Coupling Fluids Research Articles

СРАВНИТЕЛЬНЫЙ АНАЛИЗ ПРИМЕНЕНИЯ КОНТАКТНЫХ ЖИДКОСТЕЙ В ДЕФЕКТОСКОПИИ НА ПРИМЕРЕ УЛЬТРАЗВУКОВОГО КОНТРОЛЯ ПОВЕРХНОСТИ КАТАНИЯ ЦЕЛЬНОКАТАНОГО КОЛЕСА

Coupling fluids are important flaw detection materials that are used during ultrasonic testing in order to find out acoustic contact between the piezoelectric transducer and the object of control. The paper considers coupling fluids of various viscosities that can be used as a coupling medium for ultrasonic flaw detection. A comparative analysis of the effect of the studied coupling fluids on the sensitivity of the control is carried out, which is determined by the attenuation of the transmitted ultrasonic signal through the roll surface of the car wheelset wheel. The control sensitivity is assessed on the flat and inclined surfaces of the all-rolled wheel. The introduction of ultrasound into the wheel material (steel 2) is carried out by an inclined piezoelectric transducer at an angle α = 900, with an oscillation frequency f = 0.4 MHz. It is found out that by providing a reliable constant force of the ultrasonic transducer P121-90-0.4 due to the permanent magnets built into it, an increase in the viscosity of the coupling fluid can significantly affect the amplitude of the received echo signals. During the research, it is found that low-viscosity coupling fluids are characterized by stable coupling regardless of the time and clamping force of the transducer, in contrast to high-viscosity coupling media, when using them sharp fluctuations in the overall gain of the second through signal in AGC zone are observed on the flaw detector screen. Therefore, in practice, the use of high-viscosity coupling media leads to a sharp increase in signal amplification (amplitude), which may result in over reject.

Non-Contact and Self-Calibrated Photopyroelectric Method for Complete Thermal Characterization of Porous Materials.

A general theory of a photopyroelectric (PPE) configuration, based on an opaque sample and transparent pyroelectric sensor, backing and coupling fluids is developed. A combined back-front detection investigation, based on a frequency scan of the phase of the PPE signals, followed by a self-normalization of the phases' behavior, leads to the possibility of simultaneously measuring both thermal effusivity and diffusivity of a solid sample. A particular case of this configuration, with no coupling fluid at the sample/backing interface and air instead of coupling fluid at the sample/sensor interface (non-contact method) is suitable for simultaneous measurement ofboth thermal diffusivity and effusivity (in fact complete thermal characterization) of porous solids. Compared with the already proposed configurations for investigations of porous materials, this novel configuration makes use of a fitting procedure with only one fitting parameter, in order to guarantee the uniqueness of the solution. The porous solids belong to a class of materials which are by far not easy to be investigated using PPE. To the best of our knowledge, porous materials represent the only type of compounds, belonging to condensed matter, which were not taken into consideration (until recently) as potential samples for PPE calorimetric investigations. Consequently, the method proposed in this paper complete the area of applications of the PPE method. Applications on some porous building materials and cellulose-based samples validate the theory.

A Versatile and Shelf-Stable Dielectric Coupling Medium for Microwave Imaging

To develop a new class of emulsions using a protein-based emulsifier as the coupling fluid for microwave imaging systems. In this paper, we provide a theoretical basis for engineering shelf-stable dielectric fluids, a step-by-step formulation method, and measurements of complex dielectric properties in the frequency range of 0.5-3 GHz, which can be applicable for many of the recent microwave imaging systems. This medium was primarily designed for long-term stability while providing a controllable range of complex dielectric permittivities given different fractions of its constituents. Consequently, this emulsion shows dielectric stability in open air throughout a 7-day experiment and temperature insensitivity over the range of 0 ° C to 60 ° . This control over dielectric permittivity enables formulations that tune the background-to-target contrast to the linearizable regime of iterative inverse scattering algorithms. Accordingly, the emulsion conductivity can also be controlled and reduced to maintain the required signal-to-noise ratio within the dynamic range of the imaging system. The new formulation overcomes the practical challenges of engineering coupling fluids for microwave imaging systems, e.g., temporal stability, non-toxic, low sensitivity to temperature variation, and easy formulation from readily available and inexpensive materials. The achieved properties associated with this new fluid are of particular benefit to microwave imaging systems used in thermal therapy monitoring.

