The effect of low Reynolds number flows on pitot tube measurements

An investigation on the low Reynolds number effect on hemispherical-tipped Pitot tube measurements was performed by measuring the center-line velocity during the laminar flow of a Newtonian fluid in a 25 mm (1 in.) diameter vertical recirculating pipe loop. The primary objective of the study was to reconsider the available low Reynolds number Pitot tube data in the literature with modern instrumentation.Using the results of this experimental study, a correlation that accurately predicts the low Reynolds number Pitot tube behavior has been developed. The correlation accounts for an additional viscous term in the relationship for the pressure coefficient (C_p) which is not accounted for in Bernoulli's Equation. The correlation is semi-empirical and accurately fits experimental data gathered in this study, as well as a significant body of experimental data available in the literature. The correlation, which is based on a Pitot tube Reynolds number calculated using the opening diameter (d), has been shown to be provide more accurate predictions of C_p for a wide range of opening diameter to outer diameter ratios (0.22≤d/D≤0.6) than available correlations based on outer diameter.The transition Pitot tube Reynolds number, below which Bernoulli's Equation is no longer appropriate, was predicted to be approximately 35, compared to a value of 79 obtained from fitting data collected by Barker. The correlation developed in this study provides smoother transitions at both ends of the low Reynolds range. At the low end (Re<10) it converges with a Stokes Law’ analogy, while at the critical transition (Re~35) it converges asymptotically with Bernoulli's Equation. The correlation also accurately predicts the behavior of the pressure coefficient with Reynolds numbers between these ranges.     

Measurement of vertical oil-in-water two-phase flow using dual-modality ERT–EMF system

Oil-in-water two-phase flows are often encountered in the upstream petroleum industry. The measurement of phase flow rates is of particular importance for managing oil production and water disposal and/or water reinjection. The complexity of oil-in-water flow structures creates a challenge to flow measurement. This paper proposes a new method of two-phase flow metering, which is based on the use of dual-modality system and multidimensional data fusion. The Electrical Resistance Tomography system (ERT) is used in combination with a commercial off-the-shelf Electromagnetic Flow meter (EMF) to measure the volumetric flow rate of each constituent phase. The water flow rate is determined from the EMF with an input of the mean oil-fraction measured by the ERT. The dispersed oil-phase flow rate is determined from the mean oil-fraction and the mean oil velocity measured by the ERT cross-correlation velocity profiling. Experiments were carried out on a vertical upward oil-in-water pipe flow, 50 mm inner-diameter test section, at different total liquid flow rates covering the range of 8–16 m³/hr. The oil and water flow rate measurements obtained from the ERT and the EMF are compared to their respective references. The accuracy of these measurements is discussed and the capability of the measurement system is assessed.     

Smokestack gas velocity measurements using 3D pitot tubes in a coal-fired power plant

On the path to carbon neutrality to reduce greenhouse gas (GHG) emissions, the Korean government has mandated legislation for controlling and monitoring GHG emissions emitted from smokestacks. A continuous emission measurement (CEM) method is considered to be the most reliable for determining CO2 emissions from stationary sources. In Korea, an S-type Pitot tube is the most popular technique to measure the gas velocity in a smokestack, but it will result in a certain error when the non-axial velocity components exist. To vanquish this limitation, Korea Research Institute of Standards and Science (KRISS) developed a nulling smokestack flow measurement (NSFM) instrument equipped with 3D Pitot tubes for taking on-site stack gas velocity measurements. 3D Pitot tubes used in this research, such as prism Pitot tube and sphere Pitot tube, are calibrated in the KRISS airspeed system. The instrument using 3D Pitot tubes with the nulling technique is expected to diminish the restriction on S-type Pitot tubes, and to enhance the quality of the GHG emission measurements in the smokestack. The 3D Pitot tubes can measure both axial and non-axial velocity components of a flow, whereas the S-type Pitot tubes can measure only the axial velocity component. The averaged axial velocity of the stack gas as measured by this instrument has expanded uncertainty of 3.3% (P = 95%, k = 2) for both prism and sphere Pitot tubes.     

