Solid Velocity Measurement Research Articles

Advance optical fiber probe for simultaneous measurements of solids holdup and particles velocity using simple calibration methods for gas-solid fluidization systems

Advanced gas-solid optical fiber probe technique that can measure simultaneously solids velocity, solids concentration related quantity, and their time series fluctuations has been implemented with simple and new calibration methods for both solids holdup and particles velocity measurements in gas-solid spouted bed and gas-solid fluidized bed. The needed signal and data processing programs have been developed in our laboratory. New, simple, and reliable calibration methods and the related experimental setups have been established to convert the solids concentration related signal to solids holdup which is a meaningful hydrodynamic parameter and to determine the effective distance between the two tips of the probe for the solids velocity measurements. The new calibration methods have been employed to cover a wide range of particle sizes which usually used in gas-solid spouted beds and gas-solid fluidized beds. Selected results have demonstrated the appropriateness of the advanced optical fiber in measuring both solids holdup and particles velocity in the experimental setups of the gas-solid spouted and fluidized beds. The measurements have been compared against independent techniques of gamma ray computed tomography (CT) and radioactive particle tracking (RPT).

An instrumentation system for multi-parameter measurements of gas-solid two-phase flow based on Capacitance-Electrostatic sensor

In this paper, an instrumentation system for the measurements of local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate in gas-solid two-phase flow system is developed. It is based on a new type of a Capacitance-Electrostatic sensor (CES). The CES sensor is mainly composed of a capacitance electrode array and two electrostatic electrode arrays. The optimum design of the sensor is achieved by finite element method. The capacitance electrode array is employed to detect the solid distribution over the cross-section of the pipe, and the local solid volumetric concentration measurement is further derived. The electrostatic electrode arrays are used to measure the local solid velocities in conjunction with cross-correlation method. From the local solid velocity and local volumetric concentration, the solid mass flowrate and the local solid mass flowrate can be achieved. The developed system for the local solid volumetric concentration measurement is verified through analogue simulation experiments and static experiments. Finally, the system is employed to measure the local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate on a belt conveyor. The experimental results show that the measurement error of the local solid volumetric concentration measurement results are less than 10.43% for solid local volumetric concentration ranging from 0.02 to 0.56, the standard deviations of the local solid velocity measurement results are less than 0.42 for solid velocity ranging from 3.5 m/s to 15.0 m/s, and the relative error of the solid mass flowrate is within −19.6% to +14.9% for solid mass flowrate ranging from 0.006 kg/s to 0.103 kg/s, indicating that the system is capable of achieving multi-parameters measurement in gas-solid two-phase flow system.

Three-component solids velocity measurements in the outlet section of a riser.

Coincident (simultaneous) three‐component particle velocity measurements performed using two laser Doppler anemometry probes at the outlet section of a 9 m high cylindrical riser are for the first time presented for dilute flow conditions. Near the blinded extension of the T‐outlet a solids vortex is formed. Particle downflow along the riser wall opposite the outlet tube is observed, which is restricted to higher riser heights at higher gas flow rates. Increased velocity fluctuations are observed in the solids vortex and downflow region as well as at heights corresponding to the outlet tube. Contrary to the rest of the riser, in the downflow region time and ensemble velocity averages are not equal. Given the local bending of the streamlines, axial momentum transforms to radial and azimuthal momentum giving rise to the corresponding shear stresses. Turbulence intensity values indicate the edges of the downflow region. © 2016 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 62: 3575–3584, 2016

Three-component solids velocity measurements in the middle section of a riser

Coincident three-component solids velocity measurements are performed in a 8.7-m-high cylindrical riser (internal diameter 0.10m) of a pilot-scale cold-flow Circulating Fluidized Bed set-up, using two Laser Doppler Anemometry (LDA) probes. Experiments are performed with superficial gas velocities of 3.5 and 5.3m/s at riser heights from 0.9 to 5.5m and with an average solids volume fraction of 0.0002. At the lower riser heights, the solids flow is observed to be highly disturbed due to the asymmetrical position of both the air and solids inlet. A fully developed parabolic axial solids velocity field is observed about 2m above the solids inlet line. The measured radial and azimuthal particle velocity components are significantly smaller than the axial one. The particle velocity fluctuations in the axial flow direction are larger than in the radial and azimuthal directions, showing that the solids flow is anisotropic. However, both the radial and azimuthal velocity fluctuations are higher than the corresponding mean velocities, as observed when studying the turbulence intensity in the three directions. All fluctuating velocities are decreasing significantly with increasing riser height, i.e. as the flow becomes more developed. No average down-flow of solids is recorded, not even close to the wall, due to the highly diluted flow. The total particle shear stress profiles designate a mean transport of fluctuating momentum along the riser radius due to velocity fluctuations. The particle fluctuation energy calculated based on experimental data indicates that the solids flow is dominated by wall-particle rather than intra-particle collisions.

