Reference Fluid Research Articles

An Experimental Performance on Solar Photovoltaic Thermal Collector with Nanofluids for Sustainable Development

In this article, the photovoltaic thermal collector (PVT) have designed and fabricated using nanoparticle nanofluid. The cause of this is to check out the effect of using water and water-based totally graphene nanoplatelets at an awareness of 0.05 wt% on the performance of PVT structures. Outdoor assessments have been performed at quantity along with the float prices of 0.5 L/min and 1.0 L/min for the aforementioned nanofluids, respectively, using water as a reference fluid. The results that have been analyzed from an active angle confirmed and determined that, graphene water nanofluid achieved higher in phrases of photovoltaic active conversion, than water that might generate the first-class thermal performance sooner or later of the peak period of sun radiation and high mobile temperature. The inclusion of water in the PVT collector increases average daily electrical efficiency by 7.8%, and 8.5%at flow rates of 0.5 LPM and 1.0 LPM, respectively. Furthermore, using water in the PVT collector increases average daily thermal efficiency by 24.9%, and 26.3%at flow rates of 0.5 LPM and 1.0 LPM, respectively.

Nanofluids based on hydrolyzed polyacrylamide and aminated graphene oxide for enhanced oil recovery in different reservoir conditions

Partially hydrolyzed polyacrylamide (HPAM) aqueous fluids in reservoirs produces a significant increase in the produced oil volume. However, the viscosity of these fluids is highly influenced by the temperature and salinity of the medium which is crucial in some reservoir conditions for the oil recovery. Thus, addition of nanomaterials in HPAM solutions to prepare nanofluids has been shown to be a promising alternative to increase viscosity and improve the performance in enhanced oil recovery. In this work, graphene oxide (GO) was prepared using modified Hummers method through the oxidation/exfoliation of expanded graphite while the aminated graphene oxide (GOA-EDA) was prepared using ethylenediamine in an ultrasonic bath. Spectroscopic techniques, elementary and thermogravimetric analyses confirmed the chemical composition of the produced nanomaterials. Images obtained by transmission electron microscope also confirmed the interfacial interactions between GO / GOA-EDA and HPAM. Rheological measurements were performed to determine the nanofluids viscosity as a function of concentration at high temperature (70 °C) under different salinity conditions. The results indicate that the viscosity increases promoted initially by the nanofluids prepared with GOA-EDA were smaller than those obtained by the nanofluids prepared with GO. In particular, the greatest increases in viscosity values occurs in the medium with the highest ionic strength (ηi%μ=0.6>ηi%μ=0.3>ηi%μ=0.1). However, after 90 aging days, nanofluids prepared with GOA-EDA showed better performances reaching gains of up to 146% in viscositiy when compared to the HPAM reference fluids indicating that nanofluids prepared with GOA-EDA are more promising for application in enhanced oil recover.

Surface light scattering in reflection geometry: capabilities and limitations.

In the present study, the capabilities and limitations of surface light scattering (SLS) experiments in reflection geometry are investigated. Based on the study of the transparent reference fluid toluene at 303.15 K over a wide range of wave vectors between (0.3and6.6)×105m-1, the performance of two different detection schemes analyzing light scattered from the vapor-liquid interface in a perpendicular and non-perpendicular direction is assessed. Considering various aspects such as the quality of the heterodyne correlation functions, the input information for data evaluation, and the line-broadening effects, both detection schemes show comparable overall efficiency. For wave vectors larger than 4.5×105m-1, where line-broadening effects are suppressed, the results obtained for liquid viscosity and surface tension agree with measurements in transmission geometry, validating the capability of the apparatus. For wave vectors smaller than 1.5×105m-1, the SLS signals are distinctly affected by line-broadening effects, which will result in erroneous values for surface tension and in particular viscosity, even if empirical fitting approaches commonly used in literature are applied. The modeling of the influence of line broadening on the measurements results by a simple Gaussian-weighted sum of individual damped oscillations reveals the increasing complexity of the underlying wave vector distribution toward smaller wave vectors chosen for the scattering geometry.

Thermodynamic perturbation theory coefficients for ellipsoidal molecules

Perturbation theory has been the center of the development of the new generation of equations of state. First- and second-order perturbation theories are very common, but require approximations for obtaining an analytical form. Recently, a new equation of state has been proposed in which the reference fluid is based on the hard Gaussian overlap approach, and the perturbed potential is defined as a spherically symmetric square well. In such an approach, the first- and second-order coefficients were considered the same as the ones applied for a system in which the reference term is spherical. Using Monte Carlo simulations, we investigated the validity of such an approximation by calculating the first- and second-order coefficients of the high-temperature expansion series of the Helmholtz free energy. With our findings, this approximation seems to be quite reasonable for a certain range of anisotropies. We also present a calculation of the perturbed molar Helmholtz free energy using Monte Carlo simulations, which could in principle be used for improving the equation of state.