An ultra high-pressure test rig for measurements of small flow rates with different viscosities

Within the framework of a research project regarding investigations on a high-pressure Coriolis mass flow meter (CMF) a portable flow test rig for traceable calibration measurements of the flow rate (mass - and volume flow) in a range of 5 g min⁻¹ to 500 g min⁻¹ and in a pressure range of 0.1 MPa to 85 MPa was developed. The measurement principle of the flow test rig is based on the gravimetrical measuring procedure with flying-start-and-stop operating mode. Particular attention has been paid to the challenges of temperature stability during the measurements since the temperature has a direct influence on the viscosity and flow rate of the test medium. For that reason the pipes on the high-pressure side are double-walled and insulated and the device under test (DUT) has an enclosure with a separate temperature control. From the analysis of the first measurement with tap water at a temperature of 20 °C and a pressure of 82.7 MPa an extensive uncertainty analysis has been carried out. It was found that the diverter (mainly due to its asymmetric behaviour) is the largest influence factor on the total uncertainty budget. After a number of improvements, especially concerning the diverter, the flow test rig has currently an expanded measurement uncertainty of around 1.0% in the lower flow rate range (25 g min⁻¹) and 0.25% in the higher flow rate range (400 g min⁻¹) for the measurement of mass flow. Additional calibration measurements with the new, redesigned flow test rig and highly viscous base oils also indicated a good agreement with the theoretical behaviour of the flow meter according to the manufacturers׳ specifications with water as test medium. Further improvements are envisaged in the future in order to focus also on other areas of interest.     

Influence of tube wall longitudinal heat conduction on temperature measurement of cryogenic gas with low mass flow rates

Longitudinal heat conduction is an important parameter in the cryogenic field, especially in cryogenic heat exchangers. In the present study, the parasitic effect of tube wall longitudinal heat conduction on temperature measurement within the tube has been studied for cryogenic gas with low mass flow rates by finite element method and experimental tests. The effects of various parameters such as tube outlet temperature, tube wall thermal conductivity, mass flow rate, and tube wall thickness have been investigated. Axial positioning errors of temperature sensor due to tube wall longitudinal heat conduction were higher for lower gas flow rates. The results showed that the tube wall thermal conductivity leads to axial heat conduction within the tube wall, but the higher tube wall thermal conductivity does not lead to bigger axial positioning error of temperature sensor at tube outlet. According to data obtained from simulations and experiments, sensor with distance of 5 mm from tube outlet had 14.92% and 8.51% temperature measurement error (with respect to gas flow temperature at tube outlet) for tube wall thermal conductivities of 16 and 400 W m⁻¹ K⁻¹, respectively.     

The impact of geometric parameters of a S-type Pitot tube on the flow velocity measurements for greenhouse gas emission monitoring

In the monitoring of greenhouse gas emission from industrial smoke-stacks, the most common device used to measure the stack gas velocity is the S-type Pitot tube in South Korea, which is used to estimate the volumetric flow rate by what is termed the Continuous Emission Monitoring System (CEMS). The S-type Pitot tube installed in the stack is inevitably affected during velocity measurements by velocity changes, yaw and pitch angle misalignments due to the harsh environments. Various geometries of the S-type Pitot tube can affect the characteristics of the S-type Pitot tube coefficients, including the degree of sensitivity to velocity changes and yaw and pitch yaw angle misalignments. Nevertheless, there are no detailed guidelines pertaining to the S-type Pitot tube geometry considering accurate and reliable measurements in the ISO, EPA and ASTM international standards. In the present study, S-type Pitot tubes with various geometric parameters, in this case the distance between the impact and wake orifices and the bending angle of the orifices, were manufactured by a 3D printer. Wind tunnel experiments were conducted in the Korea Research Institute of Standards and Science (KRISS) air speed standard system to determine the optimal geometry of an S-type Pitot tube for the accuracy velocity measurements in actual smokestacks which undergo velocity changes and yaw and pitch angle misalignments. Particle image velocimetry was also used to understand the flow phenomena around an S-type Pitot tube under various geometric and misalignment conditions by means of qualitative visualization. The results indicate that S-type Pitot tubes with a long effective length have more constant distributions of the S-type Pitot tube coefficients when the velocity changes from 2 m/s to 15 m/s. The error indexes for yaw angle misalignments show that S-type Pitot tube models with large effective lengths are less affected by yaw angle misalignments. The S-type Pitot tube coefficients were mostly insensitive to the both positive and negative pitch angle misalignments regardless of the velocity and geometry of the various models tested.     