Simulation of Counter-Current Spontaneous Imbibition Based on Momentum Equations with Viscous Coupling, Brinkman Terms and Compressible Fluids

A numerical model is investigated representing counter-current spontaneous imbibition of water to displace oil or gas from a core plug. The model is based on mass and momentum conservation equations in the framework of the theory of mixtures. We extend a previous imbibition model that included fluid–rock friction and fluid–fluid drag interaction (viscous coupling) by including fluid compressibility and Brinkman viscous terms. Gas compressibility accelerated recovery due to gas expansion from high initial non-wetting pressure to ambient pressure at typical lab conditions. Gas compressibility gave a recovery profile with two characteristic linear sections against square root of time which could match tight rock literature experiments. Brinkman terms decelerated recovery and delayed onset of imbibition. Experiments where this was prominent were successfully matched. Both compressibility and Brinkman terms caused recovery deviation from classical linearity with the square root of time. Scaling yielded dimensionless numbers when Brinkman term effects were significant.Article HighlightsSpontaneous imbibition with viscous coupling, compressibility and Brinkman terms.Viscous coupling reduces spontaneous imbibition rate by fluid–fluid friction.Brinkman terms delay early recovery and explain seen delayed onset of imbibition.Gas compressibility accelerates recovery and can be significant at lab conditions.Gas compressibility gives recovery with two root of time lines as seen for shale.

On the replacement of water as coupling medium in scanning acoustic microscopy analysis of sensitive electronics components

The present paper studies the use of isopropyl alcohol and fluorocarbon liquids as coupling fluids for acoustic microscopy non-destructive testing of electronic flight components. For these components the standard coupling liquid water sometimes should be avoided in order to minimize sample contamination. The sound velocities of three different fluorocarbon liquids are measured, their ultrasound attenuation coefficients are estimated, and comparative failure analysis images on various electronics components are obtained by using water and these four alternative coupling liquids.

The use of non-cavitating coupling fluids for intensifying sonoelectrochemical processes.

For the first time, we have investigated the beneficial effects of non-cavitating coupling fluids and their moderate overpressures in enhancing mass-transfer and acoustic energy transfer in a double cell micro-sonoreactor. Silicon and engine oils of different viscosities were used as non-cavitating coupling fluids. A formulated monoethylene glycol (FMG), which is a regular cooling fluid, was also used as reference. It was found that silicon oil yielded a maximum acoustic energy transfer (3.05W/cm2) from the double jacketed cell to the inner cell volume, at 1bar of coupling fluid overpressure which was 2.5 times higher than the regular FMG cooling fluid. It was also found that the low viscosity engine oil had a higher acoustic energy value than that of the high viscosity engine oil. In addition, linear sweep voltammograms (LSV) were recorded for the quasi-reversible Fe2+/Fe3+ redox couple (equimolar, 5×10-3 M) on a Pt electrode in order to determine the mass-transport limited current density (jlim) and the dimensionless Sherwood number (Sh). From the LSV data, a statistical analysis was performed in order to determine the contribution of acoustic cavitation in the current density variation |Δj|average. It was found that silicon oil at 1bar exhibited a maximum current density variation, |Δj|average of ~2mA/cm2 whereas in the absence of overpressure, the high viscosity engine oil led to a maximum |Δj|average which decreased gradually with increasing coupling fluid overpressure. High viscosity engine oil gave a maximum Sh number even without any overpressure which decreased gradually with increasing overpressure. The Sh number for silicon oil increased with increasing overpressure and reached a maximum at 1bar of overpressure. For any sonoelectrochemical processes, if the aim is to achieve high mass-transfer and acoustic energy transfer, then silicon oil at 1bar of overpressure is a suitable candidate to be used as a coupling fluid.

