Unstable Mixtures Research Articles

Validation of High Speed Reactive Flow Solver in OpenFOAM with Detailed Chemistry

An OpenFOAM® based hybrid-central solver called reactingPimpleCentralFoam is validated to compute hydrogen-based detonations. This solver is a pressure-based semi-implicit compressible flow solver based on central-upwind schemes of Kurganov and Tadmor. This solver possesses the features of standard OpenFOAM® solvers namely, rhoCentralFoam, reactingFoam and pimpleFoam. The solver utilizes Kurganov & Tadmor schemes for flux splitting to solve the high-speed compressible regimes with/without hydrodynamic discontinuity. In this work, we present the validation results that were obtained from one-dimensional (1D) and two-dimensional (2D) simulations with detailed chemistry. We consider three different mixtures that fall into the categories of weakly unstable mixture (2H2 +O2 +3.76Ar and 2H2 +O2 +10Ar), and moderately unstable mixture (2H2 +O2 +3.76N2), based on their approximate effective activation energy. We performed the numerical simulations in both laboratory frame of reference (LFR) and shock-attached frame of reference (SFR) for the 1D cases. The 1D simulation results obtained using this solver agree well with the steady-state calculations of Zel’dovich von Neumann Döring (ZND) simulations with an average error below 1% in all cases. For the 2D simulations, circular hot-spots were used to perturb the initially-planar detonations to develop into spatio-temporally unstable detonation front. The convergence is declared when the front does not deviate much from the CJ speed (Chapman-Jouguet) and the regularity of cellular pattern on the numerical smoke foils reaches a steady state. We have verified from our preliminary studies that the SFR-based simulations are computationally cheaper in comparison to the LFR simulations and that the required grid resolution is always lesser in the former than the latter to reach the same level of accuracy (in terms of speed of the detonation front and cell sizes from the numerical smoke foil). We have also verified that at least 24 points per induction zone length (for weakly unstable mixture) and 40 points per induction zone length (for moderately unstable mixture) are required to sufficiently resolve the detonation structures that are independent of grids, boundary and initial conditions. Further reduction in computational cost of approximately 50% is achieved by using non-uniform grids, which converge effectively to the same solutions in comparison to the results from twice the number of grids with uniform resolution.

Curvature effect on stabilization of cellular detonations in channel, circular arc and spherical shell geometries

The stability and propagation characteristics of gaseous detonations are numerically investigated, specifically in configurations where global front surface curvature plays a significant role. The simulations use idealized constitutive models representing a weakly unstable mixture and the simulated geometries include both two-dimensional arc and spherical shell sections with rigid walls and a straight channel geometry with compliant confinement. Depending on the inner and outer arc radius, differing levels of curvature can be imparted on the propagating wave in the two curved geometries. For thinner explosive regions, cellular type instabilities develop as the wave propagates around the arc and shell. However, as the thickness of the explosive increases and progressively greater surface curvature is imposed, laminar flow regions develop which can coexist with regions dominated by unstable cellular propagation. Here, the appearance and persistence of this laminar zone is shown to coincide with a critical level of surface curvature for both the arc and shell geometries. This critical curvature concept is also tested in the corresponding straight channel configuration with a compliant confiner, which similarly produces global surface curvature on the propagating detonation front but now as function of imposed wall divergence. Similarly, the propagation in the channel is found to stabilize when the maximum surface curvature exceeds a certain critical value that is close to the analog from the curved geometries. These results support the likely existence of a critical surface curvature mechanism or criterion that ensures the stabilization of a nominally unstable cellular detonation.

