Bubble point aperture test principle - Database & Sql Blog Articles

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Kaixin micro test

Test probe P100-M3

Fundamental:

When testing a specific membrane material, the membrane is first fully wetted with a liquid that can be infiltrated. This liquid becomes trapped in the pores due to surface tension. A gradually increasing gas pressure is then applied on one side of the membrane. Once the gas pressure exceeds the surface tension of the liquid in a particular pore size, the liquid is pushed out, allowing gas to pass through. Smaller pores require higher pressure to release the liquid because the surface tension is greater at smaller diameters. As the pressure increases, the liquid is sequentially expelled from larger to smaller pores, enabling gas to flow through until all pores are open and the transmittance matches that of a dry film.

The pressure at which the first pore opens is known as the bubble point pressure, and the corresponding pore diameter is referred to as the bubble point diameter. During this process, both pressure and flow rate are continuously monitored to generate a pressure-flow curve. This curve provides valuable information about the pore size distribution and the number of pores at each size. By testing the dry film’s pressure-flow characteristics, it is possible to calculate key parameters such as the pore size, average pore size, minimum pore size, pore size distribution, and overall transmittance of the membrane sample using appropriate formulas.

The relationship between pore size and pressure is described by the Washburn equation:
D = 4γCosθ / p
In this formula:
D represents the pore diameter, γ is the surface tension of the liquid, θ is the contact angle, and p is the pressure difference.

The pore size distribution can be calculated using the following expression:
f(D) = -d[Fw/Fd × 100]/dD
Here, Fw is the flow rate of the wet sample, and Fd is the flow rate of the dry sample.