Local Velocity Measurements Research Articles

Axial dispersion and mixing of coolant gas within a separate-effect prismatic modular reactor

Multiphase Reactors Engineering and Applications Laboratory performed gas phase dispersion experiments in a separate-effect cold-flow experimental setup for coolant flow within heated channels of the prismatic modular reactor under accident scenario using gaseous tracer technique. The separate-effect experimental setup was designed on light of local velocity measurements obtained by using hot wire anemometry. The measurements consist of pulse-response of gas tracer that is flowing through the mimicked riser channel using air as a carrier. The dispersion of the gas phase within the separate-effect riser channel was described using one-dimensional axial dispersion model. The axial dispersion coefficient and Peclet number of the coolant gas phase and their residence time distribution within were measured. Effect of heating intensities in terms of heat fluxes on the coolant gas dispersion along riser channels were mimicked in the current study by a certain range of volumetric air flow rate ranging from 0.0015 to 0.0034 m3/s which corresponding to heating intensity range from 200 to 1400 W/m2. Results confirm a reduction in the response curve spreads is achieved by increasing the volumetric air velocity (representing heating intensity). Also, the results reveal a reduction in values of axial dispersion coefficient with increasing the air volumetric flow rate.

Transient Eddy Current Flow Metering: a calibration-free velocity measurement technique for liquid metals

Most inductive techniques for the velocity measurement of liquid metals have the common problem that the measured signals depend on the electrical conductivity and the temperature of the liquid metal. This is particularly unfavourable for applications with strong temperature fluctuations or for measurements that have to be performed in different liquid metals with the same sensor. Usually these sensors have to be calibrated extensively to ensure accurate measurement results. We present a new measurement technique called Transient Eddy Current Flow Metering (TECFM) which overcomes the need for prior calibration of the sensors. Its principle relies on imprinting transient eddy current systems into the liquid metal and to track their movement as they are advected with the flow. Two kinds of sensors that use this new measurement principle have been developed: An external sensor [1] for the contactless velocity measurement at the boundary of liquid metal flows, and an immersed sensor [2] which allows local velocity measurements in the vicinity of the sensor. Focusing on the latter we present the results of numerical simulations as well as the results of measurements that were performed in the eutectic alloy GaInSn at room temperature and in liquid sodium at 180 °C.

Differential diffusion effects in counter-flow premixed hydrogen-enriched methane and propane flames

The effects of differential diffusion and stretch sensitivity on propagation and stabilization of lean premixed hydrogen-enriched methane-air and propane-air flames are studied in a turbulent counter-flow apparatus. In these experiments, the unstretched laminar flame speed is kept constant through decreasing the mixture equivalence ratio, in order to minimize the effects of chemistry and highlight the effects of differential diffusion during hydrogen-enrichment. Bulk flow properties are also kept constant between laminar and turbulent flames. High-speed particle image velocimetry (PIV) is applied to quantify the flow velocity field using oil droplet seeding, enabling simultaneous flame position and velocity measurements. Data processing tools are developed through this study to quantify instantaneous local measurements of flame position, flame curvature, and apparent turbulent flame velocity within the imaged plane. Probability density functions (PDF) of instantaneous flame position show that, in hydrogen-enriched methane-air flames (effective Lewis number < 1), differential diffusion increases the turbulent burning rates throughout the whole hydrogen-enrichment range. However, in hydrogen-enriched propane-air flames, these effects are only observed at hydrogen content above 60% (by volume), where effective Lewis number falls below unity. PDFs of flame position also illustrated that the effects of differential diffusion become significant when the effective Lewis number < 0.8. In contrast, PDFs of turbulent flame velocities only showed a slight increase in local instantaneous velocities with increasing hydrogen content. Furthermore, it was illustrated that differential diffusion affects the flame front topology by increasing instantaneous flamelet curvature at below unity Lewis numbers, consistent with flame stability theory.

