Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND DEVICE FOR HARVESTING ENERGY FROM FLUID FLOW
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. Patent
Application No.
13/333,173, filed on December 21, 2011, (docket no. OSC-P007), which claims
the benefit of
U.S. Provisional Application No. 61/425,753, filed on December 21, 2010,
(docket no. OSC-
P007P) and U.S. Provisional Application No. 61/482,146, filed on May 3, 2011,
(docket no.
OSC-P009P). This application also claims the benefit of U.S. Provisional
Application No.
61/482,152, filed on May 3,2011, (docket no. OSC-P010P). This application also
claims the
benefit of U.S. Provisional Application No. 61/526,640, filed on August 23,
2011, (docket
no. OSC-P012P). This application also claims the benefit of U.S. Provisional
Application
No. 61/545,448, filed on October 10, 2011, (docket no. OSC-P013P). Each of
these
applications is incorporated by reference herein in its entirety.
BACKGROUND
[0002] Various techniques have been used for converting the energy of
a flowing fluid
to useful electrical energy. These range in scale from the multi-Megawatt
generators to sub-
microwatt MEMS based devices. The basic principle is to convert the kinetic
energy of the
fluid into motion of the energy harvester, and then use a mechanical to
electrical conversion
mechanism to produce useful electrical power. Many of the applications for
smaller-scale
(sub-kilowatt) power production preclude the use of rotating machinery
commonly used in
larger-scale applications due to a number of factors, including
inaccessibility for maintenance
and harsh operational environments. Due to these limitations, there has been
an increase in
interest in energy harvesters that can take energy inputs such as fluid flow
or pressure
differentials to generate electric power. These harvesters convert the energy
of the fluid into
an oscillatory displacements or load changes of some part of the harvester,
which then
converts these displacements or load changes to electrical energy. The
literature has many
instances of using electromagnetic or piezoelectric energy conversion
mechanisms. While
viable for very small scale power production, both of these approaches have
specific
difficulties in scaling up to power levels of 0.1 W or above, and more
specifically 1 W or
above, especially if such power production is to be maintained across a wide
range of
vibration frequencies.
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[0003] Moving magnet designs depend on significant relative motion to
be able to
produce significant power. At the high frequency (about 10-500 Hz), which
represents
moderate acceleration (about 1-10 G's) vibration environment typical of many
types of
machinery, the high displacements needed to make watts (i.e., one watt or
more) of power are
difficult to achieve in moving magnet designs. Further, if more powerful
magnets are used to
increase power density, cogging forces/torques become difficult to overcome
and structural
stiffness requirements become exceedingly more demanding.
[0004] Piezoelectrics, being semiconducting ceramics, have intrinsic
issues related to
high internal resistance and/or high internal impedance, and low structural
reliability that
prevent them from being usefully scaled up for broad band power generation of
the order of
even watts (i.e., one watt or more) and have thus been largely limited to the
micro-watt to
milli-watt ranges.
[0005] Vortex-induced Vibration energy harvesting has been explored
with both
electromagnetic and piezoelectric generators. The underlying principle is that
at certain flow
conditions, a bluff body in a flow will have localized flow separation at one
or more locations
in the fluid-body interface. This leads to the development of a shear layer,
where vortices
form. In the wake of a bluff body, there is a feedback mechanism that causes
an interaction
between the shear layers, which results in the formation of a von Karman
vortex street. The
vortex shedding produces forces on the bluff body and pressure gradients in
the vortex street,
both of which can be used in conjunction with an energy harvester to produce
electrical
energy.
[0006] Turbulence-induced vibration does not require vortex shedding,
and instead
relies on the unsteadiness of turbulent flow to produce vibrations. Because
turbulence
generally has energy content at frequencies much higher than those produced by
vortex
shedding, an energy harvester using turbulence-induced vibration can operate
at a much
higher frequency, which is desirable because the natural frequencies of small
energy
harvesting devices are generally high, owing to their inherently high
structural stiffness and
relatively small inertial masses.
[0007] Other types of flow-induced vibration also exist, and these
could be used to
produce vibrations necessary to drive an energy harvester. These include
gallop, flutter, root-
fin interactions, shock-wave/boundary-layer interactions, cavitation, and
others.
