Device and method for determining fluid streaming potential

A method (e.g., for characterizing a fluid) includes rotating an electrode assembly in a fluid at a rotation speed. The electrode assembly includes first and second electrodes. Rotation of the electrode assembly draws at least a portion of the fluid to move across the first and second electrodes. The method also includes measuring a potential difference between the first and second electrodes as the at least a portion of the fluid moves across the first and second electrodes due to rotation of the electrode assembly, and determining a streaming potential of the fluid using the potential difference.

FIELD

This disclosure relates to devices and methods for determining fluid streaming potential.

BACKGROUND

Rotating disk electrodes (RDE) are conventionally used in characterizing electrochemistry in chemical reactions, such as in redox reactions. One current device for attempting to determine the streaming potential of aqueous solutions is a rotating disk and a very small stationary silver chloride reference electrode. The function of this device is limited to being used in aqueous solutions containing chloride ions, as these very small silver chloride reference electrodes do not function in organic fluids without chloride ions. As a result, this device may not be useful for measuring a streaming potential of a non-aqueous solution, such as hydraulic fluid.

Another device for attempting to determine the streaming potential of a fluid uses two small silver chloride electrodes in a flow cell. A relatively large amount of the fluid is pumped through the flow cell and the potential difference between these electrodes is measured to characterize the streaming potential of the fluid. This device is relatively large, cumbersome, prone to leaking, and can require relatively high pressure flow of the fluid.

A system and method is needed to overcome one or more of the limitations experienced by one or more of the existing devices or methods for determining the streaming potential of a fluid.

BRIEF DESCRIPTION

In one aspect, a method for testing a fluid is disclosed. A rotating device is rotated in a fluid to cause the fluid to move across the rotating device. A voltage of the fluid is measured at a plurality of locations of the rotating device as the fluid moves across the rotating device. A streaming potential of the fluid is determined based on a difference in the measured voltage of the fluid at the plurality of the locations of the rotating device.

In another aspect, another method for testing a fluid is disclosed. A rotating ring-disk electrode is rotated in a fluid at different rotation rates to cause the fluid to move across the rotating ring-disk electrode. A streaming potential of the fluid is determined at each of the different rotation rates based on a difference in measured voltage of the fluid at a plurality of locations of the rotating ring-disk electrode as the fluid moves across the rotating-ring disk electrode at each of the different rotation rates. The rotating ring-disk electrode is rotated in a different fluid at the different rotation rates to cause the different fluid to move across the rotating ring-disk electrode. The streaming potential of the different fluid is determined at each of the different rotation rates based on the difference in the measured voltage of the different fluid at the plurality of the locations of the rotating ring-disk electrode as the fluid moves across the rotating-ring disk electrode at each of the different rotation rates. The fluid or the different fluid which has the lowest determined streaming potential at the highest revolution per minute rate is selected as the fluid to be less prone to generating streaming potentials.

In still another aspect, a system for determining a streaming potential of a fluid is disclosed. The system includes a rotating device, a control device, a motor, and a voltmeter. The motor is connected to the rotating device. The motor is configured to rotate the rotating device in a fluid at different rotation rates as controlled by the control device to move the fluid across the rotating device. The voltmeter is connected to a plurality of locations of the rotating device. The voltmeter is configured to measure a voltage of the fluid at the plurality of locations of the rotating device as the fluid moves across the rotating device in order to determine a streaming potential of the fluid based on a difference in the measured voltage of the fluid at the plurality of the locations of the rotating device.

In another aspect, different materials may be used to form the electrodes. For example, one electrode could be formed from a first metal or metal alloy while the other electrode formed from a different, second metal or metal alloy. The different metals or metal alloys may generate different streaming potentials when rotated within the same fluid. The same fluid may be examined using different combinations of metals or metal alloys in the electrodes in order to determine different streaming potentials generated in the fluid as a function of fluid velocity.

In one embodiment, a method (e.g., for characterizing a fluid) includes rotating an electrode assembly in a fluid at a rotation speed. The electrode assembly includes first and second electrodes. Rotation of the electrode assembly draws at least a portion of the fluid to move across the first and second electrodes. The method also includes measuring a potential difference between the first and second electrodes as the at least a portion of the fluid moves across the first and second electrodes due to rotation of the electrode assembly, and determining a streaming potential of the fluid using the potential difference.

