Opaque Fluids Research Articles

Fiber Optic Distributed Sensors for High-resolution Temperature Field Mapping.

The reliability of computational fluid dynamics (CFD) codes is checked by comparing simulations with experimental data. A typical data set consists chiefly of velocity and temperature readings, both ideally having high spatial and temporal resolution to facilitate rigorous code validation. While high resolution velocity data is readily obtained through optical measurement techniques such as particle image velocimetry, it has proven difficult to obtain temperature data with similar resolution. Traditional sensors such as thermocouples cannot fill this role, but the recent development of distributed sensing based on Rayleigh scattering and swept-wave interferometry offers resolution suitable for CFD code validation work. Thousands of temperature measurements can be generated along a single thin optical fiber at hundreds of Hertz. Sensors function over large temperature ranges and within opaque fluids where optical techniques are unsuitable. But this type of sensor is sensitive to strain and humidity as well as temperature and so accuracy is affected by handling, vibration, and shifts in relative humidity. Such behavior is quite unlike traditional sensors and so unconventional installation and operating procedures are necessary to ensure accurate measurements. This paper demonstrates implementation of a Rayleigh scattering-type distributed temperature sensor in a thermal mixing experiment involving two air jets at 25 and 45 °C. We present criteria to guide selection of optical fiber for the sensor and describe installation setup for a jet mixing experiment. We illustrate sensor baselining, which links readings to an absolute temperature standard, and discuss practical issues such as errors due to flow-induced vibration. This material can aid those interested in temperature measurements having high data density and bandwidth for fluid dynamics experiments and similar applications. We highlight pitfalls specific to these sensors for consideration in experiment design and operation.

Terahertz correlation spectroscopy infers particle velocity and rheological properties.

Correlation spectroscopy is an analytical technique that can identify the residence time of reflective or fluorescent particles in a measurement spot, allowing particle velocity or diffusion to be inferred. We show that the technique can be applied to data measured with a time-domain terahertz sensor. The speed of reflectors such as silica ballotini or bubbles can thus be measured in fluid samples. Time-domain terahertz sensors can therefore be used, for the first time, to measure rheological properties of optically opaque fluids that contain entrained reflectors, such as polyethylene beads.

Swarming in viscous fluids: Three-dimensional patterns in swimmer- and force-induced flows.

We derive a three-dimensional theory of self-propelled particle swarming in a viscous fluid environment. Our model predicts emergent collective behavior that depends critically on fluid opacity, mechanism of self-propulsion, and type of particle-particle interaction. In "clear fluids" swimmers have full knowledge of their surroundings and can adjust their velocities with respect to the lab frame, while in "opaque fluids" they control their velocities only in relation to the local fluid flow. We also show that "social" interactions that affect only a particle's propensity to swim towards or away from neighbors induces a flow field that is qualitatively different from the long-ranged flow fields generated by direct "physical" interactions. The latter can be short-ranged but lead to much longer-ranged fluid-mediated hydrodynamic forces, effectively amplifying the range over which particles interact. These different fluid flows conspire to profoundly affect swarm morphology, kinetically stabilizing or destabilizing swarm configurations that would arise in the absence of fluid. Depending upon the overall interaction potential, the mechanism of swimming ( e.g., pushers or pullers), and the degree of fluid opaqueness, we discover a number of new collective three-dimensional patterns including flocks with prolate or oblate shapes, recirculating pelotonlike structures, and jetlike fluid flows that entrain particles mediating their escape from the center of mill-like structures. Our results reveal how the interplay among general physical elements influence fluid-mediated interactions and the self-organization, mobility, and stability of new three-dimensional swarms and suggest how they might be used to kinetically control their collective behavior.

超音波流速分布計を用いたレオメトリについて

We introduced our recent works on development of rheometry utilizing ultrasonic velocity profiling (UVP) that can capture spatio-temporal velocity information even in opaque fluids. Rheological properties describing relations in stress, strain and strain rate are reflected into flow field, and analyzing flow information obtained in simple unsteady flow configurations may provide the rheological properties. We adopted cylindrical vessel with regular oscillation on the cylinder wall as the configuration, and evaluated effective Newtonian viscosity of viscous oil with dispersed small bubbles and time-dependent behavior of montmorillonite suspension that is one of thixotropic fluids to demonstrate applicability of the rheometry. We also explained novel idea of ‘flow surface’ that aims to describe rheological properties without using rheology models.