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SUMMARY
[0008] Embodiments described herein relate to a method and device for
harvesting
energy from a fluid flow by converting the kinetic energy of the flow into
vibrational energy,
which then may be converted to electrical energy by a magnetostrictive-based
vibrational
energy harvester. Some embodiments of this device rely on the principle of
vortex-induced
vibrations, where the frequency of the induced vibration is of the same order
as the frequency
of vortex shedding (the Strouhal number). Some embodiments of this device rely
on the
principle of turbulence-induced vibration, where the frequency of vibration
can be
significantly higher than the vortex shedding frequency, and is related to the
turbulence
frequency of the flow. Some embodiments also relate to converting energy from
pressure
pulses or differentials in the fluid. These embodiments in no way limit the
vibration induction
mechanism, and other principles of flow-induced vibration may be used in
conjunction with
the magnetostrictive-based vibrational energy harvester.
[0009] Embodiments of an apparatus are described. In one embodiment,
the apparatus
is an electrical generation device for electrical energy production. The
electrical generation
device includes a bluff body and a magnetostrictive element. The bluff body is
configured to
be disposed in a fluid flow. The magnetostrictive element is configured to be
disposed
relative to the bluff body to be subject to vibrational movement or turbulence
resulting from
fluid flow around the bluff body. The bluff body has physical dimensions to
substantially
oscillate in response to natural movement of the fluid flow, and oscillations
of the bluff body
result in a force on the magnetostrictive element. Other embodiments of the
apparatus are
also described.
[0010] Embodiments of a system are also described. In one embodiment,
the system
includes an enclosure and an energy generation device. The enclosure defines
an interior
fluid channel from an inlet to an outlet. The enclosure directs a fluid flow
from the inlet to
the outlet. The energy generation device is disposed within the channel of the
enclosure. The
energy generation device includes an electrically conductive element to induce
electrical
energy in response to stress on a magnetostrictive element based on a transfer
of mechanical
energy from the fluid flow to the magnetostrictive element. Other embodiments
of the
system are also described.
[0011] Embodiments of a method are also described. In one embodiment,
the method
is a method for electrical energy products. An embodiment of the method
includes disposing
a bluff body within a fluid flow. The bluff body has physical dimensions to
move in response
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to mechanical energy of the fluid flow. The method also includes disposing a
magnetostrictive element relative to the bluff body within the fluid flow. The
magnetostrictive element moves in response to movement of the bluff body. The
method
also includes inducing electrical energy in an electrically conductive element
disposed within
a vicinity of the magnetostrictive element. Other embodiments of the method
are also
described.
[0012] Other aspects and advantages of embodiments of the present
invention will
become apparent from the following detailed description, taken in conjunction
with the
accompanying drawings, illustrated by way of example of the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure lA depicts a diagram of one embodiment of an energy
generation device
having a bluff body supported by a cantilever beam assembly.
[0014] Figure 1B depicts an enlarged detail view of the fixed end of
the cantilever
beam assembly of Figure 1A.
[0015] Figure 1C depicts a perspective view of the energy generation
device of Figure
1A.
[0016] Figure 2 depicts a graphical diagram of deflection and power
generation as a
function of frequency for an embodiment of the energy generation device of
Figure 1A.
[0017] Figure 3A depicts a schematic diagram of a cutaway view of one
embodiment of
an energy generation assembly with multiple energy generation devices deployed
in
combination.
[0018] Figure 3B depicts a perspective view of the energy generation
assembly of
Figure 3A.
[0019] Throughout the description, similar reference numbers may be used to
identify
similar elements.
DETAILED DESCRIPTION
[0020] It will be readily understood that the components of the
embodiments as
generally described herein and illustrated in the appended figures could be
arranged and
designed in a wide variety of different configurations. Thus, the following
more detailed
description of various embodiments, as represented in the figures, is not
intended to limit the
scope of the present disclosure, but is merely representative of various
embodiments. While
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the various aspects of the embodiments are presented in drawings, the drawings
are not
necessarily drawn to scale unless specifically indicated.
