Bubble point test measurement

The bubble point test is a popular single-point physical integrity test for disc filter membranes based on Eq. (21). A fdter medium is wetted with a liquid, and test gas pressure is slowly raised until a steady stream of bubbles appears from a tube or hose attached to the downstream side of the filter and immersed in water (Fig. 9). The pressure at which the bubbles first appear is recorded as the bubble point and is related to the largest pores in the fdter medium. A pore size can be calculated from Eq. (21) however, it must be realized that the bubble point test does not measure the actual pore size, but only allows correla-... 

The bubble point test is simple, quick and reliable and is by far the most widely used method of characterizing microfiltration membranes. The membrane is first wetted with a suitable liquid, usually water for hydrophilic membranes and methanol for hydrophobic membranes. The membrane is then placed in a holder with a layer of liquid on the top surface. Air is fed to the bottom of the membrane, and the pressure is slowly increased until the first continuous string of air bubbles at the membrane surface is observed. This pressure is called the bubble point pressure and is a characteristic measure of the diameter of the largest pore in the membrane. Obtaining reliable and consistent results with the bubble point test requires care. It is essential, for example, that the membrane be completely wetted with the test liquid this may be difficult to determine. Because this test is so widely used by microfiltration membrane manufacturers, a great deal of work has been devoted to developing a reliable test procedure to address this and other issues. The use of this test is reviewed in Meltzer s book [3],... 

Although bubble point measurements can be used to determine the pore diameter of membranes using Equation (7.1), the results must be treated with caution. Based on Equation (7.1), a 0.22-pm pore diameter membrane should have a bubble point of about 200 psig. In fact, based on the bacterial challenge test, a 0.22-pm pore diameter membrane has a bubble point pressure of 40-60 psig, depending on the membrane. That is, the bubble point test indicates that the membranes has a pore diameter of about 1 pm. 

Figure 7.9 An illustration of the model of Williams and Meltzer [7] to explain the discrepancy between membrane pore diameter measurements based on the microbial challenge test and the bubble point test. Reprinted from R.E. Williams and T.H. Meltzer, Membrane Structure, the Bubble Point and Particle Retention, Pharm. Technol. 7 (5), 36 (1983) with permission from Pharmaceutical Technology, Eugene, OR...

The critically important pore size and its distribution can be determined by a host of measurement techniques. The bubble point test is used primarily for delecting any defects or hairline cracks and for estimating the average pore size. Traditionally mercury porosimetry and nitrogen adsorption/desorpiion have been the workhorse for determining the pore size distribution of a porous membrane. They arc, however, usually limited to a pore diameter range of >3 nm and 1.5-100 nm, respectively. Determination... 

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. 

An easier test which is also nondestructive is the "bubble-point" test. The maximum pore size may be determined by measuring the gas pressure required... 

Since the effective pore size is estimated from the molecular diameter of globular proteins which are retained 90% by the membrane, it is obvious that larger pores do exist. The measurement of a membrane s bubble point (see the section on the bubble point test in Chapter 2) permits calculation of the maximum pore size in the skin of the membrane. 

The integrity of sterilizing fillers is most often validated and routinely monitored by nondestructive methods. The U.S., European, and U.K. guidelines on sterile filtration refer to four methods of integrity measurement filtration flow rate, bubble point tests, diffusion (forward flow) tests, and pressure hold tests. Each of these has its uses in determining that routinely used filters are per-forming to the same standards as those validated for the particular products and processes. 

Fig. 6 depicts the type of relationship that might be found between downstream gas flow rate and upstream gas pressure in a typical in-process automated bubble point test. The transition pressure is not clearly defined. Actual bubble points (transition pressures) obtained with this type of equipment differ from theoretical bubble points calculated for the same membrane from direct measurement of pore size, and from laboratory-type bubble point testing. 

New, or recycled fibers, are sul ected to physical nondestmctive testing, eg. permeability and bubble-point tests. In the latter, the gauge pressure required to cause the passage of air bubbles through the fiber is measured whilst the cartridge is submerged in a wetring fluid , eg. isopropyl alcohol This measurement may be used to calculate the diameter of the fiber pore dp from the measured pressure diflEerence AP from the equation ... 

