TECHNICAL FIELD

An axially-oriented inlet feeds fluid directly to the vertex of a generally conical, curved profile, or campanulate flow-directing face of a rotor containing cavities on its cylindrical surface. The flow director spreads the fluid to a cavitation zone formed between the cavity-containing surface and the closely conforming interior surface of a housing. The device pumps, heats and mixes the fluid. The device may contain discs to contribute an enhanced disc pump effect. The flow patterns of the fluid material to be mixed and heated are designed to preheat and may create turbulent flow mixing of the fluid before it enters the cavitation zone. Heat generated in the cavitation zone is conducted through the rotating disc-like body of the cavitation rotor. The advantages of the central inlet and flow directing element may be facilitated by a cantilever construction to alleviate stress on the bearings.

BACKGROUND OF THE INVENTION

The phenomenon of cavitation, as it sometimes happens in pumps, is generally undesirable, as it can cause choking of the pump and sometimes considerable damage not only to the pump but also auxiliary equipment.

However, cavitation, more narrowly defined, has been put to use as a source of energy that can be imparted to liquids. Certain devices employ cavities deliberately machined into a rotor turning within a cylindrical housing leaving space for liquid to pass. A motor or other source of turning power is required as well as an external pump to force the fluid through. The phenomenon of cavitation in all previous devices relevant hereto is caused by the rapid passage of the liquid over the cavities, which creates a vacuum in them, tending to vaporize the liquid; the vacuum is immediately filled again by the liquid and created again by the movement of the liquid, causing extreme turbulence in the cavities, further causing heat energy to be imparted into the liquid. Liquids can be simultaneously heated and mixed efficiently with such a device. Also, although the cavitation technique is locally violent, the process is low-impact compared to centrifugal pumps and mixing pumps employing impellers, and therefore is far less likely to cause damage to sensitive polymers used in oilfield fluids. Centrifugal pumps tend also to break large particles such as drill cuttings into small, low gravity particles which are more difficult to separate by centrifugation. The impeller blades of many types of pumps will fracture and break solids into smaller particles which may resist separation by any conventional method.

Good mixing is especially important in mixing oil field fluids such as drilling fluids and fracturing fluids.

Proper operation of the cavitation device, until now, has generally required a separate pump. Liquid must be forced through the existing cavitation devices to accomplish substantial heating, mixing, or both. Cavitation devices are excellent for intimately mixing gases with liquids, but centrifugal pumps do not handle large volumes of gases well, sometimes losing the ability to pump at all when the gas volume is too great. A disc pump can easily handle and pump mixtures containing significant volumes of gas.

Moreover, in the conventional cavitation devices, there is a viscous or surface effect drag against the stationary end wall of the cavitation device housing.

Rotating cavitation devices in the past generally have not been designed to optimize the flow of the incoming fluid, which must find its way from an inlet on one side of the rotor to and through the cavitation zone between the cylindrical interior of the housing wall and the cavities on the periphery of the rotor. Workers in cavitation mixing and heating in the past have generally not attempted to analyze and improve the flow patterns of the treated material on either the incoming or outgoing sides of the rotor, to achieve greater uniformity of heating and mixing. They have tended to concentrate on the phenomenon of cavitation at the periphery of the cavitation rotor, after the fluid arrives there, but have paid little attention to the heating potential of the body of the rotor or the effects on flow patterns of the sides of the rotor for enhancing mixing as well as heating.

Our invention provides improved heating, improved mixing, and improved uniformity of heating and mixing of fluid materials passing through a rotating cavitation device.

Unlike many designs of the prior art, our cavitation device is “overhung,” meaning that it is supported on one side only of the housing. Because the other side of the housing is unencumbered by a support for the rotating power shaft, we are able to direct the incoming fluid to be mixed toward the center of the spinning rotor. The center of the spinning rotor, however, is modified in our invention so that the incoming fluid impacts on the vertex of a substantially conical or bell-shaped surface which provides a tapering, spreading, path for the fluid toward the side of the spinning rotor. The materials of construction of the rotor, and its shape, may also be chosen to transfer heat efficiently from the cavitation zone to the body of the rotor and then to the incoming fluid as it contacts the rotor. The overhung design is stabilized by at least one bearing on the rotating power shaft outside the housing in addition to the bearing in the housing wall. Beneficially, there are two additional bearings on the shaft, spaced from the housing wall before it connects to the motor.

In addition, the gap between the sides of the spinning rotor and the housing can be varied to optimize heating and mixing as a function of the assumed, presumed, or calculated properties of the treated fluid.

There is a need for improvements to overcome the disadvantages of the existing cavitation devices.

SUMMARY OF THE INVENTION

By the incorporation of at least one rotating disc having an open center for the passage of liquid, and with an appropriate housing design for intake and outflow, we are able to use the same motor that turns the cavitation device rotor to turn the disc also, thus utilizing the disc in combination with the cavitation rotor as a kind of disc pump to pass the liquid through the cavitation device. The rotating disc not only facilitates a pumping effect, but ameliorates the counterproductive drag imposed by the stationary housing wall of the unit.

In this continuation-in-part, the function and benefits of the central, or coaxial, inlet which facilitates the flow path through the open center of the disc have been further developed. This continuation-in-part utilizes a tapered flow director aligned with the rotating shaft and facing the central (coaxial) inlet to enhance the heating, mixing, and pumping effects of the device. The flow director is an improvement on the accelerator seen inFIG. 6.FIGS. 8-12relate to the utilization of a flow director immediately next to the coaxial inlet guiding the fluid to distribution over the cavitation surface of the rotor; InFIG. 13, the flow director receives the incoming fluid through a rotating disc.

Our combined disc pump and cavitation device is inherently safer than the conventional use of a positive displacement pump to force the mixture through a separate cavitation device, in that, if there is a blockage of some sort, excess pressure will not build up within the device. Although the disc, or discs, will continue turning, they will generate only a relatively low pressure within the device.

The shaft may pass through both end walls or only one end wall. The inlet and outlet may be independently on the respective end wall or on the cylindrical shell, providing a flow path for the fluid across the cavitation device—that is, forming an inlet end and an outlet end of the device for the flow path.

The combined device may be immersed in a mixing tank so that its intake is below the level of the materials to be mixed; the motor may be above the liquid level or its shaft may pass through the wall of the tank.

