by detecting the differential pressure at which a fluid is displaced by gas from the pores of a wetted filter, thus allowing capillary flow of the gas through the filter. 

Bubble Point Large areas of microfiltration membrane can be tested and verified by a bubble test. Pores of the membrane are filled with liquid, then a gas is forced against the face of the membrane. The Young-Laplace equation, AF = (4y cos Q)/d, relates the pressure required to force a bubble through a pore to its radius, and the interfacial surface tension between the penetrating gas and the liquid in the membrane pore, y is the surface tension (N/m), d is the pore diameter (m), and P is transmembrane pressure (Pa). 0 is the liquid-solid contact angle. For a fluid wetting the membrane perfectly, cos 0 = 1. 

Still, other researchers explained the discrepancy between theoretical and experimental bubble-points with surface tension depression. It is true that most manufacturers treat their membranes with wetting agents. It is conceivable that these surfactants can dissolve in the test fluid and lower the surface tension. 

The measurement of equivalent pore size by a bubble point procedure is perhaps the most well known and involves inunersing the fabric in a suitable wetting fluid and then measuring the air pressure that is necessary to create a bubble on the surface. The pore size can be calculated from the relationship r= 2 Tx lOVoPg, where r is the pore radius (pm), T is the surface tension of the fluid (mNm" ), o is the density of water at the temperature of test (gcm" ), P is the bubble pressure (nunH O) andg=981cms . ... 

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