Viscosity and Surface Tension of Benzene at Saturation Conditions from Surface Light Scattering

In the present study, the liquid viscosity and surface tension of benzene was determined at saturation conditions from surface light scattering (SLS) experiments between (283 and 393) K. Based on the application of the hydrodynamic theory for surface fluctuations at the vapor–liquid phase boundary which was successfully validated by the measurements, a simultaneous determination of liquid viscosity and surface tension with average relative expanded uncertainties (k = 2) of (1.0 and 0.8)% was achieved. Agreement between the measurement data and reference values available in the literature was found for the viscosity and in general also for the surface tension, where benzene constitutes a recommended reference material of relatively moderate surface tension values. All these findings demonstrate for a repeated time that SLS is a suitable method for the investigation of fluids including reference fluids such as benzene, which enables a sound representation of its surface tension, presumably as a result of a rather random molecular orientation at the surface. Overall, the experimental results from this work could contribute to an improved data situation for benzene, in particular with respect to providing viscosities and surface tensions at true saturation conditions.

Applying Common Equations of State to Three Reference Fluids: Water, Carbon Dioxide, and Helium

AbstractThermodynamic properties such as density, vapor pressure, heat of evaporation, and the speed of sound for three pure reference fluids were computed applying various common equations of state over a fairly wide range of pressures and temperatures. The results obtained by rather basic equations of state were held against those from sophisticated reference equations, and contour plots were drawn indicating the respective error margins. Thereby, it was quantitatively illustrated within which limits cubic equations of state can be used for reasonably accurate calculations of various properties.

Numerical study of supercritical octane flows with multicomponent effects by pyrolysis

This study focuses on supercritical octane flow simulation with pyrolysis reactions in a heated circular pipe to determine the multicomponent effects of changes in thermophysical properties. The reaction rate of n-octane for pyrolysis was estimated by a zeroth-dimensional simulation of hydrocarbon pyrolysis. The resulting mole fractions of the decomposed components were compared with the experimental data. The mole fraction results were then used to develop three thermophysical property models for the mixture of unreacted n-octane and decomposed hydrocarbons, i.e., 1-, 4-, and 12-component models. In the supercritical octane flow simulations, the multicomponent thermophysical properties of each component model were determined using the polynomial equations in the Reference Fluid Thermodynamic and Transport Properties Database. The conventional k−ω SST model and k−ωSST+Mτ model served as the Reynolds-averaged Navier–Stokes turbulence models. In cases with a low wall temperature, the outlet temperatures in all component models were consistent with the experimental data, in which pyrolysis did not occur. In cases with a high wall temperature above 973 K, the density change and production of kinetic energy affected the turbulent thermal diffusivity in the heated pipe. In cases where the multicomponent effects of thermophysical properties and turbulence were considered, the numerical method reproduced a reasonable outlet temperature and conversion rate, whereas the experimental results were underestimated in all the other cases. These numerical results indicate that the accurate prediction of density changes and the production of turbulent kinetic energy are the key issues in reproducing thermal fluid flows of supercritical hydrocarbons with pyrolysis reactions in uniform wall temperature cases.

Effect of the Heat Transfer Coefficient Reference Temperatures on Validating Numerical Models of Supercritical CO2

Abstract Validating turbulence models for cooling supercritical carbon dioxide (sCO2) in a horizontal pipe is challenging due to the lack of experimental data with spatially resolved local temperature measurements. Although many variables may be present to cause discrepancies between numerical and experimental data, this study focuses on how the choice of reference temperatures (both wall reference temperature and fluid bulk reference temperature) when calculating the heat transfer coefficient influences turbulence-model validation results. While it may seem straightforward to simply use the same parameters as the experimental setup, this has not been observed in practice. In this work, numerical simulations are performed for cooling sCO2 in a horizontal pipe for p = 8 MPa, d = 6 mm, G = 200, and 400 kg/(m2s), and qw = 12, 24, and 33 kW/m2. Local and average heat transfer coefficients with different reference temperatures, found to be frequently used in the literature, are presented and compared with commonly used experimental data. It was found that the choice of reference temperatures has a significant influence on the results of the numerical validation. Historically, the higher heat flux cases have been more difficult to validate, theorized due to using reference temperatures differing from the experiment; however, good agreement was found here using the reference temperatures that most closely matched the experiment. This not only highlights the need for careful selection of reference temperatures in simulations, but also the importance of clearly defining the reference temperature employed when reporting experimental results.

