Fiber optic flow meter for high temperature corrosive nuclear environments

Abstract

Embodiments can relate to a flow meter. The flow meter includes a tube having a length L. The flow meter includes a heater wire either wound about the tube or extending through the tube. The flow meter includes an optical fiber extending through the tube. An interrogator is used to interrogate the optical fiber. Electrical power can be supplied to the heater wire. The flow meter is placed in an environment in which fluid (e.g., gas or liquid) is allowed to, caused to, or anticipated to flow over the tube in a direction that is not parallel to the length L of the tube.

Description

Fiber Optic Flow Meter for High Temperature Corrosive Nuclear EnvironmentsCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to and claims the benefit of priority of U.S. provisional patent application no. 63 / 520,798, filed on August 21, 2023, the entire contents of which is incorporated herein by reference.FIELD OF THE INVENTION

[0002] Embodiments can relate to a flow meter. The flow meter can include a tube having a length L, a heater wire either wound about the tube or extending through the tube, and an optical fiber extending through the tube. An interrogator is used to interrogate the optical fiber. Electrical power can be supplied to the heater wire. The flow meter is placed in an environment in which fluid (e g., gas or liquid) is allowed to, caused to, or anticipated to flow over the tube in a direction that is not parallel to the length L of the tube. A change in temperature of the tube due to changes in flow can be detected via interrogation of spectral data of the optical fiber, wherein the spectral data is used as a proxy to determine or estimate flow rate or flow velocity.BACKGROUND OF THE INVENTION

[0003] In conventional hot-wire-based local flow sensors (US-466171-A, US-2870305-A, US- 4011756-A, and US-4471655-A) also known as thermal anemometers, a heated resistance element is employed as the sensing element that is operated by an electric circuit to control either voltage, current, or temperature (resistance). This type of sensor measures or controls the power consumption through the sensing element, and the power consumption can be converted to the velocity of fluid by proper post-processing of convective heat transfer occurring on the sensing element. However, conventional systems are only capable of measuring the velocity of the fluid at a single point in space because the systems cannot monitor the local heat transfer, instead, measure the total power consumption, which also limits the sensing element length. In addition, conventional hot wires are not rated for harsh environmental conditions (e.g., high temperature, corrosive chemistry, ionizing radiation, etc. environments) found in fission and fusion reactors or high-temperature thermal energy storages which are operated using challenging coolants such as molten salts, high-temperature gases, alkali metal vapors, etc. To enable measurements of flowvelocity distribution based on heated elements and heat transfer, measurement of local temperature distribution through the heated element is required. Also, to apply the velocity distribution measurement to harsh environments, the heated elements need to be protected from harsh conditions and the temperature measurement should operate in harsh conditions. Some fiber optic flow sensors are available, however, these sensors do not provide the flow distribution measurement. US-4976157 measures the attenuation of light using a fiber optic sensor based on the force exerted by the flow. US-7738084-B1 uses discontinued fiber optic sensors coupled with photodiodes. US-9995628-B1 utilizes a Fabry-Perot cavity. US-5827976 converts fluidic oscillation to flow rate using a fiber optic sensor. Thermal-dilation-type fiber optic flow sensors are available in US-52087650. Caldas et al.

[2011] , Chen et al.

[2014] , and Jderu et al.

[2021] install fiber optic sensors axially in a tube, which does not measure the cross-flow distribution. Zhao et al.

[2018] measure the point-wise flow based on the vibration of a cantilever caused by flow using a fiber optic sensor. Bobb et al.

[1989] , Fang et al.

[1998] , and Zhang et al.

[2021] apply a fiber optic sensor to a hot-wire flowmeter but measure a point- wise flow.SUMMARY OF THE INVENTION

[0004] An exemplary embodiment can relate to a flow meter. The flow meter can include a tube having a tube first end, a tube second end, and a tube longitudinal axis (TL) extending from the tube first end to the tube second end. The flow meter can include a heater wire wound around at least a portion of the tube. The flow meter can include an optical fiber located within the tube, the optical fiber having an optical fiber first end, an optical fiber second end, and an optical fiber longitudinal axis (OFL) extending from the optical fiber first end to the optical fiber second end. TL is parallel to OFL The flow meter can be configured to be placed in an environment in which fluid will be allowed to or caused to flow over the tube in a direction that is not parallel to OFL

[0005] In some embodiments, the tube can be made of metal or metal alloy.

[0006] In some embodiments, the heater wire can be made of a metal or metal alloy.

[0007] In some embodiments, the flow meter includes an interrogator configured to interrogate the optical fiber.

[0008] In some embodiments, the interrogator can be an interferometer. Alternatively, the optical fiber can include plural Bragg diffraction gratings and the interrogator is a spectrometer

[0009] In some embodiments, the flow meter can include a current source or a voltage source configured to apply an electrical current or a voltage potential to the heater wire.

[0010] In some embodiments, the flow meter can include plural tubes, plural heater wires, and / or plural optical fibers.

[0011] An exemplary embodiment can relate to a flow meter. The flow meter can include a ceramic tube. The ceramic tube can have a heater wire lumen and an optical fiber lumen, the optical fiber lumen extending in a direction from a ceramic tube first end to a ceramic tube second end. The flow meter can include a heater wire located within the heater wire lumen. The flow meter can include an optical fiber located within the optical fiber lumen. The flow meter is configured to be placed in an environment in which fluid will be allowed to or caused to flow over the ceramic tube in a direction that is not parallel to the optical fiber.

[0012] In some embodiments, the heater wire can be made of a metal or metal alloy.

[0013] In some embodiments, the flow meter can include an interrogator configured to interrogate the optical fiber.

[0014] In some embodiments, the interrogator can be an interferometer. Alternatively, the optical fiber includes plural Bragg diffraction gratings and the interrogator is a spectrometer.

[0015] In some embodiments, the flow meter can include a current source or a voltage source configured to apply an electrical current or a voltage potential to the heater wire.

[0016] In some embodiments, the flow meter can include plural ceramic tubes, plural heater wires, plural optical fibers, plural heater wire lumen, and / or plural optical fiber lumen.

[0017] An exemplary embodiment can relate to a flow meter. The flow meter can include a tube having a tube first end, a tube second end, and a tube longitudinal axis (TL) extending from the tube first end to the tube second end. The flow meter can include a heater wire wound around at least a portion of the tube. The flow meter can include an optical fiber located within the tube, the optical fiber having an optical fiber first end, an optical fiber second end, and an optical fiber longitudinal axis (OFL) extending from the optical fiber first end to the optical fiber second end. The flow meter can include a ceramic coating covering at least a portion of the heater wire and at least a portion of the tube. TL is parallel to OFL. The flow meter can be configured to be placed in an environment in which fluid will be allowed to or caused to flow over the tube in a direction that is not parallel to OFL.

[0018] In some embodiments, the tube can be made of a metal or metal alloy.

[0019] In some embodiments, the heater wire can be made of a metal or metal alloy.

[0020] In some embodiments, the flow meter can include an interrogator configured to interrogate the optical fiber.

[0021] In some embodiments, the interrogator can be an interferometer. Alternatively, the optical fiber includes plural Bragg diffraction gratings and the interrogator is a spectrometer.

[0022] In some embodiments, the flow meter can include a current source or a voltage source configured to apply an electrical current or a voltage potential to the heater wire.

[0023] In some embodiments, the flow meter can include plural tubes, plural heater wires, and / or plural optical fibers.

[0024] An exemplary embodiment can relate to a flow meter. The flow meter can include a tube having a tube first end, a tube second end, and a tube longitudinal axis (TL) extending from the tube first end to the tube second end. The flow meter can include an optical fiber located within the tube, the optical fiber having an optical fiber first end, an optical fiber second end, and an optical fiber longitudinal axis (OFL) extending from the optical fiber first end to the optical fiber second end. The tube can be configured to be Joule heated by applying heat or electrical current to the tube, the optical fiber can be configured to be self-heated when light propagates though the optical fiber, or the optical fiber includes an electrically resistive coating configured to be Joule heated by applying electrical current to the electrically resistive coating. TL is parallel to OFL. The flow meter can be configured to be placed in an environment in which fluid will be allowed to or caused to flow over the tube in a direction that is not parallel to OFL.