ИЗМЕРЕНИЕ ТЕМПЕРАТУРНЫХ ПОЛЕЙ ПОВЕРХНОСТИ ЖИДКОСТИ ПРИ ПОМОЩИ ТОНКОЙ ПЛАСТИНКИ И ТЕПЛОВИЗОРА

In the study of thermal convection in the opaque magnetic fluids convective rolls can be visualized using the thin textolite plate and infrared camera. The plate is one of the boundaries of the convective cavity - vertical layer. The possibility of quantitative measurements of temperature fields of the liquid surface is evaluated by this method. Temperature fields in thin textolite plate, bounding the fluid layer, non-uniform temperature, have been calculated. Laboratory modeling of periodic convective structures to study the temperature distribution along the plate, obtained with an infrared thermal imager, has been performed. According to the results of calculations and experiments systematic measurement errors of spatial harmonics of the thermal field, generated by a convective flow, have been evaluated.Received 11.11.2015; accepted 18.01.2016

Geochemistry and fluid characteristics of the Dalli porphyry Cu–Au deposit, Central Iran

The Miocene Dalli porphyry Cu–Au deposit in the central part of Urumieh–Dokhtar magmatic arc is the first reported Au-rich porphyry Cu deposit in the Zagros orogenic belt. The Cu–Au mineralization is mainly hosted in diorite and quartz diorite intrusions, presenting as numerous veinlets in the altered wall rocks, with potassic, phyllic, and propylitic alteration developed. Based on the mineral assemblages and crosscutting relations of veinlets, hydrothermal mineralization–alteration occurred in at least three stages, characterized by veinlets of (1) Qtz+Kfs+Mag±Ccp, (2) Qtz+Py+Ccp±Bn±Cv±Cc and, (3) Qtz+Chl+Bt. The ore-bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas, including LREE fractionated pattern, strong enrichment in LILE (Cs, Rb, Ba, Pb, and U), and depletion of HFSE, with marked negative Ti and Nb anomalies. The adakite-like ore-hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of Y and Eu/Eu∗ with increasing SiO2 content, respectively. Moreover, they exhibit a significant increasing trend of Sr/Y with decreasing of Y, which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma. A relatively flat HREE pattern with low Dyn/Ybn and Nb/Ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust. Based on the phase assemblages confirmed by detailed laser Raman spectroscopy analyses and proportion of solid, liquid, and gaseous components, five types of fluid inclusions were recognized, which are categorized as; (1) liquid-rich two phase (liquidH2O+vaporH2O) (IIA), (2) vapor-rich two phase (vaporH2O/CO2+liquidH2O) (IIB), (3) high saline simple fluids (IIIA; liquidH2O+vaporH2O+Hl), (4) high saline opaque mineral-bearing fluids (IIIB; liquidH2O+vaporH2O+Hl+Hem+Ccp+Py) and (5) multi-phase type (IIIAB; liquidH2O+vaporH2O+Hl+Anh+Hem+Mag+Ccp). In early stage veins, the homogenization temperature of multiphase inclusions as high as 620°C, with corresponding salinities of up to 75wt.% NaCl equivalent represent the initial ore-forming fluids. From early to late stage veins, the gradual decrease of homogenization temperature of saline inclusions (IIIAB, IIIA, and IIIB) from 620 to 340°C (corresponding salinities of 75–35wt.% NaCl equivalent) may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater. The common association of hematite and anhydrite daughter phases with the most primitive inclusions (IIIAB) in early-stage veins and the lack of CO2-bearing inclusions in the middle to late stage veins reveal CO2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization (second generation of veins). It seems that magnetite crystallization and CO2-escape have a decisive role in oversaturation of S2− and subsequent rapid and large-scale precipitation of sulfides in second generation of veins at the Dalli deposit.

Ultrasonic velocity profiling rheometry based on a widened circular Couette flow

We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling.

Accurate velocity measurements of boundary-layer flows using Doppler optical coherence tomography

Pulsed ultrasound Doppler velocimetry and nuclear magnetic resonance imaging are popular non-invasive measurement methods for flows of opaque fluids. The spatial and temporal resolution of these methods, however, is quite limited, and they lack accuracy, especially close to solid boundaries. In this paper, we show that solution to these problems is achieved by using Doppler optical coherence tomography (DOCT). DOCT provides simultaneous information about the fluid structure and velocity with very high spatial and temporal resolution. For benchmarking of the method we use water as the reference fluid. We show how DOCT gives a very good agreement with theory for the velocity profile, skin friction and viscosity directly from the measurement signal. The velocity profile extends from the turbulent region to viscous sublayer, and viscosity of the fluid can be calculated also from a turbulent flow with a good accuracy. Overall, DOCT is seen to be very well suited for providing new insight into boundary-layer flows, rheology and skin friction.

