Optical Flowmeter Research Articles

Design and fabrication of a simple and cost-effective optical flow meter using liquid crystals and textile grid.

The measurement of airflow velocity is crucial in various fields, and several sensing approaches have been developed for detecting airflow, including optical fiber-based flowmeters. However, these sensors often require complex fabrication processes and precise optical alignment. In this paper, a simpler and more cost-effective approach has been used to measure air flow rate by utilizing the birefringence property of liquid crystals (LCs). LCs possess distinct optical characteristics, and their reorientation due to airflow can be detected by observing the intensity of the output light between crossed polarizers. The novelty of this study is the utilization of a textile grid to hold the LC layer, which simplifies the fabrication process. This LC-based gas flowmeter offers a simple, low-cost setup and provides rapid performance. This research presents what we believe to be a new approach to calculate airflow by exploiting the optical properties of LCs, which is a new frontier in gas flow measurement. The proposed airflow meter is capable of detecting airflow rates ranging from 0 l/min to 7.5 l/min with an accuracy of 0.5 l/min. It exhibits a stable response time in 75 seconds, and the sensor maintains acceptable stability over time.

Indoor Localization Method of Mobile Educational Robot Based on Visual Sensor

<p>This article aims to study the mobile positioning method of mobile educational robots indoors. In order for robots to be able to unblocked indoors, they can avoid obstacles well. Vision sensors are the direct source of information for the entire machine vision system, and are mainly composed of one or two graphics sensors, sometimes accompanied by light projectors and other auxiliary equipment. This paper presents an indoor positioning method for mobile educational robots based on visual sensors. Build some models to compare which algorithm is more in line with the positioning of indoor mobile educational robots. The experimental results in this paper show that the positioning accuracy of the optical flow meter and the odometer on the short-haired carpet is equivalent (both are less than the index 4.52%); the positioning error of the optical flowmeter on the long-haired carpet is the largest 7%, and the positioning error of the odometer is the largest it reached 83%. The error of the algorithm positioning method after the visual odometer fusion is obviously smaller than that of the optical flow method. This shows that the algorithm after visual process fusion is more suitable for indoor mobile educational robot positioning than this optical flow method.</p> <p> </p>

Optical Flowmeter for Measuring the Coolant Flow Rate in the Primary Loop of a Nuclear Reactor

Optical Flowmeter for Measuring the Coolant Flow Rate in the Primary Loop of a Nuclear Reactor

Fiber optofluidic Coriolis flowmeter based on a dual-antiresonant reflecting optical waveguide.

A microfiber optofluidic flowmeter based on the Coriolis principle and a dual-antiresonant reflecting optical waveguide (ARROW) is proposed and experimentally demonstrated. A hollow hole in a hollow-core fiber is fabricated as an optofluidic channel to move the liquid sample, which forms a dual-ARROW in the hollow-core fiber. Two sides of the hollow-core fiber are used as two adjacent Fabry-Perot resonators based on the refractive index modulation of a CO2 laser, which is used to investigate the vibration signals of the two resonators. The flow rate can be measured based on the Coriolis force by calculating the phase difference between the two ARROWs. The experimental results show that a flow rate sensitivity of 8.04 deg/(µl/s) can be achieved for ethanol solution. The proposed micro Coriolis fiber optic flowmeter can be used in various fields, such as food production, medicine, bioanalysis, etc.