[0025] Further features, aspects, objects, advantages, and possible applications of the present invention will become apparent from a study of the exemplary embodiments and examples described below, in combination with the Figures, and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, aspects, features, advantages and possible applications of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0027] FIG. 1 shows a schematic of an exemplary experimental setup.

[0028] FIGS. 2A, 2B, and 2C show exemplary flow meter designs.

[0029] FIG. 3 shows a heat map for hot wire identification.

[0030] FIG. 4 shows a heat map for air flow identification.

[0031] FIG. 5 shows a heat map for multiple flow rate identification.

[0032] FIG. 6 shows flow rate spatial profiles.

[0033] FIG. 7 shows a heat map for capillary tube flow rate.

[0034] FIG. 8 shows capillary tube spatial profiles.

[0035] FIG. 9 shows spectral shift at low temperatures.

[0036] FIG. 10 shows a flow plot at low temperatures.

[0037] FIG. 11 shows a flow plot at high temperatures.

[0038] FIG. 12 shows spectral shift at high temperatures.

[0039] FIG. 13 shows a heat map for discrete change in position.

[0040] FIG. 14 shows a heat map for continuous change in position.

[0041] FIG. 15 shows spectral profiles for low temperatures.

[0042] FIG. 16 shows a heat map for flow at high temperatures.DETAILED DESCRIPTION OF THE INVENTION

[0043] The following description is of exemplary embodiments that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of the present invention. The scope of the present invention is not limited by this description.

[0044] Referring to FIGS. 1-2, embodiments can relate to a flow meter 100. The flow meter 100 can include a tube(s) 102 having a length L, a heater wire(s) 104 either wound about the tube 102 or extending through the tube 102, and an optical fiber(s) 106 extending through the tube 102.An interrogator 108 can be used to interrogate the optical fiber 106. Electrical power can be supplied to the heater wire 104. In use, the flow meter 100 can be placed in an environment in which fluid (e.g., gas or liquid) is allowed to, caused to, or anticipated to flow over the tube 102. It is contemplated for the placement of the tube 102 within the environment to be such that the fluid flow is in a direction that is not parallel to the length L of the tube 102, but the fluid flow can be parallel to the length L of the tube 102. Optical fiber 106 generally have a core, cladding,and may also include a coating over the cladding. It is contemplated for the optical fiber 106 to have a core that includes pure silica or fluorine doped silica for applications involving exposing the flow meter 100 to ionizing radiation. The optical fiber 106 can have a germanium doped core, a pure silica core, or a fluorine doped silica core for applications not exposing the flow meter 100 to ionizing radiation.

[0045] An exemplary implementation of using an embodiment of the flow meter 100 follows. Electrical power (e.g., electrical current or voltage) can be applied to the heater wire 104. This can cause the heater wire 104 and / or the tube 102 to experience an increase in temperature. As the optical fiber 106 is extending through the tube 102, changes in temperature of the heater wire 104 and / or tube 102 can change the temperature experienced by the optical fiber 106 via conduction, convection, radiation, etc. Backscatteming profile of an optical fiber 106 changes based on temperature. Thus, a predetermined amount of electrical power (e.g., 0 Watts, 0.1 Watts, 0.2 Watts, etc.), a predetermined temperature, etc. can be used as a baseline for generating a baseline backscattering profile from the optical fiber 106. For instance, the optical fiber’s 106 backscattering profilecan be interrogated when 0.1 Watts, for example, is applied to the heater wire 104 to obtain and record a backscattering profile for the optical fiber 106. The backscattering profile can be a record of backscatter at one or more locations along the length of the optical fiber 106. The temperature of the tube 102 can be measured during application of the 0.1 Watts to the heater wire 104. The backscattering profile of the optical fiber 106 can then be correlated (e.g., via regression analysis, multivariate analysis, etc.) to the measured temperature of the tube 102. Any number of baselines generated - e.g., there can be a baseline for 0 Watts, a baseline for 0.1 Watts, a baseline for 0.2 Watts, a baseline for a tube 102 temperature of X, a baseline for a tube 102 temperature of Y, a baseline for a tube 102 temperature of Z, etc.

[0046] In some embodiments, plural Bragg diffraction gratings (e.g. 6 gratings, 10 gratings, etc.) can be present along the heated section of the optical fiber 106. With the Bragg grating, a reflection spectrum or a reflection spectrum profile(s) of the optical fiber 106 can be obtained, which shows reflection peaks associated with each grating. The optical data (backscattering, reflection spectrum, etc.) can be used to derive the temperature profile along the optical fiber 106. Repeated measurements as a function of time can be compared to one or more baseline measurements of the same nature, in known reference conditions. Thus, while exemplaryembodiments discussed herein my describe interrogation techniques for genertating backscattering profile(s), it is understood that other types of optical data can be used.

[0047] The tube 102 can then be placed in an environment in which fluid (e.g., gas or liquid) is allowed to, caused to, or anticipated to flow over the tube 102. The optical fiber 106 can be interrogated while in the environment to generate backscattering profile(s). The backscattering profile can be used to determine or estimate the temperature of the tube 102, the temperature of the environment, the temperature of one or more media that occupy the space of the environment, etc.. If / when fluid flows over the tube 102, the temperature of the tube 102 will change (e.g., the fluid can act as a coolant when flowing over the tube 102). Generally, the higher the fluid flow, the greater the change (e.g., decrease) in temperature the tube 102 will experience. For instance, as the flow rate or flow velocity of the fluid over the tube 102 increases, the temperature of the tube 102 can decrease. Thus, the optical fiber 106 can be interrogated while the tube 102 is within the environment and the backscattering profile(s) generated can be compared to the baseline(s). The flow rate or flow velocity of the fluid can then be determined via an exemplary formula (described later).

[0048] In the above exemplary implementation, the baseline(s) were generated via application of electrical power to the heater wire 104 while the tube 102 is outside of the environment. In the alternative, the baseline(s) can be generated via application of electrical power to the heater wire 104 while the flow meter 100 is within the environment.

[0049] It is contemplated for the tube 102 to be a member that spans a substantial volume of space of the environment (or at least span a space of interest) so that the fluid flow rate / velocity can be determined through the span of the environment (as opposed to at a single point). It is also contemplated for the entire length of the optical fiber 106 to be able to be interrogated so that a backscattering profile can be generated as a function of position along the optical fiber 106. Thus, any number of locations along the optical fiber 106 can be interrogated. This can facilitate generating a fluid flow rate / velocity distribution across the span of the environment, across a span of interest of the environment, etc. For instance, fluid flow rate / velocity at one point in the environment may be different from fluid flow rate / velocity at a different point; yet, the flow meter 100 can effectively determine these differentiated fluid flow rates / velocities.

[0050] It is contemplated for the heater wire 104 to extend the entire length of the tube 102, but it need not to. It is also contemplated for the optical fiber 106 to span the entire length of the tube 102, but it need not to. It is also contemplated for the heater wire 104 to span the same length of the tube 102 as that of the optical fiber 106, but it need not to. While it is contemplated for the entire length of the optical fiber 106 to be able to be interrogated, it is understood that only a portion of the length of the optical fiber 106, a single point of the optical fiber 106, a segment(s) of the optical fiber 106 etc. may be interrogated. The optical fiber 106 can be interrogated continuously, periodically, at a predetermined rate, at predetermined times, on an on-demand manner, as determined by an algorithm, as determined by an artificial intelligence model, etc.

[0051] It is contemplated for the tube 102 to be an elongate member having a length L; however, the tube 102 can be any shape. The tube 102 can be a hollow member, a solid member, etc. It is contemplated for the optical fiber 106 to span a length of the tube 102 that is a straight path, but the optical fiber 106 can span a curved path, spiral path, etc.

[0052] The flow meter 100 can include or be operatively associated with a processor 112. The processor 112 can be programmed to generate the backscattering profile(s), generate the baseline(s), perform the analysis, determine flow rates / velocities, determine interrogation schemes, control operating parameters of the interrogator 108, control operating parameters of the electrical power source 110, etc. The processor 112 can be part of the interrogator 108 or be in communication with a processor of the interrogator 108. The processor 112 can also be in communication with the electrical power source 112 (e.g., electrical current source, voltage source) that supplies electrical power to the heater wire 104.