In one embodiment, a system (e.g., a measurement system for a fluid) includes an electrode assembly, an actuation device, and an electric energy sensing device. The electrode assembly includes a first electrode and a second electrode separated from each other by an insulative gap. The actuation device is configured to be coupled with the electrode assembly to rotate the electrode assembly in a fluid under examination. The electric energy sensing device is configured to be conductively coupled with the first and second electrodes of the electrode assembly. The electric energy sensing device also is configured to measure a potential difference between the first and second electrodes as the actuation device rotates the electrode assembly at a rotation speed to cause the fluid to move across the first and second electrodes. The potential difference that is measured is representative of a streaming potential of the fluid.

In one embodiment, a method (e.g., for examining a fluid) includes at least partially submerging first and second electrodes in a fluid. The first and second electrodes are separated from each other by an insulative gap. The method also includes rotating the first and second electrodes in the fluid at a common rotation speed. Rotation of the first and second electrodes at the common rotation speed causes the fluid to move across the first and second electrodes at a radial fluid velocity. The method also includes measuring a potential difference between the first and second electrodes as the fluid moves across the first and second electrodes at the radial fluid velocity, and determining a streaming potential of the fluid as a function of fluid velocity using the potential difference and the radial fluid velocity.

DETAILED DESCRIPTION

FIG. 1is a schematic diagram of a measurement system10for determining a streaming potential of a fluid12as a function of fluid velocity. The system10includes an electrode assembly16that is at least partially positioned in a container24having the fluid12disposed therein. The electrode assembly16also may be referred to as a rotating device.

The amount of fluid12included in the container24may be relatively small, such as in the tens of milliliters. For example, the container24may be a laboratory beaker capable of holding one hundred or so milliliters of a liquid. The fluid12may be an aqueous liquid, such as a water-based fluid. In one aspect, the fluid12is a non-electrolyte solution, such as a liquid that does not include a salt dissolved in a solvent. Alternatively, the fluid12may include a non-aqueous liquid, an electrolyte solution, hydraulic fluid, or another fluid.

For example, one embodiment of the system10and method of using the system10disclosed herein differs from conventional electrochemical analytic systems that measure streaming potentials of fluids in that these conventional systems may require use of electrolytic solutions that are conductive or highly conductive. These conventional systems may involve the use of electrolytic solutions having conductivities of about 0.1 microSiemens per centimeter (μS/cm) to about 150.0 microSiemens per centimeter (μS/cm). These conductivities can interfere with electrochemical analysis. For comparison purposes only, ultra-pure water has a conductivity of about 0.055 μS/cm, as a reference. High concentrations of electrolytes, e.g., molar concentrations of about 0.1 to 0.5, provides conductivity to a fluid or solution, and enables control of over the potential of the disk and ring. Eliminating high molar concentrations of electrolytes in the fluid12(as can be done with the system10) prevents the application of known systems and methods to organic fluids, including fluids having conductivity of at least 0.1 μS/cm. Low electrolyte concentrations (e.g., 1 mM or less), similarly does not work for fluids lacking chloride ions and is further unsuitable for organic or other hydrocarbon-based fluids.

The electrode assembly16includes plural electrodes26,28that are used to measure a difference between the potential (e.g., voltage) that is induced on the electrodes26,28when the fluid12moves relative to the electrodes26,28. In one aspect, the electrode26is a disk-shaped electrode and the electrode28is a ring-shaped electrode, with the disk-shaped electrode disposed inside of the ring-shaped electrode. The electrode28may extend around an entirety of the outer perimeter of the electrode26. Alternatively, the electrode28may extend around less than the entire outer perimeter of the electrode26. The electrode26may be referred to as an inner electrode and the electrode28may be referred to as an outer electrode.

The electrodes26,28are separated from each other by an insulative gap122. This insulative gap122represents a non-conductive spatial separation between the electrodes26,28. In one aspect, the insulative gap122may include an insulating ring-shaped member30coupled with the electrodes26,28and formed from a non-conductive (e.g., dielectric) material. Optionally, the insulative gap122may be formed by spatial separation between the electrodes26,28without another body disposed in the insulative gap122. The insulative gap122prevents a conductive pathway from being formed between the electrodes26,28in the electrode assembly16. As a result, the electric potential (e.g., voltage) that is induced on the electrode26can be separately measured from the electric potential induced on the other electrode28when the fluid12is moving relative to the electrodes26,28.