[0021] The present invention may be embodied in other specific forms
without
departing from its spirit or essential characteristics. The described
embodiments are to be
considered in all respects only as illustrative and not restrictive. The scope
of the invention
is, therefore, indicated by the appended claims rather than by this detailed
description. All
changes which come within the meaning and range of equivalency of the claims
are to be
embraced within their scope.
[0022] Reference throughout this specification to features,
advantages, or similar
language does not imply that all of the features and advantages that may be
realized with the
present invention should be or are in any single embodiment of the invention.
Rather,
language referring to the features and advantages is understood to mean that a
specific
feature, advantage, or characteristic described in connection with an
embodiment is included
in at least one embodiment of the present invention. Thus, discussions of the
features and
advantages, and similar language, throughout this specification may, but do
not necessarily,
refer to the same embodiment.
[0023] Furthermore, the described features, advantages, and
characteristics of the
invention may be combined in any suitable manner in one or more embodiments.
One skilled
in the relevant art will recognize, in light of the description herein, that
the invention can be
practiced without one or more of the specific features or advantages of a
particular
embodiment. In other instances, additional features and advantages may be
recognized in
certain embodiments that may not be present in all embodiments of the
invention.
[0024] Reference throughout this specification to "one embodiment,"
"an
embodiment," or similar language means that a particular feature, structure,
or characteristic
described in connection with the indicated embodiment is included in at least
one
embodiment of the present invention. Thus, the phrases "in one embodiment,"
"in an
embodiment," and similar language throughout this specification may, but do
not necessarily,
all refer to the same embodiment.
[0025] While many embodiments are described herein, at least some of
the described
embodiments may be used for power generation from a variety of fluid flows,
including
rivers/currents, exhaust flow from combustion engines, fluid flow during
drilling of wells for
oil and gas or geothermal applications, oil flow in completed production
oil/gas wells,
air/water flow around moving bodies such as ships/boats or air planes. The
power produced
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may be large (e.g. utility scale) or small (e.g. micro-watts for trickle
charging batteries), and
embodiments of this invention may be scaled up or down to meet specific power
requirements. The choice of a particular structure to generate a particular
type of flow- or
turbulence-induced vibration in no way limits the scope of this invention. The
utilization of
this invention for any particular application in no way limits the scope of
this invention.
[0026] There are many different applications where an effective flow-
induced vibration
energy harvester that may generate a relatively small amount of electric power
of the order of
micro-Watts to a few tens of Watts would prove extremely useful. A number of
these
applications may occur where remote sensing is used, and where battery
replacement would
be cost-prohibitive. The power generated by these devices may be used to power
sensing
equipment or associated electronic components, or may be able to trickle
charge rechargeable
batteries to extend the time between recharging of these batteries. Many
remote sensors not
only monitor a certain parameter, but also relay this data wirelessly, and are
expected to do so
for multiple years. Some examples of potential applications for these
harvesters include
infrastructure monitoring of bridges and buildings; river and stream
hydrology, including
depth, flow rate, and water quality monitoring; water supply, storm water and
wastewater
system monitoring; downhole power production using drilling circulating fluid
(e.g. "drilling
mud"); intelligent well monitoring with production fluids (oil and gas);
petroleum refinement
and chemical processes remote monitoring; etc. Mention of these specific
applications is in
no way intended to limit the scope of potential applications for this
invention.
[0027] An alternative to directly harvesting the kinetic energy
present in flow vibrations
is to harvest potential energy contained in the fluid pressure. These pressure
changes can be
used to deform a body in the fluid or induce motion, which can then be
converted into
electrical energy. This concept has marked potential because the pressure
fluctuations do not
have to be inherent to the flow or induced in the flow, but can be
fluctuations imposed on the
flow by an external source. Such pressure fluctuations may be induced
specifically for the
purpose of generating electrical energy using the energy harvesters, and using
this energy to
achieve a secondary purpose such as opening or closing a valve or just
recharging batteries.
In the example of pipe flow, a change in the downstream boundary condition,
such as the
throttling of a valve, can impose pressure fluctuations through the length of
the flow, which
could then be converted into useful electrical energy.