Measurement uncertainty of discharge air velocity by graphical integration in closed conduits using Pitot tubes

This paper addresses the measurement uncertainty in the determination of the discharge air velocity, using Pitot static tubes, for the flow-rate measurement in closed conduits related to ventilation installations. This indirect measurement method is supported in local air velocity measurements performed in known positions in the conduit’s cross-section. Graphical integration between extreme measuring points is one of the available techniques used for the calculation of the discharge air velocity. This paper illustrates a Monte Carlo simulation procedure for the measurement uncertainty propagation from the input quantities – local air velocities, measurement positions, conduit dimension and inner wall roughness – to the output quantity – discharge air velocity.

Local particles velocity measurement using differential linear capacitance matrix

A novel differential linear capacitance matrix (DLCM) was designed for measuring the velocity of the local particles within pneumatic conveying pipeline. The 3D simulation model of the DLCM was built and its sensitivity distribution was analyzed by the finite element method. The velocity measurement principle of the DLCM based on its spatial filtering effect was theoretically deduced, and the velocity of the local particles within the pipeline can be obtained by determining the narrow-band peak frequency of the output capacitance signal of the DLCM. Then the DLCM-based particle velocimeter was further developed and its performance was verified on a gravity-fed solids flow rig. Simulation and experimental results demonstrate that the measurement method is capable of measuring local particles velocity robustly with a relative error not greater than 5.5% and a repeatability less than ±7.78% over the velocity range of 2.4–5.8 m s−1.

Local Evaluation of Variation in Pulse Wave Velocity over the Cardiac Cycle using Single-Element Ultrasound Transducer.

A method and system for single-site measurement of local pulse wave velocity (PWV) and its variation over the cardiac cycle are presented. The proposed system employs a single-element ultrasound transducer and associated custom technology to record arterial diameter and wall thickness waveforms in real-time. Simultaneously acquired blood pressure, diameter and wall thickness parameters were used to evaluate diastolic local PWV (CD) and systolic local PWV (Cs) from an arterial site of interest. The developed prototype system was validated on a cohort of 15 subjects (age $=43\pm 12$ years) that includes normotensives and hypertensives. Cs and CD measurements were obtained from the left carotid artery. A significant difference between carotid Cs and CD $(\Delta \mathrm{C})$ was observed in all recruited subjects (group average $\Delta \mathrm{C} = 0.92\pm 0.76\mathrm{m}/\mathrm{s})$, illustrating the arterial pressure dependency of local PWV. The absolute values of Cs and CD were within a range of 3.39 m/s to 7.5 m/s and 3.12 m/s to 5.82 m/s respectively. Normotensive versus hypertensive group-wise analysis was performed to investigate the degree of variation in the carotid local PWV over a cardiac cycle among different BP categories. Study results demonstrated that the proposed approach has a potential to provide valuable surrogate markers for cardiovascular risk assessment.

Carotid Local Pulse Wave Velocity Measurement using Dual- Element Accelerometric Patch Probe.

In this work, we demonstrate an accelerometric patch probe with two microelectromechanical accelerometer sensors for local pulse wave velocity (PWV) measurement from the carotid artery. Dual acceleration plethysmogram (APG) signals were acquired from a small section of the artery by keeping the sensors at 32 mm apart. A custom analog front-end circuit (inter-channel delay $< 0.15$ ms) was used for reliable signal acquisition. Simultaneously acquired dual APG signals were processed in real-time and local PWV was evaluated in a beat-by-beat manner. A transversal study on a cohort of 15 volunteers (4 males, 11 females, mean age = $25.6 \pm 1.92$ years) was conducted to validate the developed prototype system. During the study, carotid local PWV and brachial blood pressure (BP) parameters were recorded from both sitting and standing posture. The absolute values of measured carotid local PWV were in the range of 3 m/s - 4.2 m/s (beat-to-beat variation $=$ 2.61% - 13.07%). Measured local PWV values significantly correlated with brachial systolic BP ($\textbf{R}^{\mathbf {2}} =$ 0.87) and diastolic BP ($\textbf{R}_{\mathbf {\, }}^{\mathbf {2}} \quad =$ 0.79). Logarithmic functions provided the best monotonic model for carotid local PWV versus brachial BP parameters for the recorded data points. The developed population-specific mathematical models were then used for cuffless evaluation of BP parameters from carotid local PWV. The root-mean-square error in the estimated systolic and diastolic pressure was 7.53 mmHg and 6.0 mmHg respectively. Study results illustrate the potential application of the developed dual-accelerometric system in non-invasive, continuous cuffless BP measurement techniques.