Semi-empirical and environmental assessment of the low GWP refrigerant HCFO-1224yd(Z) to replace HFC-245fa in high temperature heat pumps

Abstract This paper investigates a promising low-GWP refrigerant, HCFO-1224yd(Z), as an environmentally friendly replacement for HFC-245fa in high temperature heat pumps (HTHPs). First, the thermophysical properties of both fluids were analysed, and a single-stage cycle with Internal Heat Exchanger (IHX) was modelled. Then, a semi-empirical drop-in test replacement was assessed. The low-temperature reservoir was fixed at 80 °C, whereas the high-temperature reservoir was varied from 110 to 140 °C to cover a wide range of industrial applications. The theoretical and semi-empirical results illustrate that HCFO-1224yd(Z) heating capacity becomes around 8.9% lower than HFC-245fa. However, the higher suction density of HCFO-1224yd(Z) compared to the reference fluid can compensate for this effect, reducing the compressor power consumption. Hence, HCFO-1224yd(Z) presents a COP increase up to 4.5% compared to the reference fluid. At high-temperature reservoir of 140 °C, HCFO-1224yd(Z) shows a COP of 2.33, whereas HFC-245fa only reaches 2.23. The carbon footprint assessment illustrates a significant equivalent CO2,eq emissions reduction down to 90%, depending on the country (carbon emission factor). Therefore, HCFO-1224yd(Z) can be used as an alternative to HFC-245fa in HTHP systems due to its beneficial operating, energetic and environmental characteristics.

Pseudo-boiling and concentration gradient in an enclosed supercritical binary mixture

Recent publications have shown the effectiveness of the analogy between fluids at sub- and supercritical pressures and confirmed there is a distinguishable crossover between liquid-like and gas-like behavior in supercritical fluids. This work is devoted to extending such an analogy to miscible zeotropic binary mixtures, whose well-known feature in liquid-gas coexistence under a subcritical pressure is the concentration difference between liquid and gas. Due to the availability of thermophysical properties, C2H6−CO2 binary mixture is taken as a reference fluid. Through numerical simulations for the steady states of an enclosed binary mixture at supercritical pressures subjected to temperature differences, this paper reveals the coexistence of liquid-like and gas-like states is featured by a concentration gradient naturally established by the critically enhanced Soret effect. It suggests that the concentration gradient is enhanced as the critical pressure is approached or as the temperature difference is enlarged. Besides, the low heat-conducting nature of the gas-like state compared to the liquid-like one gives rise to a pressure drop. This work gives new insights into the similarities of binary mixtures under sub- and supercritical pressures. For the convenience of latter studies, an open-source code is provided to calculate the physical properties of C2H6−CO2 binary mixture.

Improving the SAFT-γ Mie equation of state to account for functional group interactions in a structural (s-SAFT-γ Mie) framework: Linear and branched alkanes.

The group contribution SAFT-γ Mie EoS is based on the statistical associating fluid theory for fused heteronuclear molecules. While the chain term of the model has been modified to account for the new functional group-specific parameters, it does not impose a bonding order to these functional groups, only considering intergroup interactions in the monomer reference fluid. This leaves the model unable to account for the different physical properties of structural isomers and implicitly introducing modeling bias to species where the molecular structure mimics those used in the parameter regression. In this work, a simple but physically meaningful modification to the chain term in SAFT-γ Mie is proposed that accounts for the number of intergroup bonds, thereby encoding structural information in the model, without introducing an additional regressed parameter. The resulting structural SAFT-γ Mie (s-SAFT-γ Mie) requires reparameterization of the group parameters, which we present for linear and branched alkanes (CH3, CH2, CH, and C groups) here. Following an identical parameterization procedure to the original model, validation showed that the modification actually improves prediction accuracy for linear alkanes while addressing the original inability of the framework to distinguish between structural isomers. The good predictive performance seen in this work, for both pure component and mixture properties, lays a good foundation for expansion to other functional groups in future work.

Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals Operating in Supercritical CO2 Turbomachinery

Abstract The balance piston seal in multiple-stage centrifugal compressors and axial turbines sustains the largest pressure drop through the machines and therefore plays an important role in successful full load operation at high rotational speed. This is especially true for power dense turbomachines in supercritical CO2 power cycles that generate or expend higher fluid pressures (above the critical value 7.3 MPa) and density (close to water 1000 kg/m3), because the fluid forces generated by the balance piston seals are directly proportional to the fluid density and the pressure drop across the seal. This paper presents a comprehensive assessment and comparison on the leakage and rotordynamic performance of three types of annular gas seals for application in a 14 MW supercritical CO2 turbine. These three seals represent the main seal types used in high-speed rotating machines at the balance piston location in efforts to limit internal leakage flow and achieve rotordynamic stability, including a labyrinth seal (LABY), a fully partitioned pocket damper seal (FPDS), and a hole-pattern damper seal (HPS). These three seals were designed to have the same sealing clearance and similar axial lengths. To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake was also designed and employed at seal entrance for each type seal to reduce the seal inlet preswirl velocity. Numerical results of leakage flow rates, rotordynamic force coefficients, cavity dynamic pressure, and swirl velocity developments were analyzed and compared for three seal designs at high positive inlet preswirl (in the direction of shaft rotation), using a proposed transient computational fluid dynamic (CFD)-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the National Institute of Standards and Technology reference fluid properties database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions. Results show that the inlet swirl brake can significantly reduce the preswirl velocity at seal entrance, lowering the effective damping crossover frequency fco (or even fco = 0) to maximize the full operational frequency range of the machines. In stability analysis phase of a MW-scale supercritical CO2 turbine/compressor, the seal stiffness effects on the rotor mode shape must be evaluated carefully, where the seal stiffness is sufficiently large (comparable to the bearing stiffness). From a rotordynamic viewpoint, the HPS seal with entrance swirl brake is a better seal concept for the balance piston seal in supercritical CO2 turbomachinery, which possesses the largest positive effective damping throughout the entire subsynchronous frequency range.

Algebraic second virial coefficient of the Mie m - 6 intermolecular potential based on perturbation theory.

We propose several simple algebraic approximations for the second virial coefficient of fluids whose molecules interact by a generic Mie m - 6 intermolecular pair potential. In line with a perturbation theory, the parametric equations are formulated as the sum of a contribution due to a reference part of the intermolecular potential and a perturbation. Thereby, the equations provide a convenient (low-density) starting point for developing equation-of-state models of fluids or for developing similar approximations for the virial coefficient of (polymeric-)chain fluids. The choice of Barker and Henderson [J. Chem. Phys. 47, 4714 (1967)] and Weeks, Chandler, and Andersen [Phys. Rev. Lett. 25, 149 (1970); J. Chem. Phys. 54, 5237 (1971); and Phys. Rev. A 4, 1597 (1971)] for the reference part of the potential is considered. Our analytic approximations correctly recover the virial coefficient of the inverse-power potential of exponent m in the high-temperature limit and provide accurate estimates of the temperatures for which the virial coefficient equals zero or takes on its maximum value. Our description of the reference contribution to the second virial coefficient follows from an exact mapping onto the second virial coefficient of hard spheres; we propose a simple algebraic equation for the corresponding effective diameter of the hard spheres, which correctly recovers the low- and high-temperature scaling and limits of the reference fluid's second virial coefficient.

The Data Mining Technique Using RapidMiner Software for New Zeotropic Refrigerant

This research presents the development of environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration systems that new azeotropic refrigerant mixture of hydrofluorocarbons and hydrocarbon that can retrofit in the refrigeration system using R404A. The medium back pressure refrigeration testing standard that follow CAN/ANSI/AHRI540 standard air-conditioning, heating, and refrigeration institute (AHRI) and The properties of refrigerants and refrigeration simulation system that used national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software. The methodology uses decision tree function in datamining by rapid minor software that first of KDnuggets annual software poll that showed new azeotropic refrigerant mixture had cooling capacity, refrigerant effect, GWP and boiling point were lower than R404A but work and pressure for medium temperature refrigeration system of azeotropic refrigerant mixture were higher than R404A. The artificial intelligence (AI) by data mining technic can predictive environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration. The result of refrigerant mixed by R134A, R32, R125 and R1270 and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs and HCs which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant.

