Permittivity is an important factor in determining the effectiveness of filtration media, whether employed for purposes ranging from potable water to cryogenic fluids.

A possible device that can utilize the Advanced Permittivity Testing Method for filtration purposes is shown in Figure 4.1a. The flat specimen, mounted in the specimen holder, is first inserted into the device. By means of the thrust shaft the drive motor moves the pistons at a constant speed, forcing the fluid through the filter at a constant flow rate. A motor controller will hold a variety of constant motor speeds to determine filter permittivity and delineate the transition from laminar to turbulent flow. The pressure difference can be set to typical application values.

With the quick release mechanism, the pistons can be readily removed from the device, as shown in Figure 4.1b, permitting thorough cleaning. Figure 4.2 illustrates simple specimen holder configurations. A tubular specimen can be either cemented or clamped to the insert. Of course, the effective area of the filter A=pd²/4.

The permittivity testing procedure is fully automated, as shown in Figure 4.3, using the electric valve for fluid control. Automatic motor sequencing permits a full series of tests to be run by a specially programmed central processing unit. In this manner, reproducible permittivity determinations can be made for biotextiles.

Figure 4.4a represents an example of the initiation stage of a fully automated testing procedure using the Advanced Permittivity Testing Method. After the specimen holder has been inserted, the fluid chambers are evacuated to remove air bubbles from the fabric. The electric valve then connects the test chamber to the pressurized fluid source, as shown in Figure 4.4b, and the previously de-aerated fluid is then automatically injected into the test chamber.

Piston motion at a fixed specified speed is initiated, as represented in Figure 4.5a, forcing the fluid into the mouth of the tubular specimen, shown in Figure 4.1a, with the pressure difference across the fabric recorded.

If reverse fluid flow is not desired, the chambers are connected across the electric valve, as represented in Figure 4.5b. This process is repeated at different motor speeds to obtain the information required to calculate the permittivity, as shown in Figure 2.2. If any deviation from linearity appears, this can be readily discerned.

Test completion is represented by Figure 4.6a. The fluid is evacuated from the chambers, as represented by Figure 4.6b, and air is then bled into the chambers. The specimen holder can then be removed.

Figure 4.7 shows a possible design of a commercial device using the Advanced Permittivity Testing Method. The allowable flow rate and pressure difference range for this commercial apparatus would cover essentially all filter requirements for organic and inorganic fluids. Modification for different temperature operations would be optional. Operation is fully automated. Moreover, burst pressures can be readily determined.  The multi-use Advanced Permittivity Testing device can, of course, emulate the single-use device shown in Figure 1.1.