Fluid sprinkling – spraying – and diffusing – Processes – Including electrostatic charging
Patent
1985-04-17
1987-04-21
Kashnikow, Andres
Fluid sprinkling, spraying, and diffusing
Processes
Including electrostatic charging
239690, B05B 502
Patent
active
046590129
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrostatic spraying, especially spraying of aqueous liquids and agricultural chemicals.
It has been proposed to spray liquids by atomising from a sprayhead charged to a high potential. Such a process is described in our U.K. Pat. No. 1 569 707. It has been found in practice that satisfactory atomisation at practical flow-rates can be achieved with oil-based liquids but that for reasons which are not completely understood satisfactory atomisation of aqueous formulations tends to occur only at flow-rates which are undesirably low for many purposes.
It has been observed that satisfactory spraying of oil-based formulations tends to be associated with the formation of at least one stable ligament of liquid which is ejected from the sprayhead under electrostatic forces and which breaks up into droplets at a distance from the sprayhead. Such ligamentary flow is not characteristically obtained with aqueous liquids and it is believed (although the utility of the present invention does not depend upon the correctness of the theory) that this absence of ligamentary flow may be a cause of the unsatisfactory spraying characteristics of such liquids.
We have now found that under some circumstances it is surprisingly possible to achieve ligamentary flow and satisfactory spraying characteristics with a wider range of liquids than heretofore including aqueous liquids.
According to the present invention there is provided apparatus for the electrostatic spraying of liquids, comprising a sprayhead which is chargeable to a high electrical potential so that, in use, liquid is projected from the sprayhead under the influence of electrostatic forces, at least one electrode having a sharp edge or point, and means for maintaining the said at least one electrode at an electrical potential, the arrangement of the said at least one electrode and the potential being such as to reduce the generally radially directed electrical forces acting upon the surface of liquid prior to its atomisation into droplets, whereby the liquid assumes a ligamentary form.
According to the invention there is also provided a process for electrostatic spraying of liquids, comprising delivering the liquid to a sprayhead charged to a high electrical potential so that liquid is projected from the sprayhead under the influence of electrostatic forces, and reducing the strength of the generally radially directed electrical forces acting upon the surface of the liquid after it leaves the sprayhead but prior to its atomisation into droplets, whereby the liquid assumes a ligamentary form.
The region over which one or more ligaments are formed may be thought of as a ligamentary zone although of course in the absence of the special measures which characterise the present ligaments are not formed over the whole desired range of spraying conditions according to our observations.
The extent of the ligamentary zone will vary according to operating parameters but can be determined by practical trial.
The strength of the electrical forces to which the surface of the liquid is subjected in the ligamentary zone may be decreased, according to one aspect of the present invention, by passing the liquid past one or more sharp or pointed electrodes maintained at earth potential or a potential relatively low compared with that of the sprayhead. Alternatively, such electrodes may be electrically charged to a high-potential of opposite polarity to the nozzle. We have found that selection of conditions which influence forces at the surface of the liquid is especially effective in achieving ligamentary flow.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic perspective view of an apparatus according to the invention for spraying an aqueous liquid;
FIG. 2 is a diagrammatic axial section of a second spraying apparatus according to the invention; and
FIG. 3 is a diagrammatic axial section of a modified electrode.
Referring to FIG. 1 of the drawings, one embodiment of the inven
REFERENCES:
patent: 2894175 (1959-07-01), Lamm
patent: 4157162 (1979-06-01), Benedek et al.
patent: 4264641 (1981-04-01), Mahoney et al.
Imperial Chemical Industries plc
Kashnikow Andres
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