[0053] Any of the processors 112 disclosed herein can be part of or in communication with a machine (e.g., a computer device, a logic device, a circuit, an operating module (hardware, software, and / or firmware), etc.). The processor 112 can be hardware (e.g., processor, integrated circuit, central processing unit, microprocessor, core processor, computer device, etc.), firmware, software, etc. configured to perform operations by execution of instructions embodied in computer program code, algorithms, program logic, control, logic, data processing program logic, artificial intelligence programming, machine learning programming, artificial neuralnetwork programming, automated reasoning programming, etc. The processor 112 can receive, process, and / or store data related to backscatter, for example.

[0054] Any of the processors 112 disclosed herein can be a scalable processor, a parallelizable processor, a multi-thread processing processor, etc. The processor 112 can be a computer in which the processing power is selected as a function of anticipated network traffic (e.g. data flow). The processor 112 can include any integrated circuit or other electronic device (or collection of devices) capable of performing an operation on at least one instruction, which can include a Reduced Instruction Set Core (RISC) processor, a Complex Instruction Set Computer (CISC) microprocessor, a Microcontroller Unit (MCU), a CISC-based Central Processing Unit (CPU), a Digital Signal Processor (DSP), a Graphics Processing Unit (GPU), a Field Programmable Gate Array (FPGA), etc. The hardware of such devices may be integrated onto a single substrate (e.g., silicon "die"), or distributed among two or more substrates. Various functional aspects of the processor 112 may be implemented solely as software or firmware associated with the processor 112.

[0055] The processor 112 can include one or more processing or operating modules. A processing or operating module can be a software or firmware operating module configured to implement any of the functions disclosed herein. The processing or operating module can be embodied as software and stored in memory 114, the memory 114 being operatively associated with the processor 112. A processing module can be embodied as a web application, a desktop application, a console application, etc.

[0056] The processor 112 can include or be associated with a computer or machine readable medium. The computer or machine readable medium can include memory 114. Any of the memory 114 discussed herein can be computer readable memory configured to store data. The memory 114 can include a volatile or non-volatile, transitory or non-transitory memory, and be embodied as an in-memory, an active memory, a cloud memory, etc. Examples of memory 114 can include flash memory, Random Access Memory (RAM), Read Only Memory (ROM), Programmable Read only Memory (PROM), Erasable Programmable Read only Memory (EPROM), Electronically Erasable Programmable Read only Memory (EEPROM), FLASH- EPROM, Compact Disc (CD)-ROM, Digital Optical Disc DVD), optical storage, optical medium, a carrier wave, magnetic cassettes, magnetic tape, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by the processor 112.

[0057] The memory 114 can be a non-transitory computer-readable medium. The term "computer-readable medium" (or "machine-readable medium") as used herein is an extensible term that refers to any medium or any memory, that participates in providing instructions to the processor 112 for execution, or any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). Such a medium may store computer-executable instructions to be executed by a processing element and / or control logic, and data which is manipulated by a processing element and / or control logic, and may take many forms, including but not limited to, non-volatile medium, volatile medium, transmission media, etc. The computer or machine readable medium can be configured to store one or more instructions thereon. The instructions can be in the form of algorithms, program logic, etc. that cause the processor to execute any of the functions disclosed herein.

[0058] Embodiments of the memory 114 can include a processor module and other circuitry to allow for the transfer of data to and from the memory 114, which can include to and from other components of a communication system. This transfer can be via hardwire or wireless transmission. The communication system can include transceivers, which can be used in combination with switches, receivers, transmitters, routers, gateways, wave-guides, etc. to facilitate communications via a communication approach or protocol for controlled and coordinated signal transmission and processing to any other component or combination of components of the communication system. The transmission can be via a communication link. The communication link can be electronic-based, optical-based, opto-electronic-based, quantumbased, etc. Communications can be via Bluetooth, near field communications, cellular communications, telemetry communications, Internet communications, etc.

[0059] Transmission of data and signals can be via transmission media. Transmission media can include coaxial cables, copper wire, fiber optics, etc. Transmission media can also take the form of acoustic or light waves, such as those generated during radio-wave and infrared data communications, or other form of propagated signals (e.g., carrier waves, digital signals, etc.).

[0060] Any of the processors 112 can be in communication with other processors of other devices (e.g., a computer device, a computer system, a laptop computer, a desktop computer,etc.). For instance, the processor 112 can be in communication with a processor of a computer device, the processor of the computer device can be in communication with the processor of a display, etc. The display can generate outputs related to the determined flow rates / velocities, temperatures, electrical power supplied to the heater wire, other operating parameters, etc. Any of the processors 112 can have transceivers or other communication devices / circuitry to facilitate transmission and reception of wireless signals. Any of the processors 112 can include an Application Programming Interface (API) as a software intermediary that allows two or more applications to talk to each other. Use of an API can allow software of the processor 112 to communicate with software of the processor 112 of the other device(s), for example.

[0061] Referring to FIG. 2A, an exemplary flow meter 100 can include a tube 102 (e.g., ceramic, metal, metal alloy, etc.). In the embodiment of FIG. 2A, the tube 102 can be metal or metal alloy (e.g., stainless steel). The tube 102 can be an elongate member having a length L that spans a longitudinal axis Laxis of the elongate member.

[0062] The flow meter 100 can include a heater wire 104. The heater wire 104 can be metal or metal alloy (e.g., nickel-chrome, copper, etc.). The heater wire 104 is bound, affixed, attached, connected to, etc. to the tube 102. For instance, the heater wire 104 can be wound about an outer surface of the tube 102 (e.g., wound about at least a portion of the tube 102) . It is contemplated for the heater wire 104 to be wound about an outer surface of the tube 102 so as to span a length of the tube 102 in a direction parallel to the tube’s 102 longitudinal axis. It is further contemplated for the heater wire 104 to span the entire length of the tube 102 or at least a substantial portion of the entire length of the tube 102. How much of the length of the tube 102 the heater wire 104 spans, how the heater wire 104 is bound, affixed, etc. to the tube 102, the pitch of the winding, the number of heater wires 104, the material of the heater wire 104, etc. can be selected based on design criteria, optimization, cost-benefit analyses, etc.

[0063] The flow meter 100 can include an optical fiber 106 (e.g., silica (SiO2)-based, plasticbased, fluoride-based, etc.). The optical fiber 106 is bound, affixed, attached, connected to, etc. to the tube 102. It is contemplated for the optical fiber 106 to be located within the tube 102. For instance, the tube 102 can have one or more optical fiber lumen 118 (e.g., channel, conduit, etc.) that facilitate placement and retention of one or more optical fibers 106. It is contemplated for the optical fiber 106 to span a length of the tube 102 in a direction parallel to the tube’s 102longitudinal axis Laxis. It is further contemplated for the optical fiber 106 to span the entire length of the tube 102 or at least a substantial portion of the entire length of the tube 102. It is further contemplated for the optical fiber 106 to at least span a portion of the tube 102 that the heater wire 104 spans. How much of the length of the tube 102 the optical fiber 106 spans, how the optical fiber 106 is bound, affixed, etc. to the tube 102, the number of optical fibers 106, the material of the optical fiber 106, the configuration (e.g., size and number of cores, claddings, coatings, jackets, etc.) of the optical fiber 106, etc. can be selected based on design criteria, optimization, cost-benefit analyses, etc.

[0064] The flow meter 100 can include an electrical power source 110 (e.g., an electrical current source or generator, an electrical voltage source or generator, etc.). The electrical power source 110 can be electrically connected to the heater wire 104 such that electrical current and / or electrical voltage potential can be selectively supplied to the heater wire 104. The electrical power source 110 can be a constant power source, a variable power source, etc.

[0065] The flow meter 100 can include a light source 116. The light source 116 can be a laser, light emitting diode, a fiber optic backlight, etc. The light source 116 can be coupled to a first end 106a of the optical fiber 106.

[0066] The flow meter 100 can include an interrogator 108 (e.g., interferometer, fiber Bragg grating (FBG), spectrometer, etc.). The interrogator 108 can be configured to interrogate (e.g., measure, sense, and / or obtain backscatter information (e.g., backscattering profile(s)) about electromagnetic radiation propagating through the optical fiber 106. As a non-limiting example, the interrogator 108 can be coupled to a second end 106b of the optical fiber 106.