Electro-Microfluidic Viscometer with Integrated Microcontroller and Pumping System for Point-of-Care Biosensing Applications

Viscometers are extensively utilized for a wide variety of sensing and monitoring applications like biomedical diagnostics, biochemical optimization, fluid adulteration detection and quality control in pharmaceuticals. Realizing the viscometer in the lab-on-chip/microfluidic domain increases its potential to be a point-of-care device by making it completely automated and robust. This work presents the development of a simplified, cost-effective and time efficient 3D Printed (3DP) Electro-Microfluidic Viscometer (EMV), with microchannel and intersecting electrodes, in a single-step process. A completely automated, integrated and handheld EMV was realized and comprised an in-house made 3DP peristaltic pump and motherboard of a microcontroller, along with a display unit and the microcontroller to estimate viscosity. Here, the viscosity values of bovine serum albumin (BSA), human serum albumin (HSA), and lysozyme enzyme were measured with respect to the reference fluid before and after denaturation. The developed device is capable of measuring viscosity values ranging from 0.5 cP to 10 cP. These values are within a ±6% limit when compared with a benchtop viscometer, showing the commercial potential of the present device with innumerable add-on features.

SUBSTANCE CONCENTRATION IS AN INFORMATION INDICATOR OF TECHNOLOGICAL PROCESSES IN OIL PRODUCTION

Background The parameter «substance concentration» is used in all areas of science, technology and life, characterizes, to one degree or another, practically all processes known to us. In the article, this parameter is considered from several angles. Based on the definition of the term, examples of technological processes are considered in which the concentration of either a single-component substance or a single-phase one (the concentration of the first type) changes. The processes occurring in reservoir conditions, during movement and separation in wells, pipelines and storage equipment, are usually described using the concentration of a substance of the second type, when the quantitative presence of one component is estimated relative to all constituents of the substance. An objective relationship between the concentration of substances of both types and such characteristics of fluids as pressure, temperature, speed of movement is shown using well-known examples of the theory and practice of oil production. Aims and Objectives: o to conduct a typology of the term «substance concentration» based on a comparative analysis of methods and technologies used to assess the characteristics of oil production processes; o to prove the change in the substance concentration in reference technologies by assessing the internal state of lift pipes of wells and production pipelines, which is recorded by known measuring instruments. Methods The concentration of a substance is estimated by the density, pressure, temperature and speed of movement of fluids in the studied area of the oil production object. The volume of deposits in oilfield equipment is determined by the volumetric method after fixing the amount of reference fluid in the studied cavity. Results It is proposed in oilfield practice to conditionally distinguish two types of substance concentration, which differ in the method of determination in field conditions. Examples of reference technologies based on changes in the concentration of a substance of the first type are given.

A new oscillatory instability in Rayleigh–Bénard convection of a binary mixture with positive separation ratio

It is well-known that for the onset of Rayleigh–Bénard (RB) convection in a binary mixture with Soret effect and negative separation ratio, the competitions between temperature and concentration gradients can lead to oscillatory instability. In this paper, through linear stability analysis, a new oscillatory instability is discovered in a binary mixture with positive separation ratio, thanks to the rich physics of a near-critical binary mixture, i.e., a binary mixture under supercritical pressure near the pseudo-critical state. The rich physics includes cross-diffusion effects (i.e., Soret and Dufour effects) and gravity-related effects (i.e., adiabatic temperature gradient and gravitational diffusion). The linear stability problem is governed by six dimensionless parameters, and the positive separation ratio is shown to be general. It is revealed that there are monotonic and oscillatory instabilities, corresponding to the monotonic and oscillatory growths of small perturbations. The conditions for the unexpected oscillatory instability can be interpreted as there are large enough stabilizing concentration gradient, and total diffusivity rate of concentration is less than that of temperature. Under a positive separation ratio, the stabilizing concentration gradient is a result of gravity-related effects. Besides, based on the physical properties of the reference fluid, when oscillatory instability occurs, gravity-related effects have already been the dominant obstacle for instability. This work provides analytical equations to predict the RB instability. More importantly, the newly discovered oscillatory instability overturns the stereotype of the conceptual connection between oscillatory instability and negative separation ratio.

