Acoustically controlled rheological valve for thixotropic fluid flow control
View Patent ↗An acoustic choke provides valve functionality for thixotropic fluids without mechanical components. One or more ultrasonic transducer elements is positioned radially around a smooth bore constriction in a corrosion-resistant body. When no acoustic energy is applied, the yield stress of a thixotropic fluid occupying the bore exceeds the available driving pressure and flow is blocked. When acoustic energy is applied at sufficient intensity to generate local shear rates exceeding the yield-stress threshold, the fluid transitions from gel state to liquid state and flow proceeds under the available driving pressure. Rapid state transition provides inherent fail-safe behavior. The device eliminates sealing surfaces, moving parts, and mechanical wear from fluid control systems handling corrosive, abrasive, or particle-laden thixotropic fluids. A self-cleaning mechanism uses periodic high-intensity acoustic pulses to dislodge accumulated material. Applicable to flow battery systems, pharmaceutical processing, food manufacturing, cementitious material handling, and any application requiring corrosion-resistant, particulate-tolerant flow control.
1 . An acoustic choke for controlling a flow of a thixotropic fluid, comprising:
a constriction body defining a smooth bore channel forming a flow restriction in a fluid conduit, the smooth bore channel having no mechanical member configured to move within the smooth bore channel to open or close the flow restriction;
one or more ultrasonic transducer elements positioned exterior to the constriction body and arranged to direct focused acoustic energy into the smooth bore channel; and
a driver circuit electrically connected to the one or more ultrasonic transducer elements and configured to supply alternating current at an operating frequency to generate the focused acoustic energy;
wherein the smooth bore channel is dimensioned relative to an available driving pressure in the fluid conduit and to a yield stress of the thixotropic fluid such that, when no acoustic energy is applied, a wall shear stress produced at the bore by the available driving pressure is less than the yield stress of the thixotropic fluid, the thixotropic fluid within the smooth bore channel remains in a gel state, and flow through the smooth bore channel is blocked to provide a normally-closed, zero-flow state; and
wherein, when acoustic energy is applied at an intensity sufficient to generate local shear rates within the smooth bore channel exceeding a yield-stress threshold of the thixotropic fluid, the thixotropic fluid within at least a portion of the smooth bore channel transitions from the gel state to a liquid state of substantially reduced viscosity, and the available driving pressure drives flow of the thixotropic fluid through the smooth bore channel without movement of any mechanical member within the bore.
2 . The acoustic choke of claim 1 , wherein said smooth bore channel has a circular cross-section with an internal diameter in a range of 2-5 mm and an axial length in the range of 10-20 mm, the dimensions being selected such that, in combination with an available driving pressure and a yield stress of the thixotropic fluid, a wall shear stress at the smooth bore channel is less than the yield stress in the absence of applied acoustic energy, thereby maintaining a normally-closed, zero-flow state.
3 . The acoustic choke of claim 1 , wherein said one or more ultrasonic transducer elements comprise a plurality of piezoelectric elements arranged radially around a circumference of said constriction body, centered axially at a midpoint of said smooth bore channel, to create a focused acoustic zone at or near a central axis of the bore channel in which local shear rates exceed a yield-stress threshold of the thixotropic fluid during operation.
4 . The acoustic choke of claim 1 , wherein said operating frequency is in a range of 20-60 kHz and is selected to produce acoustic streaming within the thixotropic fluid sufficient to generate shear rates in the bore channel exceeding 100 s −1 in an ON state.
5 . The acoustic choke of claim 1 , wherein said driver circuit is configured to supply acoustic intensity to the smooth bore channel in a range of 10-100 W/cm 2 , producing acoustic streaming velocities exceeding 10 cm/s and shear rates exceeding 1,000 s −1 within the bore channel when the acoustic choke is in an ON state.
6 . The acoustic choke of claim 1 , wherein transition from gel state to liquid state upon application of acoustic energy occurs within 100 milliseconds, and recovery from liquid state to gel state upon cessation of the acoustic energy occurs within 1-2 seconds solely through passive thixotropic recovery of the thixotropic fluid, thereby providing a rapidly opening and passively, fail-safe closing valve without movement of any mechanical member within the smooth bore channel.
7 . The acoustic choke of claim 1 , wherein volumetric flow rate Q of fluid through said smooth bore channel is related to applied acoustic power P_acoustic according to the relationship Q=K(P_acoustic) 1.7 , where K is a fluid-specific constant, such that modulation of acoustic power by the driver circuit provides proportional flow control without mechanical actuation.
8 . The acoustic choke of claim 1 , wherein said constriction body is fabricated from a material selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxy alkane, polyvinylidene fluoride, borosilicate glass, and alumina ceramic, and wherein each such material provides a chemically inert, smooth bore surface free of seats, crevices, and moving parts that contact the thixotropic fluid.
9 . The acoustic choke of claim 1 , wherein said driver circuit is further configured to deliver periodic high-intensity acoustic pulses at a power exceeding 100 W for durations of approximately 1 second, inducing acoustic cavitation within said smooth bore channel to dislodge accumulated material from the wall of the smooth bore channel and thereby provide a self-cleaning function without mechanical disassembly.
10 . The acoustic choke of claim 1 , wherein said thixotropic fluid comprises an aqueous acid solution modified with 0.5-2 wt % hydrophobic fumed silica having a BET surface area of 110-130 m 2 /g, the thixotropic fluid exhibiting a yield stress of 50-200 Pa at rest and an apparent viscosity below 2 Pa·s under acoustic activation in the smooth bore channel.