[0067] In use, tube 102 can be positioned in an environment through which fluid will be caused to flow, allowed to flow, or is anticipated to flow. It is contemplated for the direction of the fluid flow to be perpendicular, or at least substantially perpendicular, to the longitudinal axis Laxis of the tube 102. However, the direction of the fluid flow can be at any direction with respect to the longitudinal axis Laxis of the tube 102, can be a constant direction, can be a variable direction, can be multiple directions (e.g., some currents can be in one direction, while some currents are at a different direction), etc.

[0068] It is contemplated for the tube 102 to be held stationary within the environment, but the tube 102 can be moved (e.g., changed in pitch, yaw, roll, caused to reciprocate along its longitudinal axis, caused to oscillate, etc.).

[0069] If / when fluid flows over or passed the tube 102, the temperature of the tube 102 will change. For instance, as fluid flows (as compared to no fluid flow), the temperature of the tube 102 will decrease. The temperature will increasingly decrease as the rate or velocity of fluid flow increases. As the temperature of the tube 102 changes, the temperature of the optical fiber 106 also changes. This change in temperature will generate spectral shift(s) in the spectral emission(s) measured by the interrogator 108. The spectral shift(s) can be processed by the processor 112 and / or stored in memory 114 for later processing. The memory 114 can also have spectral data related to the baseline(s) stored thereon (e.g., stored as a data table). The processor 112 can compare the spectral shift(s) to the spectral data in the memory 114 to determine or estimate (using an exemplary formula described later) the flow rate / velocity of fluid.

[0070] While exemplary embodiments describe and illustrate a system using one flow meter 100, there can be any number of flow meters 100 used. In addition, there can be any number of tubes 102 used for a flow meter 100, any number of heater wires 104 used for a tube 102, any number of optical fibers 106 used for a tube 102, etc.

[0071] Referring to FIG. 2B, an exemplary flow meter 100 can include a tube 102 (e.g., ceramic, metal, metal alloy, etc.). In the embodiment of FIG. 2B, the tube 102 can be metal or metal alloy (e.g., stainless steel). The tube 102 can be an elongate member having a length L that spans a longitudinal axis Laxis of the elongate member. The flow meter 100 can include a heater wire 104. The heater wires 104 can be metal or metal alloy (e.g., nickel -chrome, copper, etc.). The heater wire 104 is bound, affixed, attached, connected to, etc. to the tube 102. For instance, the heater wire 104 can be wound about an outer surface of the tube 102 (e.g., wound about at least a portion of the tube 102) . It is contemplated for the heater wire 104 to be wound about an outer surface of the tube 102 so as to span a length of the tube 102 in a direction parallel to the tube’s 102 longitudinal axis Laxis. It is further contemplated for the heater wire 104 to span the entire length of the tube 102 or at least a substantial portion of the entire length of the tube 102. How much of the length of the tube 102 the heater wire 104 spans, how the heater wire 104 is bound, affixed, etc. to the tube 102, the pitch of the winding, the number of heater wires 104, thematerial of the heater wire 104, etc. can be selected based on design criteria, optimization, costbenefit analyses, etc.

[0072] The flow meter 100 can include a ceramic coating (e.g., high temperature ceramic paint) placed over at least a portion of the heater wire 104 and / or at least a portion of the tube 102. It is contemplated for the ceramic coating to be placed over the entire heater wire 104 and portion(s) of the tube 102 about which the heater wire 104 is wound. How much of the length of the heater wire 104 to cover with the ceramic coating, how thick the coating, the type of material used for the coating, whether to use the same type or thickness of coating for one section of the tube 102 as is used for another section of the tube 102, etc. can be selected based on design criteria, optimization, cost-benefit analyses, etc.

[0073] The flow meter 100 can include an optical fiber 106 (e.g., silica (SiO2)-based, plasticbased, fluoride-based, etc.). The optical fiber 106 is bound, affixed, attached, connected to, etc. to the tube 102. It is contemplated for the optical fiber 106 to be located within the tube 102. For instance, the tube 102 can have one or more optical fiber lumen 118 (e.g., channel, conduit, etc.) that facilitate placement and retention of one or more optical fibers 106. It is contemplated for the optical fiber 106 to span a length of the tube 102 in a direction parallel to the tube’s 102 longitudinal axis Laxis. It is further contemplated for the optical fiber 106 to span the entire length of the tube 102 or at least a substantial portion of the entire length of the tube 102. It is further contemplated for the optical fiber 106 to at least span a portion of the tube 102 that the heater wire 104 spans. How much of the length of the tube 102 the optical fiber 106 spans, how the optical fiber 106 is bound, affixed, etc. to the tube 102, the number of optical fibers 106, the material of the optical fiber 106, the configuration (e.g., size and number of cores, claddings, coatings, jackets, etc.) of the optical fiber 106, etc. can be selected based on design criteria, optimization, cost-benefit analyses, etc.

[0074] The flow meter 100 can include an electrical power source 110 (e.g., an electrical current source or generator, an electrical voltage source or generator, etc.). The electrical power source 110 can be electrically connected to the heater wire 104 such that electrical current and / or electrical voltage potential can be selectively supplied to the heater wire 104. The electrical power source 110 can be a constant power source, a variable power source, etc.

[0075] The flow meter 100 can include a light source 116. The light source 116 can be a laser, light emitting diode, a fiber optic backlight, etc. The light source 116 can be coupled to a first end 106a of the optical fiber 106.

[0076] The flow meter 100 can include an interrogator 108 (e.g., interferometer, fiber Bragg grating (FBG), spectrometer, etc.). The interrogator 108 can be configured to interrogate (e.g., measure, sense, and / or obtain backscatter information (e.g., backscattering profile(s)) about electromagnetic radiation propagating through the optical fiber 106. As a non-limiting example, the interrogator 108 can be coupled to a second end 106b of the optical fiber 106.

[0077] In use, tube 102 can be positioned in an environment through which fluid will be caused to flow, allowed to flow, or is anticipated to flow. It is contemplated for the direction of the fluid flow to be perpendicular, or at least substantially perpendicular, to the longitudinal axis Laxisof the tube 102. However, the direction of the fluid flow can be at any direction with respect to the longitudinal axis Laxis of the tube 102, can be a constant direction, can be a variable direction, can be multiple directions (e.g., some currents can be in one direction, while some currents are at a different direction), etc.

[0078] It is contemplated for the tube 102 to be held stationary within the environment, but the tube 102 can be moved (e.g., changed in pitch, yaw, roll, caused to reciprocate along its longitudinal axis, caused to oscillate, etc.).

[0079] If / when fluid flows over or passed the tube 102, the temperature of the tube 102 will change. For instance, as fluid flows (as compared to no fluid flow), the temperature of the tube 102 will decrease. The temperature will increasingly decrease as the rate or velocity of fluid flow increases. As the temperature of the tube 102 changes, the temperature of the optical fiber 106 also changes. This change in temperature will generate spectral shift(s) in the spectral emission(s) measured by the interrogator 108. The spectral shift(s) can be processed by the processor 112 and / or stored in memory 114 for later processing. The memory 114 can also have spectral data related to the baseline(s) stored thereon (e.g., stored as a data table). The processor 112 can compare the spectral shift(s) to the spectral data in the memory 114 to determine or estimate (using an exemplary formula described later) the flow rate / velocity of fluid.

[0080] While exemplary embodiments describe and illustrate a system using one flow meter 100, there can be any number of flow meters 100 used. In addition, there can be any number oftubes 102 used for a flow meter 100, any number of heater wires 104 used for a tube 102, any number of optical fibers 106 used for a tube 102, etc.

[0081] Referring to FIG. 2C, an exemplary flow meter 100 can include a tube 102 (e.g., ceramic, metal, metal alloy, etc.). In the embodiment of FIG. 2C, the tube 102 can be ceramic. The tube 102 can be an elongate member having a length L that spans a longitudinal axis Laxis of the elongate member. The tube 102 can have one or more heater wire lumen 120. The heater wire lumen 120 can be a channel, conduit, etc. formed within the tube 102 can configured to facilitate placement and retention of a heater wire 104. It is contemplated for the heater wire lumen 120 to extent the length of the tube 102, but it need not to. It is further contemplated for the heater wire lumen 120 to span the length of the tube 102 in a direction that is parallel with that of the longitudinal axis Laxis of the tube 102, but it need not to. The heater wire lumen 120 can be straight, curved, in a sinusoidal formation, a spiral formation, etc. There can be any number of heater wire lumen 120. Any one heater wire lumen 120 can have the same or different configuration, length, profile, etc. as that of another heater wire lumen 120.