Flow Measurement Optimization Using Surface Measurements and Downhole Sound Speed Measurements from Local or Distributed Acoustic Sensors

Summary The litmus test for downhole multiphase flowmeters is to compare the measured phase flow rates with the rates from a test separator or other surface measurement systems. In most cases, the composition of the measurand is required for flowmeters. This is typically obtained from bottomhole fluid samples. Extracting and analyzing fluid samples is an expensive process mostly done at the initial stages of field development. In some cases, the composition may be old or unavailable, leading to subpar flowmeter performance compared to surface systems. In this work, it is shown that when the data from a surface system such as a test separator are used in conjunction with the mixture sound speed measured downhole, it is possible to optimize a downhole multiphase flowmeter system without obtaining new fluid samples. The optimization process is independent of the downhole measurement device because the required flow-velocity and sound-speed measurements may be obtained from separate devices. For example, the fluid bulk velocity and mixture sound speed can be measured by a local measurement device and a distributed acoustic sensing (DAS) system, respectively. The main challenge in a flow-velocity/sound-speed measurement system is determining individual phase sound speeds so that the mixture phase fraction can be correctly determined using Wood’s mixture sound speed model. The phase fraction from the separator tests can be used as the target value to optimize the performance of the system. The system has two operation modes. In optimization mode, the individual phase sound speeds are calculated backward using the predicted phase fractions from surface measurements. Pressure and temperature variations at measurement locations, as well as pipe compliance effects, are accounted for during the process. After the adjustment of individual phase sound speeds, steady-state operation mode takes over, and a forward calculation is implemented using the same model. The final phase fraction agrees well with the actual value and can be improved further with an iterative approach. This novel method is demonstrated in a North Sea case history. A downhole optical flowmeter in a North Sea field measured mixture velocity and sound speed. Well-test results indicated that water cut from the flowmeter was underreported and phase flow rates did not match test-separator rates. Instead of halting production and going through a fluid sample analysis cycle, the test-separator water cut was used as the target value to optimize oil phase sound speed using Wood’s model in the optimization mode. The difference between the initial and optimized oil sound speeds was extrapolated to other pressure and temperature conditions, and steady-state operation mode showed that separator tests and flowmeter measurements closely matched. Subsequent flowmeter and test-separator data confirmed excellent agreement. Using surface measurements and downhole mixture sound speed to optimize phase flow rates is a novel method that has not been previously demonstrated. This method is independent of device type, is broadly applicable, and improves the understanding of multiphase flow measurement.

Vortex Shedding Optical Flowmeter based on Photonic Crystal Fiber

In the present work we propose a PCF (photonic crystal fiber) based Modal interferometer detector for sensing low flow velocity by detecting the frequency of vortices shed from a bluff body. The proposed novel design encapsulates the interferometric arm inside a metal casing to protect the sensor from harsh process fluids. The characterization of the developed probe is conducted under no flow conditions using a piezo actuator to evaluate the sensor response over wide frequency range (0–500 Hz). The developed sensors shows a reasonably flat response in the tested frequency range. Experiments are conducted by employing the developed sensor behind a bluff body of a vortex flowmeter to measure the frequency of the shed vortices and hence, the fluid flow rate. The low flow rate sensitivity of the vortex flowmeter is improved many folds by using the present sensor and the minimum Reynolds number detected is Re = 5000. A linear trend is observed between the frequency of the vortices and the flow velocity which is desirable for fluid flow measurement. The PCF based interferometric sensor with metal encapsulation makes the vortex flowmeter, sensitive at low flow rates, robust and economical to be used in industrial application.

Fiber-Optic Anemometer Based on Bragg Grating Inscribed in Metal-Filled Microstructured Optical Fiber

A compact all-fiber optical anemometer based on a fiber Bragg grating inscribed in a metal-filled microstructured optical fiber (MOF) is presented. Six-hole MOF (SHMOF) with a suspended core is fabricated to engineer the evanescent field of the fundamental guided mode, and low-melting-point alloy is filled in the micro-holes to achieve highly efficient light-heat conversion. Such a metal-filled SHMOF can strongly absorb pumping light at 1450 nm to generate heat and forms a fiber-optic “hot wire.” The Bragg grating at 850 nm is inscribed in the core of SHMOF and acts as an in-fiber sensor for monitoring wind-speed dependent temperature of the “hot wire.” Experimental results show the sensitivity of the fiber-optic anemometer is as high as ∼0.091 nm/(m/s) at wind speed of around 2 m/s. Such a compact anemometer is promising as a low-power-consumption optical flow-meter for remote sensing and on-chip integration.