Enhancing Biodiesel-Methanol blends with 1-Butanol for stable and efficient fuels

The quest for sustainable fuels has led to the exploration of biodiesel as an eco-friendly alternative to conventional fossil fuels. While biodiesel holds promise due to its renewable nature and lower emissions, challenges occur when blending it with methanol. This study addresses these issues by adding 1-butanol as a cosolvent in biodiesel-methanol blends, improving their stability and performance. Gas chromatography mass spectrometry identifies the dominant compound in biodiesel as 2,6-di-tert-butylphenol, known for its stability-enhancing properties. Adding alcohols to biodiesel aiming to reduce the ignition delay time in and shorten the combustion time in diesel engines. The scientific explanation regarding the role of 1-butanol in stabilizing the biodiesel-methanol blend has not yet been revealed. Methanol's tendency to form an unstable mixture due to water affinity is mitigated by 1-butanol, which raises the critical phase separation temperature, a key indicator of blend stability. The study validates that adding 1-butanol produces a stable, homogenous blend. 1-butanol's as a third fuel blend option is underscored by its higher energy content, lower volatility, and reduced hydrophilicity compared to ethanol and methanol, making it a valuable advantage for fuel development. Investigations into ignition delay and burning speed reveal their difference with blend compositions. In conclusion, 1-butanol appears as a promising solution for enhancing the efficiency and stability of biodiesel-methanol blends, contributing to the development of sustainable and eco-friendly fuels for a more responsible and energy-efficient future.

A-posteriori analysis of a data-driven filtered wrinkled flamelet model for thermodiffusively unstable premixed flames

State-of-the-art turbulent combustion models do not account for the effects of intrinsic flame instabilities, which are known to have a non-negligible effect, under technically relevant conditions, in thermodiffusively unstable flames such as those of hydrogen-based fuels. In this work, a data-driven modeling framework for filtered, laminar, self-wrinkling flames subject to intrinsic instabilities is presented and proposed as a stepping stone for the development of turbulent combustion models for large eddy simulation. In this context, data-driven refers to the use of small- and medium-sized resolved simulations, explicitly filtered in physical space, as data sources for the development of filtered tables. For consistency, all the unclosed terms of the filtered governing equations are then written according to the filtered tabulated chemistry formalism. The a-posteriori analysis of the modeling framework indicates that medium-scale simulations, which conversely to the small-scale ones feature at least one characteristic flame-finger, are needed for the generation of the data-driven tables. Furthermore, a laminar wrinkling factor, accounting for the sub-filter cellular wrinkling, should also be used. The presented results show promise for the extension of this modeling framework to the simulation of turbulent flames, as well as to multi-step chemistry and detailed thermo-transport modeling. Statement of SignificanceIt is nowadays well-known that intrinsic flame instabilities have a leading order impact on the propagation of premixed flames in thermodiffusively unstable mixtures, such as lean hydrogen-air premixed flames. This work presents the first a-posteriori analysis of a combustion model for filtered, albeit laminar, large-scale, intrinsically unstable premixed flames. The novelty of the presented data-driven model lies in the use of data obtained from filtering direct numerical simulations performed for paradigmatic small and medium-scale cases, instead of standard one-dimensional flamelets.

Heat transfer by transiently superheated fluids: Decay of unstable water-based mixtures

The present study sets out to elucidate the characteristic features of instantaneous heat transfer accompanying transient superheating of partially miscible mixtures having a lower critical solution temperature (LCST) with respect to the liquid–liquid binodal and the diffusion (liquid–liquid) spinodal. The research has employed the method of controlled pulsed heating of a wire probe, which can be used to directly measure heat flux into the medium at a strictly fixed heater temperature Tst. At a characteristic heating time of 100 ms, values of Tst were gradually increased from 100 to 500 °C, while the corresponding pressures varied from 0.1 to 35 MPa. The objects of study were aqueous solutions of PPG-425 and PPG-2000 polypropylene glycols, as well as 2,6-Lutidine, all having LCST in the range convenient for achieving large superheats. The values of the heat transfer coefficient (whose highest values reached 90 kW/m2 K for the solution with 5 wt% PPG-2000 content at the superheat degree of about 390 °C) and the energy absorbed by the solution were calculated on the basis of the primary data. The calculation results related the individual features of the studied systems to the phase diagram and characteristic system relaxation times depending on the concentration and superheat degree with respect to the spinodal. The applicability of such systems as coolants under conditions of high-power heat release for elements with a short response time is demonstrated. Based on the experimental results, we validated the selection of solutions as coolants in the concentration range from the left branch of the spinodal to the critical concentration of the solution.