When a test gas (for example ambient air) is applied over a water moistened filter, just below the pressure level of the bubble point, test gas diffusion will occur through the water in the wetted membrane filter. This diffusion happens in all water filled pores, not only in the largest. This principle is the basis for two tests, which use different approaches to measure gas diffusion the pressure hold test and the diffusive-flow (forward flow) test. Other names for the same principle tests exist. These tests are performed at a pressure of about 80 % of the theoretical bubble point pressure of the filter. It is important that the largest pores are still filled with liquid. In this phase, diffusion occurs more or less linearly with the pressure drop over the... 

Pretest predictions were performed based on Equation (3.16). To do so, knowledge of mixture surface tension, mixture contact angle, and effective pore diameters is required. Here, pore diameters were based on Method 1 in Table 4.2, pure reference fluid bubble point tests. Mixture surface tension for all mass fractions was estimated from an equation of state and Langmuir isotherm (1916) fit to data available in the literature. Mixture contact angles were measured as a function of methanol mass fraction. 

Liquid/Vapor Surface Tension of the Methanol/Water Mixture Surface tension values were previously measured at different mass fractions of methanol in water at constant temperature from 293 to 323 K, and are available in the literature (Vazquez et al., 1995). Bubble point tests here were conducted over a colder range of temperatures ( 275-295 K), so measurements from Vazquez et al. (1995) at 293 K are used to... 

Room temperature reseal pressure data was collected simultaneously with bubble point data. The same inverted bubble point test configuration used to measure the bubble point was used to measure reseal pressures. A bubble point test ceases once pressurant gas breaks through the wetted pore. To commence a reseal point test, the pressurant gas flow rate beneath the screen is slowly reduced in fixed quasi-static increments to slowly encroach upon the differential pressure across the screen at which the screen reseals. Eventually the screen rewets/reseals itself as evident in visualization of no more bubbles... 

A picture of the pipe assembly used for FTS testing is shown in Figure 9.11. Two 5.08 cm (2 in.) OD screen samples were mounted inside the pipe assembly as shown. Pressure taps were mounted to measure the differential pressure across the screen as a function of flow rate. The second screen was spaced far enough from the first sample to minimize entrance effects at the highest flow rates tested, thus ensuring single phase liquid flow at each screen. The assembly was mounted from the top of the tank and so the flow was routed vertically upward. Both screens passed pre-test IPA bubble point tests to ensure that they were defect free. 

With the exception of warm pressurant gas bubble point tests conducted in Chapter 8, the majority of data in the literature was taken with the temperature of the pressurant gas approximately equal to the liquid temperature. This is due to the standard inverted testing configuration used for measuring cryogenic bubble point pressures which forces uniform,... 

The pressure required to force water to enter the pore is called the breakthrough pressure. Bubble point as measured and reported in the literature is the air pressure needed to push out liquid imbibed in the pore of the membrane. The procedure for a bubble point test is described in ASTM Method F-316. The relationship between pore size and bubble point pressure is based on the application of the Young-Laplace equation. The smaller the... 

The tests described so far have all been challenge tests, in which a known suspension is fed to a test filter. The bubble point test, on the other hand, measures a characteristic of the filter medium without use of particles. 

The bubble point test is based on the fact that, for a porous filter medium, immersed in and thoroughly wetted by a specific liquid, the pressure required to force a gas bubble through a pore is inversely proportional to the diameter of the pore. In practice, this means that the pore size of a filter element can be established by wetting the element completely with the liquid and measuring the pressure at... 

The pressure at which the slope changes is the bubble-point pressure of the mixture. The volume at this point is the volume of the bubble-point liquid. Often it is given the symbol Vsat. The volume of the bubble-point liquid can be divided by the mass of reservoir fluid in the cell to obtain a value of specific volume at the bubble point. Specific volume at the bubble point also is measured during other tests and is used as a check on the quality of the data. 

The subscript S indicates that this is a result of a separator test, and the subscript b indicates bubble-point conditions in the reservoir. The volume of liquid expelled from the cell is measured at bubble-point conditions. The volume of stock-tank liquid is measured at standard conditions. 

There are a number of special symbols which are used only in referring to the results of a black oil reservoir fluid study. These symbols are defined in Table 10-3. The subscripts o and g refer to liquid and gas, as always. The subscripts F, D, and S refer to flash vaporization, differential vaporization, and separator test, respectively. The subscript b is added to indicate that the quantity is measured at the bubble point. 

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