[0028] There are a number of potential applications specifically
related to downhole
power generation for which the energy harvesters described here can be used
for. The
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applications can potentially reduce operator's costs, increase reliability and
allow for
applications currently considered impossible. Downhole power generation could
be deployed
in non-"smart" completions to provide power for measurements of downhole
conditions
(typically just pressure and temperature) and telemetry systems, thereby
avoiding costly
interventions that are expensive, especially on subsea wells (c. $10 million,
significantly
more in ultra-deep water). The power generation could eliminate the need for
electric or
fiber-optic cable, which can be time-consuming and expensive to install
(typical additional
cost of running the cable - $100,000 ¨$200,000). "Smart" completions offer
more potential
deployment locations, as power is needed not only for the sensors and
telemetry, but also to
control the production from each interval of the completion. Currently, many
of the valves
that control the production are hydraulic or electro-hydraulic, but all-
electric valves do exist,
and the ability to meet the power requirements of these valves without running
wires or
relying on batteries could greatly accelerate their adoption. Additionally, a
downhole power
source could eliminate the need for "wet-connection" of wires between the
smart completion
and the upper completion. Wet connections introduce a reliability concern and
are avoided
whenever possible.
[0029] The specific combination of downhole power generation with
downhole gauges
has many advantages:
a. Significantly reduced installation costs (no cable to run)
b. The ability to position the gauge where it is optimum. This could be in the
lower completion (e.g. beside screens) rather than higher up the well above
the
packer. The closer the data point is to the reservoir, the better quality the
data
would be. The purpose of the gauge is to avoid the error-prone extrapolation
of surface pressure to downhole conditions with multiphase flow. Penetrations
and wet-connects are complications and potential interferences with good
reliability. Some completion types are virtually impossible to connect to with
a
wire ¨ multilaterals being a significant class of wells like this.
c. Ability to retrofit gauges into an existing well. This would be a through
tubing
application and very different to the permanent application considered above.
Such an application could allow a gauge to be positioned anywhere in the well
but would provide a significant restriction to flow but in doing so could
directly take advantage of the flow.
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[0030] Clearly any sensor needs to be integrated with a data
transmission route.
Existing technology is available through pressure pulse telemetry by creating
a temporary
restriction in the production flow. This method is common in drilling
applications (mud pulse
telemetry). A better method is radio transmission (no restriction to flow).
Downhole power
generation (and long-life rechargeable batteries) would significantly enhance
this technology
to permanent completions.
[0031] Downhole power generation could also be a key enabling
technology for "smart
gas lift" applications. A power source would allow for data acquisition and
transmission to
the surface of the conditions at the valve, and would also allow for the
variation of the valve
orifice, which would promote stable flow between the annulus and the tubing.
This
application could take advantage of the high flow velocities through the valve
as well as in-
line vibration (power generation directly in the flow path).
[0032] The device could also provide a power source for isolation and
clean-up valves.
As an example, these valves are deployed inside a completion to act as a deep-
set barrier to
allow the upper completion to be recovered. The limitation of this
configuration is often
battery life, and a power source that could provide trickle charging to the
valve control could
greatly extend the capabilities of these valves. Additionally, the power
source could also
allow for data to be collected at the valve and transmitted to the surface (or
stored for later
mechanical retrieval).
[0033] Another potential application for the downhole power source is in
horizontal
well stimulation. These wells currently have the ability to stimulate
production through
opening of valves, but there are no options to close an interval as there are
with a smart well.
This device would allow for the remote opening and closing of these valves to
facilitate re-
stimulation, and would alleviate limitations on the number of valves in a
well.
[0034] Embodiments herein include at least one structure designed to
oscillate or
vibrate when in the presence of a flowing fluid. These induced oscillations
and/or vibrations
are then used to generate electricity from a magnetostrictive-based vibration
energy harvester.
The device may include at least one magnetostrictive element and one or more
electrically
conductive coils or circuits. The device may also include one or more magnetic
circuits
which are coupled with one or more electrical circuits to increase or maximize
power
production. The flow-induced vibrations cause a forced oscillation response in
the device,
and this oscillation causes stress and strain in the magnetostrictive
elements, which may be
converted into electrical energy through electromagnetic induction.