Suggestions for automatic quantitation of endoscopic image analysis to improve detection of small intestinal pathology in celiac disease patients

Although many groups have attempted to develop an automated computerized method to detect pathology of the small intestinal mucosa caused by celiac disease, the efforts have thus far failed. This is due in part to the occult presence of the disease. When pathological evidence of celiac disease exists in the small bowel it is visually often patchy and subtle. Due to presence of extraneous substances such as air bubbles and opaque fluids, the use of computerized automation methods have only been partially successful in detecting the hallmarks of the disease in the small intestine—villous atrophy, fissuring, and a mottled appearance. By using a variety of computerized techniques and assigning a weight or vote to each technique, it is possible to improve the detection of abnormal regions which are indicative of celiac disease, and of treatment progress in diagnosed patients. Herein a paradigm is suggested for improving the efficacy of automated methods for measuring celiac disease manifestation in the small intestinal mucosa. The suggestions are applicable to both standard and videocapsule endoscopic imaging, since both methods could potentially benefit from computerized quantitation to improve celiac disease diagnosis.

Optical Coherence Tomography Velocimetry with Complex Fluids

We present recent results obtained with an Optical Coherence Tomography Velocimetry technique. An optical interferometer measures the velocity of a sheared fluid at specific depths of the sample using the coherence length of the light source. The technique allows the dynamics of 3 pico liter volumes to be probed inside opaque complex fluids. In a study of opaque starch suspensions, classical bulk rheology experiments show non-linear shear thickening, whereas observations of the velocity profiles as a function of distance across the gap show Newtonian behavior. The ability of the technique to measure velocity fluctuations is also discussed for the case of polyacrylamide samples which were observed to display shear banding behavior. A relationship between the viscoelasticity of the sample and the size of the apparent fluctuations is observed.

Quantifying ultraviolet inactivation kinetics in nearly opaque fluids

The use of ultraviolet light for inactivation of pathogens is an engrained, low-cost, eco-friendly method for disinfection of nearly transparent (UVT254 > 30%/cm) contaminated fluids for which a standard-collimated beam apparatus is typically used for measurement of intrinsic inactivation kinetics. However, such a device cannot be used for low ultraviolet transmittance (UVT254 < 30%/cm) and nearly opaque (UVT254 < 10%/cm) fluids because of the lack of sufficient mixing and intrinsic inactivation kinetics controlled by dose distribution and mass-transfer effects. In this paper, a computational fluid dynamics (CFD) model was used to determine the validity regime for accurate ultraviolet inactivation kinetics studies in low transmittance and nearly opaque fluids when a new Taylor–Couette collimated beam apparatus, which exploits flow instability through the formation of toroidal counter-rotating vortices, is used for irradiations. A Taylor number of ∼ 46,500 was sufficient to overcome the very short UV light penetration at UVT254 ∼ 0.001%/cm as long as the log10 reduction value was used as controlling parameter. Specifically, it was identified that, in case of first-order inactivation kinetics, the applied average dose (AD) should not be higher than three times the dose required for one log10 inactivation (also known as D10) in order to generate data for accurate kinetic studies.

Photocatalytic degradation of malic acid using a thin coated TiO2‐film: Insights on the mechanism of photocatalysis

Decontamination of opaque fluids using photocatalysts and near Ultraviolet (UV) irradiation involves major technical challenges. This study considers a thin TiO2 layer placed in a new Chemical Reactor Engineering Centre (CREC)‐photoreactor cell. This new photoreactor cell is used for the photocatalytic degradation of malic and malonic acids, typical apple juice components. Conversion of organic species can only proceed through the “dark side” of the TiO2 layer, which is in direct contact with the fluid. Under the selected operating conditions both external mass‐transfer limitations and photolysis are found to be negligible. Macroscopic radiation balance shows that 92% of near UV radiation is absorbed by the ‘back side” of the TiO2‐film. Photocatalytic degradation experiments with 10, 20, 30, and 40 ppm malic acid initial concentrations, show that malonic acid is a main intermediate. Complete malic acid conversion occurs after 5–8 h of irradiation. Kinetic modeling of malic and malonic acid photodegradation with kinetic parameter estimation is performed using both an “in series” and an “in series‐parallel” reaction networks. The “in series‐parallel” reaction network displays better ability for predicting CO2 formation, showing maximum quantum yields of 14.2%. Given that in the CREC‐photoreactor cell with a thin TiO2‐film, photocatalysis can only proceed via the transfer of mobile “h+” sites from the irradiated side to the “dark side', this study demonstrates the significance of this step on the overall photocatalysis mechanism. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3286–3299, 2014

New insight into rheology and flow properties of complex fluids with Doppler optical coherence tomography.