In one aspect, the electrodes26,28are rotated together within the fluid12to cause the fluid12to move past (e.g., flow across) the electrodes26,28. The electrodes26,28may be coupled with each other and to a shaft124of the system10. The shaft124can be rotated to cause the electrodes26,28to rotate at the same speed. For example, the electrodes26,28may be coupled with each other, coupled with the same shaft124, or both coupled with each other and with the shaft124such that rotation of the shaft124or one of the electrodes26or28causes both of the electrodes26,28to simultaneously rotate at the same rotation speed. While the outer electrode28may have a greater angular velocity than the inner electrode26due to the outer electrode28being radially disposed farther from the shaft124than the inner electrode26, the speeds at which the electrodes26,28are rotating about (e.g., around) the shaft124may be equivalent.

With continued reference to the electrode assembly16shown inFIG. 1,FIGS. 2 and 3schematically illustrate an example of flow of the fluid12when the electrodes26,28in the system10are rotated in the fluid12.FIG. 2illustrates velocity vectors (vyand vr) of the fluid12, whileFIG. 3illustrates flow paths300of the fluid12(e.g., the paths along which the fluid12flows).

The electrodes26,28may be coaxially aligned such that the electrodes26,28rotate about (e.g., around) a common axis200(which also can represent the axis of rotation of the electrodes26,28). As the electrodes26,28rotate, the fluid12is drawn upward in the container24(shown inFIG. 1) toward the electrodes26,28at a vertical fluid velocity (vy). The fluid12that is drawn toward the electrodes26,28also flows radially outward away from the common axis200at a radial velocity (vr), as shown by the flow paths300inFIG. 3. Movement of the fluid12by the electrodes26,28can induce an electric charge (e.g., voltage) on the electrodes26,28. For example, as the fluid12moves across the electrodes26,28, negatively charged ions, particles, or both ions can be swept away from surfaces of the electrodes26,28by the fluid12. To balance this movement of charge, electrons in the electrodes26,28may flow in an opposite direction and create an electronic potential (e.g., voltage) at the electrodes26,28.

The difference in these potentials is referred to as a streaming potential of the fluid12. The streaming potential can be represented by the following relationship:

⁢X=[Ψ0⁢⁢ɛ4⁢⁢π⁢⁢η⁢⁢σ]⁢Δ⁢⁢P
where X represents a gradient of the streaming potential of the fluid12, Ψ0represents a potential the an outer Helmholtz plane (OHP) between the fluid12and the electrodes26,28, ∈ represents the dielectric constant of the fluid12, η represents the fluid viscosity of the fluid12, σ represents the fluid conductivity of the fluid12, and ΔP represents the differential pressure in the fluid12.

In one aspect of the inventive subject matter described herein, the streaming potential can be measured for the fluid12as a function of fluid velocity. Streaming potentials for fluids12can be examined as a function of fluid velocity (e.g., the radial velocity vrof the fluid flow) in order to characterize the fluids12. This fluid velocity can represent the rate at which the fluid12is moving across or parallel to the surfaces of the electrodes26,28that are facing the fluid12(e.g., facing in a downward direction in the perspective ofFIG. 1). The streaming potentials for different fluids12can be measured in order to determine which fluid12may be less prone to cause contamination, corrosion, or the like, when the fluid12is used as a hydraulic fluid in a machine. Fluids12having smaller streaming potentials may be less likely to contribute to contamination, corrosion, or the like, when compared to fluids12having larger streaming potentials. Additionally or alternatively, the streaming potential for a fluid12in a machine (e.g., a hydraulic or other fluid) can be measured, monitored over time, or both in order to determine when to replace the fluid12. Over time, the streaming potential of fluid12in a machine may change. A changing streaming potential can indicate a change in the chemistry of the fluid and a corresponding need to change or replace the fluid12.

By putting different fluids12in the container24and measuring the streaming potentials of the fluids12as a function of fluid velocity (e.g., radial velocity vr), the system10may be used to measure the streaming potentials of different fluids12at different rotation rates of the electrodes26,28. The fluid12which has the lowest determined streaming potential at the highest revolution per minute rate may then be selected for use in a fluidic system, such as a hydraulic system, in one embodiment. Optionally, fluids12with streaming potentials below a designated threshold at fluid velocities in which the fluids12move in the machines may be selected. In other aspects, the selected fluid12may be used in varying devices or for further evaluation or modification.