[0082] The flow meter 100 can include a heater wire 104. The heater wire 104 can be metal or metal alloy (e.g., nickel-chrome, copper, etc.). The heater wire 104 can be routed through the tube 102 via the heater wire lumen 120 - e.g., the heater wire 104 can be located within the heater wire lumen 120. It is contemplated for the heater wire 104 to be routed through the tube 102 so as to span a length of the tube 102 in a direction parallel to the tube’s 102 longitudinal axis. It is further contemplated for the heater wire 104 to span the entire length of the tube 102 or at least a substantial portion of the entire length of the tube 102. How much of the length of the tube 102 the heater wire 104 spans, the number of heater wires 104, the material of the heater wire 104, etc. can be selected based on design criteria, optimization, cost-benefit analyses, etc.

[0083] The tube 102 can have one or more optical fiber lumen 118. The optical fiber lumen 118 can be a channel, conduit, etc. formed within the tube 102 can configured to facilitate placement and retention of an optical fiber 106. It is contemplated for the optical fiber lumen 118 to extent the length of the tube 102, but it need not to. It is further contemplated for the optical fiber lumen 118 to span the length of the tube 102 in a direction that is parallel with that of the longitudinal axis of the tube 102, but it need not to. The optical fiber lumen 118 can be straight, curved, in a sinusoidal formation, a spiral formation, etc. There can be any number of opticalfiber lumen 118. Any one optical fiber lumen 118 can have the same or different configuration, length, profile, etc. as that of another optical fiber lumen 118.

[0084] The flow meter 100 can include an optical fiber 106 (e.g., silica (SiO2)-based, plasticbased, fluoride-based, etc.). The optical fiber 106 can be routed through the tube 102 via the optical fiber lumen 118 - e.g., the optical fiber 106 can be located within the optical fiber lumen 118. It is contemplated for the optical fiber 106 to span a length of the tube 102 in a direction parallel to the tube’s 102 longitudinal axis. It is further contemplated for the optical fiber 106 to span the entire length of the tube 102 or at least a substantial portion of the entire length of the tube 102. It is further contemplated for the optical fiber 106 to at least span a portion of the tube 102 that the heater wire 104 spans. How much of the length of the tube 102 the optical fiber 106 spans, the number of optical fibers 106, the material of the optical fiber 106, the configuration (e.g., size and number of cores, claddings, coatings, jackets, etc.) of the optical fiber 106, etc. can be selected based on design criteria, optimization, cost-benefit analyses, etc.

[0085] The flow meter 100 can include an electrical power source 110 (e.g., an electrical current source or generator, an electrical voltage source or generator, etc.). The electrical power source 110 can be electrically connected to the heater wire 104 such that electrical current and / or electrical voltage potential can be selectively supplied to the heater wire 104. The electrical power source 110 can be a constant power source, a variable power source, etc.

[0086] The flow meter 100 can include a light source 116. The light source 116 can be a laser, light emitting diode, a fiber optic backlight, etc. The light source 116 can be coupled to a first end 106a of the optical fiber 106.

[0087] The flow meter 100 can include an interrogator 108 (e.g., interferometer, fiber Bragg grating (FBG), spectrometer, etc.). The interrogator 108 can be configured to interrogate (e.g., measure, sense, and / or obtain backscatter information (e.g., backscattering profile(s))) about electromagnetic radiation propagating through the optical fiber 106. As a non-limiting example, the interrogator 108 can be coupled to a second end 106b of the optical fiber 106.

[0088] In use, tube 102 can be positioned in an environment through which fluid will be caused to flow, allowed to flow, or is anticipated to flow. It is contemplated for the direction of the fluid flow to be perpendicular, or at least substantially perpendicular, to the longitudinal axis of the tube 102. However, the direction of the fluid flow can be at any direction with respect to thelongitudinal axis of the tube 102, can be a constant direction, can be a variable direction, can be multiple directions (e.g., some currents can be in one direction, while some currents are at a different direction), etc.

[0089] It is contemplated for the tube 102 to be held stationary within the environment, but the tube 102 can be moved (e.g., changed in pitch, yaw, roll, caused to reciprocate along its longitudinal axis, caused to oscillate, etc.).

[0090] If / when fluid flows over or passed the tube 102, the temperature of the tube 102 will change. For instance, as fluid flows (as compared to no fluid flow), the temperature of the tube 102 will decrease. The temperature will increasingly decrease as the rate or velocity of fluid flow increases. As the temperature of the tube 102 changes, the temperature of the optical fiber 106 also changes. This change in temperature will generate spectral shift(s) in the spectral emission(s) measured by the interrogator 108. The spectral shift(s) can be processed by the processor 112 and / or stored in memory 114 for later processing. The memory 114 can also have spectral data related to the baseline(s) stored thereon (e.g., stored as a data table). The processor 112 can compare the spectral shift(s) to the spectral data in the memory 114 to determine or estimate (using an exemplary formula described later) the flow rate / velocity of fluid.

[0091] While exemplary embodiments describe and illustrate a system using one flow meter 100, there can be any number of flow meters 100 used. In addition, there can be any number of tubes 102 used for a flow meter 100, any number of heater wire lumen 120 and heater wires 104 used for a tube 102, any number of optical fiber lumen 118 and optical fibers 106 used for a tube 102, etc.

[0092] It is understood that the flow meter 100 is not limited to the embodiments disclosed. For instance, a flow meter 100 can be configured to have a heater wire 104 wound about an outer surface of the tube 102 and have a heater wire 104 extending though a heater wire lumen 120 of the tube 102. As another example, a flow meter 100 can have one heater wire wound about a surface of the tube 102 that has a ceramic coating and another heater wire 104 wound about the tube 102 without a ceramic coating. It is also understood that embodiments of the flow meter 100 can be used as a system or a kit in which multiple flow meters 100 can be used in the same environment. Any one flow meter 100 can be configured the same as or different from another flow meter 100.

[0093] Exemplary embodiments discuss a flow meter 100 having one or more heater wires 104 to heat the tube 102 and / or optical fiber 106. However, some embodiments can omit the heater wire 104. For instance, the tube 102 itself can be configured to be Joule heated by applying heat or electrical current to the tube 102. In this embodiment, the tube 102 can made of metal or metal alloy or coated with metal or metal alloy to facilitate heat transfer when heat its applied or heat generation when electrical current is applied. As another example, the optical fiber 106 can be configured to be self-heated when light (e.g., light having a wavelength that differs from a wavelength for probing the optical fiber 106) propagates though the optical fiber 106. As another example, the optical fiber 106 can include an electrically resistive coating (e.g., metal alloy) formed thereon which is configured to be Joule heated by applying electrical current to the electrically resistive coating).

[0094] EXAMPLES

[0095] The following examples include exemplary implementations and test results of embodiments disclosed herein.

[0096] The process of determining fluid flow rates has applications in a variety of settings. In nuclear applications, such as advanced fission reactors or fusion tokamak blankets, these instruments have the additional requirement of tolerating harsh environmental factors, such as high temperatures, corrosive chemistry, and ionizing radiation. This paper shows results related to development and experimental demonstration of flow measurements using a hot wire based on optical fibers. More specifically, we report on the development of several fiber optic hot-wire designs, including experimental results at various temperatures, validation against conventional techniques, and pros and cons of each conceptual design. Experimental results obtained using this approach show the ability to measure flow rates at fluid temperatures as high a 460 °C, as well as spatially resolve velocity profiles.

[0097] Introduction.

