GB2506247A

GB2506247A - Porometry Apparatus

Info

Publication number: GB2506247A
Application number: GB201312944A
Authority: GB
Inventors: Christopher Mark Gribble; Giuliano Maurizio Laudone; Graham Peter Matthews
Original assignee: Plymouth University
Current assignee: Plymouth University
Priority date: 2012-07-30
Filing date: 2013-07-19
Publication date: 2014-03-26
Also published as: GB201312944D0; GB201213483D0

Abstract

A porometry apparatus comprises a sample housing 10 containing a sample support 12, vacuum drawing means 32 connected by pipe 30 to the housing to one side of the support, and a wetting fluid tank 20 connected to the housing to the other side of the support such that wetting fluid from the tank can be drawn through a material sample 14 located upon the support to fully saturate the sample. The apparatus also includes gas supply means 44 whereby gas under pressure can be applied to the sample, wetting fluid reservoir 18 beneath the support, and a pressure control means for maintaining fluid pressure within the reservoir at ambient pressure. It may further comprise an outlet passage 26 connected to the reservoir 18 along which wetting fluid is displaced as it exits the sample, and monitor means 74 for monitoring the displacement of wetting fluid along the outlet passage. Detection means 86, 96 (Fig 2) may be located beneath the support to monitor for the emergence of a gas bubble 100 from a sample located upon the support.

Description

Porometry Apparatus This invention relates to an apparatus for use in conducting porometry measurements upon samples of materials. It also relates to a method of use of such an apparatus in conducting tests to measure the porosity characteristics of the material samples.

One technique by which porometry measurements can be taken involves saturating a material sample in a wetting fluid which fully wets the void structure of the material sample. The wetting fluid should have a low vapour pressure. Whilst a range of different wetting fluids could be used, and the choice of wetting fluid may depend upon a number of criteria, for example it may depend upon the material sample upon which the tests are being conducted, one wetting fluid suitable for use in this application is a perfluorinated ether.

The saturation of the material sample may be achieved by immersion of the material sample in the wetting fluid. Another approach involves placing the material sample in a vacuum chamber, and then introducing the wetting fluid using a syringe.

Once saturated with the wetting fluid, the material sample is placed upon a support within a sealed housing, and gas is applied to the material sample under pressure. It will be appreciated that the application of gas under pressure to the material sample will tend to drive the wetting fluid through and from the material sample. The gas used is typically nitrogen, but other gases may be used. Initially, as the voids within the material sample contain the wetting fluid, the gas is unable to flow through the material sample. However, as the wetting fluid is driven from the material sample! it will be appreciated that a point will be reached at which flow paths through the material sample become clear of the wetting fluid, and the gas is able to flow through the material sample. The point at which the gas breaks through the material sample and starts to flow through the material sample at a measurable rate is known as the bubble point', and the applied gas pressure at that point is the bubble point pressure'. It will be appreciated that by the use of sensors monitoring the gas flow rate and the gas pressure, the bubble point pressure for the material sample can be measured. In practice, the definition of the bubble point and associated pressure is somewhat arbitrary, for example it may be taken to be the point at which a predetermined flow rate is attained, and so does not accurately reflect the point at which the gas actually breaks through the material sample.

After the bubble point has been attained, the gas pressure can be raised further and measurements of the gas flow rate at a range of pressures may be taken to produce flow rate data for the wet' sample. Once the flow of gas has driven all of the wetting fluid from the material sample, and so the material sample is dry, the gas pressure can be reduced to ambient. Subsequently, the gas pressure is raised and the gas flow rate monitored to produce flow rate data for the dry' sample.

The wet', dry' and bubble point data can be used to provide information about the distribution and size of the voids of the material sample.

Whilst such a test provides useful information, it is an object of the invention to provide an enhanced porometry apparatus and method, the use of which allows the derivation of additional information for use in modelling of the void structure and filtration properties, or the like, of a material sample. The modelling may be undertaken using a suitable computer modelling or simulation software package.

One area in which enhancements may be made is in the preparation of the sample material to ensure that it is properly saturated with wetting fluid prior to the conducting of the tests, as failure to fully saturate the material sample may lead to inaccuracies in the measured data.