Arterial Blood Pressure Estimation From Local Pulse Wave Velocity Using Dual-Element Photoplethysmograph Probe

An arterial compliance, dual-element photoplethysmograph probe for local pulse wave velocity (PWV) measurement was developed. Initially, the experimental validation study was performed on 25 young volunteers (age =24.5 ± 4 years). Local PWV was assessed from a small section (23 mm) of the carotid artery. The prototype device demonstrated its capability of measuring reliable, repeatable, and reproducible carotid local PWV. Further, in 15 healthy male volunteers (age = 22.25 ± 3.5 years), carotid local PWV and brachial blood pressure (BP) were continuously recorded during their postexercise recovery period. Local PWV followed the changes in arterial BP parameters. The group average correlation coefficients (r) of local PWV versus BP parameters were between 0.772 ± 0.033 and 0.934 ± 0.028. In a population of 50 patients (normotensive and hypertensive) aged 24–80 years, local PWV–BP correlations were investigated. Local PWV tended to follow the diastolic BP (DBP; $r = 0.82$ ) and mean arterial pressure ( $r = 0.83$ ) better than systolic BP (SBP; $r = 0.69$ ). It was significantly inferior in tracking pulse pressure values ( $r = 0.35$ ). Cuffless estimation of arterial pressure was also performed on the same patients using measured carotid local PWV with best-case calibrations. Local PWV yielded good DBP prediction than SBP prediction. Statistically, significant correlation ( $r = 0.79$ ) and a root-mean-square error of 5.26 mmHg versus reference brachial DBP were achieved. The introduced technique has a potential for short- or long-term noninvasive, cuffless monitoring of BP parameters from superficial arteries.

Carotid stiffness is significantly correlated with wall-to-lumen ratio of retinal arterioles.

Wall-to-lumen ratio of retinal arterioles (W/L ratio) might serve as an in-vivo parameter of microvascular damage. No study has investigated the relationship between carotid stiffness and W/L ratio of retinal arteries. Therefore, the aim of the current study was to assess the correlation between local carotid stiffness, as assessed by echotracking technique, and W/L ratio of retinal arterioles, as assessed by noninvasive flowmetry in normotensive patients and in patients with primary hypertension. Two hundred and twenty-seven patients underwent renal arteries W/L ratio and local carotid-pulse wave velocity (carotid PWV) measurement. One hundred and fifteen patients had a diagnosis of primary hypertension, whereas 112 were normotensive patients. W/L ratio and carotid PWV were both related with clinic SBP (r = 0.17, P < 0.05; r = 0.50, P < 0.001), clinic pulse pressure (r = 0.22, P < 0.001; r = 0.55, P < 0.001), carotid SBP (r = 0.18, P < 0.05; r = 0.51, P < 0.001) and carotid pulse pressure (r = 0.24, P < 0.001; r = 0.56, P < 0.001). W/L ratio was correlated with carotid PWV (r = 0.18, P < 0.005). At multivariate analysis, carotid PWV remained independently associated with W/L ratio. In hypertensive and normotensive patients, carotid stiffness is significantly correlated with W/L ratio of retinal arteries, independently of possible confounders.