Experimental Study on the Effect of Disturbed Tube on the Propagation Mechanism of Methane-Oxygen Detonation

The detonation experiments of unstable mixture CH4 + 2O2 were carried out in smooth and disturbed tube under different initial pressures(P 0) to study the effects of inner tube disturbance(d) on the propagation velocity of detonation wave and the characteristics of cellular structure. The results show that these are mainly affected by the initial pressure and boundary conditions (confined wall). With the increase of P 0, the change trend of cell size remains unchanged whether there is disturbance or not. However, when P 0 rises to 15kPa, it can not offset the detonation failure caused by the d = 60mm tube. While, the turbulence effect caused by d = 20mm tube maintains the wave propagation through the flow fluctuation of leading shock wave and the interaction of boundary layer. When P 0 increases to 14kPa, the shear wave intensity of the detonation wave increases. The high initiation energy leads to the instability of the detonation wave front. A relatively fine secondary cellular structure is observed near the main cellular structure. So after inserting the inner tube disturbance, the decrease of cell size is due to the generation of secondary cellular structure, and the size of main cellular structure actually becomes larger.

Effects of detonation instability and boundary layer on flame propagation behavior in millimeter-scale smooth tubes

Small pre-detonators have potential applications in practical pulse detonation engines or rotating detonation engines. The effects of detonation stability parameter and area divergence on flame propagation in capillary tubes are experimentally analyzed using high-speed cinematography. The four mixtures (namely, stoichiometric methane/oxygen, ethylene/oxygen, propane/oxygen and stoichiometric acetylene/oxygen/50% Ar mixtures) used have different values of stability parameter. The inner diameters of the tubes (namely, 0.5, 1.0, 2.0, and 4.0 mm) investigated provide a variation in area divergence at initial pressures p0 ranging from 5 to 100 kPa. The results show that stability parameter and area divergence play positive and inhibitory roles, respectively, in the process of flame propagation. Five propagation modes are observed (namely, steady detonation, stuttering detonation, galloping detonation, deflagration, and no flame), among which the stuttering detonations have three different forms, depending on the product of stability parameter and area divergence. For the most-unstable mixture (stoichiometric methane/oxygen, with the largest values of stability parameter), the range of the product of stability parameter and area divergence in which steady detonation can occur is the narrowest. The results also indicate that the stoichiometric ethylene/oxygen and stoichiometric propane/oxygen, with similar values of the product of stability parameter and area divergence, have the same propagation modes. Further analysis suggests that the Chapman–Jouguet deflagration-to-detonation transition (DDT) distance L decreases with increasing of stability parameter and area divergence for all four mixtures. Compared with the other three mixtures, stoichiometric methane/oxygen, which has the smallest values of L because it is the most unstable mixture with the greatest propensity for hotspot formation, is most likely to undergo DDT under the same initial and boundary conditions. These conclusions agree well with the various characteristics of L obtained for larger tubes.

Characteristic Features of Heat Transfer in the Course of Decay of Unstable Binary Mixture

This article is devoted to the study of the phenomenon of superheating of partially miscible mixtures having a lower critical solution temperature and the thermal effect accompanying the relaxation of an unstable mixture, within the framework of the problem of high-density heat flux removal. The study was carried out by using the method of the controlled pulse heating of a platinum wire probe. The characteristic heating time was from 0.2 to 180 ms. The superheating degree of the mixture relative to the diffusion spinodal exceeded 100 K. The heat flux density from the heater surface reached 13.7 MW/m2. The object of research was an aqueous solution of polypropylene glycol-425 (PPG-425). The obtained results clearly indicate that such mixtures can be used as coolants in processes where the possibility of powerful local heat release cannot be excluded. They also form the basis for expanding the phase diagram by involving in the study not-fully-stable and unstable states of the mixture.

