Fluid Mixtures Research Articles

Rheology, viscoelasticity and microstructural properties of OAPB-SDS mixtures at different temperature and pH conditions

Viscoelastic surfactant (VES) fluids are widely used in the hydraulic fracturing process to increase oil and gas productivity. Zwitterionic (carbon-18) surfactant solution, which is commonly used in VES fluids, has high critical micelle concentration, resulting in high used concentration and lack of economy. Furthermore, it is not applicable to high-temperature conditions. The oleylamidopropyl betaine (OAPB, carbon-25) with longer carbon chain has lower critical micelle concentration (CMC) and better high temperature resistance. In addition, it behaves better viscosity increasing capacity combining with anionic sodium dodecyl sulfate (SDS) surfactant. In this study, the viscoelasticity and microstructural properties of OAPB-SDS (OADS) mixtures at different temperature and pH conditions were investigated deeply. Rheology and structural morphology properties of the OADS mixed fluids were investigated by rheometer, and transmission electron cryo-microscopy. The results showed that OADS solution demonstrated elastic gel-like fluid behavior with zero shear viscosity of 3.5 × 106 mPa.s at neutral pH and room temperature, while OAPB solution demonstrated viscous fluid behavior with zero shear viscosity (ηo) of 62 mPa.s. The viscoelasticity and microstructural properties of OADS solution were influenced by concentration, pH and temperature. It was gel-like fluid at 25–40 °C, viscoelastic fluid at 60–80 °C and totally viscous fluid at 90 °C. The OADS was viscous at 0.5 wt% concentration, viscoelastic at 0.6 wt% concentration and elastic at 0.75 wt% concentration. The OADS solution showed viscous, viscoelastic and elastic behaviors at pH value of 3, 4, and 7 respectively. The fluid exhibited viscosity switch ability by reversibly altering pH values. The Cryo-TEM images confirmed that the OADS micelle experience microstructural transformed from long wormlike micelles (WLMs) to spherical micelles as the pH changes. The mixture fluid improved viscoelastic and aggregation properties than that of individual surfactant component, possessing lower used surfactant concentration. This study is useful in understanding the properties of mixed zwitterionic-anionic fluids, which is thermo-pH responsive, valuable in the fracturing.

Phase inversion identification in Electrical Submersible Pumps using mechanical vibrations

Electric Submersible Pumps (ESPs) are multistage centrifugal pumps used in the artificial lift and transport of multiphase fluid mixtures. The flow regime is a liquid–liquid flow when the fluids correspond to two non-miscible fluids. Liquid–liquid flow is a mixture with a continuous and dispersed phase. As the amount of fluid in the dispersed phase increases, the dispersed phase suddenly becomes continuous and vice-versa. This transition phenomenon is called phase inversion. The flow regimes in oil–water mixtures are oil-in-water (o/w) and water-in-oil (w/o) flow regimes. This work demonstrates a correlation between the flow regime and the flow-induced vibration (FIV) in ESP operating with an oil–water mixture. This research proposes a novelty method to flow regime identification based on the Root Mean Square (RMS) of the vibration acceleration of the Fast Fourier Transform (FFT) signal.The experimental setup consists of an 8-stage Electrical Submersible Pump (ESP) and a vibration acquisition system with six accelerometers uniformly distributed along the ESP. The experimental procedure consists of changing the water cut (percentage of water) from the oil flow regime to the water flow regime, maintaining stable ESP rotational speed, the total flow rate, and the oil viscosity. For each water cut, mechanical vibration is collected. The operational conditions consider 30, 40, and 50 Hz rotational speeds and viscosities between 70 and 210 cP.Frequency domain analysis involves studying FFT between 0 and 5000 Hz, considering different water cuts and frequency ranges. Statistical features – mean, variance, geometric mean harmonic mean, and RMS – were extracted from the FFT for each frequency range. Results showed a strong correlation between the RMS of FFT and the phase inversion phenomena considering the rotational speed. A logistic regression model was employed to establish a transition boundary between oil-in-water and water-in-oil using 10% of the data. The model successfully separated at least 95.67% of the remaining data in the least favorable scenario.