According to a first aspect of the invention there is provided a porometry apparatus comprising a sample housing containing a sample support, vacuum drawing means connected to the housing to one side of the sample support, and a wetting fluid tank connected to the housing to the other side of the support such that, in use, welling fluid from the tank can be drawn through a material sample located upon the sample support to fully saturate the material sample.

In use, once a material sample has been positioned upon the sample support and the housing sealed, operation of the vacuum drawing means evacuates the housing.

Wetting fluid from the reservoir flows into and progressively fills the housing, saturating the material sample.

The vacuum drawing means conveniently comprises a vacuum pump. A trap is conveniently provided between the housing and the vacuum pump to collect welling fluid overflowing from the housing. A sensor, for example an optical sensor, is conveniently arranged to monitor for the presence of wetting fluid within the trap, and may be used to switch off the vacuum pump and close a number of control valves when the wetting fluid is detected in the trap.

Another area in which enhancements can be made is in ensuring that the wetting fluid pressure beneath the sample is at ambient pressure, as this may allow detection of the bubble point with enhanced accuracy.

According to a second aspect of the invention there is provided a porometry apparatus comprising a sample housing containing a sample support, gas supply means whereby gas under pressure can be applied to a material sample located upon the sample support, a welling fluid reservoir beneath the sample support, and a pressure control means for maintaining the pressure of wetting fluid within the welling fluid reservoir at ambient pressure.

The wetting fluid pressure control means conveniently takes the form of a U-shaped tube, one limb of which communicates with the wetting fluid reservoir and the other limb of which extends to a height above the height of the wetting fluid reservoir, an overflow passage being connected to the said other limb at the same height as the upper surface of the material sample, the overflow passage being at ambient pressure.

It will be appreciated that, in use, opening of appropriate control valves allows welling fluid to drain from the housing, wetting fluid escaping through the overflow, until the wetting fluid level within the housing matches the height of the overflow at which point draining of wetting fluid from the housing will cease. By aligning the overflow with the upper surface of the material sample, it will be appreciated that the wetting fluid within the housing and contained within the voids of the material sample will be at ambient pressure.

Known measurement techniques provide little or no information regarding the ingress of gas into the material sample or egress of welling fluid therefrom prior to the bubble point being reached.

According to a third aspect of the invention there is provided a porometry apparatus comprising a housing, a sample support located within the housing, gas supply means whereby gas under pressure can be applied to a material sample located upon the sample support, a wetting fluid reservoir beneath the sample support, an outlet passage connected to the wetting fluid reservoir and along which wetting fluid is displaced, in use, as wetting fluid is displaced from the material sample, and monitor means for monitoring the displacement of wetting fluid along the outlet passage.

Conveniently, the apparatus includes means for injecting a gas bubble into the wetting fluid within the outlet passage, the gas bubble being displaced with the wetting fluid along the outlet passage, in use. To detect the position of the gas bubble, a single or multiple source of visible or other electromagnetic or ultrasonic radiation, for example in the form of a laser, may be mounted opposite a detector on the other side of the outlet passage, on a mounting that can be moved along the outlet tube with a, for example, motor-driven micrometer screw. It will be appreciated that these are just some of many options for monitoring the position of the gas bubble.

In use, the application of gas under pressure to the material sample results in wetting fluid being displaced therefrom. Monitoring of the position of the gas bubble provides an indication of the quantity of wetting fluid displaced from the material sample. By monitoring the gas bubble position as the applied gas pressure is increased, it will be appreciated that additional data relating to the porosity characteristics of the material sample can be obtained.

Another area by which enhancements may be made is in detection of the bubble point.

According to a fourth aspect of the invention, therefore, there is provided a porometry apparatus comprising a housing, a sample support located within the housing, and detection means located adjacent and beneath the sample support and operable to monitor for the emergence of a gas bubble from the material sample located upon the support, in use.

The detection means conveniently comprises an optical or ultrasonic detector. By way of example, the housing of an optical detector may be of circular cross-section and the detection means may comprise a laser operable to transmit a laser beam along a path slightly offset from a diameter of the housing, the laser beam being reflected numerous times by the inner surface of the housing before being incident upon a light detector.