Particle Removal From Sandbed Deposits in Horizontal Annuli Using Viscoelastic Fluids

SummaryThis paper presents results of an experimental study on how fluid viscoelastic properties would influence the particle removal from the sandbed deposited in horizontal annuli. Water and two different viscoelastic fluids were used for bed-erosion experiments. The particle-image-velocimetry (PIV) technique was used to measure the local fluid velocity at the fluid/sandbed interface, allowing for accurate estimation of the fluid-drag forces and the turbulence stresses.It was found that polymer fluids needed to exert higher level drag forces (than those of water) on the sandbed to start movement of the particles. Results have also shown that, at the critical flow rate of bed erosion, the polymer fluids yielded higher local fluid velocities and turbulent stresses than those of water. Moreover, the local velocity measurements by means of the PIV technique and the resultant bed-shear-stress calculations indicated that enhancing polymer concentration under the constant flow rate should also enhance the drag forces acting on the sandbed. However, these improved fluid hydrodynamic forces did not result in any improvement in the bed erosion. Therefore, the mechanism causing the delay in the bed erosion by polymer additives could not be explained by any decrease in the local fluid velocity and the turbulence.The primary reason for the delayed bed erosion by the polymer fluids was suggested to be linked to their viscoelastic properties. Two possible mechanisms arising from the elastic properties of the polymer fluids that hinder bed erosion were further discussed in the paper. The stress tensor of the viscoelastic-fluid flow was analyzed to determine the normal stress differences and the resultant normal fluid force acting on the particles at the fluid/sandbed interface. The normal force induced by the normal stress differences of the viscoelastic fluid was identified as one of the possible causes of the delayed bed erosion by these types of fluids.

Single-source PPG-based local pulse wave velocity measurement: a potential cuffless blood pressure estimation technique

Objective: A novel photoplethysmograph probe employing dual photodiodes excited using a single infrared light source was developed for local pulse wave velocity (PWV) measurement. The potential use of the proposed system in cuffless blood pressure (BP) techniques was demonstrated. Approach: Initial validation measurements were performed on a phantom using a reference method. Further, an in vivo study was carried out in 35 volunteers (age = 28 ± 4.5 years). The carotid local PWV, carotid to finger pulse transit time (PTTR) and pulse arrival time at the carotid artery (PATC) were simultaneously measured. Beat-by-beat variation of the local PWV due to BP changes was studied during post-exercise relaxation. The cuffless BP estimation accuracy of local PWV, PATC, and PTTR was investigated based on inter- and intra-subject models with best-case calibration. Main results: The accuracy of the proposed system, hardware inter-channel delay (<0.1 ms), repeatability (beat-to-beat variation = 4.15%–11.38%) and reproducibility of measurement (r = 0.96) were examined. For the phantom experiment, the measured PWV values did not differ by more than 0.74 m s−1 compared to the reference PWV. Better correlation was observed between brachial BP parameters versus local PWV (r = 0.74–0.78) compared to PTTR (|r| = 0.62–0.67) and PATC (|r| = 0.52–0.68). Cuffless BP estimation using local PWV was better than PTTR and PATC with population-specific models. More accurate estimates of arterial BP levels were achieved using local PWV via subject-specific models (root-mean-square error ⩽2.61 mmHg). Significance: A reliable system for cuffless BP measurement and local estimation of arterial wall properties.