Propagation characteristics of unstable detonation waves in a round tube with annular perturbation

The detonation propagation characteristics of the mixtures, 2H2 + O2+3Ar and CH4 + 2O2, were investigated. Accordingly, the mixtures were tested in round tube with inner diameter of D = 80 mm and annular tubes with widths of w = 25 mm, 15 mm, and 5 mm. The two mixtures represent stable mixture with regular cell pattern and unstable mixture with irregular cell pattern, respectively. Smoked foils were utilized to record cellular structure under various initial conditions. Subsequently, the length scale Ldsc was measured, which represents the length from the start of the test section to the position where the cellular structure changes drastically (the cell size obviously increases or the structure disappears). The results reveal that both mixtures can successfully propagate in round tube and annular tubes of 25 mm and 15 mm, but fail in 5 mm annular tube. The Ldsc value of 2H2 + O2 + 3Ar is higher than that of CH4 + 2O2 in 80 mm and 15 mm tubes, but it is opposite in 25 mm tube. Moreover, the relationship between Ldsc and hydraulic diameter DH was analysed. For a given tube, the values of Ldsc and Ldsc/DH increased when the initial pressure increased. And the variation trend of Ldsc and Ldsc/DH of CH4 + 2O2 is steeper. Furthermore, the mixtures 2H2 + O2 + 3Ar and CH4 + 2O2 resulted in over-driven detonation in 15 mm and 25 mm annular tubes, respectively. The ratio between the total reaction length (sum of the induction length and exothermic length) and the hydraulic diameter (DH/(Δi + Δe)) correspond to critical values of 18 for hydrogen-oxygen-argon and 6 for methane-oxygen, below which the detonation will fail.

Antioxidative capacity of microalgal carotenoids for stabilizing n-3 LC-PUFA rich oil: Initial quantity is key

The health-beneficial long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA) are easily affected by the undesired process of lipid oxidation in fish oil, while being stable in the lipid extracts of photoautotrophic microalgae. The current research investigates the role of carotenoids by evaluating the oxidative stability of mixtures of fish oil with total lipid extracts of two different microalgae (Phaeodactylum and Isochrysis) throughout an accelerated storage experiment of 4 weeks at 37 °C. A clear separation between oxidatively stable and oxidatively unstable mixtures was observed for which the initial amount of carotenoids relative to the amount of n-3LC-PUFA was a good indicator. The lipid class composition, clearly differing between the two algae, was probably of minor influence. The antioxidative role of fucoxanthin, and diatoxanthin and β–carotene as minor carotenoids, was illustrated by their gradual degradation throughout storage. However, when their initial contents were too low, this role could not be exerted leading to thorough lipid oxidation.

On the role of transverse detonation waves in the re-establishment of attenuated detonations in methane–oxygen

This investigation concerns the problem of detonation attenuation in stoichiometric methane-oxygen and its re-establishment following its interaction with obstacles, using high resolution numerical simulation. The main focus was on the role of the transverse detonation on the re-establishment of the detonation wave, and the importance of applying a numerical combustion model that responds appropriately to the thermodynamic state behind the complex shock wave dynamics. We applied an efficient thermochemically derived four-step global combustion model using an Euler simulation framework to investigate the critical regimes present. While past attempts at using one- or two- step models have failed to capture transverse detonations, for this scenario, our simulations have demonstrated that the four-step combustion model is able to capture this feature. We thus suggest that to correctly model detonation re-initiation in characteristically unstable mixtures, an applied combustion model should contain at least an adequate description to permit the correct ignition and state variable response when changes in temperature and pressure occur, i.e., behind shocks. Our simulations reveal that (1) there is a relationship between the critical outcomes possible and the mixture cell size, and (2) while pockets of unburned gas may exist when a detonation re-initiates, it is not the direct rapid consumption of these pockets that gives rise to transverse detonations. Instead, the transverse detonations are initiated through pressure amplification of reaction zones at burned/unburned gas interfaces whose combustion rates have been enhanced through Richtmyer–Meshkov instabilities associated with the passing of transverse shock waves, or by spontaneous ignition of hot spots, which can form into detonations through the Zeldovich gradient mechanism. In both situations, non-uniform ignition delay times are found to play a role. Finally, we found that the transverse detonations are in fact Chapman–Jouguet detonations, but whose presence contributes to overdriving the re-initiated detonation along the Mach stem.