Conveniently, appropriate adjustment means are provided to allow accurate positioning of the laser. In use, prior to the bubble point being reached, the transmitted laser beam will be incident upon the light detector, providing an indication that gas bubbles are not yet emerging from the material sample and hence that the bubble point has not yet been reached. When the first gas bubble emerges from the material sample, it will interrupt the laser beam with the result that the light detector will no longer register the laser beam and so will provide an accurate indication that the bubble point has been reached.

An ultrasonic detector might comprise an ultrasonic source and detector, mounted so that any bubble or bubbles appearing under the surface of the wetted sample may be detected.

The aforementioned aspects of the invention may be, and conveniently are, used in combination with one another to produce an apparatus having significant benefits over known porometry measurement techniques.

The invention further relates to methods of use of the apparatus defined hereinbefore.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a pororrietry apparatus in accordance with one embodiment of the invention; and Figures 2 and 3 are diagrams illustrating part of the apparatus of Figure 1 in greater detail, in the case where the bubble point detector involves a laser.

For the avoidance of doubt, it should be noted that the accompanying drawings are diagrammatic and so none of the features or any details or characteristics of the features therein are drawn to scale.

Referring firstly to Figure 1, a porometry apparatus is illustrated which comprises a housing 10 containing a sample support 12 upon which a material sample 14 to be tested is located, in use. The sample support 12 divides the housing 10 into an upper section 16 and a lower, wetting fluid reservoir section 18. A header tank 20 is located at a vertical height above the housing 10 and is connected to the wefting fluid reservoir section 18 of the housing 10 by way of an inlet pipe or conduit 22 which is connected to an outlet pipe 26 connected, in turn, to the wetting fluid reservoir section 18 of the housing 10. An inlet valve 24 is provided in the inlet pipe 22 to control the passage of wetting fluid along the pipe 22, and an outlet valve 28 is provided in the outlet pipe 26 to control the passage of wetting fluid through the outlet pipe 26. The inlet and outlet valves 24, 28 are conveniently motor driven valves, preferably precisely adjustable and controllable by an associated computer.

Connected to the upper section 16 of the housing 10 is a vacuum pipe 30 with which a vacuum pump 32 communicates. Part way along the length of the vacuum pipe 30 is located a wetting fluid trap 34. Valves 36, 37, 38 are provided in or communicate with the vacuum pipe 30. A sensor arrangement 40 is provided to monitor for the presence of wetting fluid within the trap 34. In the arrangement illustrated, the sensor arrangement comprises a laser 40a operable to transmit a laser beam across the trap 34 to a detector 4Db located on the opposite side of the trap 34. When the trap 34 is free of wetting fluid, the detector 4Db senses the laser beam. When wetting fluid is present within the trap 34 and is of a depth such that the wetting fluid interferes with the transmission of the laser beam to the detector 4Db, the absence of the detection of the laser beam by the detector 40b provides an indication that the trap 34 contains wetting fluid.

Also connected to the upper section 16 of the housing 10 is a gas inlet pipe 42 connected to a source 44 of gas under pressure, such as a gas cylinder or a compressor. A gas inlet control valve 46 is provided in the pipe 42, controlling the supply of gas from the source 44 to the housing 10. A flow rate sensor 48 and a gas pressure sensor 50 are provided to monitor the pressure and rate of flow of gas to the housing 10.

The outlet pipe 26 communicates, via a valve 52. with a generally U-shaped tube 54.

The U-shaped tube 54 includes a first limb 56 connected to the outlet pipe 26, a second limb 58 which extends upwards to a position higher than the height of the upper surface of the material sample 14, and a horizontal connecting part 60. The connecting part 60 is of transparent form, or includes a window therein, to allow visual or optical inspection of the interior of the connecting part 60 along a significant part of its length.

The connecting part 60 is of relatively small diameter.

An overflow pipe 62 is connected to the second limb 58 at a weir 62a positioned at the same height as the upper surface of the material sample 14, as denoted by the broken line 64. The overflow pipe 62 communicates with a sump 66 from which wetting fluid may be supplied by a pump 70, via a removable filter 68, to the header tank 20.