Flow properties of complex fluids such as colloidal suspensions, polymer solutions, fiber suspensions and blood have a vital function in many technological applications and biological systems. Yet, the basic knowledge on their properties is inadequate for many practical purposes. One important reason for this has been the lack of effective experimental methods that would allow detailed study of the flow behavior of especially opaque multi-phase fluids. Optical Coherence Tomography (OCT) is an emerging technique capable of simultaneous measurement of the internal structure and motion of most opaque materials, with resolution in the micrometer scale and measurement frequency up to 100 kHz. This mini-review will examine the recent results on the use of Doppler-OCT in the context of flows and rheological properties of complex fluids outside biomedical field.

Thermofluidynamics of the multiphase flow inside cylindroconical fermenters with different scales

In this work the experimental investigations of the flow and the temperature field during the fermentation of beer in cylindroconical tanks are presented. The flow stability is affected of the height/diameter ratio. Increasing the ratio leads to an unsteady, three-dimensional flow with several smaller vortices. In the course of our research the experiments have been performed with real fermentation fluid (wort) under various height/diameter ratio. In the study, two tanks have been used in the laboratory and on an industrial scale, which were equipped with special design features. The velocity fields during a real fermentation process are measured by means of Ultrasound Doppler Velocimetry. It permits measurements in opaque fluids. Furthermore temperature measurements are conducted to analyse the interrelationship between the heat transfer and flow structure.

Experimental Investigation of Parameters, Influencing Velocity Fields during Beer Fermentation

In the course of the research aiming on the optimisation of beer fermentation, a large number of fermentations have been performed under various boundary conditions. We carried out different measurements, including temperature and velocity investigations. Due to turbidity, the latter cannot be performed easily by using common techniques like laser Doppler anemometry or particle image velocimetry. Therefore the ultrasound Doppler velocimetry got utilised. It permits measurements in opaque fluids and provides velocity fields for any time during the fermentation.

Using tomography to visualize the continuous-flow mixing of biopolymer solutions inside a stirred tank reactor

The vast majority of non-Newtonian fluids are naturally opaque; therefore, visualizing the flow field of such fluids inside a reactor is a challenging task. To identify non-ideal flows, such as dead volumes and channeling, in a continuous-flow mixing system, the flow field inside a stirred tank reactor was visualized using electrical resistance tomography (ERT), an efficient non-intrusive measurement technique. The key objective of this study was to employ the ERT technique in order to explore the effects of the inlet and outlet locations (four configurations: top inlet–bottom outlet, bottom inlet–top outlet, bottom inlet–bottom outlet, and top inlet–top outlet), fluid rheology (0.5–1.5% xanthan gum concentration), jet velocity (0.317–1.660ms−1), feed flow rate (5.3×10−5–2.36×10−4m3s−1), impeller type (the Rushton turbine and Maxblend impellers), and impeller speed (54–250rpm) on the flow patterns generated in the continuous-flow mixing of the xanthan gum solution, which is a pseudoplastic fluid exhibiting yield stress. Using 2D and 3D tomography images, this article effectively presents a competent method to visualize the flow of opaque fluids in laminar and transitional regions inside a reactor. In this study, the existence of non-ideal flows in a stirred tank reactor for opaque fluids was identified using ERT. The quantitative results showed that the tracer distribution (or mixing quality) inside stirred vessel was enhanced by decreasing the fluid yield stress, increasing the impeller speed, increasing the jet velocity, and using the close clearance impeller. The results also showed that the location of the inlet and outlet streams has a significant effect on the mixing quality. To improve the design of the continuous-flow mixing of non-Newtonian fluids, the findings of this study can be integrated into the design criteria to achieve optimal mixing results.