Influence of adsorbed and nonadsorbed polymer additives on the viscosity of magnesium oxide suspensions

ABSTRACTAdsorbed polymer additives have been employed to reduce water content and improve cement workability through lowering viscosity, but the influence of over‐dosage and the presence of nonadsorbed chains have yet to be fully understood. Model magnesium oxide (MgO) suspensions were used to investigate the potential processing effect of “free” chain concentration on cementitious mixtures. The rheological impact of the free chains was measured through incorporation of nonadsorbing poly(ethylene glycol) (PEG) to suspensions stabilized with an adsorbed comb‐polymer superplasticizer. Analyses of the rheological data, that showed viscosity‐increases and viscosity‐reduction due to free PEG concentrations revealed a transition from depletion flocculation to depletion stabilization that contributed to the flow properties of the suspensions. The viscosity‐reduction observed for high concentrations of free chains may be useful for improved mixing of cements with free polymer in addition to the adsorbed polycarboxylate ether‐based superplasticizer. Additionally, the influence of free PEG on the macroscale flow behavior was also examined through local velocity measurements under shear. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45696.

Optical Rheology of a Polydimethylsiloxane Fluid in Jeffrey-Hamel Type Flow

The rheo-optical behavior of a viscoelastic polydimethylsiloxane (PDMS) fluid was examined at room temperature for various pressure drops (flow rates) across a Jeffrey Hamel type converging wedge flow cell. The strain-rates were computed from local velocity measurements using laser Doppler anemometry (LDA), and the planar extensional flow behavior of the polymer melt was studied via birefringence measurements along the centerline of the flow cell. The linear relation between the stress and polarizability tensors were confirmed over a range of strain rates that extended well into the non-Newtonian region. The first normal stress difference (FNSD) was calculated from the local velocity measurements using a two-term Goddard-Miller model with a single Maxwell-type relaxation time constant of 0.0174 s computed from Rouse model and a zero-shear viscosity of 300 Pa.s. A linear stress-optical coefficient of 1.41 x 10-10 Pa-1 was obtained for PDMS in planar extensional flow at room temperature from the flow birefringence measurements and the first normal stress difference (FNSD) computed using the Goddard-Miller model. This compares well with values for PDMS in the range of 0.909 – 1.84 x 10-10 Pa-1 at room temperature as reported by various researchers.

A Magnetic Plethysmograph Probe for Local Pulse Wave Velocity Measurement.

We present the design and experimental validation of an arterial compliance probe with dual magnetic plethysmograph (MPG) transducers for local pulse wave velocity (PWV) measurement. The MPG transducers (positioned at 23 mm distance apart) utilizes Hall-effect sensors and permanent magnets for arterial blood pulse detection. The MPG probe was initially validated on an arterial flow phantom using a reference method. Further, 20 normotensive subjects (14 males, age = 24 ± 3.5 years) were studied under two different physical conditions: 1) Physically relaxed condition, 2) Postexercise condition. Local PWV was measured from the left carotid artery using the MPG probe. Brachial blood pressure (BP) was measured to investigate the correlation of BP with local PWV. The proposed MPG arterial compliance probe was capable of detecting high-fidelity blood pulse waveforms. Reliable local pulse transit time estimates were assessed by the developed measurement system. Beat-by-beat local PWV was measured from multiple subjects under different physical conditions. A profound increment was observed in the carotid local PWV for all subjects after exercise (average increment = 0.42 ± 0.22 m/s). Local PWV values and brachial BP parameters were significantly correlated (r ≥ 0.72), except for pulse pressure (r = 0.42). MPG arterial compliance probe for local PWV measurement was validated. Carotid local PWV measurement, its variations due to physical exercise and correlation with BP levels were examined during the in vivo study. A novel dual MPG probe for local PWV measurement and potential use in cuffless BP measurement.

Simultaneous Concentration and Velocity Maps in Particle Suspensions under Shear from Rheo-Ultrasonic Imaging

We extend a previously developed ultrafast ultrasonic technique [Gallot et al., Rev. Sci. Instrum. 84, 045107 (2013)] to concentration field measurements in non-Brownian particle suspensions under shear. The technique provides access to time-resolved concentration maps within the gap of a Taylor-Couette cell simultaneously to local velocity measurements and standard rheological characterization. Benchmark experiments in homogeneous particle suspensions are used to calibrate the system. We then image heterogeneous concentration fields that result from centrifugation effects, from the classical Taylor-Couette instability and from sedimentation or shear-induced resuspension.