[0098] The process of determining fluid flow rates has applications in a variety of settings. In nuclear applications, such as advanced fission reactors or fusion tokamak blankets, these instruments have the additional requirement of tolerating harsh environmental conditions, such as high temperatures, corrosive chemistry, and ionizing radiation. Current forms of measurement under these conditions include ultrasonic and thermal flow meters.Conventional hot-wire flow meters have widespread use due to their relatively simple design, while optical fibers are able to work under extreme conditions. In addition, conventional hot wires are only capable of an integrated measurement over a certain width, yielding effectively a point-wise measurement. Optical fibers interrogated via Raleigh backscattering have the distinct advantage of being able to take distributed measurements over an array of positions with a single fiber, with sub-millimeter spatial resolution, which can create an accurate representation of velocity distributions. Recently, Cabral et al. performed a feasibility test to apply a fiber-optic distributed temperature sensor to hot-wire concept in a heated stainless steel tube. They also reported two previous works done by Chen et al. [2] and Ohanian et al. Although these efforts proved the concept, those sensors were tested at relatively low temperatures such as below 200 °C. Advanced nuclear reactors such as sodium-cooled fast reactors, molten salt reactors, high-temperature gas-cooled reactors, heat pipe microreactors, or fusion tokamak blankets, however, are targeting temperatures from 500 °C to greater than 800 °C.

[0099] The designs in the present study are tested at high temperatures and compared to conventional techniques or theoretical velocity profiles.

[0100] There is a lack of local velocity data of high-temperature coolant channels in fission and fusion reactors. In sodium-cooled heat pipe reactors, no experimental velocity data in the sodium vapor core region of the heat pipe is available. For molten salt, there is a recent flow rate measurement in a molten salt loop using an ultrasonic flow meter by Arora et al. For rough estimations, thermocouples were used by Arora et al. and Britsch et al. However, the ultrasound flow meter has a geometric limit to circular tubes, and thermocouple methods showed large uncertainties. For sodium fast reactors to evolve past a handful of small individual projects and into viable generation IV deployment much analysis is needed. Velocity profiles are not well defined around wrapped rod bundles, at core inlets and outlets, as well as in the coolant loop piping. Fully characterizing these flow regimes is crucial to the approval and licensing of these designs. The complex flow patterns of fusion breeding blankets are being modeled and studied extensively. Complicated by high magnetic fields, thermal gradients, and large inertial and viscous effects, these flow structures are difficult tostudy using conventional means and most experiments have only investigated these flow conditions in simplified geometries.

[0101] As part of the effort to develop a flow sensor for those advanced fission and fusion reactor environments, this work aims at investigating the effectiveness of measuring flow using a hot wire based on optical fibers. More specifically, we report on the development of several fiber-optic hot-wire designs, including experimental results at various temperatures, validation against conventional techniques, and pros and cons of each conceptual design.

[0102] The principle of hot-wire anemometry is to correlate the cooling of a heated wire to the velocity of a fluid flow that acts as a coolant for the hot wire. The general technique can be further classified into constant current anemometry (CCA), constant voltage anemometry (CVA), and constant temperature anemometry (CTA). Although the present concept can be operated at constant voltage, it does not have to be categorized by the above classification because it measures the temperature of the heated tube directly.

[0103] Once the temperature distribution is known, the local resistance distribution (resistance profile) can be determined, and the local power, as well. By assuming that an equilibrium condition can be achieved quickly and the convective heat transfer is dominant, the power generated by the heated tube and the Nusselt number for the forced convection can be used to finally determine the flow velocity. kfWe = VI = Qconv = hA(Tw- T f) = Nu—A(Tw - Tf) where Weis the power generated by Joule heating, V is the voltage applied to the wire heater, I is the current through the wire heater, Qconvis the convective heat transfer, h is the heat transfer coefficient, A is the sensor tube surface area, Tlvis the sensor wall temperature, Tf is the fluid temperature, Nu is the Nusselt number, kf is the fluid thermal conductivity, and d is the sensor tube diameter.

[0104] The current concept of hot wire consists of an electrically conducting material (wire heater) that heats up a structure (sensor tube) housing one or more optical fibers. The embedded optical fibers can then measure the temperature distribution at baseline conditions. Convective heat transfer to the fluid causes a change in the temperature distribution read bythe optical fibers, which can in turn be calibrated into a velocity profile. As mentioned above, optical fiber distributed sensors have been used in a variety of applications, and have shown to be robust over large temperature spans, from cryogenic to high temperatures, and to have great promise to be used in presence of ionizing radiation. This work tests the validity of several different methods of producing heat via a conducting material, as well as configurations of optical fibers and housing materials and structures.

[0105] Technical approach.

[0106] It is worth noting that the hot wire designs that are illustrated in this section are only those that wereused to produce the results included in this manuscript. A broader variety of different embodiments, however, were conceived and will be the subject of future experiments.

[0107] Hot wire designs.

[0108] As part of this work, three different hot wire designs were developed, fabricated and tested. All hot wires employ nichrome wire as the heating element, while the tube and the optical fibers vary by design. The optical fiber used for all designs is an SMF-28 Ultra single mode fiber, and was used in conjunction with a LUNA ODiSI-B interrogator. The design specifications for the three hot wire embodiments are identified in FIGS. 2A, 2B, and 2C including: the low-temperature (LT) tube length (LLT), outer diameter (ODLT), inner diameter (IDLT), fiber diameter (Du), heating wire length (LLHW) and diameter (DLHW); the high- temperature (HT) tube length LHT), outer diameter (ODHT), inner diameter (IDHT), fiber diameter (DHF), heating wire length (LHHW) and diameter (DHHW); and the ceramic capillary tube length (LCT), outer diameter (ODCT), inner diameter (fDCT).

[0109] Experimental procedures.

[0110] The first hot wire design (the low-temperature metal tube sensor in FIG. 2A used a length of 16.5 cm of nickel chromium heater wire wound around a length of 7.6 cm of hollow stainless-steel tube. An optical fiber was then placed at the center of the tube. The first measurement consisted in recording the spectral shift generated by the heater wire alone, with no fluid flow. To do so, 0.1 W of heat was applied to a steel tube with a fiber in it for 40 seconds. Once the heater wire was recognized, fluid flow was added to the system. A 2 mm diameter tube directed 20 °C airflow orthogonally against the stainless-steel tube. Aconventional hot wire was used to calibrate the velocity of this airflow. This power produced a hot wire temperature of 65 °C. While the heater wire applied a constant heat of 0.15 W, airflow was applied for 70 seconds. Once it was clear that it was possible to measure airflow with the fiber, its ability to measure changes in flow rate was evaluated. A higher airflow rate was applied for 60 seconds, and then a lower flow rate was applied for 20 seconds, during the same experimental run.

[0111] The second hot wire design in FIG. 2C) used a multi-bore capillary alumina ceramic tube with 4 holes, two containing a single optical fiber and two containing a nickel chromium heating wire. Similarly to the experiments involving the previous design, the heating wire was energized with 0.15 W of power and airflow was orthogonal to the axis of the tube, in this case for 20 seconds. The two sensor holes were situated on a plane orthogonal to both the airflow and the axis, such that they were equidistant from the airflow tube. The same low temperature experiments were used to test this design as the first design.

[0112] The third design, comprising a high temperature metal tube as shown in FIG. 2B, was able to perform well at both high and low temperatures. As the insulated heating wire was not able to withstand high temperatures, uninsulated heating wire was wrapped around a stainless- steel tube coated in high temperature ceramic paint. This layer electrically insulated the wire from the steel tube without significantly preventing the transfer of heat to the fiber at the center of the tube. This design was also tested at low temperature to have a comparison for high temperature tests. To simulate high temperature flow, a heat gun was utilized to apply a series of six different flow rates on intervals of 20 seconds. The temperature of the airflow was 460 °C, while the hot wire itself had a temperature of near 550 °C. One area of note is that while temperature compensation was not implemented in these designs, it is the subject of current and future work.

[0113] In all experiments, the hot wire was energized by means of a KEPCO DC power supply that was controlled remotely using a Lab VIEW software, while the current flowing through the heating wire was measured independently via a shunt resistor. This ensures that the power being dissipated by the hot wire can be determined precisely without relaying on a current or voltage reading of the power supply. The optical fiber was interrogated viaLUNA’s ODiSI B interrogator, obtaining a spectral shift with a 2.6 mm spatial resolution and a 50 Hz measurement rate.

[0114] Results.