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[0035] For any embodiment of this device, the fluid may be liquid, gas
or a two-phase
mixture. An advantage of at least one embodiment described herein is its
ability to operate in
flows that contain multiple phases, e.g. river flows with bio-matter, waste-
water systems, and
crude oil flows with waxy parrafins and condensates.
[0036] One embodiment of this device is an electric power generator for use
in a fluid
flow. The embodiment includes a magnetostrictive element; a coil assembly; a
source of
magnetomotive force (MMF), comprising permanent magnet material and/or
electromagnets;
and a mass assembly.
[0037] In some embodiments the power generation components of the
device will be
enclosed in a packaging to protect them from contact with the fluid. This
enclosure may
comprise a rigid enclosure or be designed to deflect with the device. The
latter may be
accomplished by coatings or jackets.
[0038] The magnetostrictive elements are arranged to enable mechanical
and/or
magnetic coupling between them. In some embodiments, the mass assembly may be
mechanically coupled to the overall assembly or to the magnetostrictive
elements directly. In
some embodiments, the source of magnetomotive force may be magnetically
coupled to the
magnetostrictive member assembly. In some embodiments, the magnetostrictive
elements
may be electromagnetically coupled to the coil assembly.
[0039] In some embodiments, at least one magnetostrictive element may
be arranged to
form a cantilever beam with the fixed end rigidly attached to a supporting
structure (e.g., a
sidewall of a pipe, a mesh or other grating spanning at least a portion of the
inner diameter of
a pipe, and so forth) and the free end allowed to oscillate in response to
vibration. The
vibration movement alters the magnetic characteristics of the magnetostrictive
elements,
which may result in a change in magnetic flux flowing through a magnetic
circuit including
the magnetostrictive element, which causes a voltage/current to be produced in
the coil
assembly.
[0040] In some embodiments, the mass is configured to be a bluff body,
which would
produce a vortex street in a fluid flow. The structural natural frequency of
the device may be
tuned to match the vortex shedding frequency of the bluff body mass, thereby
causing a self-
excited oscillatory response to the fluid flow. An example of this embodiment
is illustrated
in Figures 1A, 1B, and 1C.
[0041] Figure lA depicts a diagram of one embodiment of an energy
generation device
100 having a bluff body 102 supported by a cantilever beam assembly 104. The
bluff body
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102 may be any shape, size, and/or material suitable for generating
vibrational or other
oscillating motions of the cantilever beam assembly 104 when subjected to
fluid flow and/or
pressure.
[0042] In one embodiment, the bluff body 102 is located at a free 106
end of the energy
generation device 100, while the opposite end of the cantilever beam assembly
104 is at a
fixed end 108 where the energy generation device 100 is attached or coupled to
another
structure (see Figures 3A and 3B). In this way, the fixed end 108 of the
cantilever beam
assembly 104 forms a stationary point relative to which the bluff body 102
oscillates or
moves.
[0043] In the depicted embodiment, the cantilever beam assembly 104
includes a pair
of magnetostrictive elements 110 that are individually enclosed in
electrically conducting
coils 112. Although two magnetostrictive elements 110 are shown in the
depicted
embodiment, other embodiments may incorporate more than two magnetostrictive
elements
and corresponding coils. In this arrangement, when the bluff body 102 deflects
upward, the
top magnetostrictive element 110 is compressed in the direction along its
length, and the
bottom magnetostrictive element 110 is tensed in the direction along its
length. The
mechanical stress induced on each of the magneto strictive elements 110 can be
converted
into electrical energy which is induced in the corresponding coils 112. In the
depicted
configuration, the induced electrical energy is opposite (positive and
negative, or vice versa)
in the pair of coils 112. One or more electrical leads 114 are electrically
coupled to each coil
112 in order to transfer the induced electrical energy to additional circuitry
(not shown)
configured to manage the electrical power transmissions.