Reactive Bubbly Flows

AbstractNo abstract.

A Local Air Velocity Measurement Method for Estimating Infiltration Heat Load through Doorway of the Cold Store

The frequent infiltration heat load through doorways accounts for a very large proportion of the total heat load of the cold store. Quantifying the air exchange rate (AER) can support the prediction of the infiltration heat load. In this paper, a local air velocity measurement method is proposed to estimate the AER. A vertical plane around the doorway area, the relation between local wind velocity and flow rate are mainly analyzed. The transient AER can be calculated by a simple equation based on the limited number of the local wind velocity around the vertical plane. The proposed method is verified by the tracer gas decay method. It is concluded that the proposed method shows good performance in accuracy. The rated errors are between ± 10% comparing to the results of tracer gas decay method. The transient infiltration heat load of the cold store can be calculated based on this method.

Human-walking-induced wake flow – PIV experiments and CFD simulations

Quantitative measurement of indoor air distribution or local air velocity around a moving occupant is necessary to study the contaminant transport and energy efficiency in a building. This study measured the longitudinal and cross-sectional air flow distributions at different moving speeds. Experiments were conducted in a small-scale chamber with a moving cylinder, which served as a surrogate of a scaled-down human body. The flow field was measured by the particle image velocimetry technique. The measurements revealed an upward air vortex and a strong downward airflow behind the moving body along the vertical centreline. A vertical mixing and recirculation could be predicted, and such air movements would likely carry the contaminants on and near the floor upwards along the moving path. Symmetric downward and expansive vortices were also observed in the wake flow during the movement, from the top corners of the moving object to the floor. The disturbance range of the moving body was related to the moving speed, especially in consideration of the initial position of the vortex. The experimental results were used to validate a computational fluid dynamic model, which captured these fundamental flow features reasonably well. The large eddy simulation model yielded a higher accuracy than the Reynolds Average Navier-Stokes model in predicting the unsteady instantaneous flow in the entire domain.

Transition of plug to slug flow and associated fluid dynamics

Transition of plug to slug flow is associated with bubble detachment from elongated bubble tail or bubble entrainment inside the liquid slug. The mechanism responsible for this transition was earlier identified by Ruder and Hanratty (1990) and Fagundes Netto et al. (1999) based on the shape of the hydraulic jump observed at elongated bubble tail region. The transition mechanism reported by Ruder and Hanratty (1990) and Fagundes Netto et al. (1999) was only based on their flow visualization study. Plug to slug transition and associated dynamics of bubble detachment from the elongated bubble is analysed in the present paper using flow visualization and local velocity measurements. Experiments are reported for 13 different inlet flow conditions of air and water phases. Images of plug/slug flow structures are captured at a rate of 4000 FPS using FASTCAM Photron camera and the local values of axial liquid velocity are measured using LDV system synchronised with a 3D automated traverse system. LDV measurement of local liquid velocity in the liquid slug and liquid film establishes the reason for detachment of bubbles from the slug bubble tail.

Simulation and experimental validation of reactive bubble column reactors

Bubble columns are widespread in chemical process engineering. The overall performance of these reactors relies on the interaction between the hydrodynamics, interfacial mass transfer and chemical reactions. The layout of these columns is commonly based on simplified integral models that are not able to track the complex interactions between the local hydrodynamics and the reactions. Hence, a detailed knowledge about the ongoing interactions is required. The local and temporal evolution of the carbon dioxide (CO2) chemisorption in aqueous NaOH solution in a cylindrical bubble column is investigated. Therefore, local measurements of hydrodynamics, bubble size and velocity, liquid velocity and concentration (pH-value) are done using a high speed PIV/LIF system combined with shadowgraphy. The results are compared to Euler-Euler based computational fluid dynamics simulations that take into account the ongoing reaction.