[0115] As shown in FIG. 3 for the low-temperature metal tube hot-wire, a clear spectral shift distribution was registered between about 1 and 7 cm, indicating that a temperature profile was generated by the hot wire. More specifically, the spectral shift decreases due to an increase in temperature, and the length of fiber that experiences this spectral shift matches the location and length of the hot wire precisely. Heat maps are used to show the spectral shift dependence on time and position, allowing the change in temperature distribution over time to be displayed. As shown by the map in FIG. 4, there is a clear increase in spectral shift at the center of the tube, corresponding to a decrease in temperature from the incident airflow. Note that the position axis in FIG. 4 only spans the length of the hot wire. These initial results shown in FIGS. 3 and 4 are thought to be qualitative in nature, but they indeed show that the spatial distribution of airflow can be traced using this technique.

[0116] The results from the higher airflow rate for 60 seconds and then a lower flow rate for 20 seconds are presented in FIG. 5, where a clear difference can be seen between the two areas of increase in spectral shift. The lower airflow rate causes a decrease in convection of heat at the surface of the steel tube, and this decrease in heat loss is reflected in a lower spectral shift.

[0117] FIG. 6 shows the spectral shift as a function of position during the higher flow rate (at 100 s) and during the lower flow rate (at 180 s). Due to the similarities in spatial profile for the two flow rates, it may be possible to correlate these distributions with flow velocity. However, it is possible that the high thermal conductivity of the steel tube caused the profile to appear more uniform. Nevertheless, this thermal conductivity does provide a faster response time, which can be useful in several scenarios.

[0118] FIG. 7 shows a spectral shift map generated for the second design, the ceramic tube hot-wire in FIG. 2C, while FIG. 8 shows a spatial profile taken at 40 seconds, corresponding to a time when the flow had created an approximately equilibrium spectral shift distribution. In this design, the temperature distribution (measured here as spectral shift), can be seen twice by the same optical fibers at different regions (from 0.0-0.1 m and from 0.2-0.3 m) and isapproximately the same, consistent with the symmetries of this design. Additionally, the ability to record the temperature profile in two positions within the hot wire cross section could enable multidimensional analysis of the flow. This design also allows for more uniform wire spacing and heat distribution.

[0119] The result of the series of six different flow rates, applied on intervals of 20 seconds, are shown in FIG. 9, with the spectral shift is plotted as a function of time at the position of 0.151 meters. Before the hot wire is exposed to any air flow, the spectral shift increases as a result of the hot wire being heated to the 65 °C operating temperature for this low temperature experiment, attaining an average spectral shift of 55 GHz. After this there are six distinct decreases in spectral shift for each flow rate (with a fluid temperature of 20 °C), increasing in magnitude as the flow rate increases and cools the hot wire correspondingly. This can be seen more clearly in FIG. 10, which displays the spatial average maximum spectral shift as a function of flow rate, in meters per second. The spatial average maximum was found by finding the time where a maximum spectral shift occurred and then averaging this over several positions on the hot wire. This trend clearly shows that the optical fiber can distinguish changes in flow rate.

[0120] At higher temperatures, we are able to see the same characteristics, although with less accuracy than at low temperature. In this instance, the operating temperature of the hot wire was near 550 °C, while the temperature of the surrounding fluid was 460 °C. Similar to the low temperature case, FIGS. 11 and 12 show the spectral shift as a function of time (at the position 0.160 meters) during the application of six separate flow rates as well as the average maximum spectral shift as a function of flow rate. The two plots evidently convey the same trends as the low temperature case. The main difference being the spectral shift order of magnitude, due to the higher temperature. The flow rates used in this instance were also higher so this may have affected the resulting spectral shift, as the trend in Figure 12 is noticeably not as defined as that in FIG. 10.

[0121] Owing to the ability to carry out spatially resolved measurement of the velocity, the optical fiber is also able to distinguish changes in nozzle position. FIG. 13 shows flow measured when the nozzle was moved between two discrete positions along the hot wire, hopping from a position centered at about 0.17 m to a position of about 0. 135 m. FIG. 14shows a continuous motion of the nozzle along the length of the hot wire, with an approximately constant translational speed. From this spectral shift map, it is possible to calculate the rate at which the flow is moving along the length of the hot wire, being kept perpendicular to the optical fiber (hot wire) direction. Beyond this, the optical fiber’s spatial distribution can be correlated to the velocity distribution of the flow. In FIG. 15, the spatial spectral shift follows the same trend, increasing as the flow rate increases. However, it is important to note that this becomes less clear at high temperatures. FIG. 16 shows a heat map of the spatial distribution over time. This distribution has large concentrations of noise at specific positions that likely correspond to high thermal gradients in the hot wire. This is an area that can be improved upon in future iterations to reduce noise and have more accurate high temperature data. Overall, the characteristics of a flow, specifically spatial distribution and flow rate, can be determined using a fiber optic hot wire at low and high temperatures.

[0122] Conclusions.

[0123] A fiber optic hot wire flow meter was developed and its ability to measure velocities of air up to a fluid temperature exceeding 450 °C was demonstrated. During the high temperature measurements, the hot wire is kept at temperatures well above 500 °C, showing that there are no fundamental limitations for this approach to be applied to flow measurements at temperatures that are relevant to advanced nuclear reactors. Three hot wire embodiments have been fabricated and tested at different temperatures and flow rates in air. Designs included both metallic and ceramic tubings, internal and external heating, and optical fibers with one of a polymer coating, a gold coating, or no coating. Results show that the various designs can all measure different fluid velocities, as well as resolve the velocity distribution along the length of the hot wire, and potential time dependent changes in flow. Additionally, when the nozzle is smaller than the length of the hot wire, the position of the nozzle is detected, as well as its motion along the length of the hot wire. Overall, the results included in this paper suggest that the fiber optic flow meter show promise as a valuable tool to support advanced reactors design, as well as monitoring of flow parameters during operation.

[0124] References.