[0044] Figure 1B depicts an enlarged detail view of the fixed end 108
of the cantilever
beam assembly 104. In one embodiment, the cantilever beam assembly 104
includes a
permanent magnet 116 disposed between the magnetostrictive elements 110. The
permanent
magnet 116 may enhance the changes in magnetic flux and, hence, increase the
amount of
electrical energy that is induced in the coils 112. Insulators 118, such as an
electrically
insulating material, may be placed between the permanent magnet 116 and each
magnetostrictive element 110. Other embodiments may include further structural
elements,
for example, to facilitate mounting the device 100 to another structure. Other
embodiments
may include further structural elements, for example, to provide pre-
compression to the
magnetostrictive elements. In some embodiments, more than one magnetostrictive
element is
configured to form a substantially closed magnetic flux path.
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[0045] Figure 1C depicts a perspective view of the energy generation
device of Figure
1A. In some embodiments, a bluff body mass may be positioned either upstream
or
downstream of the cantilever beam within a fluid stream.
[0046] One embodiment may include design considerations such that the
bluff body is
larger than the beam in the beam's transverse direction (i.e., the dimension
orthogonal to the
dominant vibration direction that is not along the beam axis) or may have a
multitude of
beams supporting the mass with at least one space between them. These
considerations are
taken to avoid forming a "splitter-plate" like assembly downstream of the
bluff body mass,
which has been shown to be an effective way of limiting the feedback mechanism
in vortex-
induced vibrations, thereby significantly reducing the amplitude of the
vibrations.
[0047] In some embodiments, the magnetostrictive element(s) may be
used to form a
flexible tube-like structure that may be excited into vortex-induced vibration
as fluid flows
over the structure. In this embodiment, the axis of the structure is
perpendicular to the flow
direction, and the induced vibration is in a radial direction. An array of
these structures may
be placed in the flow to further excite oscillation through vortex-street
impingement on
downstream structures.
[0048] In another embodiment, the magnetostrictive material may be
formed into a thin
sheet that will oscillate in response to vortices advecting past it. These
vortices may be
caused by a bluff body or flow obstruction upstream of the magnetostrictive
element, or may
be turbulent structures inherent to the flow. As the vortices advect by, they
cause a
deformation of the magnetostrictive material, which leads to stresses and
strains within the
material. These in turn cause changes in the magnetic properties (e.g.
magnetic permeability)
of the element, which are then converted into electrical energy through
induction. The
magnetostrictive element in this particular embodiment may be completely
immersed in the
fluid flow, thereby forming an "eel-like" structure, or in the case of an
internal flow (e.g. pipe
or duct flow) may be incorporated into the structure that bounds the flow.
[0049] Another embodiment of this device is one in which the flow
separation is caused
by a bluff body or some other means, and the resulting vortex street impinges
on a flexible
structure. The structure includes a magnetostrictive energy harvester, and the
fluctuations in
pressure caused by the impinging vortex street lead to deformations in the
magnetostrictive
element(s), which are then converted into electrical energy.
[0050] Another embodiment of this device is one where pressure
fluctuations inherent
to the flow or imposed by an external mechanism, e.g. the throttling of a
valve upstream or
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downstream of the device, causes the deformation of a flexible structure. The
structure
includes a magnetostrictive energy harvester, and the fluctuations in pressure
lead to
deformations in the magnetostrictive element(s), which are then converted into
electrical
energy. A particular embodiment of this would consist of a pipe with an inner
wall that can
transmit load changes to one or more magnetostrictive energy harvesters, and
with the one or
more magnetostrictive energy harvester disposed outside this inner wall such
that pressure
fluctuations would cause a change in loading of the magnetostrictive energy
harvesters,
which would then be converted into electrical energy. This device
configuration has the
advantage that the energy harvesters are clearly outside of the pipe carrying
the fluid, and
therefore will not be prone to any failures caused by exposure to the fluid.
This is especially
important in production wells where hot hydrocarbons with solid content can
cause
degradation and deterioration of energy harvesters that are directly in the
fluid stream. It is
recognized that there is an advantage to deploying the device outside of the
primary flow path
in downhole energy generation applications. Any restriction to the flow in a
well decreases
production and is generally not desirable. There is also the need to be able
to perform well
interventions, and the presence of a device in the primary flow path could
make these
necessary operations impossible. As such, all reasonable efforts should be
taken to avoid
deploying the energy harvester in such a way that it presents and obstruction
to either the
flow or well interventions.
