Patent Application
20190316487
A turbine is a type of transducer capable of converting kinetic energy from a flowing fluid in to mechanical energy of a rotating rotor. A great variety of turbines exist and are used for a range of purposes, such as measuring a parameter of the fluid flow or converting the rotational energy into useful work. Some turbines, known as axial turbines, rotate about an axis parallel to the direction of fluid flow. Others, known as tangential turbines, rotate about an axis when fluid tangent to the axis impacts the turbine.
When fluid is traveling through a bore, axial turbines are typically positioned concentrically with the bore such that a majority of the fluid is forced through the turbine. This generally leads to maximum energy conversion and a substantially linear relationship between flow and rotation. This linear relationship may be important for accurate flow measurement across an assortment of fluids and flow rates. Such a configuration may cause problems, however, if solids are traveling with the fluid. In these situations, the solids may get caught on the turbine slowing its rotation or jamming it completely which may disrupt its linearity.
A tangential turbine, with a rotational axis positioned outside of a flow bore may allow solids to pass more easily. However, linearity may suffer even more than with a comparable axial turbine due to viscous boundary considerations. Additionally, turbines impacted by fluid flowing tangent to the axis thereof may wear prematurely when that fluid comprises solids traveling therewith. Turndown ratio, which indicates a range of flow that a turbine is able to measure with acceptable accuracy, may decrease significantly as well.
A turbine transducer, capable of passing fluids comprising significant solids therein while maintaining a substantially linear relationship between flow and rotation, may comprise an axial turbine only partially exposed to a fluid flow. Specifically, a turbine, comprising a plurality of blades extending radially from a hub, may rotate around a bearing axle positioned parallel to, but offset from, a central axis of a flow bore. Fluid may flow through the flow bore and past the turbine blades.
The flow bore may be formed in a housing that holds the turbine in place. In various embodiments, this housing may also comprise an internal wall spaced radially from the turbine so as to limit unwanted pumping of the turbine. The internal wall of the housing may form a cavity adjacent the turbine and opposite from the flow bore. This cavity may comprise an axis planar with and set at an angle from the central axis of the flow bore.
To maintain substantial linearity between the flow rate and rotation speed, the bearings of the turbine may be protected from the flow and provide minimal resistance. In some embodiments, these objectives may be accomplished by attaching the bearing axle to the housing at only one end thereof opposite from an origin of the flow. Additionally, the bearing axle may comprise a cylinder rotatable relative to both the turbine and the housing.
To easily allow solids to pass the turbine, the turbine blades may be tapered toward a first end of the bearing. A matching flow straightener, comprising multiple blades protruding from the housing into the flow bore, may also aid in allowing solids to pass unobstructed while improving linearity.
Referring now to the figures,
Each of the blades 214 may taper towards the hub 215 at a leading end of the turbine 210. This leading end may face the origin of a fluid flow such that solids may pass the blades 214 without hindering rotation of the turbine 210. In the embodiment shown, the blades 214 taper at an angle of 30° to 45° from a rotational axis of the turbine 210. It was found that smaller angles may not shed solids off of the blades 214 as well while larger angles could lead to non-linearity and reduced turndown ratios, presumably due to vortex shedding off of leading edges of blades.
This turbine 210 may comprise a relatively high turndown ratio (defined as a ratio of flow that is able to be measured accurately) of over 8:1 compared to analogous concentrically-positioned axial turbines. For instance, the embodiment shown may comprise a maximum flow of over 365 gallons per minute (0.0230 cubic meters per second) and a minimum flow of under 45 gallons per minute (0.0028 cubic meters per second).
It was found that maintaining linearity between fluid flow rate and turbine rotational velocity was aided by reducing bearing resistance. Keeping bearing resistance low may become more challenging when solids are introduced into a fluid flow, especially if they are able to infiltrate into the bearing mechanics.
Having only one attachment end, however, may increase the friction experienced by that end. The bearing axle 416 shown comprises a cylinder 440 held within two tubes. A first tube 441 may be rotationally fixed to a turbine while a second tube 442 may be rotationally fixed to a housing. This may create two possible bearing surfaces. In this configuration, the average velocity experienced by each bearing surface may be half of what it would be if there were only one bearing surface. As drag may increase with the square of velocity, the drag may be one-quarter of that experienced by a single bearing surface. In addition, having two independent bearing surfaces may allow a turbine to continue rotating even if one freezes for some reason, thus providing an extra layer of safety.
Referring back to
The internal wall 117 may also form a cavity 118 adjacent the turbine 110 on an opposite side of the turbine 110 from the flow bore 112. It is believed that this cavity 118 may provide space for fluid expelled from the turbine 110 to go without disrupting fluid flow through the flow bore 112. The cavity 118 may comprise a generally tubular shape with a cross-sectional area substantially similar to a cross-sectional area of the flow bore 112. The cavity 118 may comprise a cavity axis 119 positioned in a similar plane with the central axis 113 of the flow bore 112. The cavity axis 119 may be tilted toward an origin of flow through the flow bore 112 at an angle less than 80° from the central axis 113 (in the embodiment shown, this tilt angle is 45%). This tilting may allow solids within the cavity 119 to exit therefrom, due to motion of fluid flowing through the flow bore 112, without getting dynamically trapped therein.
The housing 111 may also provide sufficient room between the interior wall 117 and the turbine 110, on an end of the turbine 110 facing a destination of the fluid. This open back may allow fluid to flow from the turbine 110 back to the flow bore 112 without adding excessive turbulence thereto.
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.