As one example, the electrodes26,28may be rotated at a designated rotation speed (e.g., as expressed in terms of revolutions, radians, degrees per unit time, such as per minute, or as otherwise expressed) and the voltages sensed by each of the electrodes26,28are measured. A difference between these voltages may be calculated as the streaming potential of the fluid12at the rotation speed of the electrodes26,28. The rotation speed of the electrodes26,28can be converted into the speed at which the fluid12is flowing across or parallel to the electrodes26,28. The calculated streaming potential may then be associated with the fluid velocity (e.g., the radial velocity vr) for this fluid12. In one aspect, the rotation speed of the electrodes26,28can be converted into the fluid velocity using the following relationship:

⁢vr=0.51⁡[ω⁢⁢23]⁡[v-0.5]⁢ry
where vrrepresents the radial velocity, ω represents the rotation speed of the electrodes26,28(e.g., in terms of radians per second), v represents the kinematic viscosity of the fluid12, r represents the radius electrodes26,28at which the fluid velocity is being calculated, and y represents a distance from the surfaces of the electrodes26,28that face the moving fluid12(e.g., that faces downward in the view ofFIG. 1). The radial velocity of the fluid12may be expressed as a function of radius, or distance from the axis200that the electrodes26,28rotate around. For example, for a designated rotation speed (ω) of the electrodes26,28, the radial velocity (vr) of the fluid12may be different at different distances away from the axis200. Therefore, several radial velocities may be measured for the fluid12in one embodiment. Alternatively, the streaming potential of the fluid12may be measured and associated with the rotation speed of the electrodes26,28instead of the radial velocity of the fluid12.

The radial velocity of the fluid12that is calculated may represent the radial velocity of a portion of the fluid12that is located relatively close to the ends or surfaces of the electrodes26,28that face the moving fluid12(e.g., the surfaces facing in a downward direction in the perspective ofFIG. 4). For example, the rotation of the electrodes26,28can drag a fluid layer of the fluid12that constitutes less than all of the fluid12in the container26. The radial velocity of the fluid12can represent the speed at which this fluid layer is moving outward from the common axis200of the electrodes26,28. The fluid layer can be referred to as a hydrodynamic boundary layer of the fluid12, and the thickness of this fluid layer (e.g., as measured in distances from the surfaces of the electrodes26,28in directions that are oriented parallel to the common axis200) can be referred to as a Prandtl number of the fluid12.

The Prandtl number may depend on the kinematic viscosity of the fluid12and the rotation speed (ω) of the electrodes26,28. In one example, the Prandtl number of the fluid12is represented by the following relationship:

⁢yh=3.6⁢(vω)12
where yhrepresents the Prandtl number of the fluid12(e.g., the thickness of the boundary layer of the fluid12that is moving across the electrodes26,28), v represents the kinematic viscosity of the fluid12, and ω represents the rotation speed of the electrodes26,28(e.g., in terms of radians per second). Alternatively, the thickness of the boundary layer may be measured or calculated in another manner.

FIG. 4illustrates a graph800showing the Prandtl numbers of the fluid12(e.g., the thicknesses of a boundary layer of the fluid12that is dragged by the rotating electrodes26,28) at different rotation speeds of the electrodes26,28according to one example. The Prandtl numbers are shown alongside a horizontal axis400representative of rotation speeds of the electrodes26,28(expressed in terms of revolutions per minute, or RPMs) and a vertical axis402representative of the Prandtl number (e.g., the thickness of the boundary layer of fluid12, expressed in terms of centimeters). As shown in FIG.4, the thickness of the boundary layer of the fluid12is larger at slower rotation speeds of the electrodes26,28, and decreases as the rotation speeds increase.

FIG. 5illustrates a graph90showing radial velocities (vr) of a boundary layer of the fluid12at different rotation rates of the electrodes26,28in accordance with one example. The radial velocities are shown alongside a horizontal axis500representative of radial velocity (expressed in terms of centimeters per second) and a vertical axis502representative of rotation speed of the electrodes26,28(expressed in terms of revolutions per minute, or RPMs). As shown inFIG. 4, the radial velocity of the boundary layer of the fluid12is slower at distances that are closer to the common axis200of the electrodes26,28(as shown inFIG. 2), at slower rotation speeds of the electrodes26,28, and at both smaller distances from the common axis200and at slower rotation speeds. Conversely, when the radial distance (e.g., radius) from the common axis200increases (e.g., the location where the radial velocity is calculated for), the rotation speed of the electrodes26,28increases, or both the radial distance and the rotation speed increase, then the radial velocities increase.