A gas bubble injection device 72 is connected to the connecting pad 60 and is operable to allow the injection of a gas bubble into the wetting fluid within the connecting part 60.

The size of the gas bubble injected by the device 72 is such that the gas bubble completely fills the diameter of the connecting part 60. The gas bubble is visible from the exterior of the connecting pad 60 by virtue of the transparent form thereof or the window formed therein.

Adjacent the connecting part 60 is provided a gas bubble detector arrangement 74.

The detector arrangement 74 takes the form of a laser 74a and detector 74b, both of which are mounted upon a stepper motor driven micrometer screw 74c such that the laser 74a and detector 74b can be moved along the length of the connecting part 60, and the position read with good accuracy from the scale or output of the micrometer screw. The laser is chosen and arranged such that the wetting fluid is opaque to the emission of the laser. In use, the detector arrangement 74 is used to monitor the position of the gas bubble injected into the connecting part 60 by moving the laser 74a and detector 74b until such time as the laser beam output by the laser 74a is sensed or detected by the detector 74b, providing an indication that the laser 74a and detector 74b are aligned with one end of the gas bubble. Once that position has been attained, the micrometer screw reading provides an accurate indication of the location of the gas bubble.

As mentioned above, the sump 66 is arranged to collect wetting fluid from the overflow pipe 62. In addition, it can collect wetting fluid from the housing 10 via a second outlet pipe 76, the flow along which is controlled by a control valve 78, and to collect wetting fluid from the trap 34 via a trap outlet pipe 80, the flow along which is controlled by a control valve 82.

Figures 2 and 3 show a possible design of bubble point detector, in the case where the detector uses a laser. The bubble point detector comprises a laser 86 mounted in such a manner as to permit the transmission of a laser beam 88 through a window ba formed in the housing 10. Adjustment means 90, for example in the form of a micrometer screw adjuster, are operable to adjust the height of the laser 86 so as to result in the laser beam 88 being transmitted just below the level of the sample support 12. A second adjustment means 92 sets the angle of the laser 86 such that the beam 88 is transmitted parallel to the sample support 12. A third adjustment means 94 (see Figure 3) allows the laser 86 to be, effectively, pivoted relative to the housing 10 such that the laser beam 88 is transmitted along a path slightly offset from the diameter of the housing 10.

The internal surface of the housing 10 is reflective. As the beam 88 is transmitted along a path slightly offset from the diameter of the housing 10, it will be appreciated that the beam 88, when incident upon the opposite side of the housing 10, will be reflected along a different path, also slightly offset from a diameter of the housing 10.

As best shown in Figure 3, after multiple reflections, the beam 88 will be incident upon, and transmitted through, a window lOb formed in the housing 10. A detector 96 is positioned to detect the beam 88 transmitted through the window lob.

Should the bubble point detector be sonic, then an ultrasonic source and detector are mounted in such as a way that the detector can detect one or more bubble appearing below the surface of the sample.

It will be appreciated that the apparatus described hereinbefore includes a number of valves. In each case, these valves are conveniently computer controlled, motorised, and accurately positionable valves. The wetting fluid used in the apparatus should be such that is fully wets the void structure of the material sample. One example of a wetting fluid suitable for use in the apparatus is a perfluorinated ether, but it will be appreciated that the invention is not restricted in this regard. The gas may comprise, for example, nitrogen. However, again, this need not always be the case and other gases could be used.

In use, a sample of the material to be tested is positioned upon the sample support 12 within the housing. An 0-ring seal 98 is used to form a gas tight seal between the material sample 14 and the housing 10. Once the material sample 14 is correctly positioned, the housing 10 is closed. As shown in Figure 3, the housing 10 is conveniently of two part form, having a removable lid which can be sealed to the remainder of the housing 10 and removed to allow access to the interior of the housing.

The gas inlet pipe 42 and vacuum line 30 are conveniently in the form of flexible hoses to allow the lid to be moved. The closing of the housing 10 may conveniently press into place the 0-ring seal 98, causing the seal to become vacuum and pressure tight.