Effect of Al2O3, SiO2, and ZnO Nanoparticle Concentrations Mixed with EG–Water on the Heat Transfer Characteristics through a Microchannel

Nanofluids have gained attention for their potential to solve overheating problems in various industries. They are a mixture of a base fluid and nanoparticles dispersed on the nanoscale. The nanoparticles can be metallic, ceramic, or carbon based, depending on the desired properties. While nanofluids offer advantages, challenges such as nanoparticle agglomeration, stability, and cost effectiveness remain. Nonetheless, ongoing research aims to fully harness the potential of nanofluids in addressing overheating issues and improving thermal management in different applications. The current study is concerned with the fluid flow and heat transfer characteristics of different nanofluids using different types of nanoparticles such as Al2O3, SiO2, and ZnO mixed with different base fluids. Pure water and ethylene glycol–water (EG–H2O) mixtures at different EG–H2O ratios (ψ = 0%, 10%, 30%, 40%) are used as the base fluid. Furthermore, a rectangular microchannel heat sink is used. Mesh independent study and validation are performed to investigate the current model, and a good agreement is achieved. The numerical analysis evaluates the influence on the heat transfer coefficient and flow characteristics of nanofluids for Reynolds numbers 500 to 1200 at a 288 K inlet flow temperature. The results show that ZnO nanofluid and 40% EG–H2O increase the heat transfer coefficient by 63% compared to ZnO–H2O nanofluid obtained at Re = 1200 and φ = 5%. Conversely, the pressure drop by ZnO is nearly double that obtained by Al2O3 and SiO2.

Quasi-Gasdynamic Model and Numerical Algorithm for Describing Mixtures of Different Fluids

An elegant and easy-to-implement numerical algorithm for simulating flows of homogeneous gas mixtures with component temperatures and velocities assumed to be equal is constructed and tested. The algorithm yields monotone density profiles for the components even if their specific heat ratios are widely different. The algorithm can be used to simulate some flows of gas–liquid mixtures.

Quasi-Gasdynamic Model and Numerical Algorithm for Describing Mixtures of Different Fluids

Quasi-Gasdynamic Model and Numerical Algorithm for Describing Mixtures of Different Fluids

Numerical simulations of cavitating water jet by an improved cavitation model of compressible mixture flow with an emphasis on phase change effects

Focusing on cavitation phenomena caused by high-speed submerged water jets, this paper presents an improved cavitation model for a compressible fluid mixture based on a concise estimation of fluid compressibility that considers phase change effects. The homogeneous two-phase flow assumption is adopted, and the gas phase is assumed to consist of vapor and non-condensable components. Equations of state for a pure liquid and an ideal gas are employed to evaluate the compressibility of the liquid and non-condensable components, and the compressibility of the vapor is treated semi-empirically as a constant. The model is embedded in an unsteady Reynolds-averaged Navier–Stokes solver, with the realizable k-ε model employed to evaluate the eddy viscosity. The turbulent cavitating flow caused by an impulsively started submerged water jet is treated. The pattern of periodic cavitation cloud shedding is acceptably captured, and the mass flow rate coefficient and its fluctuation frequency evaluated by simulations agree with the experimental results well. The validity of the proposed method is confirmed. The results reveal that cavitation occurs when pin/Pin reaches 0.65 and fluid flow begins to pulsate. In the well-developed stage, the leading cavitation cloud and a subsequent cloud are successively shed downstream, and this process is repeated. The subsequent cloud catches the leading cloud, and they coalesce in the range x/d≈ 2–3. The pressure fluctuations concentrate in the range of x/d≈2–5 corresponding to the periodic shedding of cavitation clouds. The mass flow rate coefficient pulsates from 0.59–0.66 under the effect of cavitation.