There may be a high variation of the radial velocity at the boundary layer of the fluid12from the center of the disk-shaped electrode26to the ring-shaped electrode28as a function of rotation rates. For example, at 1,000 revolutions per minute of the electrodes26,28, the radial velocity changes insignificantly from the center of the disk-shaped electrode26(e.g., the common axis200) to the ring-shaped electrode28. At 5,000 revolutions per minute, the radial velocity changes less than 100 cm/s to 500 cm/s from the center of the disk-shaped electrode26to the ring-shaped electrode28. A more dramatic change in radial velocity occurs at 10,000 revolutions per minute of the electrodes26,28, where the radial velocity changes from about 100 cm/s to greater than 900 cm/s from the center of the disk-shaped electrode26to the ring-shaped electrode28. This acceleration in the flow of the fluid12provides increased streaming potential attainable using the rotating electrodes26,28as measured by the potential difference between the disk-shaped electrode26and the ring-shaped electrode28.

As described above, the streaming potentials for different fluids12may be measured at different rotation speeds of the electrodes26,28in order to calculate the streaming potentials of the fluids12as a function of the radial velocity at which the fluid12is moving across the electrodes26,28. One or more of these fluids12may be selected for use in a machine based on a comparison of these streaming potentials. For example, the fluid12having a lower streaming potential than one or more other fluids12at radial velocities that are equal to or relatively close to the speeds at which the fluid12is expected to move in the machine (e.g., within 90% to 110% of the speed at which the fluid12moves in the machine) may be selected for use in the machine (e.g., as hydraulic fluid).

Additionally or alternatively, relatively small samples (e.g., in the tens of milliliters or less) of the fluid12being currently used in a machine may be extracted from the machine (e.g., when the machine is deactivated) and the streaming potentials for the fluid12may be measured at one or more designated radial velocities (e.g., the radial velocities that are equal to or approximately the same as the speeds at which the fluid12flows in the machine). The streaming potentials may be compared to one or more thresholds to determine if the streaming potentials indicate that the fluid12may need to be at least partially replaced or entirely replaced. For example, over time, the streaming potential of the fluid12may change (e.g., increase or decrease) such that the fluid12may be more prone to contamination or corrosion of the machine.

FIG. 6illustrates a perspective view of one embodiment of the measurement system10. In addition to the electrode assembly16, the system10may include a moveable frame14mechanically coupled to the electrode assembly16and a control device18. The moveable frame14can move relative to the container24, such as by moving upward, downward, or both upward and downward in the view ofFIG. 6. The moveable frame14can be used to raise the electrode assembly16out of the fluid12in the container24and/or lower the electrode assembly16down into the fluid12in the container24. The moveable frame14also allows the rotating device16to rotate while partially disposed in the fluid12held within the container24. For example, the rotating device16may be coupled with an actuation device20, such as a motor, by the moveable frame14and/or by one or more other components (e.g., gears, rods, or the like). The actuation device20can rotate the rotating device16such that the electrodes26,28(shown inFIG. 1) rotate with in the fluid12in the container24, as described above.

With continued reference to the embodiment of the system10shown inFIG. 6,FIG. 7illustrates a perspective view of the rotating device16(e.g., the electrode assembly) according to one embodiment. The rotating device16comprises a rotating ring-disk electrode (RRDE) that includes the disk-shaped inner electrode26, the ring-shaped outer electrode28, an inner insulating ring-shaped member or body30, and an outer insulating ring-shaped member or body32. The inner insulating ring-shaped member30is disposed in-between and against an outer diameter of the disk-shaped inner electrode26and an inner diameter of the ring-shaped outer electrode28. The inner insulating ring-shaped member30includes or is formed from a dielectric material that prevents conduction of electric current through the member30from the inner electrode26to the outer electrode28, and from the outer electrode28to the inner electrode26. The inner insulating member30can represent the insulative gap122shown inFIGS. 1 through 3, and prevents the disk-shaped inner electrode26from being in contact with the ring-shaped outer electrode28. Alternatively, the insulative gap122may be formed by spatial separation between the electrodes26,28, without the member30being present. Optionally, a portion of the member30may be disposed between the electrodes26,28without the member30filling the entire space between the electrodes26,28.

The outer insulating ring-shaped member32is disposed against and around an outer diameter of the ring-shaped outer electrode28. Optionally, the electrode assembly16may not include the outer member32. The disk-shaped inner electrode26, the ring-shaped outer electrode28, and the insulating members30and32can be coupled with each other (e.g., by press-fit connections, adhesive, or the like) so that the electrodes26,28and members30,32rotate together. The electrodes26,28can each be made of a conducting material which is chosen to be the conducting material in contact with the fluid12. The electrodes26,28may be made from any suitable material, including but not limited to the following examples of conductive materials, e.g., stainless steel, gold, silver, platinum, carbon, steel, etc. In one aspect, one or more of the electrodes26,28is formed from the same material in which the fluid12is disposed when the fluid12is used in a machine.