Universal fast mode regime in wetting kinetics.

We present simulation results from a comprehensive molecular dynamics (MD) study of surface-directed spinodal decomposition (SDSD) in unstable symmetric binary mixtures at wetting surfaces. We consider long-ranged and short-ranged surface fields to investigate the early stage wetting kinetics. The attractive part of the long-ranged potential is of the form V(z)∼z^{-n}, where z is the distance from the surface and n is the power-law exponent. We find that the wetting-layer thickness R_{1}(t) at very early times exhibits a power-law growth with an exponent α=1/(n+2). It then crosses over to a universal fast-mode regime with α=3/2. In contrast, for the short-ranged surface potential, a logarithmic behavior in R_{1}(t) is observed at initial times. Remarkably, similar rapid growth is seen in this case too. We provide phenomenological arguments to understand these growth laws. Our MD results firmly establish the existence of universal fast-mode kinetics and settle the related controversy.

The re-initiation of cellular detonations downstream of an inert layer

The current work aims to examine how the nature of cellular instabilities controls the re-initiation capability and dynamics of a gaseous detonation transmitting across a layer of inert (or non-detonable) gases. This canonical problem is tackled via computational analysis based on the two-dimensional, reactive Euler equations. Two different chemical kinetic models were used, a simplified two-step induction-reaction model and a detailed model for hydrogen-air. For the two-step model, cases with relatively high and low activation energies, representing highly and weakly unstable cellular detonations, respectively, are considered. For the weakly unstable case, two distinct types of re-initiation mechanisms were observed. (1) For thin inert layers, at the exit of the layer the detonation wave front has not fully decayed and thus the transverse waves are still relatively strong. Detonation re-initiation in the reactive gas downstream of the inert layer occurs at the gas compressed by the collision of the transverse waves, and thus is referred to as a cellular-instability-controlled re-initiation. (2) If an inert layer is sufficiently thick, the detonation wave front has fully decayed to a planar shock when it exits the inert layer, and re-initiation still occurs downstream as a result of planar shock compression only, which is thus referred to as a planar-shock-induced re-initiation. Between these two regimes there is a transition region where the wave front is not yet fully planar, and thus perturbations by the transverse waves still play a role in the re-initiation. For the highly unstable case, re-initiation only occurs via the cellular-instability-controlled mechanisms below a critical thickness of the inert layer. Additional simulations considering detailed chemical kinetics demonstrate that the critical re-initiation behaviors of an unstable stoichiometric mixture of hydrogen-air at 1 atm and 295 K are consistent with the finding from the two-step kinetic model for a highly unstable reactive mixture.

Heat transfer under high-power heat release: Not fully stable fluids as potential heat carriers

• Significant disturbance in heat transfer under high-power heating was detected. • Supercritical-pressure water and highly unstable aqueous mixture were studied objects. • Heat transfer deterioration stage preceding macroscopic phase transition was revealed. • This stage is assumed to have universal character for fluid phase transitions. • Its nature is associated with the violation of homogeneity of not fully stable system. In this paper, we present new data on non-stationary heat transfer in sub- and supercritical liquids due to high-power heat release in a wire probe immersed in an investigated liquid. In the performed experiments, the characteristic heating time was from 5 to 180 ms, while the corresponding thickness of the heated layer was in the magnitude order of 10 1 µm. The impetus for the study came from the previous discovery of two unexpected effects. The first was a deterioration of heat transfer during the rapid transition of a compressed fluid to the supercritical region of temperatures along the isobar. The second was the distinctive character of the change in the heat flux density of a binary, partially miscible liquid when going deeper into the region of its unstable states. The study is aimed at clarifying the prospects of using supercritical fluids and mixtures with lower critical solution temperatures as potential heat carriers in processes where the possibility of powerful local heat release cannot be excluded.