[0051] Embodiments of such a device that utilizes pressure fluctuations may
include
rod based or cantilever based magnetostrictive energy harvesters. Since the
fluid pressures
downhole are of the order of 15,000 psi, and pressure fluctuations can be of
the order of 10%
of that value, rod based designs that take advantage of axial load changes in
the rods may be
particularly attractive from the perspective of producing power of the order
of Watts, and
from the perspective of high reliability. The devices may be activated by
pressure pulses
transmitted through the fluid medium. A variety of methods are known for
transmitting
pressure pulses in a fluid medium, and a particular example may be found in
U.S. Patent No.
6,970,398 specifically useful for oil wells.
[0052] Pressure fluctuations in the pipe may be transmitted to one or
more
magnetostrictive rods, whose permeability is a function of the stress in the
magnetostrictive
rod. The magnetostrictive rod or rods are part of flux paths that may comprise
additional
magnetically permeable components and permanent magnets. In some embodiments,
the flux
paths will be substantially closed with no significant air gaps. The stress
changes inducted by
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the pressure fluctuations in the pipe will result in axial stress changes in
one or more
magnetostrictive elements, which will result in changes in the magnetic
permeability of these
elements, and therefore changes in magnetic flux density in the
magnetostrictive elements
and induce currents in conductive coils around the magnetostrictive elements
and/or other
flux path components.
[0053] As an example of a particular application, an example embodiment may
be
considered for use on an oil well producing 10,000 bbl/day of 350 API crude.
This would
equate to a mass flow rate of 15.1 kg/s, and with a dynamic viscosity of 1500
cP, the
Reynolds number (Re) range based on production tubing inner diameter would
range from
100 to 340 for tubing inner diameters from 1.5" to 5", respectively. For these
Reynolds
numbers, the Strouhal number (St) for a cylindrical mass has been shown to be
0.2. For a 1"
diameter mass, this means that the frequency of vortex shedding ranges from
about 127 Hz
for the smallest tubing diameter to about 11 Hz for the 5" ID. These
calculations are
presented in Table 1.
Table 1: Calculation parameters.
Tubing ID Pipe area Fluid Velocity Vortex Frequency
(in) (m) (m2)
(m/s) (Hz) Re
1.5 0.0381 0.0011 16.14 127.09 337.40
2 0.0508 0.0020 9.08 71.49 253.05
2.5 0.0635 0.0032 5.81 45.75 202.44
3 0.0762 0.0046 4.04 31.77 168.70
3.5 0.0889 0.0062 2.96 23.34 144.60
4 0.1016 0.0081 2.27 17.87 126.52
4.5 0.1143 0.0103 1.79 14.12 112.47
5 0.127 0.0127 1.45 11.44 101.22
[0054] Additionally, a mass with a non-circular cross section can be used
to alter the
Strouhal number, which will in turn change the vortex-shedding frequency. For
instance, the
use of a square cross section will decrease the vortex-shedding frequency by
25%, and this
will also alter the amplitude of the vibrations.
[0055] A particular embodiment might be implemented as a cantilever that is
14.7 in
long, and 1.5" wide, with each magnetostrictive element being 0.125" thick
with a 0.2" gap
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between them. A 1 kg mass on the end of the cantilever would bring the natural
frequency to
31.5 Hz (this assumes an added mass of 0.05 kg). This corresponds to the
vortex-shedding
frequency for the 3" pipe in Table 1. If the tip deflection is about 0.2", the
power production
from the cantilever is conservatively calculated to be on the order of about 1
W. This is well
below the kinetic energy flux of the fluid, which is around 125 W. Figure 2
depicts a
graphical diagram 130 of deflection and power generation as a function of
frequency for an
embodiment of the energy generation device 100 of Figure 1A.
[0056] The Reynolds number will increase by over two orders of
magnitude if the fluid
is natural gas instead of crude. This will allow for more creative use of mass
shaping and
other factors, as the unstable response of many shapes in vortex-induced and
flutter vibrations
occur more readily at higher Reynolds number. However, the Strouhal number
remains fairly
constant over a very large range of Re (e.g., for circular cylinders St = 0.2
for Re from 102 to
105), and the vortex-induced vibrations might be expected to occur in a
frequency range that
is consistent with the above calculations.