Thermal Effusivity Investigations of Solid Thermoelectrics Using the Front Photopyroelectric Detection

The front photopyroelectric configuration (FPPE), making use of air as a coupling fluid between the sample and sensor, was applied to measure the thermal effusivity of some solid thermoelectric materials. The investigated samples were ZnO, CuCrO2, Cu4Sn7S16, TiS3 and two samples of high manganese silicide (HMS) thermoelectric materials. Most of these materials are porous and consequently, the classical PPE method, making use of standard coupling fluids between sensor and sample, cannot be used due to the fact that the coupling fluid penetrates inside the sample and leads to incorrect results. With this work we extend (to thermoelectric solids) the area of application of a method, recently proposed by Salazar et al. (Measurement 121: 96, 2018). Experimentally, the thermal effusivity is obtained from a multi-parametric fit of the phase of the FPPE signal as a function of the modulation frequency (with sample’s thermal effusivity, thickness of the sensor-sample air gap and heat losses by convection and radiation, as fitting parameters). It was demonstrated that, in some particular cases, the three parameters are independent and consequently, the solution of the fit is unique. Where possible, the obtained results have been compared with data from the literature and good agreement was found.

Experimental design and numerical investigation of a photoacoustic sensor for a low-power, continuous-wave, laser-based frequency-domain photoacoustic microscopy.

.We have developed a photoacoustic (PA) sensor using a low-power, continuous- wave laser and a kHz-range microphone. The sensor is simple, flexible, cost-effective, and compatible with commercial optical microscopes. The sensor enables noncontact PA measurements through air, whereas most current existing PA techniques require an acoustic coupling liquid for detection. The PA sensor has three main components: one is the chamber that holds the sample, the second is a resonator column used to amplify the weak PA signals generated within the sample chamber, and the third is a microphone at the end of the resonator column to detect the amplified signals. The chamber size was designed to be as the thermal diffusion length and viscous-thermal damping of air at room pressure and temperature are 2 and 1 mm, respectively. We numerically and experimentally examined the effect of the resonator column size on the frequency response of the PA sensor. The quality factor decreased significantly when the sample chamber size was reduced from to due to thermos-viscous damping of the air. The quality factor decreased by 27%, demonstrating the need for optimal design for the sample chamber and resonator column size. The system exhibited noise equivalent molecular sensitivity (NEM) per unit bandwidth () of or or 33 zeptomol, which is an improvement of 2.2 times compared to the previous system design. This PA sensor has the potential for noncontact high-resolution PA imaging of materials without the need for coupling fluids.

Systematic study of the effect of ultrasound gel on the performances of time-domain diffuse optics and diffuse correlation spectroscopy.

Recently, multimodal imaging has gained an increasing interest in medical applications thanks to the inherent combination of strengths of the different techniques. For example, diffuse optics is used to probe both the composition and the microstructure of highly diffusive media down to a depth of few centimeters, but its spatial resolution is intrinsically low. On the other hand, ultrasound imaging exhibits the higher spatial resolution of morphological imaging, but without providing solid constitutional information. Thus, the combination of diffuse optical imaging and ultrasound may improve the effectiveness of medical examinations, e.g. for screening or diagnosis of tumors. However, the presence of an ultrasound coupling gel between probe and tissue can impair diffuse optical measurements like diffuse optical spectroscopy and diffuse correlation spectroscopy, since it may provide a direct path for photons between source and detector. A systematic study on the effect of different ultrasound coupling fluids was performed on tissue-mimicking phantoms, confirming that a water-clear gel can produce detrimental effects on optical measurements when recovering absorption/reduced scattering coefficients from time-domain spectroscopy acquisitions as well as particle Brownian diffusion coefficient from diffuse correlation spectroscopy ones. On the other hand, we show the suitability for optical measurements of other types of diffusive fluids, also compatible with ultrasound imaging.

Pressure Influence on Acoustic Cavitation Phenomenonin Ionic Liquids: Electrochemical Study