Optic flow odometry operates independently of stride integration in carried ants.

Cataglyphis desert ants are impressive navigators. When the foragers roam the desert, they employ path integration. For these ants, distance estimation is one key challenge. Distance information was thought to be provided by optic flow (OF)-that is, image motion experienced during travel-but this idea was abandoned when stride integration was discovered as an odometer mechanism in ants. We show that ants transported by nest mates are capable of measuring travel distance exclusively by the use of OF cues. Furthermore, we demonstrate that the information gained from the optic flowmeter cannot be transferred to the stride integrator. Our results suggest a dual information channel that allows the ants to measure distances by strides and OF cues, although both systems operate independently and in a redundant manner.

Application of Image Technique and Optical Fiber Sensor for Air-water Mixture Flow

Measurements of multiphase flows containing bubbles have been limited because most existing methods target one phase flows. Especially, multiphase flows with a high void ratio have been rarely successful in measurements due to the sudden change of density and thick interfaces between air and water. This study introduces two methods that are capable of measuring flow fields regardless of bubble void ratio, named bubble image velocimetry and bundle fiber optic flow meter. The calculation of the depth of field is suggested to reduce and estimate errors by perspective image velocimetry. The bundle fiber optic flow meter is designed to increase a measurement rate using many optical fibers with a thin diameter. The two methods measured bubble plumes to test reliability and the velocity measurements show good agreement. In addition a hydraulic jump, one of the multiple flows in rivers was measured to test applicability of the methods.

A Correlation-Based Optical Flowmeter for Enclosed Flows

<abstract> <bold><sc>Abstract.</sc></bold> A low-cost flowmeter would be very useful in a wide variety of monitoring situations. This article discusses the development of such a flowmeter based on optical components and its testing with water in an enclosed flow system. The sensor consisted of two sets of LEDs and phototransistors spaced 4 cm apart, monitoring the optical properties of the fluid at upstream and downstream locations, respectively. A small amount of dye was injected into the flow, which caused a change in the optical properties of the fluid at both locations. The time required for this change to move from the upstream to the downstream locations was determined using the biased estimate of the cross-covariance between the upstream and downstream signals. The velocity was then calculated using this time difference and the known distance between the locations. Tests were conducted at fluid velocities from 0.125 to 4.5 m s^-1, and separate results were calculated using phototransistors located 45° and 180° from the LEDs. The mean percent error was between 5% and 0% for individual measurements using the 180° phototransistors at velocities from 0.5 to 4.5 m s^-1 and between 2% and -8% for measurements using the 45° phototransistors in the same velocity range. Error increased when the velocity was reduced to 0.5 m s^-1 and was greater than 20% at 0.125 m s^-1 for both sets of phototransistors. A regression model was developed to correct the velocity estimate. This regression model was validated by conducting an independent test of the sensor under the same conditions. After using the regression model for calibration, errors in the validation set were between 9.1% and -5% for the 180° phototransistors and between 10.5% and -3.6% for the 45° phototransistors for the entire velocity range tested (0.125 to 4.5 m s^-1). Finally, the cross-correlation coefficient for each measurement was calculated to determine the degree of similarity between the signals recorded by the phototransistors at the upstream and downstream locations. The cross-correlation coefficient was higher at lower velocities and higher for measurements using the 180° phototransistors.

Optical flow sensor through near-field grating diffraction

A novel optical flow-meter has been developed, especially designed for very-high flow speed. The system is a variant of laser Doppler velocimeter (LDV), realized by means of an optical phase-grating. Standard LDV generates a fringes pattern by means of two laser beams, intersecting at an angle α. For fast flow rates, the fringe period has to be very long, in order to avoid too high output frequencies, therefore a very low angle α is required. For the realization of such pattern we propose a different approach, employing an optical grating, working in the near-field range. This technique has been demonstrated by measuring the flow-speed distribution in a water-jet machine.