Temporal and spatial apodization in defocused acoustic transmission microscopy

Two non-confocally adjusted spherical transducers are employed to implement an acoustic microscope operating in transmission with an approximately line-shaped point spread function (PSF). Such a PSF is of advantage in acoustic transmission line tomography and spatially resolved velocity measurements in solids. The foci of the transducers are viewed as diffraction-limited point transducers and appropriate time-selective signal acquisition is designed to restrict the ultrasound wave paths to the line connecting them. It is found that for typical commercially available transducers the largest contribution to the detected signal is not due to the direct ultrasound wave but due to the edge waves emanating from the rim of the focusing transducer. This poses constraints on achieving a line-shaped PSF in defocused acoustic transmission microscopy. It is shown that, due to the strong contribution from edge waves, it is impossible to achieve a line-shaped PSF in the case of application of a long exciting toneburst. The influence of the exciting pulse length, as well as the position of the time gate on the obtainable PSF is investigated.

Design and evaluation of electrostatic sensors for the measurement of velocity of pneumatically conveyed solids

Electrostatic sensing technology in combination with correlation signal processing offers a promising solution to the on-line continuous measurement of velocity of particulate solids in pneumatic pipelines. This paper describes the fundamental mechanism of the electrostatic sensing and identifies the important aspects of the design of constituent elements of the sensor including electrodes, amplifiers and sensing heads. Experimental evaluation of a prototype commercial product called V-TESS 500 was conducted on 36 mm bore vertical and horizontal sections of a pneumatic conveyor circulating corn-flour and pulverised coal over a velocity range of 6 to 45 m/s for mass concentration of particles between 0.014 and 5.7 kg/m 3. The performance of the instrument was quantified in terms of repeatability, linearity and response time. The uncertainty of the system was studied by comparing the measured solids velocity to the superficial air velocity in the pipeline. Effects of particles' accretion on the inner surface of the pipe wall on the measurement are also included. Results obtained demonstrate that the system is capable of providing solids velocity measurements with repeatability better than ±2% and response time less than 2.5 s.

Pressure and particle velocity measurements in solids subjected to dynamic loading

The behavior of a material subjected to dynamic loading conditions should include sufficient information about the major hydrodynamic variables (pressure, volume, and particle velocity) to properly describe an equation of state. Shock speed, a phase component of particle velocity and the easiest characteristic to measure, does not provide sufficient information to serve as the universal experimental diagnostic. Pressure and particle velocity, parameters which yield to relatively accurate experimental measurements, provide direct ties to theoretical studies, as well as to determining tables of coefficients for an equation of state. At the Lawrence Livermore National Laboratory, pressure and particle velocity gauge measurements in both reactive and nonreactive materials are conducted at our large-bore gun facility, where projectiles of up to 1.5 kg reach speeds as high as 2.2 mm/μs. Described here are in-situ foil gauges for both pressure and particle velocity measurements. In addition, the optical Fabry-Perot interferometer for observing particle and free surface velocities in transparent media is discussed. Although these techniques are not new, they have been continuously improved and upgraded at our facility to yield greater accuracy, reliability, and state-of-the-art performance. The emphasis in this paper is on the operational features of the measuring techniques, but examples of experimental results are also included.

Measurement of solid velocity in the vertical pneumatic transport of powdery material at a high solid-loading ratio.

In the pneumatic transport of PVC powder whose mean diameter and material density are 134 μm and 1 330 kg/m3, respectively, the solid velocity is measured by the activable tracers method, whereby tracers can be activated when required, in a vertical line 100.0 mm in inside diameter and 24 m in length, when the air velocity is changed from 16.5 m/s to 28.9 m/s and the solid-loading ratio between 48.8 and 82.5. The used nuclide was 56Mn or 82Br. The pipe friction factor for the solid phase was also obtained for the same conditions. The present method is applicable to measurements at high solid-loading ratios.

Measurement of solid velocity in vertical pneumatic transport of powdery material at a high solid loading ratio.

In pneumatic transport of P.V.C. powder of which the mean diameter and material density are 134μm and 1 330 kg/m3, the solid velocity is measured by the activable tracers method in a vertical line of 100.0 mml.D. and 24 m length, where the air velocity is changed from 16.5 m/s to 28.9 m/s and the solid loading ratio is between 48.8 and 82.5. It is possible for the method to measure solid velocity at the highest solid loading ratio that have not ever been measured.

