Producing electrosuspensions

Details Producing electrosuspensions Producing electrosuspensions

1992-03-10

1995-10-31

Pellinen, A. D.

Electricity: electrical systems and devices

Electric charge generating or conducting means

H01H 1900

Patent

active

054635241

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to improvements in apparatus used to produce electrosuspension of particulate matter such as powders.


BACKGROUND ART

Electrosuspension, also known as electrodispersion, is a technique for suspending fine particulate matter within closed or open containers and is usually produced by applying high DC-potential to appropriately configured stationary electrodes fixed within a dispersing chamber. The suspension effect is produced by the interaction between the applied electric field and the particles. The suspensions are typically in the form of a dust-cloud which partially fills the container above a static powder bed. Concentration of the cloud may be adjusted by raising or lowering, as required, the voltage that is applied to the electrodes. A typical but not exclusive electrode configuration is one where an electrode is embedded within the static powder bed, while the other is positioned some 20-30 mm above the surface of the powder. Although there are a number of possible polarity combinations which can be used, it is often the case that the embedded electrode is at earth potential. While the applied voltage necessary to cause suspensions is determined by factors such as the relative spacing of the electrodes, the weight, size and shape of particles, it is mostly well above 10 kV and can be as high as 30-40 kV. Particle sizes are typically in the range of from a few microns to several hundred microns.
Developments in the art of electrosuspensions have been reported in the J. of Appl. Phys., 1980, 51 (10 5215-5222 and 5223-5227, and in the J. of Appl. Phys., 1984 55 (11) 4088-4094. Examples of applications of these developments are also given in the United Kingdom patents 2074610B and 2143989.
Prior art electrosuspension apparatus have sufferred several inherent disadvantages:
Firstly, particles easily polarized by the electric field, such as contained by many crystalline dielectrics (e.g.: KCl, NaCl, sugar, ascorbic acid, nicotinamid), tend to align themselves with the field and with each other, forming chains, filaments or needles in the process. There is a tendency for these formations to attach themselves to one of the electrodes and act as field-concentrators, giving rise to intermittent and later continuous ionization of air within the dispersing space. As ionized air is electrically conducting, this mechanism can collapse the high voltage field, resulting in the sharp reduction of the suspended cloud. The formation of filaments can be especially prevalent in case of fibrous dust, such as asbestos and cellulose, and it is often the case that these type of powders form solid bridges extending between the electrodes, while voltage is applied.
Additionally, in applications which involve the treatment or us of the suspended dust, (such as the vapour coating of particles), it is often necessary to remove the suspension from within the electrode space. While removal can sometimes be effected by a cross-airstream through the system, this is not always viable. Removal techniques based on the tendency of particles to `shoot past` the upper electrode, being propelled by their own upward momentum have not generally succeeded, as the fixed upper electrode acts as a physical barrier to the particles. This difficulty has ben addressed by adapting electrode design, for example, by using a wiremesh type configuration. However, the tendency of the particles to eventually block up openings can not be easily eliminated and is particularly prevalent with dielectric dust. A factor further limiting the amount and concentration of dust which can emerge through the electrode region is the reverse charging of particles by physical contact with the electrode, effectively reversing the charge and therefore the direction of force which the particles experience.
Yet another difficulty exists in relation to the electrosuspension of particles having a size of a few microns. Particles of this size are often referred to as micronised particles and as used herein this term refers to particles

REFERENCES:
patent: 3233156 (1966-02-01), Jarvis et al.
patent: 3670699 (1972-06-01), Sargent
patent: 3806763 (1974-04-01), Masuda
patent: 3958162 (1976-05-01), Kuehnle
patent: 4161765 (1979-07-01), Itoh et al.
patent: 4240125 (1980-12-01), Kuehnle
patent: 4389225 (1983-06-01), Willett et al.
patent: 4440552 (1984-04-01), Uchiya et al.
patent: 4440800 (1984-04-01), Morton et al.
patent: 4467332 (1984-08-01), Akutsu
patent: 4701941 (1987-10-01), Szirmai et al.
patent: 4737885 (1988-04-01), Akutsu
Derwent Publications Ltd., Translated Abstract of Japan 60-140669, Jul. 1985.
J. Appl. Phys. 55 (11), 1 Jun. 1984 "Vapor Coating of Electrostatically Dispersed Powders" (1984 American Inst. Physics).
J. Appl. Phys. 51(10), Oct. 1980 "The Dispersion of Powders by Intense Electrostatic Field" (1980 American Inst. of Phys.).
Derwent Publications Ltd., London, Database WPIL, Accession No. 85-322427, GB & SU-A-1161 181 (Leonov S.B.), Jun. 1985.

Affiliated with

Also associated with

Rating

Producing electrosuspensions does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Producing electrosuspensions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Producing electrosuspensions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1778143