The electrodes26,28may be coupled with each other (e.g., by the inner insulating member30) such that the electrodes26,28move with each other. For example, in one embodiment, the electrodes26,28may be coupled with each other such that the electrodes26,28enter into the fluid12together, rotate at the same rotation speed while in the fluid12, and are removed from the fluid12together. Additionally, while each of the electrodes26,28shown inFIG. 7represents a single conductive body, optionally, one or both of the electrodes26,28may be formed from plural separate conductive bodies (e.g., rings, cylinders, dots, and the like).

Returning to the description of the embodiment of the system10shown inFIG. 6, the system10also includes a control device18that is used to operate the actuation device20. The control device18can include or represent one or more hardware circuits or circuitry that includes or is coupled with one or more processors, controllers, or other logic-based computer devices. In one embodiment, the control device18represents a computer or computing device operating based off of instructions that are hard-wired into circuits (e.g., circuit boards) of the device18. Optionally, the control device18may operate based off of instructions stored on a tangible and non-transitory computer readable storage device (e.g., a hard drive memory).

The control device18can be used by an operator of the system10to control the speed at which the actuation device20rotates the electrodes26,28in the fluid12. The control device18can include one or more input devices (e.g., knobs, switches, an electronic mouse, touchscreen, or the like) that are actuated by the operator to change the speed at which the actuation device20rotates the electrodes26,28. An electric energy sensing device22is conductively coupled with the electrodes26,28. The sensing device22includes one or more devices that measure the amounts of electric energy induced on the electrodes26,28by movement of the fluid12and the electrodes26,28relative to each other. For example, the sensing device22can include one or more voltmeters that measure an electric potential difference between the electrodes26,28in an electric circuit that includes the electrodes26,28. This circuit may be open between the electrodes26,28. The sensing device22can measure the open circuit potential of this circuit between the electrodes26,28. For example, the sensing device22can measure a voltage of the fluid12at the plurality of locations (e.g., the electrodes26,28) of the rotating device16as the fluid12moves across the rotating device16in order to determine a streaming potential of the fluid12based on a difference in the measured voltage of the fluid12at the plurality of locations of the rotating device16. The voltmeter22is configured to determine that the streaming potential of the fluid12is greater for larger differences in the measured voltage of the fluid12at the plurality of locations of the rotating device16.

The sensing device22is configured to measure the streaming potential of the fluid12at each of the different rotation rates based on the difference in the measured voltage of the fluid12at the plurality of locations of the rotating device16at each of the different rotation rates. In one aspect, the different rotation rates each fall within a range of 0 to 10,000 revolutions per minute. In other aspects, different rotation rates may be used and can exceed 10,000 revolutions per minute. In still other aspects, the sensing device22may be configured to determine the streaming potential of the fluid12based on varying properties.

FIG. 8is a flowchart illustrating one aspect of a method40for testing a fluid. The method40may utilize the system10described above to characterize streaming potentials as a function of fluid velocity for one or more fluids12. In other aspects, the method40may utilize another system. At42, a rotating device is placed into and rotated in a fluid disposed in a container. This device includes plural conductive electrodes, such as the electrodes26,28. Rotation of the rotating device causes the fluid to move across the electrodes and induce potentials (e.g., voltages) on the electrodes. As described above, the rotating device may comprise a rotating ring-disk electrode comprising a disk-shaped inner electrode, a ring-shaped outer electrode, and an inner insulating gap (e.g., ring-shaped member).

At44, a voltage of the fluid is measured at a plurality of locations of the rotating device as the fluid moves across the rotating device. For example, a voltmeter or other device can be used to measure the electric potentials at the electrodes26,28as the electrodes26,28are rotated together in the fluid12. The speed at which the electrodes26,28are rotated may be determined and associated with the measured potential difference.

At46, a streaming potential of the fluid is determined based on a difference in the measured potentials of the fluid at the plurality of the locations of the rotating device. The difference in the measured potentials of the fluid at the locations (e.g., the electrodes26,28) represents the streaming potential of the fluid for the radial velocity of the fluid flowing across the electrodes26,28.