Pulsed signal distortion in dispersive constant‐group‐velocity media

Ultrasonic velocity measurements in solids are often made by measuring the transit times through known distances by short transient pulses. In dispersive and/or attenuative media the signal may be distorted, and the question often arises as to which part, or parts, of the initial and transmitted waves are to be used in the transit time measurement, and just what velocity—phase, group, signal, etc.—is actually being measured. A theoretical and computer study has been made of the distortion undergone by three types of pulses in transmission through nonattenuative dispersive constant‐group‐velocity media, and the effect that this may have on velocity measurements. Theory shows that a pulsed sine wave in such media does not spread out as is normally the case for dispersive media, but repeats itself at definite repetition distances. Computer plots showing the changes that the pulses undergo during transmission will be presented, and how these changes effect velocity measurements will be discussed.

Improvements in the Sing-Around Technique for Ultrasonic Velocity Measurements

A highly sensitive sing-around system was developed for ultrasonic velocity measurements in solids. In the developed system, a selected cycle of a selected echo is gated out, to retrigger the transmitter. Highly stable circuitry is employed. The timing system incorporates two modified commercial electronic counters and associated circuitry to maximize stability and detection sensitivity. Environmentally induced sample velocity changes of the order one part in 107 may be detected, provided that the accompanying attenuation change is negligible, or that steps taken to compensate for ultrasonic attenuation changes by adjusting electronic attenuation, produce phase shifts which are known to sufficient accuracy.

A Method of Sound Velocity Measurements in Solids and Liquids Using a Pulse Technique

In this method a modulated pulse from a pulse generator is sent through a sample, amplified, rectified, and sent back into the pulse generator, thus triggering the next pulse. The velocity is determined from the measured pulse repetition rate, taking into account the electronic delay time. The equipment, described in a previous paper, has been improved and checked experimentally. Measurements have been made on distilled water over the temperature range 29°C to 50°C and compared with results from the other sources. An analysis of the major sources of error has been made for the equipment as it exists at present together with a discussion of the limit of accuracy obtainable by this method.

A Precise Recording Ultrasonic Interferometer and Its Application to Dispersion Tests in Liquids

A precise recording ultrasonic interferometer is presented which is particularly well suited for measuring dispersion in liquids. The device is an interferometer of the two-crystal type in which the separation of the crystals is continuously varied. The recording process is equivalent to placing a mark on a rotating recording drum whenever the receiving crystal has moved a distance of one wavelength of sound in the liquid. Thus the wavelength of sound may be derived from the known mechanical constants of the system. The precision of the dispersion measurement is about 0.8 part in 10,000; the precision of the absolute determination of sound velocity is 0.2 m/sec. The instrument has been applied also to sound velocity measurements in solids under restricted conditions. Sound velocity in distilled water at 25°C as measured with this instrument is 1496.2±0.2 m/sec, a value somewhat lower than that obtained by earlier investigators. Dispersion in the frequency range 5–25 Mc is shown to be no greater than 0.8 part in 10,000, the limit of experimental error, for all the liquids studied: water, geraniol, xylene, isobutyl alcohol, and solutions of sucrose, NaCl, MgSO4, NaHCO3, CdCl2, CdSO4, Na3PO4, Pb(NO3)2, ZnSO4, and K3Fe(CN)6.

A Pulse Technique for Sound Velocity Measurements in Solids and Liquids

A device developed to measure small changes in sound velocity is being redesigned to measure sound velocities in solids and liquids. A 10‐megacycle pulse of approximately 2‐microsecond width from a pulse generator is sent through the sample, amplified, rectified, and sent back into the pulse generator thus triggering the next pulse. The combined acoustical and electrical delay time is determined by counting the number of pulses which traverse the sample in an accurately determined time interval. The electrical delay time is eliminated by using another specimen of slightly different length. From the acoustical delay time and the measured dimensions of the sample, the sound velocity is then calculated.

Applications of the Acoustic Sing-Around Circuit

The sing-around circuit has been suggested for air navigation use and has been employed for sound velocity measurements in solids. It consists of a triggered pulse generator which transmits a pulse into the medium and a receiver which picks up the pulse and returns it to the generator as a trigger voltage to set off a new pulse. The frequency of the resulting repetitive signal depends upon the time of travel of the pulse between the two points in the medium. A discussion will be given of the use of the circuit to measure temperature, distance, and air velocity and as a tool for exploring the acoustic properties of auditoriums.