Effects of CO2 binary mixtures on pipeline performance for Carbon Capture and Storage

Captured CO2 from the manufacturing industries and power generation sources are not pure and may contain usually some amount of impure components, which affect the flow dynamics of the CO2 in the pipelines. Major component of impure components includes N2, H2, H2S, O2, Ar etc., depending on the capture technology used for the removal of CO2 streams. To design efficient CO2 pipeline transportation systems, it is imperative to understand the effect of these impure components on the flow behaviour. The simulation of the effect of CO2 binary mixture on pipeline performance is carried out in this study. The steady-state flow in pipeline is described by a set of parabolic mass, momentum and energy conservation equations. To solve the set of equations subject to the boundary and the inlet conditions of the pipeline, the non-linear algebraic solver library DNSQE in Fortran is used to study the behaviour of 90 vol% CO2, and 10 vol% single impure component (N2, H2, H2S, O2 and Ar). The phase diagram and pertinent fluid properties are calculated using the Peng-Robinson (PR) equation of state implemented in NIST Reference Fluid Thermodynamics and Transport Properties database program REFPROP. The results reveal that the bubble point curves were lifted up to higher pressures by impure components. The changes in the bubble point would affect the operating conditions of CO2 pipeline. The presence of impure components also changed the properties of the flowing fluid. From the results, H2 shows the most significant impact on the performance of CO2 pipeline as the highest pressure drop by ca. 0.18 bar/km which has smaller density and greater flow velocity against other CO2 streams. The results also show that Ar had the mildest effect followed by O2, N2 and CO. In the case of H2S, the flow parameters are found to be nearly identical to those for pure CO2. The pressure drop for binary mixture contains H2S shows the same value with pure CO2 stream by ca. 0.13 bar/km.

Stability analysis of a thinning electrified jet under nonisothermal conditions.

The linear stability of a jet propagating under an electric field is analyzed under nonisothermal conditions. The electrified jet of a Newtonian fluid is modeled as a slender filament, and the leaky dielectric model is used to account for the Maxwell stresses within the fluid. The convective heat transfer from high-temperature jet to the surroundings results in formation of thicker fibers owing to increased viscosity upon cooling. The jet exhibiting substantial thinning under the action of tangential electric field is examined for stability toward axisymmetric nonperiodic disturbances. This is in contrast to most prior studies which analyzed the stability of a cylindrical jet of uniform radius without thinning under extensional flow by examining only periodic disturbances. Two case studies of reference fluids differing in viscosity and electrical properties are examined. The spectrum of discrete growth rates for axisymmetric disturbances reveal qualitatively distinct instabilities for the two fluids. For a fluid with high electrical conductivity, the conducting mode driven by the coupling of surface charges and an external electric field is found to be the dominant mode of instability. On the contrary, for low conductivity materials, the surface-tension-driven capillary mode is found to be the most critical mode. Heat transfer from the jet to the surroundings tends to stabilize both types of instability mode. Under sufficiently strong heat transfer, the axisymmetric instability, which is believed to be responsible for producing nanofibers with diametric oscillations in electrospinning process, is suppressed. The stabilization is attributed to the enhancement of viscous stress in the thinning jet upon cooling. It is observed that the stabilization effect is relatively more pronounced in a thinning jet compared to the cylindrical jet of uniform radius. The effects of various material and process parameters on the stability behavior is also examined.

Experimental quantification of oscillating flow in finite-length straight elastic vessels for Newtonian and non-Newtonian fluids

To better understand the complex flow in arteries it is necessary to analyze the fluid–structure interaction between the time dependent velocity field, the non-Newtonian fluid, and the elastic blood vessels and to investigate the wall-shear stress distribution that develops in the elastic vessel during an oscillation cycle. The scope of this study is to quantify the influence of the viscoelastic fluid properties on the fluid–structure interaction and the wall-shear stress of a straight elastic vessel by analyzing oscillatory flow of both a Newtonian reference fluid and a non-Newtonian fluid. Unlike in Womersley’s analyses, an elastic vessel of finite length with a non-Newtonian fluid is investigated in this study. Furthermore, quantitative benchmark data for numerical fluid–structure interaction methods are provided. Time-resolved particle-image velocimetry, static pressure measurements, and wall detection are used to measure the velocity field, the pressure distribution, and the vessel dilatation with high temporal and spatial resolution. The mechanical properties of the vessel material are determined by a dynamic mechanical analysis and the viscosities of the Newtonian and the non-Newtonian fluid are measured by a rheometer. The fluid–structure interaction is measured for a sinusoidal oscillating flow in a Reynolds number range 472≤ReNF≤971 and 503≤ReNNF≤1065 for the Newtonian reference fluid and the non-Newtonian fluid. The Womersley number range is 5.97≤WoNF≤8.53 for the Newtonian reference fluid and 6.14≤WoNNF≤8.79 for the non-Newtonian fluid. The results show that the wall-shear stress maximum increases up to 32%–38% for the non-Newtonian fluid despite a 10%–45% higher wall-shear rate for the Newtonian reference fluid. Furthermore, the amplitudes of the dilatation and the pressure in the vessel are more pronounced for the non-Newtonian fluid.