[0057] In another embodiment, the turbulence of the flow itself is used to
induce
vibrations that cause stresses/strains in the magnetostrictive elements. This
mechanism does
not rely on vortex shedding, and thus has no Strouhal number dependence. The
turbulence
contains broadband fluctuations, and these couple into the natural frequencies
of the
immersed body to produce a vibrational response. While it may be advantageous
in some
embodiments to avoid reliance on vortex shedding, the amplitudes of turbulence
induced
vibration are generally smaller than those caused by vortices. A sample
calculation from
Blevins (Chapter 8, Turbulence-Induced Vibration in Parallel Pipe Flow) shows
that a 12" x
18" x 0.125" plate on the wall of a square duct with air flow at 61 m/s has a
maximum
deflection of 5 i.tm for the fundamental mode. If the plate were a beam of
magnetostrictive
elements, the power output for vibration at the natural frequency of 119 Hz
would be on the
order of about 1 mW. Compare this with the total kinetic energy flux of this
flow, which is
38 kW.
[0058] Another embodiment has multiple devices deployed to increase
the total power
generation. Each individual device could be any one of the aforementioned
embodiments,
and this embodiment would allow for any combination thereof. An illustration
of an
embodiment comprised of two cantilever-based flow energy harvesters is
illustrated in
Figures 3A and 3B.
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[0059] Figure 3A depicts a schematic diagram of a cutaway view of one
embodiment of
an energy generation assembly 150 with multiple energy generation devices 100
deployed in
combination. Figure 3B depicts a perspective view of the energy generation
assembly 150 of
Figure 3B. In the illustrated embodiments, the energy generation devices 100
are arranged in
series within a flow enclosure 152. In general, the flow enclosure 152 directs
a stream of
fluid (not shown) through an interior channel within the vicinity of the
energy generation
devices 100. Depending on the arrangement of the devices 100 within the
enclosure 152, the
fluid may flow past one or more devices 100 at approximately the same time, or
the fluid may
flow past separate devices in series.
[0060] Additionally, the fluid may be directed to flow from the fixed end
108 of the
devices 100 toward the free end 102 (as shown) or, alternatively, in the
opposite direction. In
some embodiments, the devices 100 within the enclosure 152 are all oriented in
the same
direction, either in series or parallel. In other embodiments, at least some
of the devices 100
are oriented in opposite directions, with either the free end 106 or the fixed
end 108 first
receiving the fluid impact. In other embodiments, one or more of the devices
100 may be
oriented at a non-zero angle relative to another device 100 so that there is
an angular
difference between two or more devices 100 within the same enclosure 152.
[0061] In further embodiment, the interior structure of the enclosure
152 may be
configured to facilitate a predetermined fluid pattern within the enclosure
152. By altering
the interior sidewall dimensions, angles, and other geometrical
characteristics, it may be
possible to enhance the vibrational movement of the energy generation devices
100 within
the enclosure 152. Additionally, it may be possible to reduce eddy current
effects from one
device 100 that might otherwise decrease the vibrational movements of another
downstream
device 100.
[0062] In the above description, specific details of various embodiments
are provided.
However, some embodiments may be practiced with less than all of these
specific details. In
other instances, certain methods, procedures, components, structures, and/or
functions are
described in no more detail than to enable the various embodiments of the
invention, for the
sake of brevity and clarity.
[0063] Although the operations of the method(s) herein are shown and
described in a
particular order, the order of the operations of each method may be altered so
that certain
operations may be performed in an inverse order or so that certain operations
may be
performed, at least in part, concurrently with other operations. In another
embodiment,
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instructions or sub-operations of distinct operations may be implemented in an
intermittent
and/or alternating manner.
[0064] Although specific embodiments of the invention have been
described and
illustrated, the invention is not to be limited to the specific forms or
arrangements of parts so
described and illustrated. The scope of the invention is to be defined by the
claims appended
hereto and their equivalents.
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