Gas separation: processes – Deflecting – Centrifugal force
Reexamination Certificate
2000-01-13
2002-08-27
Hopkins, Robert A. (Department: 1724)
Gas separation: processes
Deflecting
Centrifugal force
C055S426000, C055S459100, C055S465000, C055S418000, C055S420000, C055SDIG003
Reexamination Certificate
active
06440197
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to cyclonic separators. In one particular application, the invention relates to the cyclonic separation of particulate material from an air flow. In a preferred embodiment, the cyclonic separator is used in a vacuum cleaner to remove entrained particulate matter from an air stream.
BACKGROUND OF THE INVENTION
The use of a cyclone, or multiple cyclones connected in parallel or series, has long been known to be advantageous in the separation of particulate matter from a fluid stream. Typically, a relatively high speed fluid stream is introduced tangentially to a generally cylindrical or frusto-conical container, wherein the dirty air stream is accelerated around the inner periphery of the container. The centrifugal acceleration caused by the travel of the fluid in a cyclonic stream through the cyclone causes the particulate matter to be disentrained from the fluid flow and, eg., to collect at the bottom of the container. A fluid outlet is provided for the extraction of the fluid from the centre of the top of the cyclone container, as is well known in the art.
A typical flow path in a cyclone separator is as follows. Fluid to be treated is introduced tangentially at a fluid inlet located at an upper end of the cyclone container. The fluid stream rotates around the inner surface of the cyclone container, and spirals generally downwardly around the inner surface of the container (if the cyclone container is vertically disposed). At a bottom end of the cyclone container the fluid stream travels radially inwardly, generally along the bottom of the container and then turns upwardly and proceeds vertically up and out of the cyclone container. The particulate matter separating action of the cyclonic flow occurs substantially around the inner surface of the container. Once the fluid moves inwardly to the centre of the container, and upwardly there through, there is little or no dirt separation achieved.
The difficulty experienced with prior art cyclonic separators is the reentrainment of the deposited particles back into the outgoing fluid flow. Deposited particles exposed to a high speed cyclonic flow thereover have a tendency to be reentrained. This is particularly problematic when the container has a solid bottom portion in which the dirt collects. However, there is a potential reentrainment problem even if the bottom of the container has a passageway provided in the bottom thereof to convey the separated particulate material away from the container.
If a high degree of separation is required, it is known to connect a plurality of cyclones in series. While using several cyclones in series can provide the required separation efficiency, it has several problems. First, if the separators are to be used in industry, they generally need to accommodate a high flow rate (eg. if they are to be used to treat flue gas). The use of a plurality of cyclones increases the capital cost and the time required to manufacture and install the separators. Further, the use of a plurality of cyclones increases the space requirements to house the cyclones as well as the back pressure caused by the air flow through the cyclones. These latter issues are particularly acute for cyclone separators which are to be contained in a small housing, such as a vacuum cleaner. Accordingly, there is a need for an improved anti-reentrainment means for cyclonic separators.
SUMMARY OF THE INVENTION
In has now been discovered that a single cyclone having improved efficiency (eg. up to 99.9% efficiency) may be manufactured by positioning in the cyclone chamber a particle separation member for creating a dead air space beneath the cyclonic flow region of the cyclone chamber wherein the dead air space is in communication with the cyclonic flow region by a plurality of openings or apertures in the member. This construction effectively traps separated material beneath the cyclonic flow region and inhibits the reentrainment of the separated material. Thus, a single cyclone may be used in place of a plurality of cyclones to achieve the same separation efficiency.
As the fluid flow travels through the cyclone chamber, a boundary layer forms. Generally, the interior surface of a cyclonic chamber is smooth so as to provide for an uninterrupted cyclonic flow in the chamber. However, in the chamber, a boundary layer is still formed on all surfaces over which the fluid passes. According to the instant invention, the system (i.e. the motor means to move the fluid through the chamber, the fluid inlet to the chamber, the fluid outlet to the chamber and/or the construction of the separation member) is designed to minimize the thickness of the boundary layer in the vicinity of the apertures in the separation member.
In particular, as the fluid travels over the upper surface of the particle separation member, a boundary flow layer will form. The boundary layer will thicken until a thickness is reached at which the boundary layer has sufficient energy to break off and travel away from the upper surface. Generally at this point, the fluid travels upwardly to the fluid outlet from the cyclone. When the boundary layer breaks off from the upper surface, vortices are formed in the fluid stream adjacent the apertures in the separation member causing localized turbulence. The turbulent flow reentrains particles that had been separated from the fluid flow and may even pull some of the separated particles out of the dead air space beneath the cyclonic flow region of the cyclone chamber.
In one embodiment of the instant invention, the cyclonic separator is constructed to minimize the thickness of the boundary layer when it breaks off thereby reducing turbulent flow in the vicinity of the apertures. This may be achieved by varying one or more of the number of apertures in the particle separation member, the length of the apertures, the width of the apertures, the included angle between the upstream edge of the apertures and the upper surface of the particle separation member, the included angle between the downstream edge of the apertures and the upper surface of the particle separation member, and the position of a baffle beneath the particle separation member with respect to the point at which the cyclonic air flow changes direction at the bottom of the cyclone chamber. The actual design of the system will changes in the size of the cyclone chamber, the velocity of the fluid flow in the cyclone chamber and the viscosity of the fluid flow in the cyclone chamber.
In another embodiment, the flow of the fluid itself may be modified to minimize the thickness of the boundary layer when it breaks off. For example, the fluid flow may be pulsed with the frequency of the pulses set to reduce the maximum thickness of the boundary layer. By pulsing the fluid flow, the fluid flow is cyclically accelerated and decelerated. This cyclicling is set to encourage the boundary layer to break off when it is thinner than when the fluid flow is not pulsed. The acceleration after the deceleration provides sufficient energy to cause the boundary layer to delaminate sooner than it would in a constant flow regime thereby reducing turbulent flow in the vicinity of the apertures. This pulsed flow may be achieved in several ways such as by sending a pulsed electrical signal to the fluid pump which produces the fluid flow through the cyclone chamber, by pulsing the fluid as it passes through the cyclone air inlet (eg. the inlet may have an aperture that may be cyclically opened and closed at produce the pulsed flow), by pulsing the fluid as it passes through the cyclone air outlet (eg. the outlet may have an aperture that may be cyclically opened and closed at produce the pulsed flow), or by rotating the particle separation member in its plane (eg. by mounting the particle separation member with a spring biasing means so that the particle separation member will cyclically rotate clockwise and then counter clockwise).
The prior art teaches the need for a plurality of cyclones in order achieve ultra-high particle separation
Conrad Wayne Ernest
Petersen Dave Andrew
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