Performance tests of a new non-invasive sensor unit and ultrasound electronics

Industrial applications involving pulsed ultrasound instrumentation require complete non-invasive setups due to high temperatures, pressures and possible abrasive fluids. Recently, new pulser-receiver electronics and a new sensor unit were developed by Flow-Viz. The complete sensor unit setup enables non-invasive Doppler measurements through high grade stainless steel. In this work a non-invasive sensor unit developed for one inch pipes (22.5 mm ID) and two inch pipes (48.4 mm ID) were evaluated. Performance tests were conducted using a Doppler string phantom setup and the Doppler velocity results were compared to the moving string target velocities. Eight different positions along the pipe internal diameter (22.5 mm) were investigated and at each position six speeds (0.1–0.6 m/s) were tested. Error differences ranged from 0.18 to 7.8% for the tested velocity range. The average accuracy of Doppler measurements for the 22.5 mm sensor unit decreased slightly from 1.3 to 2.3% across the ultrasound beam axis. Eleven positions were tested along the diameter of the 48.4 mm pipe (eight positions covered the pipe radius) and five speeds were tested (0.2–0.6 m/s). The average accuracy of Doppler measurements for the 48.4 mm sensor unit was between 2.4 and 5.9%, with the lowest accuracy at the point furthest away from the sensor unit. Error differences varied between 0.07 and 11.85% for the tested velocity range, where mostly overestimated velocities were recorded. This systematic error explains the higher average error difference percentage when comparing the 48.4 mm (2.4–5.9%) and 22.5 mm (1.3–2.3%) sensor unit performance. The overall performance of the combined Flow-Viz system (electronics, software, sensor) was excellent as similar or higher errors were typically reported in the medical field. This study has for the first time validated non-invasive Doppler measurements through high grade stainless steel pipes by using an advanced string phantom setup.     

Refined reconstruction of liquid–gas interface structures for stratified two-phase flow using wire-mesh sensor

Wire-mesh sensors (WMS), developed at HZDR [4], [13], are widely used to visualize two-phase flows and measure flow parameters, such as phase fraction distributions or gas phase velocities quantitatively and with a very high temporal resolution. They have been extensively applied to a wide range of two-phase gas–liquid flow problems with conducting and non-conducting liquids. However, for very low liquid loadings, the state of the art data analysis algorithms for WMS data suffer from the comparably low spatial resolution of measurements and from boundary effects, caused by e.g. flange rings – especially in the case of capacitance type WMS. In the recent past, diverse studies have been performed on two-phase liquid–gas stratified flow with low liquid loading conditions in horizontal pipes at the University of Tulsa. These tests cover oil–air flow in a 6-inch ID pipe and water–air flow in a 3-inch ID pipe employing dual WMS with 32×32 and 16×16 wires, respectively. For oil–air flow experiments, the superficial liquid and gas velocities vary between 9.2 m/s≤ν_SG≤15 m/s and 0.01 m/s≤ν_SL≤0.02 m/s, respectively [2]. In water–air experiments, the superficial liquid and gas velocities vary between 9.1 m/s≤ν_SG≤33.5 m/s and 0.03 m/s≤ν_SL≤0.2 m/s, respectively [17], [18]. In order to understand the stratified wavy structure of the flow, the reconstruction of the liquid–gas interface is essential. Due to the relatively low spatial resolution in the WMS measurements of approximately 5 mm, the liquid–gas interface recognition has always an unknown uncertainty level. In this work, a novel algorithm for refined liquid–gas interface reconstruction is introduced for flow conditions where entrainment is negligible.     

