Measuring and testing – With fluid pressure – Porosity or permeability
Patent
1985-01-17
1988-01-12
Levy, Stewart J.
Measuring and testing
With fluid pressure
Porosity or permeability
G01N 1508
Patent
active
047182709
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to porosimeters and to methods of assessing pore size characteristics, such as pore size distribution.
A widely accepted standard apparatus and method for testing assessing pore size is to be seen in ASTM F 316-80 by the American Society for Testing and Materials.
According to such apparatus and method, the material is saturated with test liquid, held in a holder and subjected to progressively increasing pressure of a test gas. The initial breakthrough of gas through the wet filter is noted by a bubble point detector and thereafter the relationship between pressure applied and flow through the material is observed using a pressure gauge and a rotameter downstream of the material and directly impelled by the flow of gas. Such prior art test method is highly dependent on the manual skill and dexterity and the intellectual ability of the operator requiring as it does the simultaneous operation of the inlet pressure regulator and observation of the pressure gauge and the flow rate. Thereafter these readings have to be converted manually by drawing graphs and these are then interpreted. Despite these drawbacks this method is one of the accepted methods of testing porosity.
SUMMARY OF THE INVENTION
I have examined this prior art and have in the present invention provided substantial improvements in various respects and in particular from the point of view of avoiding reliance upon manual skill. The object of this invention is to gain information about the maximum pore size and the distribution of pore sizes in a porous material under test.
In my apparatus and method I use a pressure gauge and flow meter only in an initial calibration, which need not be done in the presence of the material to be tested. I further locate the flow-rate sensor upstream of the material to be tested. In operation, take both pressure and flow-rate readings directly from the respective sensors. These readings can be fed directly into an automatic recorder, which draws mechanically the output in the form of a graph, or may feed them to, for example, an integrating computer. Pore size characteristics then are computed and can be presented in a number of ways.
The siting of the flow-rate sensor upstream of the material to be tested is of great importance, since that sensor works at a higher pressure on that side of the test material than it would on the downstream side and furthermore the upstream positioning avoids any contamination of that sensor by the test liquid being swept from the material. In the ASTM method, a liquid trap is provided behind or downstream of the material, but will not prevent vapour and is not totally successful in preventing access of liquid into the subsequent stages of the apparatus, which therefore can affect the accuracy of the flow meter.
I further improve the process by standardising the test liquid. Those mentioned in the ASTM F 316-80 are water, petroleum distillate, de-natured alcohol or mineral oil. I find that various characteristics of volatility, surface tension or reactivity will not allow any one of those materials to be used over a wide range of materials to be tested. I have selected a liquid which is of the widest possible applicability, having very low surface tension and vapour pressure and in particular very low reactivity for the materials which are likely to form the materials under test. An example of such a liquid is known as Fluorinert (Registered Trade Mark), which is recommended by its makers Minnesota Mining and Manufacturing as a cooling liquid for electronic components and devices. The preferred Fluorinert liquid is known as FC43 having: a nominal boiling point of 174.degree. C., a viscosity of 2.6 cs, a vapour pressure at 25.degree. C. of 1.3 mmHg and a surface tension at the same temperature of 16 dynes per cm. Chemically, the liquid is a clear colourless perfluorocarbon fluid.
To relieve the operator further of the need for manual intervention, one may provide a motorised drive for the inlet flow regulator, whereby to achieve
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W. Fischer et al. "Eine Methode zur Ermittlung der Porengrobenverteilung" from Messtechnik 12/68, pp. 309-313, Jun. 24, 1968.
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ASTM F316-80, "Standard Test Method for Pore Size Characteristics of Membrane Filters for Use with Aerospace Fluids", pp. 298-304.
Coulter Electronics, Ltd.
Hibnick Gerald R.
Levy Stewart J.
Williams Hezron E.
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