At48, the speed at which the rotating device is rotated in the fluid may be changed. In one embodiment, flow of the method40may return to42so that the streaming potential of the fluid can be measured at this different rotation speed of the electrodes26,28. The streaming potential can be measured several times at different speeds of rotation of the electrodes26,28in order to determine how the streaming potential of the fluid changes with respect to the velocity of the fluid across the electrodes26,28. For example, for the same fluid12, the streaming potential of the fluid12may increase with increasing radial velocities of the fluid12across the electrodes26,28and may decrease with decreasing radial velocities of the fluid12across the electrodes26,28. As described above, the fluid velocity may be derived from the speed at which the electrodes26,28rotate in the fluid12. The relationship between the measured streaming potential and the fluid velocities that are determined can be examined to obtain the streaming potential of the fluid12as a function of fluid velocity. In one aspect, the different rates at which the electrodes26,28are rotated may fall within a range of 0 to 10,000 revolutions per minute. In other aspects, different rotation rates may be used.

In one embodiment, the streaming potential or potentials that are determined for the fluid may be used to determine whether the fluid needs to be changed or replaced. As described above, over time, the streaming potential of a fluid in a machine may increase, thereby indicating that the fluid is more prone to contamination or corrosion. The streaming potential of the fluid at one or more fluid velocities may be compared to one or more thresholds to determine if the streaming potential is too large and, as a result, the fluid needs to be replaced. If no further examination of the current fluid or another fluid is to be performed, the method40can terminate. Alternatively, the method40can continue, as described below.

At50, the fluid in the container can be changed to a different fluid. The streaming potential of the different fluid can be measured for one or more rotation speeds of the electrodes, as described above in connection with42to48, so that the streaming potential of the different fluid as a function of fluid velocity can be determined. The streaming potentials of additional fluids can be determined in a similar manner.

At52, the streaming potentials of the fluids at one or more fluid velocities or rotation speeds are compared. In one aspect, the fluid is identified as having the lowest determined streaming potential or a streaming potential that is lower than one or more other fluids at the fastest fluid velocity, a fluid velocity that is faster than one or more other fluid velocities, the fastest rotation speed of the electrodes26,28, or the rotation speed of the electrodes26,28that is faster than one or more other rotation speeds. This fluid may be less prone to contaminate or corrode a conductive body or container in which the fluid is disposed.

At54, the selected fluid can be used inside a machine or other fluidic device. As described above, because this fluid has a relatively low streaming potential, the fluid may be less likely to contaminate or corrode the machine or device. In other aspects, any of the operations of the method40may be altered in substance or order, may not be followed, or one or more additional steps may be added.

In one embodiment, a method (e.g., for characterizing a fluid) includes rotating an electrode assembly in a fluid at a rotation speed. The electrode assembly includes first and second electrodes. Rotation of the electrode assembly draws at least a portion of the fluid to move across the first and second electrodes. The method also includes measuring a potential difference between the first and second electrodes as the at least a portion of the fluid moves across the first and second electrodes due to rotation of the electrode assembly, and determining a streaming potential of the fluid using the potential difference.

In one aspect, the method also includes determining the streaming potential of the fluid as a function of fluid velocity at which the fluid moves across the first and second electrodes.

In one aspect, the streaming potential of the fluid is determined as the function of fluid velocity by rotating the electrode assembly in the fluid at plural different rotation speeds, measuring plural different potential differences between the first and second electrodes at the corresponding plural different rotation speeds, determining plural different fluid velocities at which the fluid moves across the first and second electrodes when the electrode assembly is rotated at the corresponding different rotation speeds, and determining one or more streaming potentials of the fluid at the corresponding different fluid velocities.

In one aspect, the electrode assembly comprises the first electrode as an inner electrode and the second electrode as an outer electrode with the inner and outer electrodes separated by an insulative gap.

In one aspect, the method also includes rotating the electrode assembly in one or more additional fluids, measuring one or more additional potential differences between the first and second electrodes for the one or more additional fluids, determining one or more additional streaming potentials for the one or more additional fluids using the one or more additional potential differences, and selecting at least one of the fluid or the one or more additional fluids for use in a machine by comparing the streaming potential of the fluid and the one or more additional streaming potentials of the one or more additional fluids.

In one aspect, the potential difference that is measured represents an open circuit voltage between the first and second electrodes for an electronic circuit that includes the first and second electrodes.

In one aspect, rotating the electrode assembly causes both the first and second electrodes to be rotated at the rotation speed.