The propagation of an acoustic wave into a solution can lead to the break of liquid cohesion strengths. This results in the nucleation, growth and collapse of cavitation bubbles feed by solvent vapors and dissolved gases. This collapse may be beneficial as in the case of cleaning processing, but is clearly detrimental in some application as in the case of therapeutic treatments such as tumor ablation, or for the ultrasonic power transmission in coupling fluids. For the electrochemical processes assisted by ultrasound, its control is mandatory. Then, this phenomenon must be reduced by the application of over-pressures into the reactors [1]. To be able to determine the respective contributions of dissolved gases and of vapors into the cavitation bubble collapse, the present work will seek the effect of a limitation in dissolved gases into a sonoreactor by controlling the pressure in a low vapor pressure media: ionic liquids. Those solvents are constituted of a dissymmetric anion and cation, are liquid at room temperature, and show excellent properties for our tests such as a great conductivity. As their vapor pressure is exceptionally low, only the dissolved gases will contribute to the cavitation: as the content in dissolved gas is driven by the pressure, its reduction will result in a reduction of the cavitation activity. In order to quantify this level, the diffusion study of electrochemical species was used as mass transfer sensor [2]. An electroactive species (Ferrocene) forming a rapid and reversible system is present in the solution at low concentration, and in presence of ultrasound, two contribution to the current in steady state conditions can be observed: one depending of the time and the other independent. Both are respectively proportional to the flow generated by the acoustic convection and to the bubble collapse at the electrode interface. The results show an important decrease of the cavitation phenomenon for argon pressure lower than 0.6 bar. A mathematical treatment of the curves allows the extrapolation up to the absolute cavitation quenching, at which the single contribution comes from convection. [1] Parag R. Gogate, Aniruddha B. Pandit. 2005, Ultrasonic Sonochemistry , 12 , 21_27. [2] Pollet B.G.,Hihn J-Y.,Doche M.L., Mandroyan A., Lorimer J-P., Mason T.J. 2007 , Journal of Electrochemistry Society, 154 , 131-138. Figure 1

A novel temperature swing adsorption process for natural gas purification: Part I, model development

Abstract This article investigates a novel TSA-based gas separation cycle that uses a microchannel monolith with a hollow polymer-adsorbent matrix coated along the inner walls of each microchannel. CO2 is removed from CH4 by passing impure feed gas through the microchannels, followed by a sequential flow of desorbing hot liquid, cooling liquid, and purge gas through the same microchannels. This configuration is expected to augment the heat and mass transfer to the adsorbent due to direct contact between the transfer fluid and the adsorbent layer, and also reduce the overall system size due to flow of the working and coupling fluids through the same microchannels. In this Part I of a two-part study, computational models are developed to study the relevant fluid dynamics, heat transfer, and mass transfer in each process. Parametric studies are conducted to determine the optimum microchannel geometry and adsorbent and heat transfer fluid (HTF) materials. The process is expected to purify up to two orders of magnitude greater gas throughput compared to bed-based designs. In the accompanying paper, Part II, a comprehensive process performance map and optimization of energy requirements for the process are discussed.

A novel temperature swing adsorption process for natural gas purification, Part II: Performance assessment

A novel temperature swing adsorption-based natural gas purification cycle using a monolith consisting of adsorbent-coated microchannels is investigated in this two-part study. In the accompanying paper, Part I, the development of a full process simulation model, and selection of geometric parameters and adsorbent and heat transfer fluid were reported. This paper, Part II, develops a comprehensive performance map of the process that involves determination of ranges of product purity, CH4 recovery and process capacity, and energy requirements. The TSA-based process in the present work is found to produce up to two orders of magnitude more purified product than that from adsorbent bed-based PSA processes reported in the literature, while product purity and CH4 recovery values remain competitive. This concept is also found to reduce the system footprint by 82% when compared with a TSA process that uses separate microchannels for the flow of working and coupling fluids. Additionally, methods for reducing process energy requirements are considered, along with enhancement of product purity via a staged purification scheme. The energy requirement for the process is found to be lower than that for MEA absorption systems, indicating the potential for large-scale installations based on this process.