Characterization of gas-liquid two phase flows using dielectric Sensors

Two phase flow regime identification and void fraction measurement is an area of considerable interest because of its wide applications in process industries. The principle involved in dielectric measurement is that the two phase flow regime is characterized by the changes in effective permittivity of the two phase fluid mixture. In the present work, a pair of parallel copper electrodes on the two sides of a glass tube acts as a dielectric sensor. As the void fraction in the glass tube changes, the effective permittivity of the medium changes. This causes a variation in the capacitance value across the electrodes. A standard IC, Oscillator 555 is employed as a tool to generate a rectangular wave. The variation in dielectric constant is analyzed based on the change in time period of the trough (T₀) of the rectangular wave that is recorded online by a data acquisition system. Experiments were performed in a 4.7 mm diameter tube with air-water, air-palmolein oil two phase fluids to study the variation in dielectric constant which is indicated as a change in time period of trough. The effect of conductivity of water on the capacitance variation is examined with water having Total dissolved solids (TDS) which is a measure of movable ions in the range 10-4000 ppm (16 µS/cm–6.3 mS/cm). The novelty in the present work is the determination of changes in capacitance value based on the change in time of trough of the rectangular wave. The technique does not require amplification or a filtering circuit, thereby leading to a precise identification of two phase flow regime.     

Effects of flow patterns and salinity on water holdup measurement of oil-water two-phase flow using a conductance method

This research investigates the effects of flow pattern and salinity of oil-water two-phase flow on water holdup measurement using a conductance method. Firstly, vertical upward oil-water two-phase flow experiment is conducted in a 20 mm inner diameter (ID) pipe, in which the salinities of aqueous solutions are set as 151 ppm, 1003 ppm, 2494 ppm and 4991 ppm respectively. Experimental water-cut and mixture velocity are set as 80–100% and 0.0184–0.2576 m/s. In the experiment, three different flow patterns, i.e., dispersed oil-in-water slug flow (D OS/W), dispersed oil-in-water flow (D O/W) and very fine dispersed oil-in-water flow (VFD O/W) are observed and recorded by a high speed camera. Meanwhile, we collect the response of Vertical Multiple Electrode Array (VMEA) conductance sensor excited by a sine voltage signal. The result shows that, for VFD O/W, the water holdup from VMEA sensor shows a satisfied agreement with that of quick closing valve (QCV) method under certain salinities, i.e., 1003 ppm as well as 2494 ppm. For D OS/W flow and D O/W flow characterized by dispersed oil droplets with various sizes, considerable deviations of water holdup between VMEA sensor and QCV method under four kinds of salinity aforementioned are presented. Afterward, according to experimental analysis along with theoretical deviation, it is concluded that the deviation of the measurement system reaches its minimum when reference resistance in the measurement circuit and salinity of the aqueous solution satisfy constraint conditions, and the accuracy of water holdup using the conductance method can be improved through adjusting reference resistance to match the salinity of water phase. Finally, the recurrence plot algorithm is utilized to identify typical flow patterns mentioned above and it shows satisfied results on comprehending the discrepancies among different flow patterns, demonstrating that the recurrence plot algorithm can be effectively applied in flow pattern identification regarding oil-water flows.     

Force coefficients for a large clearance open ends squeeze film damper with a central feed groove: Experiments and predictions

The paper describes a large load squeeze film damper (SFD) test rig, details measurements of dynamic loads inducing circular orbits conducted on a large clearance (c=0.250 mm) open ends centrally grooved SFD, and presents the identified experimental SFD force coefficients for operation at three static eccentricities. The rig has a bearing cartridge supported atop four elastic rods and a stationary journal, 0.127 mm in diameter. The damper consists of two parallel film lands, 12.7 mm in length, separated by a central groove, 6.35 mm 9.5 mm in depth. In the journal, three equally spaced holes, 120° apart, supply a light lubricant into the central groove and squeeze film lands. The experimental SFD force coefficients are compared to test results obtained earlier for a damper with the same film land lengths but with a smaller clearance (c=0.140 mm) and against predictions obtained from an advanced physical model that accounts for the flow field in the central groove and the interaction with the adjacent film lands. Dynamic pressures in the film lands and in the central groove are (not) surprisingly of the same order of magnitude. The central groove affects the dynamic forced response of the test damper to generate large direct damping coefficients, ~3.5 times those derived from classical lubrication formulas. Experimental added mass coefficients are ~7.4 times the predictive classical values. Predictions from an advanced model correlate well with the test data when using a shallow groove depth. The measurements and analysis advance knowledge on the dynamic forced performance of SFDs, point out to the limited value of simplistic predictive formulas, and validate the accuracy of a modern predictive tool.     