With the material sample 14 so positioned, and with all of the valves closed, the vacuum pump 32 is operated. Then valves 36 and 38 are opened, and the vacuum pump 32 draws a vacuum within the housing 10. Subsequently, the valves 24 and 28 are opened to allow wetting fluid from the header tank 20 to flow into and fill the housing 10, saturating the material sample 14. Once the housing is filled, wetting fluid will enter the pipe 30 and pass to the trap 34. Once the level of the wetting tluid within the trap 34 reaches the point at which the sensor arrangement 40 detects the presence of the welling fluid, the valve 36 is closed, the vacuum pump 32 is switched off, and the valve 37 is immediately opened.

From this condition, the valve 24 is closed to prevent the introduction of further welling fluid into the housing 10, and the valves 36 and 52 are opened to bring the pressure of the welling fluid above the material sample 10 to ambient. As, at this stage, the housing 10 is full of welling fluid to a level higher than the level 64 of the outlet weir 62a, it will be appreciated that welling fluid will gradually drain from the housing 10 through the outlet pipe 26 and U-shaped tube 54 to the outlet pipe 62 and sump 66.

Such drainage will continue until the level of the wetting fluid within the housing 10 is the same as that of the weir 62a at the level 64. Since the level 64 is chosen to match the level of the upper surface of the material sample 14, it will be appreciated that the material sample 14 remains fully saturated.

Next, the gas injection device 72 is operated to inject a bubble into the wetting fluid within the horizontal connecting part 60 of the U-shaped tube 54. The valve 36 is closed and the valve 46 opened to allow the commencement of the supply of gas under pressure to the housing 10. Initially, the applied gas pressure with be relatively low, the valve 46 being opened in such a manner as to allow the applied gas pressure to be raised, gradually, overtime. The gas pressure meter 50 is used to monitor the applied gas pressure. The application of gas under gradually increasing pressure to the housing 10 will gradually result in the gas being able to displace wetting fluid from the voids of the material sample 14 into the section 18 of the housing 10. Such displacement of wetting fluid result in wetting fluid being displaced along the outlet pipe 26 and U-shaped tube 54, and this results in movement of the gas bubble along the connecting part 60. By appropriate operation of the detector arrangement 74, the position of the gas bubble can be monitored to provide an indication of the volume of wetting fluid displaced from the voids of the material sample 14. By monitoring the position of the gas bubble as the applied gas pressure is increased, data relating to the relationship between the applied gas pressure and the volume of wetting fluid displaced from the material sample 14 can be obtained.

Whilst the above operation is being performed, the bubble point detector is monitored to ascertain whether or not the bubble point has been reached. If the detector is ultrasonic, then the ultrasonic detector is monitored to show evidence of a bubble. It the detector is optical, for example with a laser as described above, then detection is achieved by checking whether the laser beam 88 is being received by the detector 96.

If the laser beam 88 is being detected, then the bubble point has not yet been attained.

When the bubble point is reached, one or more gas bubbles 100 (see Figure 2) will protrude from the material sample 14 through the sample support 12 and interrupt the laser beam 88 with the result that the laser beam 88 is no longer detected by the detector 96. The applied gas pressure at which the bubble point is reached is noted.

Once the bubble point is reached, the valve 28 is closed and the valve 78 is opened to allow the remaining wetting fluid to drain from the housing 10 into the sump 66. The applied gas pressure continues to be raised in a controlled fashion, and the output of the flow meter 48 for a range of applied gas pressures is noted to derive the wet flow data for the sample as outlined hereinbefore. After it is determined that the sample is effectively dry, the gas pressure is relieved and subsequently raised whilst flow rate measurements are taken to allow dry' flow late data to be obtained.

After the data has been acquired, the valve 82 can be opened to drain the fluid from the trap 34 to the sump 66, the valve 66a located beneath the sump 66 opened, and the pump 70 operated to return the fluid from the sump 66 to the header tank 20 ready for conducting tests on another material sample. If required, the filter 68 may be removed and cleaned or replaced.