Low-power noncontact photoacoustic microscope for bioimaging applications

An inexpensive noncontact photoacoustic (PA) imaging system using a low-power continuous wave laser and a kilohertz-range microphone has been developed. The system operates in both optical and PA imaging modes and is designed to be compatible with conventional optical microscopes. Aqueous coupling fluids are not required for the detection of the PA signals; air is used as the coupling medium. The main component of the PA system is a custom designed PA imaging sensor that consists of an air-filled sample chamber and a resonator chamber that isolates a standard kilohertz frequency microphone from the input laser. A sample to be examined is placed on the glass substrate inside the chamber. A laser focused to a small spot by a 40 × objective onto the substrate enables generation of PA signals from the sample. Raster scanning the laser over the sample with micrometer-sized steps enables high-resolution PA images to be generated. A lateral resolution of 1.37 ?? ? m was achieved in this proof of concept study, which can be further improved using a higher numerical aperture objective. The application of the system was investigated on a red blood cell, with a noise-equivalent detection sensitivity of 43,887 hemoglobin molecules ( 72.88 × 10 ? 21 ?? mol or 72.88 zeptomol). The minimum pressure detectable limit of the system was 19.1 ?? ? Pa . This inexpensive, compact noncontact PA sensor is easily integrated with existing commercial optical microscopes, enabling optical and PA imaging of the same sample. Applications include forensic measurements, blood coagulation tests, and monitoring the penetration of drugs into human membrane.

On the optimization of experimental parameters in photopyroelectric investigation of thermal diffusivity of solids

In this paper, the possibility of optimizing the experimental conditions for a correct photopyroelectric evaluation of the thermal diffusivity of solid samples is studied. For this purpose, a glassy carbon sample, with known thermal properties, was selected as test material and two types of techniques were applied in order to get the value of its thermal diffusivity: (i) the photopyroelectric calorimetry in back detection configuration and (ii) the infrared thermography. Assuming that the values of thermal diffusivity obtained by thermography are correct (a non-contact technique), we studied how to eliminate the underestimation (due to the presence of the coupling fluid) of the results in the back photopyroelectric calorimetry investigations. Experiments with different types of coupling fluids and numerical simulations were performed in order to evaluate the influence of the coupling fluid on the value of the thermal diffusivity. The conclusion is that a proper choice of the type of coupling fluid and some improvements performed in the experimental design of the photopyroelectric calorimetry detection cell (with the purpose of reducing the coupling fluid’s thickness), can eliminate the difference between the results obtained with the two photothermal (contact and non-contact) techniques.

Reconstruction of Temperature Distribution in a Steel Block Using an Ultrasonic Sensor Array

Permanently installed ultrasonic sensors have the capability of measuring much smaller changes in the signal than conventional sensors that are used for ultrasonic inspections. This is because uncertainties associated with coupling fluids and positional offsets are eliminated. Therefore it is potentially possible to monitor the onset of material degradation. A particular degradation mechanism that we are keen to monitor is high temperature hydrogen attack; where the amount of damage is linked to a drop in ultrasonic velocity which we hope can be monitored for with an ultrasonic array. The changes introduced in the ultrasonic propagation velocity are expected to be of the order of 1 % and in practice they are observable only from a very limited field of view (i.e. from the outside of a pipe) and therefore the reconstruction is challenging to accomplish. In order to explore the feasibility of this, we are investigating the reconstruction of a non-uniform temperature distribution which allows us to quickly evaluate the sensitivity of our method to small spatial variations in ultrasonic velocity of the material. Two reconstruction algorithms were implemented and their performance compared in simulated and real measurements. The results of the tests were encouraging: local temperature differences as low as $$10~{^\circ }$$ C could be detected, which corresponds to a local propagation velocity change of $$5$$ m/s ( $$0.15~\%$$ relative velocity change).

Enhanced live cell imaging via photonic crystal enhanced fluorescence microscopy.

We demonstrate photonic crystal enhanced fluorescence (PCEF) microscopy as a surface-specific fluorescence imaging technique to study the adhesion of live cells by visualizing variations in cell-substrate gap distance. This approach utilizes a photonic crystal surface incorporated into a standard microscope slide as the substrate for cell adhesion, and a microscope integrated with a custom illumination source as the detection instrument. When illuminated with a monochromatic light source, angle-specific optical resonances supported by the photonic crystal enable efficient excitation of surface-confined and amplified electromagnetic fields when excited at an on-resonance condition, while no field enhancement occurs when the same photonic crystal is illuminated in an off-resonance state. By mapping the fluorescence enhancement factor for fluorophore-tagged cellular components between on- and off-resonance states and comparing the results to numerical calculations, the vertical distance of labelled cellular components from the photonic crystal substrate can be estimated, providing critical and quantitative information regarding the spatial distribution of the specific components of cells attaching to a surface. As an initial demonstration of the concept, 3T3 fibroblast cells were grown on fibronectin-coated photonic crystals with fluorophore-labelled plasma membrane or nucleus. We demonstrate that PCEF microscopy is capable of providing information about the spatial distribution of cell-surface interactions at the single-cell level that is not available from other existing forms of microscopy, and that the approach is amenable to large fields of view, without the need for coupling prisms, coupling fluids, or special microscope objectives.