Miniaturized liquid film sensor (MLFS) for two phase flow measurements in square microchannels with high spatial resolution

Two miniaturized liquid film sensors (MLFS) based on electrical conductance measurement have been developed and tested. The sensors are non-intrusive and produced with materials and technologies fully compatible and integrable with standard microfluidics. They consist of a line of 20 electrodes with a purpose-designed shape, flush against the wall, covering a total length of 5.00 and 6.68 mm. The governing electronics achieve 10 kHz of time resolution. The electrode spacing of the two sensors is 230 μm and 330 μm, which allows measurements of liquid films up to 150 μm and 400 μm for sensors MLFS_A and MLFS_B, respectively. The sensor characteristics were obtained by imposing static liquid films of known thickness on top of the actual sensor. Further dynamic measurements of concurrent air-water flow in a horizontal microchannel were performed. The line of electrodes is placed across the flow direction with an angle of 3.53° from the direction of flow, allowing for a spatial resolution perpendicular to the flow of 14.2 μm for sensor MLFS_A and 20.5 μm for sensor MLFS_B. The high time and spatial resolution allows for fast and accurate detection of the presence of bubbles, and even measurement of film thickness and bubble velocity. Further information, such as the bubble shape, can be gathered based on the shape of the liquid layer underneath the bubble, which is particularly important for heat transfer studies in microchannels.     

Coriolis mass flow metering for three-phase flow: A case study

Previous work has described the use of Coriolis mass flow metering for two-phase (gas/liquid) flow. As the Coriolis meter provides both mass flow and density measurements, it is possible to resolve the mass flows of the gas and liquid in a two-phase mixture if their respective densities are known. To apply Coriolis metering to a three-phase (oil/water/gas) mixture, an additional measurement is required. In the work described in this paper, a water cut meter is used to indicate what proportion of the liquid flow is water. This provides sufficient information to calculate the mass flows of the water, oil and gas components. This paper is believed to be the first to detail an implementation of three-phase flow metering using Coriolis technology where phase separation is not applied.Trials have taken place at the UK National Flow Standards Laboratory three-phase facility, on a commercial three-phase meter based on the Coriolis meter/ water cut measurement principle. For the 50 mm metering system, the total liquid flow rate ranged from 2.4 kg/s up to 11 kg/s, the water cut ranged from 0% to 100%, and the gas volume fraction (GVF) from 0 to 50%. In a formally observed trial, 75 test points were taken at a temperature of approximately 40 °C and with a skid inlet pressure of approximately 350 kPa. Over 95% of the test results fell within the desired specification, defined as follows: the total (oil+water) liquid mass flow error should fall within ±2.5%, and the gas mass flow error within ±5.0%. The oil mass flow error limit is ±6.0% for water cuts less than 70%, while for water cuts between 70% and 95% the oil mass flow error limit is ±15.0%.These results demonstrate the potential for using Coriolis mass flow metering combined with water cut metering for three-phase (oil/water/gas) measurement.     

Copper alloys disintegration using pulsating water jet

This paper deals with on the investigation of surface topography, morphology and anisotropy of copper alloys – brass and bronze, created by pulsating water jet with frequency 20.38 kHz. The material was disintegrated using more passes of a pulsating water jet using flat nozzle, at pressure 40 MPa and stand off distance z = 55 mm. The average values of Ra, Rq, Rz roughness were analyzed at changing traverse speed and number of transitions. The effect of tensile strength and material hardness as mechanical properties of material affecting the average value of the roughness has been evaluated. It is assumed that this new way of metal eroding can be used in the automotive and engineering industries in the future e.g. for surface treatment.     