Tomography images to analyze the deformation of the cavern in the continuous‐flow mixing of non‐Newtonian fluids

Tomography, an efficient nonintrusive technique, was employed to visualize the flow in continuous‐flow mixing and to measure the cavern volume (Vc) in batch mixing. This study has demonstrated an efficient method for flow visualization in the continuous‐flow mixing of opaque fluids using two‐dimensional (2‐D) and 3‐D tomograms. The main objective of this study was to explore the effects of four inlet‐outlet configurations, fluid rheology (0.5–1.5% xanthan gum concentration), high‐velocity jet (0.317–1.660 m s−1), and feed flow rate (5.3 × 10−5−2.36 × 10−4 m3 s−1) on the deformation of the cavern. Dynamic tests were also performed to estimate the fully mixed volume (Vfully mixed) for the RT, A310, and 3AM impellers in a continuous‐flow mixing system, and it was found that Vfully mixed was greater than Vc. Incorporating the findings of this study into the design criteria will minimize the extent of nonideal flows in the continuous‐flow mixing of complex fluids and eventually improve the quality of end‐products. © 2013 American Institute of Chemical Engineers AIChE J, 60: 315–331, 2014

Novel ultrasound array measurement system for flow mapping of complex liquid metal flows

In magnetohydrodynamics, model experiments are commonly conducted to investigate the interaction between magnetic fields and electrically conductive fluids. The available flow instrumentation for opaque fluids usually lacks the ability to capture and visualize a velocity field in one shot. We present a multidimensional ultrasound array Doppler velocimeter that employs multiple line arrays of transducers and allows the resolution of small scale structures in complex flows. The system achieves a lateral resolution up to 3 mm, an axial resolution of approx. 1.4 mm and frame rates up to 30 Hz in metal melts at room temperature. A flexible sensor arrangement allows for various measurement configurations, e.g. four planes can be measured simultaneously with one velocity component, two planes with two components or two lines with three components. We present an experiment in a square-shaped container driven by a rotating magnetic field and results of a model experiment for continuous steel casting. The measurement system has proven to be a powerful tool for research in magnetohydrodynamics.

Echo Particle Image Velocimetry

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.(1) Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.(2) For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.(3,4,5,6) In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine(7) with a PC running commercial particle image velocimetry (PIV) software(8) is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported. For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/δt. (See 9 for a review of ultrasound imaging.) For a typical EPIV experiment, the frame rate is between 20-60 fps, depending on flow conditions, and 100-1000 B-mode images of the spatial distribution of the tracer particles in the flow are acquired. Once acquired, the B-mode ultrasound images are transmitted via an ethernet connection to the PC running the PIV commercial software. Using the PIV software, tracer particle displacement fields, D(x,y)[pixels], (where x and y denote horizontal and vertical spatial position in the ultrasound image, respectively) are acquired by applying cross correlation algorithms to successive ultrasound B-mode images.(10) The velocity fields, u(x,y)[m/s], are determined from the displacements fields, knowing the time step between image pairs, ΔT[s], and the image magnification, M[meter/pixel], i.e., u(x,y) = MD(x,y)/ΔT. The time step between images ΔT = 1/fps + D(x,y)/B, where B[pixels/s] is the time it takes for the ultrasound probe to sweep across the image width. In the present study, M = 77[μm/pixel], fps = 49.5[1/s], and B = 25,047[pixels/s]. Once acquired, the velocity fields can be analyzed to compute flow quantities of interest.

Optimisation of Pulsed Ultrasonic Velocimetry system and transducer technology for industrial applications

Pulsed Ultrasonic Velocimetry, commonly referred to as Ultrasonic Velocity Profiling (UVP) in research and engineering applications, is both a method and a device to measure an instantaneous one-dimensional velocity profile in opaque fluids along a measurement axis by using Doppler echography. Studies have suggested that the accuracy of the measured velocity gradient close to wall interfaces need to be improved. The reason for this is due to distortion caused by cavities situated in front of ultrasonic transducers, measurement volumes overlapping wall interfaces, refraction of the ultrasonic wave as well as sound velocity variations (Doppler angle changes). In order to increase the accuracy of velocity data close to wall interfaces and solve previous problems a specially designed delay line transducer was acoustically characterised and evaluated. Velocity profiles measured using the delay line transducer, were initially distorted due to the effect of finite sample volume characteristics and propagation through the delay line material boundary layers. These negative effects were overcome by measuring physical properties of the ultrasonic beam and implementing a newly developed deconvolution procedure. Furthermore, custom velocity estimation algorithms were developed, which improved the time resolution and penetration depth of the UVP system. The optimised UVP system was evaluated and compared to standard transducers in three different straight pipes (inner diameters of 16, 22.5 and 52.8mm). Velocity data obtained using the optimised UVP system showed significant improvement close to wall interfaces where the velocity gradients are high. The new transducer technology and signal processing techniques reduced previously mentioned problems and are now more suitable for industrial process monitoring and control.