On molecular unmixedness between the ejected original and entrained ambient fluids in a turbulent jet

The present study investigates the molecular unmixedness between the injected and entrained fluids in a turbulent jet as well as its dependence on the initial conditions. This unmixedness can be quantified as the parameter of molecular segregation between the ejecting “fuel” fluid (A) and the entrained “oxidizer” fluid (B), defined by α≡cAcB¯/C¯AC¯B (overbar denotes time-averaging). For the first time, an expression of the parameter has been derived for the two-fluid mixing in a heated turbulent nonreactive jet. That is, α=−θ2¯/Θo−Θ¯Θ¯−Θa, where Θo and Θa denote the ejected “warm” and entrained “cold” fluid temperatures, whereas Θ and θ are the instantaneous and fluctuating temperatures of the local fluid mixture. This expression of α is well validated by comparing the measured natural-gas flames from a smooth-contraction nozzle with those from a long-pipe nozzle. Moreover, the jet-nozzle configuration is found to show a strong effect on α. Likewise, the jet density ratio (Rρ) is a highly influential factor: e.g., an increase in Rρ reduces α substantially. In contrast, the effect of the jet-exit Reynolds number is less significant. In the present paper, we try to explain these observations.

Starch/Silicone Elastomers and Foams

While the beneficial physical properties of silicone polymers are exploited in many sustainable applications, the high energy requirement for their synthesis compromises to a degree their sustainability. We report a strategy to mitigate this issue by filling the silicone with inexpensive and renewable starch. Elastomeric materials with covalently grafted starch, utilizing anhydride-modified silicones, permits loading of up to about 75% starch while maintaining many of the properties of the silicone. Alternatively, 50 wt.% starch-filled silicone foams can be prepared simply by mixing powdered starch with a mixture of HSi-functional silicone fluids in the presence of B(C6F5)3. The physical properties of the resulting foams are determined by the quantity of SiH, which controls the final density of the foams (ranging from 0.258–0.875 g mL−1), their Young’s modulus, and their degree of elasticity; both rigid and flexible foams were prepared. Materials with a high natural and renewable material content better adhere to green chemistry principle 7, should enhance the ease of degradation at end of life, and augment the sustainability of these silicone composites.

Effective broadband electromagnetic wave absorption performance of nano-Fe3O4 magnetic fluid-modified resin geopolymer by metamaterial with a novel patterned structure

It is challenging to achieve high-strength absorption and effectively broaden the absorbing bandwidth when using conventional flat microwave-absorbing cementitious materials. To address this challenge and achieve excellent microwave-absorptive performance, this study proposes a novel two-layered periodic stepped absorbing structure (PSAS) composed of a mixture of nano-Fe3O4 magnetic fluid and a resin geopolymer. Additionally, the incident angle-dependent absorption performance, the impact of geometrical parameters, and the shape of the unit cell were investigated. The results demonstrate that the absorption of the designed metamaterial absorber exceeds 90% in the total frequency range of 2–18 GHz. A mean reflection value of −18.3 dB was obtained in this study. The outstanding absorption performance of PSAS results from the cooperative effect of multiple λ/4 resonances and edge diffraction effects, which improve the impedance matching to the level of the free space in a broad frequency domain. Combining the effect of electromagnetic field regulation with metamaterial structure, the ultra-broadband absorption can be significantly enhanced by adjusting the geometrical parameters of the unit cell for absorption resonance.

Optimum operation of an ejector-assisted combined flash-binary geothermal cycle using R245fa-isopentane mixture-based secondary working fluids

Combined flash binary geothermal cycle (CFBGC) is a traditional geothermal energy conversion technology. However, in a CFBGC, substantial exergy destruction occurs during the steam flashing. To address this issue, in the present study, the steam flashing device of the conventional CFBGC is replaced by an ejector. The ejector enhances steam cycle power output by ensuring a higher steam flow rate through the high-pressure steam turbine stage. The modified cycle is designated as the ejector assisted combined flash binary geothermal cycle (EACFBGC). To take advantage of temperature glide, various compositions of R245fa-isopentane mixture are considered as secondary working fluid. Optimum operating parameters corresponding to the maximum second law efficiencies of the proposed and conventional cycles are explored by applying an iterative method. Both considered cycles yield the highest second law efficiencies with the 0.7 mol fraction of isopentane in the working fluid mixture. For geo-fluid available at 170 °C, the second law efficiency of the optimized EACFBGC is about 8.08% higher than that of the optimized conventional CFBGC. The corresponding levelized cost of electricity (LCOE) is also 5.7% lower. In a word, the proposed EACFBGC can be considered as the upgraded CFBGC with higher energy conversion efficiency and a lower LCOE.