It will be appreciated that the use of the apparatus as outlined hereinbefore allows accurate detection of the bubble point, and enables additional data relating to the porosity characteristics of the material sample to be obtained, whilst still allowing the data conventionally collected to be obtained. The apparatus allows all of the applied wetting fluid to be collected, and the collected wetting fluid can be filtered ready for reuse, if desired. Data accuracy is enhanced by ensuring that the sample is fully saturated before the tests are conducted. Bubble point measurement accuracy is enhanced by the use of an accurate, adjustable detection arrangement to detect the emergence of the first gas bubble from the material sample, and also because the wetting fluid beneath the material sample is at ambient pressure at the bubble point.

To maximise accuracy, it is desirable for the volume of the connecting part 60 of the U-shaped tube 54 to match the volume of the pores or voids of the material sample 14 so that the injected gas bubble is displaced along substantially the full length of the connecting part 60, approaching the end of the connecting part 60 as the bubble point is reached. In order to permit this, a range of different diameter pipes may be provided to serve as the connecting part 60, the appropriate diameter pipe being chosen prior to commencement of the test, for example by conducting pycnometry tests on the material sample to ascertain the approximate porous volume thereof.

Whilst the arrangements described hereinbefore represent various embodiments incorporating the invention, it will be appreciated that a number of modifications and alterations may be made thereto.

Claims

CLAIMS: 1. A porometry apparatus comprising a sample housing containing a sample support, vacuum drawing means connected to the housing to one side of the sample support, and a wetting fluid tank connected to the housing to the other side of the support such that, in use, wetting fluid from the tank can be drawn through a material sample located upon the sample support to fully saturate the material sample.
2. Apparatus according to Claim 1, wherein the vacuum drawing means comprises avacuumpump.
3. Apparatus according to Claim 1, wherein a trap is provided between the housing and the vacuum pump to collect wetting fluid overflowing from the housing.
4. Apparatus according to Claim 3, further comprising a sensor arranged to monitor for the presence of wetting fluid within the trap.
5. Apparatus according to Claim 4, wherein the sensor is an optical or ultrasonic sensor.
6. A porometry apparatus comprising a sample housing containing a sample support, gas supply means whereby gas under pressure can be applied to a material sample located upon the sample support, a wetting fluid reservoir beneath the sample support, and a pressure control means for maintaining the pressure of wetting fluid within the wetting fluid reservoir at ambient pressure.
7. Apparatus according to Claim 6, wherein the wetting fluid pressure control means takes the form of a U-shaped tube, one limb of which communicates with the wetting fluid reservoir and the other limb of which extends to a height above the height of the wetting fluid reservoir, an overflow passage being connected to the said other limb at the same height as the upper surface of the material sample, the overflow passage being at ambient pressure.
8. A porometry apparatus comprising a housing, a sample support located within the housing, gas supply means whereby gas under pressure can be applied to a material sample located upon the sample support, a wetting fluid reservoir beneath the sample support, an outlet passage connected to the wetting fluid reservoir and along which wetting fluid is displaced, in use, as wetting fluid is displaced from the material sample, and monitor means for monitoring the displacement of wetting fluid along the outlet passage.
9. Apparatus according to Claim 8, wherein the means for monitoring comprises means for injecting a gas bubble into the welling fluid within a tube connected to or forming part of the outlet passage, the gas bubble being displaced with the wetting fluid along the outlet passage, in use.
10. Apparatus according to Claim 9, wherein the means for monitoring further comprises a laser and detector, or other optical or ultrasonic devices, mounted upon a micrometer screw thread and used to detect the position of the gas bubble.
11. A porometry apparatus comprising a housing, a sample support located within the housing, and detection means located adjacent and beneath the sample support and operable to monitor for the emergence of a gas bubble from a material sample located upon the support, in use.
12. Apparatus according to Claim 11, wherein the detection means comprises an optical detector.
13. Apparatus according to Claim 12, wherein the housing is of circular cross-section and the detection means comprises a laser operable to transmit a laser beam along a path slightly offset from a diametei of the housing, the laser beam being reflected numerous times by the inner surface of the housing before being incident upon a light detectoi.
14. Apparatus according to Claim 13, further comprising appropriate adjustment means to allow accurate positioning of the laser.
15. Apparatus according to Claim 11, wherein the detection means comprises an ultrasonic source and detector.