Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1998-09-09
2000-10-03
Bell, Bruce F.
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204600, C25B 1500
Patent
active
06126802&
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for regulating and optimizing transport of liquid in porous structures by means of electroosmosis, wherein there are employed one or more electrode pairs, wherein each electrode pair constitutes an electrical circuit comprising an anode in the porous structure and a cathode in earth, where the anode and the cathode are connected to respective outputs on a power source which supplies a pulse voltage to the electrode pair in the form of a sequence of pulse patterns, and wherein each pulse pattern comprises a first positive pulse with a given amplitude V.sub.s and a duration t.sub.1, a negative pulse with the same amplitude V.sub.s, but substantially shorter duration t.sub.2 than the positive pulse, and subsequently a neutral pulse whose duration t.sub.3 is initially much less that the duration of the negative pulse and constitutes only a small fraction of the pulse pattern's T.sub.p. The invention also concerns a device for implementing the method.
In Swedish patent publication No. 450 264 a method is disclosed for the removal of humidity in a brick wall by means of electroosmosis. An alternating voltage with a positive mean value is fed to electrodes in a concrete or masonry structure and to an earth electrode. The positive pulse is 2-20 times longer than the negative pulse, which must be at least 20 ms. According to this publication, similar method is also employed for introducing a hydrophobic liquid into the structure, again by means of an alternating voltage of the same type as that used in the removal of humidity, but now a positive pulse of 1 s and a negative pulse of 200 ms are used, while between the negative pulse and the subsequent positive pulse a neutral interval of 200 ms is employed.
When using electroosmosis for transport of liquids in porous media, especially for the expulsion of humidity from masonry, there is a problem that the process comes to a stop due to the build-up of a potential on the electrodes. In order to maintain the process until the relative humidity in the structure has dropped to a level where electroosmotic transport processes will no longer occur, the electrodes therefore have to be depolarized. According to the above-mentioned Swedish patent publication this takes place during the negative pulse.
It has been shown, however, that it is not possible to reduce the relative humidity by this means to a level where ionic transport phenomena entirely cease, which is one of the main objects of the removal of humidity by means of electroosmosis.
In U.S. Pat. No. 5,368,709 a method is disclosed for removing or controlling humidity in concrete or masonry structures by means of electroosmosis, where a pulse voltage is employed with a pulse pattern consisting of a positive pulse followed by a negative pulse of substantially shorter duration than the positive pulse and subsequently a neutral pulse whose duration can initially be much shorter than, e.g., the duration of the negative pulse. By increasing the duration of the neutral pulse in the course of the process and possibly also the duration of the pulse pattern, it will be possible to achieve an approximately complete depolarization of the electrodes, with the result that the electroosmotic process is maintained until the relative humidity in the structure has dropped to a level where the ionic transport phenomena in the liquid and thereby the electroosmosis entirely cease. The electrodes are then fed with a pulse voltage, where the pulse pattern has a form and duration which substantially correspond to those it had when the electroosmotic process stopped.
With this method, however, there is a problem that the pulse pattern and the adjustment thereof are performed without direct reference to the actual polarization state of the electrodes and mainly on an empirical or heuristic basis, with the result that the electroosmotic process is not optimal, even though the final result will generally be good.
Thus it is an object of the present invention to provide a method which permits regulation an
REFERENCES:
patent: 4600486 (1986-07-01), Oppitz
patent: 5015351 (1991-05-01), Miller
patent: 5368709 (1994-11-01), Utklev
Bell Bruce F.
Electro Pulse Technologies of America, Inc.
Parsons Thomas H
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