Ultrasound imaging in neurosurgery: approaches to minimize surgically induced image artefacts for improved resection control

BackgroundIntraoperative ultrasound imaging is used in brain tumor surgery to identify tumor remnants. The ultrasound images may in some cases be more difficult to interpret in the later stages of the operation than in the beginning of the operation. The aim of this paper is to explain the causes of surgically induced ultrasound artefacts and how they can be recognized and reduced.MethodsThe theoretical reasons for artefacts are addressed and the impact of surgery is discussed. Different setups for ultrasound acquisition and different acoustic coupling fluids to fill up the resection cavity are evaluated with respect to improved image quality.ResultsThe enhancement artefact caused by differences in attenuation of the resection cavity fluid and the surrounding brain is the most dominating surgically induced ultrasound artefact. The influence of the artefact may be reduced by inserting ultrasound probes with small footprint into the resection cavity for a close-up view of the areas with suspected tumor remnants. A novel acoustic coupling fluid developed for use during ultrasound imaging in brain tumor surgery has the potential to reduce surgically induced ultrasound artefacts to a minimum.ConclusionsSurgeons should be aware of artefacts in ultrasound images that may occur during brain tumor surgery. Techniques to identify and reduce image artefacts are useful and should be known to users of ultrasound in brain tumor surgery.

Global existence of weak solutions to the FENE dumbbell model of polymeric flows

Systems coupling fluids and polymers are of great interest in many branches of sciences. One of the most classical models to describe them is the FENE (Finite Extensible Nonlinear Elastic) dumbbell model. We prove global existence of weak solutions to the FENE dumbbell model of polymeric flows. The main difficulty is the passage to the limit in a nonlinear term that has no obvious compactness properties. The proof uses many weak convergence techniques. In particular it is based on the control of the propagation of strong convergence of some well chosen quantity by studying a transport equation for its defect measure. In addition, this quantity controls a rescaled defect measure of the gradient of the velocity.

A 3-dimensional time-resolved photothermal deflection “Mirage” method

A three-dimensional time-resolved theory and experiment for photothermal deflection spectroscopy is developed. The heat conduction equations for two semi-infinite media consisting of an opaque sample and a fluid are solved considering temperature and energy flux balance conditions for a Gaussian heat source. The time dependent perpendicular deflection signal is calculated and compared to experimental measurements on glassy carbon and copper samples. Excellent agreement with literature values for thermal diffusivity of the samples is found. The transient behavior is analyzed for different coupling fluids.

Characterization of mineral paper by air-coupled ultrasonic spectroscopy

A novel technology in the paper industry makes possible to produce paper by using a mineral powder and a polymer instead of cellulose fibers. This new product is called mineral paper, it presents some potential environmental advantages compared with conventional paper, while it exhibit a similar appearance and properties. The purpose of this work is to determine the possibilities of an air-coupled ultrasonic technique using wide band signals and spectral analysis to study this kind of materials. As no direct contact nor coupling fluids between the paper and the transducers is required, this technique is specially well suited to this problem. It also offers good perspectives for the development of a on-line quality control system. A through transmission technique (0.15–2.3MHz) is employed and Fourier analysis is performed to obtain both magnitude and phase spectra of the transmission coefficient. Properties in the thickness direction as well as in the paper plane has been determined by the excitation and analysis of thickness and plate resonances at several incident angles and different directions within the paper plane. Different paper grades (from 140 to 480g/m2) have been studied. Very high attenuation coefficients and very low propagation velocities (and hence elastic constant) have been obtained for most cases, this can be explained by considering the large porosity of this material (up to 50%) and the microstructure: a mixture of solid grains with a resin with a relatively large fraction of air-filled pores. Measurements show that unlike conventional cellulose machine made paper this material is transversely isotropic (isotropic in the paper plane) and that the degree of anisotropy (when in-plane directions are compared with the thickness direction) largely depends on the level of resin impregnation.