Experimental and numerical investigations of the factors affecting the S-type Pitot tube coefficients

In greenhouse gas emission monitoring from industrial stacks, the most common device used to measure stack gas velocity is the S-type Pitot tube. Various factors such as the Reynolds number and misalignment of the installation angle can be additional error sources for the S-type Pitot tube coefficients due to harsh environments. Manufacturing quality of the S-type Pitot tube is also a factor affecting on the measurement uncertainty of stack gas velocity. In the present study, wind tunnel experiments were conducted in Korea Research Institute of Standards and Science (KRISS) standard air speed system to examine the effects of various factors on the S-type Pitot tube coefficients. Numerical simulations were also used to understand flow phenomena around the S-type Pitot tube in the presence of misalignment and distortion of the geometry. The results indicate that misalignment of the pitch and yaw angle change within ±10° changes the S-type Pitot tube coefficients by approximately 2% compared with normal values. The manufacturing quality resulted in unstable values of the coefficients within 2%. However, variations of the Reynolds number (Re_D=3.0×10³–2.2×10⁴) had no significant effect on the S-type Pitot tube coefficients.     

A high frequency digital induction system for condutive flow level measurements

A highly integrated, Field Programmable Gate Array (FPGA) based induction measurement system for conductive flow level measurement is presented. Exploiting under-sampling and digital I/Q demodulation techniques, the system use direct digital sampling and can operate at multiple frequencies (from 100 kHz to over 10 MHz). Details are discussed in both hardware and software aspects. Simulations and experiments at 2.6 MHz and 8.3 MHz are carried out using saline solutions with conductivities of 1.8 S/m and 4.3 S/m to verify the performance of the system. Application of the system for saline level monitoring is implemented and studied, which further proves the applicability of the system in low conductivity object measurements.     

Pulverized coal flow metering on a full-scale power plant using electrostatic sensor arrays

On-line continuous monitoring of pulverized coal in fuel injection pipes will allow power plant operators to optimize fuel conveying conditions and ultimately to achieve higher combustion efficiency and lower atmospheric emissions. This paper presents the design, implementation and trials of a prototype instrumentation system for the on-line measurement of pulverized coal on a full-scale power plant. An array of three identical arc-shaped electrostatic electrodes is housed in a sensing head to derive particle flow signals. Pulverized coal flow parameters such as velocity, mass flow rate and fuel distribution among the injection pipes from the same pulverizing mill are obtained by processing the signals and fusing the resulting measurements. On-plant demonstration trials on 560 mm bore pneumatic conveying pipes feeding a 600 MW boiler were undertaken following system evaluation tests on a 50 mm bore laboratory test rig. Experimental results demonstrate that reliable monitoring of pulverized coal flow parameters is achieved and that the system is able to track both transient and long-term fluctuations of pulverized coal flow in fuel injection pipes under real power plant conditions.     

Compact and inexpensive iodine-stabilized diode laser system with an output at 531 nm for gauge block interferometers

A compact and inexpensive iodine-stabilized diode laser system with an output at 531 nm has been applied to long gauge block measurements. Although the optical frequency of the output beam was widely modulated (modulation width of ∼22 MHz), the coherence length and interference phase stability are sufficiently long and high, respectively, for the interferometric measurement of long gauge blocks of up to 1000 mm in length. The effective uncertainty of laser frequency in the interferometric measurement was theoretically and experimentally confirmed to be less than 10⁻⁹.     

Research on signal amplitude of the Kármán vortex street in gas–liquid two-phase flow with high void fraction

Based on Biot–Savart law and single-phase flow Kármán vortex characteristics, flow field has been analyzed when gas–liquid flow past a fixed bluff body with high void fraction. Vortex signal characteristics have been studied for stratified two-phase flow on atmospheric conditions in a horizontal pipe. To discuss the relation between void fraction and vortex signal amplitude spectrum, this paper sets up the vortex-induced pressure field model for gas–liquid two-phase flow and gives the relationship between void fraction and relative amplitude spectrum of two-phase flow to single-phase flow. An algorithm is proposed for predicting the two-phase flow parameters. Experiments were performed using air–water as working fluid along with a test tube diameter of 50 mm, at gas volume flow rate of 20–68 m³/h, and void fraction of 0.9–1. The results indicate that calculations by the vortex-induced pressure field model on the amplitude spectrum of vortex signal are in good agreement with the experimental data, and relative errors of the algorithm predictions on gas volume flow rate and liquid volume flow rate are 0.08 and 0.56, respectively.