11 . The acoustic choke of claim 1 , wherein said driver circuit operates in a pulse-width modulation mode in which acoustic energy is applied at a switching frequency exceeding an inverse of a gel-state recovery time of the thixotropic fluid, such that the thixotropic fluid within the smooth bore channel remains in a partially liquefied state throughout a duty cycle and a time-averaged flow rate is proportional to a duty-cycle fraction.
12 . The acoustic choke of claim 1 , further comprising one or more acoustic coupling layers of compliant material interposed between said ultrasonic transducer elements and an exterior surface of said constriction body to maximize acoustic energy transmission into the smooth bore channel while maintaining all solid components of the acoustic choke fixed in position during operation.
13 . A method for controlling a flow of a thixotropic fluid through a fluid conduit, comprising:
providing a constriction in said fluid conduit, said constriction having a smooth bore channel with no mechanical member configured to move within the smooth bore channel to open or close the smooth bore channel;
filling said smooth bore channel with said thixotropic fluid having a yield stress and selecting a smooth bore length and diameter and an available driving pressure in the fluid conduit such that a wall shear stress at the smooth bore produced by the available driving pressure is less than the yield stress in the absence of applied acoustic energy, thereby blocking flow through the bore channel in a normally-closed state;
selectively applying focused acoustic energy to the thixotropic fluid within said bore channel at an intensity sufficient to generate local shear rates exceeding a yield-stress threshold of the thixotropic fluid having a yield stress, thereby transitioning the fluid within at least a portion of the bore channel from a gel state to a liquid state of substantially reduced viscosity and enabling flow through the bore channel under the available driving pressure without movement of any mechanical member within the bore; and
selectively removing the applied acoustic energy, whereby the thixotropic fluid within the bore channel passively recovers from the liquid state to the gel state through thixotropic restructuring and flow through the bore channel is again blocked to restore the normally-closed state.
14 . The method of claim 13 , further comprising modulating an intensity of applied acoustic energy to control a volumetric flow rate of the thixotropic fluid through the smooth bore channel in proportion to an applied acoustic power according to a power-law relationship Q=K(P_acoustic) n , where Q is volumetric flow rate, P_acoustic is the applied acoustic power, K is a fluid-specific constant, and n is greater than 1.
15 . The method of claim 13 , wherein applying focused acoustic energy comprises driving one or more piezoelectric transducer elements positioned radially around an exterior of said constriction at a frequency in a range of 20-60 kHz and at an acoustic intensity in a range of 10-100 W/cm 2 , thereby generating acoustic streaming within the thixotropic fluid sufficient to produce local shear rates exceeding 1,000 s −1 within the bore channel.
16 . The method of claim 13 , further comprising periodically applying acoustic energy at an intensity and duration sufficient to induce cavitation within said smooth bore channel, thereby dislodging accumulated material from a bore wall and providing a self-cleaning function without mechanical disassembly of the constriction or introduction of any moving valve component into the smooth bore channel.
17 . A fluid processing system comprising:
a plurality of fluid processing chambers arranged in a series flow path;
a plurality of acoustic chokes, each acoustic choke positioned between adjacent ones of said processing chambers and each comprising a smooth bore constriction having no mechanical member configured to move within the smooth bore channel to open or close the smooth bore channel and one or more ultrasonic transducer elements positioned to direct focused acoustic energy into a thixotropic fluid within the smooth bore channel; and
a control system connected to the ultrasonic transducer elements of each of said acoustic chokes and configured to apply acoustic energy selectively to individual ones of said acoustic chokes to control flow of the thixotropic fluid through the series flow path;
wherein the thixotropic fluid flows between adjacent fluid processing chambers only when acoustic energy is applied to the intervening acoustic choke at sufficient intensity to transition the thixotropic fluid within the bore from a gel state to a liquid state and thereby permit flow under an available driving pressure, and flow is blocked when the focused acoustic energy is absent through passive gel-state recovery of the thixotropic fluid within the bore to provide a normally-closed state without movement of any mechanical member in the smooth bore channel.
18 . The system of claim 17 , wherein said control system is configured to activate said acoustic chokes in a sequential pattern from a first end to a second end of the series flow path, creating a controlled wave of fluid flow through the fluid processing chambers while maintaining the acoustic chokes in a normally-closed state in the absence of applied acoustic energy.
19 . The system of claim 17 , wherein said control system further comprises a fail-safe controller having an isolated power supply, said fail-safe controller configured to command all acoustic chokes to an OFF state by interrupting electrical power to all transducer elements upon detection of a system fault condition, whereby passive thixotropic recovery of the thixotropic fluid in each smooth bore channel returns all acoustic chokes to their normally-closed, gel-state condition.
20 . The system of claim 17 , wherein the series flow path is a gravity-fed cascade in which said fluid processing chambers are arranged at descending elevations and gravity provides a driving pressure for fluid flow through each acoustic choke when in an ON state, and wherein each acoustic choke is dimensioned relative to a yield stress of the thixotropic fluid and a gravity-induced pressure head such that the yield stress exceeds a wall shear stress at the smooth bore channel in the absence of applied acoustic energy, thereby maintaining a normally-closed state under gravity alone.