Start-up and heat transfer characteristics of oscillating heat pipe charged with binary partially miscible organic fluid mixtures

The development of highly-efficient, cost-effective and reliable cooling schemes is still a crucial need for prospective applications in energy- and thermal-related areas, and oscillating heat pipes become a promising option due to their simple structures, high performance and versatilities. In this work, an oscillating heat pipe fabricated by a copper flat-plate evaporator and a capillary copper-tube condenser has been developed, and the experimental study was conducted to investigate the start-up and heat transfer characteristics of the heat pipe device using partially miscible HFE7100-ethanol mixtures at mixing ratios in the range of 1:8 to 8:1 due to the advantage of complementary thermo-physical characteristics and the figure of merit with respect to an OHP. Results demonstrate that the oscillating heat pipe performance was mixing ratio dependent, and there existed optimal mixing ratios of 3.5:1 and 3:1 with respect to the start-up temperature/duration and thermal resistance, respectively. At the optimal mixing ratio of 3.5:1, the time and temperature constants related to the startup performance were reduced by 50.5 s and 5.9 °C, respectively, in comparison with that of ethanol. Besides, the thermal resistance of the oscillating heat pipe charged with HFE7100-ethanol mixture was maximally reduced by 35.5% as compared with that of ethanol at an optimal mixing ratio of 3:1. The complementary thermo-physical properties of partially miscible organic fluids as well as the phase transition suppression and easy transition to unidirectional flow circulation account for the performance improvement. Different from single organic mixtures, the binary organic mixtures exhibited distinctive capabilities to improve the oscillating heat pipe performance, and provides a promising candidate for oscillating heat pipe applications.

Uncertain characterization of reservoir fluids due to brittleness of equation of state regression

Equations of state (EoS) play a central role in modeling the phase equilibrium of fluid mixtures. Their parameterization involves fitting a model to experimental data, i.e., solving a nonlinear, non-convex, multivariate optimization problem. The latter requires one to select design variables, domains of definition for each variable, and weights assigned to individual measurements. We demonstrate that subjective choices of an optimization algorithm and an initial guess also impact the regression process. Consequently, EoS predictions are fundamentally uncertain even after the EoS tuning to a limited set of experimental data points. We demonstrate this observation for two hydrocarbon reservoir fluids, in which five properties of the heaviest carbon fraction are treated as design variables. While all the optimization algorithms and initial guesses match experimental data for the gas and liquid properties, the resulting EoS parameterizations lead to dramatically different predictions of the fluid’s thermophysical behavior in the unsampled pressure and temperature regions. We propose the probabilistic treatment of design variables to quantify the predictive uncertainty of the resulting fluid models.

On the phase behaviors of CH4-CO2 binary clathrate hydrates: Two-phase and three-phase coexistences.

We develop a statistical mechanical theory on clathrate hydrates in order to explore the phase behaviors of clathrate hydrates containing two kinds of guest species and apply it to CH4-CO2 binary hydrates. The two boundaries separating water and hydrate and hydrate and guest fluid mixtures are estimated, which are extended to the lower temperature and the higher pressure region far distant from the three-phase coexisting conditions. The chemical potentials of individual guest components can be calculated from free energies of cage occupations, which are available from intermolecular interactions between host water and guest molecules. This allows us to derive all thermodynamic properties pertinent to the phase behaviors in the whole space of thermodynamic variables of temperature, pressure, and guest compositions. It is found that the phase boundaries of CH4-CO2 binary hydrates with water and with fluid mixtures locate between simple CH4 and CO2 hydrates, but the composition ratios of CH4 guests in hydrates are disproportional to those in fluid mixtures. Such differences arise from the affinities of each guest species to the large and small cages of CS-I hydrates and significantly affect occupation of each cage type, which results in a deviation of the guest composition in hydrates from that in fluid on the two-phase equilibrium conditions. The present method provides a basis for the evaluation of the efficiency of the guest CH4 replacement to CO2 at the thermodynamic limit.

Revised Enskog theory for Mie fluids: Prediction of diffusion coefficients, thermal diffusion coefficients, viscosities, and thermal conductivities.