Cross-Correlation-Based Optical Flowmeter

In this paper, an optical flowmeter based on the cross-correlation technique is proposed. Two parallel laser beams are made to cross a transparent pipe wherein a turbulent air flows. The laser beams are detected by two position-sensitive detectors (PSDs) whose output signals are processed by software. The cross-correlation function between the signals is calculated, which yields the time delay between them. The flow velocity is then obtained by the ratio of the distance between the laser beams to the time delay. The flowmeter is applicable for measuring human respiratory flow in a noninvasive way. An experimental prototype is built, and results are provided. A detailed description of the experimental setup and of measurement procedures are presented and discussed. Results have been very promising and have shown the potential of the system developed here in performing human respiratory flow measurements, particularly those suitable for neonates.

A Simple Fiber-Optic Flowmeter Based on Bending Loss

The characteristics of a macrobending fiber used as an optical flowmeter are discussed. When a liquid flows through the bending area of the fiber sensor, it will result to the variation of the bending curvature and modulate the bending loss of the fiber, due to the impact or/and the drawing force of the flow which is relative to the speed of the flow. Different curvatures in initial state have different performances in the measurement. An optimum performance of the curvature radius of 8 mm in the range of flow rate from 0 to 3 m/s is found in the experiment. A block hung up the bending fiber to enhance the sensitivity and the dynamic range is demonstrated. Twenty times larger of the loss change is achieved by hanging an 11 times 11 mm2 block. The experiment shows the influences of temperature and hysteresis can be ignored.

Optical flowmeter using a modal interferometer based on a single nonadiabatic fiber taper

A novel in-fiber modal interferometer is presented that is based on a nonadiabatic biconical fused taper that couples light between the cladding and the core, combined with the Fresnel reflection at the fiber end. It is observed that the returned light from this fiber structure shows a channeled spectrum similar to that of a two-wave Michelson interferometer. The application of this device as a fiber optic flowmeter sensor is demonstrated.

Performance Evaluation of a Three-dimensional Optical Volume Flow Meter

Optical sensors in combine grain elevator housings have been used for volume flow measurements. Several parameters affecting the accuracy of optical volume flow detection are described. Parameters considered were the slope, the kernel type, the moisture content, and the clean grain elevator capacity. A positive linear relationship was found between the optical sensor output and the volume flow. Using the output of only one horizontal sensor to explain the volume flow of all the runs showed maximum deviations from the sample regression that ranged up to 13%. Using four optical sensors, two mounted transverse to the elevator chain and two mounted perpendicular to the chain and symmetrically on both sides of the chain, the maximum deviation from the sample regression was reduced to 9%. These results were obtained after reduction of the gap between the paddles and the housing.

Integrated Optic Flow Meter with Cantilever Structure on Silicon Substrate.

An integrated optic flow meter with a cantilever structure is proposed and was built for the first time on a silicon substrate. The sensor with a narrow gap along the cantilever edge is sandwiched between tubes in which a fluid flows. The gap induces pressure difference between the front and back regions of the lever. Cantilever deformation due to the pressure difference is transformed into the intensity change of the lightwave by an integrated optic interferometer. We analyzed the operation and designed a flow meter. A device fabricated was examined for a nitrogen gas flow using a TM-like light mode at 633 nm. The output intensity measured monotonously decreased with increase in the flow from 0 to 600 cc/min at which the output light intensity was 30% of the maximum value at 0 cc/min.

Vortex shedding fluid flowmeter using optical fibre sensor

An optical fibre flowmeter is described which uses a single fibre mounted transversely to the fluid flow within the pipe. The fibre is vibrated by the natural phenomenon of vortex shedding, causing phase modulation of the optical carrier within. The modulation is detected at the fibre exit by the fibredyne technique, and the flow rate determined from the vibration frequency.