In one aspect, the fluid is a non-electrolyte solution or an aqueous solution. Optionally, the fluid can be an aqueous or non-aqueous solution (e.g., fluid) that does or does not include an electrolyte.

In one embodiment, a system (e.g., a measurement system for a fluid) includes an electrode assembly, an actuation device, and an electric energy sensing device. The electrode assembly includes a first electrode and a second electrode separated from each other by an insulative gap. The actuation device is configured to be coupled with the electrode assembly to rotate the electrode assembly in a fluid under examination. The electric energy sensing device is configured to be conductively coupled with the first and second electrodes of the electrode assembly. The electric energy sensing device also is configured to measure a potential difference between the first and second electrodes as the actuation device rotates the electrode assembly at a rotation speed to cause the fluid to move across the first and second electrodes. The potential difference that is measured is representative of a streaming potential of the fluid.

In one aspect, the actuation device is configured to rotate the electrode assembly in the fluid at plural different rotation speeds and the electric energy sensing device is configured to measure plural different potential differences between the first and second electrodes at the corresponding plural different rotation speeds. The different rotation speeds cause the fluid to move across the first and second electrodes at corresponding plural different fluid velocities. The streaming potential of the fluid can be determined as a function of the fluid velocities using the plural different potential differences and the plural different fluid velocities.

In one aspect, the electrode assembly includes the first electrode as an inner electrode and the second electrode as an outer electrode with the inner and outer electrodes separated by an insulative gap.

In one aspect, the inner electrode is a disk-shaped electrode, the insulative gap is a ring-shaped separation between the inner electrode and the outer electrode, and the outer electrode is a ring-shaped electrode.

In one aspect, the insulative gap of the electrode assembly includes a dielectric body disposed between the first and second electrodes.

In one aspect, electric energy sensing device is configured to measure the potential difference as an open circuit voltage between the first and second electrodes for an electronic circuit that includes the first and second electrodes.

In one aspect, the actuation device is configured to rotate the electrode assembly such that both the first and second electrodes are rotated at the rotation speed.

In one embodiment, a method (e.g., for examining a fluid) includes at least partially submerging first and second electrodes in a fluid. The first and second electrodes are separated from each other by an insulative gap. The method also includes rotating the first and second electrodes in the fluid at a common rotation speed. Rotation of the first and second electrodes at the common rotation speed causes the fluid to move across the first and second electrodes at a radial fluid velocity. The method also includes measuring a potential difference between the first and second electrodes as the fluid moves across the first and second electrodes at the radial fluid velocity, and determining a streaming potential of the fluid as a function of fluid velocity using the potential difference and the radial fluid velocity.

In one aspect, the first electrode is an inner disk-shaped electrode and the second electrode is an outer ring-shaped electrode that at least partially encircles an outer perimeter of the inner disk-shaped electrode. The inner disk-shaped electrode and the outer ring-shaped electrode are coupled with each other by a dielectric body such that rotation of the first and second electrodes causes the inner disk-shaped electrode and the outer ring-shaped electrode to both rotate around a common axis of rotation at the common rotation speed.

In one aspect, the streaming potential of the fluid is determined as the function of fluid velocity by rotating an electrode assembly that includes the first and second electrodes at plural different rotation speeds, measuring plural different potential differences between the first and second electrodes when the electrode assembly is rotated at the plural different rotation speeds, determining plural different fluid velocities at which the fluid moves across the first and second electrodes at the plural different rotation speeds, and determining plural different streaming potentials of the fluid at the plural different fluid velocities.

In one aspect, the fluid is a non-electrolyte solution or an aqueous solution. Optionally, the fluid can be an aqueous or non-aqueous solution (e.g., fluid) that does or does not include an electrolyte.

In one aspect, the method also includes determining one or more additional streaming potentials of one or more additional fluids as functions of fluid velocities of the one or more additional fluids, and selecting at least one of the fluid or the one or more additional fluids for use in a machine based on the corresponding streaming potential or one or more additional streaming potentials as functions of fluid velocities.

One or more of the operations described above in connection with the methods may be performed using one or more processors. The different devices in the systems described herein may represent one or more processors, and two or more of these devices may include at least one of the same processors. In one embodiment, the operations described herein may represent actions performed when one or more processors (e.g., of the devices described herein) are hardwired to perform the methods or portions of the methods described herein, and/or when the processors (e.g., of the devices described herein) operate according to one or more software programs that are written by one or more persons of ordinary skill in the art to perform the operations described in connection with the methods.