Since the 1920s, the Enskog solutions to the Boltzmann equation have provided a route to predicting the transport properties of dilute gas mixtures. At higher densities, predictions have been limited to gases of hard spheres. In this work, we present a revised Enskog theory for multicomponent mixtures of Mie fluids, where the Barker-Henderson perturbation theory is used to calculate the radial distribution function at contact. With parameters of the Mie-potentials regressed to equilibrium properties, the theory is fully predictive for transport properties. The presented framework offers a link between the Mie potential and transport properties at elevated densities, giving accurate predictions for real fluids. For mixtures of noble gases, diffusion coefficients from experiments are reproduced within ±4%. For hydrogen, the predicted self-diffusion coefficient is within 10% of experimental data up to 200 MPa and at temperatures above 171K. Binary diffusion coefficients of the CO2/CH4 mixture from simulations are reproduced within 20% at pressures up to 14.7 MPa. Except for xenon in the vicinity of the critical point, the thermal conductivity of noble gases and their mixtures is reproduced within 10% of the experimental data. For other molecules than noble gases, the temperature dependence of the thermal conductivity is under-predicted, while the density dependence appears to be correctly predicted. Predictions of the viscosity are within ±10% of the experimental data for methane, nitrogen, and argon up to 300bar, for temperatures ranging from 233 to 523K. At pressures up to 500bar and temperatures from 200 to 800K, the predictions are within ±15% of the most accurate correlation for the viscosity of air. Comparing the theory to an extensive set of measurements of thermal diffusion ratios, we find that 49% of the model predictions are within ±20% of the reported measurements. The predicted thermal diffusion factor differs by less than 15% from the simulation results of Lennard-Jones mixtures, even at densities well exceeding the critical density.

Existence and weak–strong uniqueness for Maxwell–Stefan–Cahn–Hilliard systems

A Maxwell–Stefan system for fluid mixtures with driving forces depending on Cahn–Hilliard-type chemical potentials is analyzed. The corresponding parabolic cross-diffusion equations contain fourth-order derivatives and are considered in a bounded domain with no-flux boundary conditions. The nonconvex part of the energy is assumed to have a bounded Hessian. The main difficulty of the analysis is the degeneracy of the diffusion matrix, which is overcome by proving the positive-definiteness of the matrix on a subspace and using the Bott–Duffin matrix inverse. The global existence of weak solutions and a weak–strong uniqueness property are shown by a careful combination of (relative) energy and entropy estimates, yielding H^2(\Omega) bounds for the densities, which cannot be obtained from the energy or entropy inequalities alone.

Equilibrium thermodynamic properties of Lennard–Jones fluid mixtures from a single-component effective fluid model

ABSTRACT The equilibrium thermodynamic properties of binary Lennard–Jones mixtures are determined by means of a Monte Carlo-based perturbation theory for an effective single-component fluid. The results for the equation of state and the excess energy are compared with simulation data obtained for two equimolar binary Lennard–Jones fluid mixtures at different temperatures along a wide range of densities. The satisfactory accuracy achieved seems to suggest that this approach might be a useful tool to deal with mixtures with a wide variety of intermolecular interactions including mixtures of real fluids.

Dynamics of Williamson Hybrid Nanofluid Over an Extending Surface with Non-Linear Convection and Shape Factors

Combined effects of the magnetic field, heat source/sink, and homogeneous–heterogeneous chemical reaction on the three-dimensional fluid flow over a stretching sheet have been examined in this paper. For originality and practicality, the influence of non-linear convection on hybridised nanoparticles of titanium dioxide (TiO2) and silver (Ag) in the non-Newtonian engine oil (EO) are introduced into the governing equations, which are then dimension-free by utilizing appropriate transformations. Williamson fluid model has been employed to determine the rheological features of the considered fluid mixture. MATLAB inbuilt bvp4c solver and Keller box method are proposed for the numerical solution of current fluid theories. Physical elaboration of the graphs is given to recognize the influence on fluid flow and heat transport mechanism in different rising conditions. Based on results, the implication of magnetic field and Williamson parameters restrict the fluid flow for both nanofluid (TiO2/EO) and hybrid nanofluid (TiO2 + Ag/EO). Special case studies of the shape factor effect show more enhancement in heat transfer rate for cylindrically shaped nanoparticles 25.8162% followed by brick-shaped 20.3286% and spherical-shaped 17.0583%. This study will provide better insight into applications including aircraft refrigeration, lubrication, plastic processing, engine and generator cooling, and so forth.