[0125] The following references are incorporated herein by reference in their entireties.• Cabral, C. Wiggins, and L. Carasik, “Novel Distributed Flow Velocity Using aTemperature Fiber Optic in Gas Flow,” 2021 American Nuclear Society Winter Meeting, (2021)• T. Chen, Q. Wang, B. Zhang, R. Chen, and K. P. Chen, "Distributed flow sensing using optical hot-wire grid.," Optics Express, 20, (2012).• O. J. Ohanian 111, A. J. Boulanger, and K. T. Lowe, "Distributed Anemometry via High-Definition Fiber Optic Sensing," AIAA SciTech Forum, (2019).• D. A. Arostegui and M Holt. "Advanced nuclear reactors: technology overview and current issues." Congressional Research Service Report for Congress, Washington, DC, Report. No. R45706. 2019.• Van Oost, G., A. V. Dedov, and V. P. Budaev. "The Plasma-Facing Materials of Tokamak Thermonuclear Reactors: Requirements, Thermal Stabilization, and Tests (a Review)." Thermal Engineering 68 (2021): 185-200.• Boullon, Remi, Jean-Charles Jaboulay, and Julien Aubert. "Molten salt breeding blanket: Investigations and proposals of pre-conceptual design options for testing in DEMO." Fusion Engineering and Design 171 (2021): 112707.• O. Arora, B. Lancaster, S.R. Yang, R. Vaghetto, and Y. Hassan, “Advanced flow andtemperature measurements in a forced convection molten salt test loop,” Annals of Nuclear Energy, 159 (2021).• K. Britsch, M. Anderson, P. Brooks, and K. Sridharan, “Natural circulation FLiBe loop overview,” International Journal of Heat and Mass Transfer, 134(2019).• D. Tenchine, “Some thermal hydraulic challenges in sodium cooled fast reactors .’’Nuclear Engineering and Design, 240(5) (2010).• L. Buhler and C. Mistrangelo, “Determination of flow distribution in a HCLL blanketmock-up through electric potential measurements,” Fusion engineering and design, 86(9-11) (2011).• D. Suarez, E. Iraola, C. Lampon, E.M. de les Valls, and L Batet, “Liquid metal MHD flow influence on heat transfer phenomena in fusion reactor blankets,” Fusion Engineering and Design, 170 (2021).■ Mistrangelo, L. Buhler, S. Smolentsev, V. Kltiber, I. Maione, and J. Aubert, “MHD flow in liquid metal blankets: Major design issues, MHD guidelines and numerical analysis,” Fusion Engineering and Design, 173 (2021).• F. Scurti, J. McGarrahan, and J. Schwartz, 2017. Effects of metallic coatings on the thermal sensitivity of optical fiber sensors at cryogenic temperatures.Optical Materials Express, 7(6), pp.1754-1766.• F. Scurti, S. Ishmael, G. Flanagan, and J. Schwartz. "Quench detection for high temperature superconductor magnets: a novel technique based on Rayleigh- backscattering interrogated optical fibers." Superconductor Science and Technology 29, no. 3 (2016): 03LT01.• F. Scurti, S. Sathyamurthy, M. Rupich, and J. Schwartz. "Self-monitoring ‘SMART’(RE) Ba2Cu3O7- x conductor via integrated optical fibers." Superconductor Science and• Technology 30, no. 11 (2017): 114002.• E. Li, "Rayleigh scattering based distributed optical fiber sensing." In AOPC 2017: Fiber Optic Sensing and Optical Communications, vol. 10464, pp. 381-387. SPIE, 2017.• T. W. Wood, B. Blake, T. E. Blue, C. M. Petrie, and D. Hawn. "Evaluation of the Performance of Distributed Temperature Measurements With Single-Mode Fiber Using Rayleigh Backscatter up to 1000$A{\circ}{\rm C} $." IEEE Sensors Journal 14, no. 1 (2013): 124-128.• S. D. Rountree, O. J. Ohanian, A. Boulanger, D. Kominsky, M. Davis, M. Wang, K. Chen et al. "Multi-parameter fiber optic sensing for harsh nuclear environments." In Fiber Optic Sensors and Applications XVII, vol. 11739, pp. 63-82. SPIE, 2021.• Bobb, L.C., Davis, J.P., Samouris, A. and Larson, D.C., 1990, February. An optical fiber hot-wire anemometer. In Fiber Optic and Laser Sensors VII (Vol. 1169, pp. 567-572). SPIE.• Fang, J.X., Taylor, H.F. and Choi, H.S., 1998. Fiber-optic Fabry-Perot flow sensor. Microwave and optical technology letters, 18(3), pp.209-211.• Caldas, P., Jorge, P.A., Rego, G., Frazao, O., Santos, J.L., Ferreira, L.A. andAraujo, F., 2011. Fiber optic hot-wire flowmeter based on a metallic coated hybrid long period grating / fiber Bragg grating structure. Applied Optics, 50(17), pp.2738- 2743.• Chen, R., Yan, A., Wang, Q. and Chen, K.P., 2014. Fiber-optic flow sensors for high-temperature environment operation up to 800 C. Optics letters, 39(13), pp.3966-3969.• Zhao, Q., Zheng, H.K., Lv, R.Q., Gu, Y.F., Zhao, Y. and Yang, Y., 2018. Novel integrated optical fiber sensor for temperature, pressure and flow measurement. Sensors and Actuators A: Physical, 280, pp.68-75.• Jderu, A., Soto, M.A., Enachescu, M. and Ziegler, D., 2021. Liquid flow meter by fiber-optic sensing of heat propagation. Sensors, 27(2), p.355.• Zhang, T., Guo, T., Wang, R. and Qiao, X., 2021. A hot-wire flowmeter based on fiber Extrinsic Fabry-Perot Interferometer with assistance of fiber Bragg grating. Optics Communications, 497, p.126952.

[0126] It should be understood that the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. It should also be appreciated that some components, features, and / or configurations may be described in connection with only one particular embodiment, but these same components, features, and / or configurations can be applied or used with many other embodiments and should be considered applicable to the other embodiments, unless stated otherwise or unless such a component, feature, and / or configuration is technically impossible to use with the other embodiment. Thus, the components, features, and / or configurations of the various embodiments can be combined together in any manner and such combinations are expressly contemplated and disclosed by this statement.

[0127] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible considering the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications andalternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.

[0128] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. Therefore, while certain exemplary embodiments of the systems, compositions, materials, apparatuses, and methods of using and making the same disclosed herein have been discussed and illustrated, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A flow meter, comprising: a tube having a tube first end, a tube second end, and a tube longitudinal axis (TL) extending from the tube first end to the tube second end; heater wire wound around at least a portion of the tube; and an optical fiber located within the tube, the optical fiber having an optical fiber first end, an optical fiber second end, and an optical fiber longitudinal axis (OFL) extending from the optical fiber first end to the optical fiber second end; wherein:TL is parallel to OFL; and the flow meter is configured to be placed in an environment in which fluid will be allowed to or caused to flow over the tube in a direction that is not parallel to OFL.

2. The flow meter of claim 1, wherein: the tube comprises metal or metal alloy.

3. The flow meter of claim 1, wherein: the heater wire is a metal or metal alloy.

4. The flow meter of claim 1, further comprising: an interrogator configured to interrogate the optical fiber.

5. The flow meter of claim 4, wherein: the interrogator is an interferometer; or the optical fiber includes plural Bragg diffraction gratings and the interrogator is a spectrometer.

6. The flow meter of claim 1, further comprising:a current source or a voltage source configured to apply an electrical current or a voltage potential to the heater wire.

7. The flow meter of claim 1, further comprising: plural tubes; plural heater wires; and / or plural optical fibers.

8. A flow meter, comprising: a ceramic tube, the ceramic tube having a heater wire lumen and an optical fiber lumen, the optical fiber lumen extending in a direction from a ceramic tube first end to a ceramic tube second end; a heater wire located within the heater wire lumen; and an optical fiber located within the optical fiber lumen; wherein the flow meter is configured to be placed in an environment in which fluid will be allowed to or caused to flow over the ceramic tube in a direction that is not parallel to the optical fiber.

9. The flow meter of claim 8, wherein: the heater wire is a metal or metal alloy.

10. The flow meter of claim 8, further comprising: an interrogator configured to interrogate the optical fiber.

11. The flow meter of claim 10, wherein: the interrogator is an interferometer; or the optical fiber includes plural Bragg diffraction gratings and the interrogator is a spectrometer.

12. The flow meter of claim 8, further comprising:a current source or a voltage source configured to apply an electrical current or a voltage potential to the heater wire.

13. The flow meter of claim 1, further comprising: plural ceramic tubes; plural heater wires; plural optical fibers; plural heater wire lumen; and / or plural optical fiber lumen.

14. A flow meter, comprising: a tube having a tube first end, a tube second end, and a tube longitudinal axis (TL) extending from the tube first end to the tube second end; heater wire wound around at least a portion of the tube; an optical fiber located within the tube, the optical fiber having an optical fiber first end, an optical fiber second end, and an optical fiber longitudinal axis (OFL) extending from the optical fiber first end to the optical fiber second end; and a ceramic coating covering at least a portion of the heater wire and at least a portion of the tube wherein:TL is parallel to OFL; and the flow meter is configured to be placed in an environment in which fluid will be allowed to or caused to flow over the tube in a direction that is not parallel to OFL.

15. The flow meter of claim 14, wherein: the tube comprises metal or metal alloy.

16. The flow meter of claim 14, wherein: the heater wire is a metal or metal alloy.

17. The flow meter of claim 14, further comprising: an interrogator configured to interrogate the optical fiber.

18. The flow meter of claim 17, wherein: the interrogator is an interferometer; the optical fiber includes plural Bragg diffraction gratings and the interrogator is a spectrometer.

19. The flow meter of claim 14, further comprising: a current source or a voltage source configured to apply an electrical current or a voltage potential to the heater wire.

20. The flow meter of claim 14, further comprising: plural tubes; plural heater wires; and / or plural optical fibers.

21. A flow meter, comprising: a tube having a tube first end, a tube second end, and a tube longitudinal axis (TL) extending from the tube first end to the tube second end; and an optical fiber located within the tube, the optical fiber having an optical fiber first end, an optical fiber second end, and an optical fiber longitudinal axis (OFL) extending from the optical fiber first end to the optical fiber second end; at least one of: the tube is configured to be Joule heated by applying heat or electrical current to the tube; the optical fiber is configured to be self-heated when light propagates though the optical fiber; orthe optical fiber includes an electrically resistive coating configured to be Joule heated by applying electrical current to the electrically resistive coating; wherein:TL is parallel to OFL; and the flow meter is configured to be placed in an environment in which fluid will be allowed to or caused to flow over the tube in a direction that is not parallel to OFL.

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