Impact of controlled prewetting on part formation in binder jet additive manufacturing

Binder jetting is an additive manufacturing process that bonds powder through selectively depositing binder by inkjet printing. The part is then extracted and densified by sintering and/or infiltration. The process offers low costs and fast build rates, but properties can be poor due to residual porosity after sintering. The inkjet printing process may contribute to this residual porosity by creating large pores. The droplet kinetic energy ejects some powder particles from the bed and rearranges others. Particle ejection and rearrangement are theorized to create porous regions in binder-jetted parts. In this work, small amounts of moisture are added to the spread powder before printing and the impact on part formation, part properties, and printing parameters measured with varied droplet spacing, droplet velocity, and print frequency. Moisture is added by applying an atomized fluid mixture to the powder between layer spreading and binder printing. The fluid mixture partially evaporates but leaves a stable residue to increase cohesion and enhance imbibition. Moisture addition to the powder increases the range of droplet spacings for line formation while reducing particle ejection, powder rearrangement, and balling in layer and multilayer parts. Excessive moisture addition decreases the effective saturation of printed lines, but saturation in 3D parts is less impacted. Increased surface roughness in the first few layers of a print was also mitigated with prewetting. High-speed X-ray imaging verified prewetting reduction in particle ejection and rearrangement.

Simulation studies on GAX based absorption cooling and power cycle using a mixture of ammonia-water working fluid and aluminium oxide nano particles

The present work is focused on analyzing the influence of nano material aluminium oxide on the performance of generator absorber heat exchange ammonia-water absorption refrigeration system. Matlab code has been used to simulate the performance of the combined cycle. The effect of refrigeration, absorber and condenser temperatures on the combined cycle performance have been studied. The results of the analysis indicate that the performance of the combined cycle is higher by 15 to 20% when Al2O3 nano particles were added when compared to the same cycle without the addition of nano particles.

Investigation on ethylene glycol and glycerol mixture concentration dependent optical, dielectric, electrical, rheological, and thermophysical properties of EG+Gly/ZnO semiconductor nanofluids

Wide energy bandgap metal oxide nanomaterials containing semiconductor nanofluids (SNFs) are technologically established as advanced multifunctional materials for progress in high performance soft condensed devices. Therefore, to strengthen this field of materials, the present study reports in detail the optical, dielectric, electrical, rheological, and thermophysical properties of the SNFs based on ethylene glycol (EG) and glycerol (Gly) mixture of an entire concentration range (Gly volume fractions; 0.00, 0.25, 0.50, 0.75, and 1.00) with a fixed amount of zinc oxide (ZnO) semiconductor nanomaterial (0.05 wt%). These green-formulated EG + Gly/ZnO SNF materials showed a longer stability of the suspended nanoparticles in the highly viscous hydrogen bonded base fluid and exhibited an increase in absorbance with the decrease wavelength of visible range photons and the ZnO electronic transition at about 3.2 eV energy of ultraviolet radiations. Dielectric measurements over the 20 Hz–1 MHz range of these SNFs, at 298.15 K, explained a dominant contribution of the electrode and interfacial polarization processes at low frequencies and the molecular dipole polarization of static permittivity about 40 at the higher frequencies. Electrode polarization and conductivity relaxation times enhanced exponentially when the Gly concentration increased in the EG + Gly base fluid which governs the electrical conductivity decrement from 0.79 to 0.04 μS/cm for these SNFs. The rheological study explained the Newtonian characteristics of EG + Gly/ZnO nanofluids with their base fluid mixture concentration controllable dynamic viscosity in the wide range of 17–702 mPa s, at 298.15 K. The density, refractive index, ultrasound velocity, prominent acoustic parameters, and thermal conductivity are determined and discussed to explore the solid-liquid interaction and interfaces formed in these innovative SNF materials.