Atomic-scale mechanism of carbon nucleation from a deep crustal fluid by replica exchange reactive molecular dynamics simulation

We present a mechanistic model of carbon nucleation and growth from a fluid at elevated temperature (T) and pressure conditions, typical of those found in the shallow Earth’s lithosphere. Our model uses a replica exchange reactive molecular dynamics framework in which molecular configurations are swapped between adjacent T replica at regular intervals according to underlying statistical mechanics. This framework allows predicting complex molecular structures and thermodynamics while remaining computationally efficient. Here we simulate the reactivity of an unstable mixture of CO2 and CH4 at 1000 K and 1 GPa. We find that the path to thermodynamic equilibrium is initially entropy-driven, producing a diversity of short-lived species, including various alcohols with intermediate carbon oxidation states. Cyclic and polycyclic radicals that are sometimes resonance-stabilized form next and set the stage for carbon nucleation. The carbon exsolution process releases abundant water, is exothermic and starts with the nucleation of a large aggregate of hydrogenated graphene flakes from covalently bonded polycyclic units. The carbon backbone of this nucleus subsequently grows into a hydrogen-depleted fullerene-like structure, before evolving toward a partially bilayered graphene layer. Overall, our results show that the mechanism of graphitic C formation is certainly not bimolecular, and that it may involve a combination of key condensation and radical chain reactions. This will help understand the isotopic, and reactive characteristics of carbon-bearing fluids during their upward transit through the Earth’s mantle and crust. Moreover, the mechanistic insights outlined here present intriguing similarities with the process of soot and interstellar dust formation, which suggests that the widespread distribution of abiotic polyaromatic and graphitic material on Earth and beyond may reflect the prevalence of a fundamental chemical pathway.

Investigation on the laminar burning velocity and flame stability of premixed n-dodecane-air mixtures at elevated pressures and temperatures

N-Dodecane is an important representative in several surrogates of multicomponent fuels like gasoline and jet fuels. The choice of a surrogate combination to estimate the combustion characteristics of a complex fuel depends strongly on its individual component’s combustion properties, and its physical and chemical properties. Therefore, it is essential to have a precise reaction mechanism to predict the combustion characteristics such as laminar burning velocity (LBV) and ignition delay times of individual components and the surrogate. The present work aimed to measure the unstretched LBV and burned gas Markstein length of premixed n-dodecane-air mixtures at pressure = 1–4 bar, temperature = 400–450 K, and ϕ = 0.8–1.4. The flame stability analysis of all experiments emphasized that a transition of stable to unstable flame occurred at ϕ = 1.4 due to preferential diffusion effects. The capability of existing Lewis number models to predict the transition was examined, and the BM model showed excellent agreement with all experiments. The local flame equivalence ratio estimated from the simulated reactant species profiles shot up by 15% than the global equivalence ratio for preferentially unstable mixtures. Markstein length was influenced significantly by an increase in pressure than temperature due to a substantial reduction in flame thickness. The comparison of measured unstretched LBV with available n-dodecane mechanisms indicated that JetSurF2.0, You et al., PoliMi were the best candidates. Off-stoichiometric varieties of n-dodecane-air were more responsive to pressure and temperature effects. Finally, the unstretched LBV of premixed n-dodecane-air mixtures increased/ decreased with an initial temperature/ pressure hike. Raise in initial temperature increased the flame temperature and improved the flame propagation rate. An increase in initial pressure amended the reaction rate, but decreased the flame propagation rate due to the dominance of three-body reactions and increased unburned gas density.

Experimental and numerical studies on detonation failure and re-initiation behind a half-cylinder

Mach reflection causes the re-initiation of decoupled detonation owing to changes in the boundary. A complementary series of experiments and numerical simulations, illustrating detonation failure and subsequent reinitiation processes, have been presented. Immediately across the half-cylinder, the decoupled detonation owing to the diffraction effect wave is reflected on the bottom wall to form a regular reflection, and then changes into the Mach reflection, which further determines the detonation reinitiation. Two different reinitiation modes after detonation wave diffraction were observed for the stable mixtures: the direct Mach reflection re-initiation mode and Mach reflection combined with the transverse detonation. However, for unstable detonations, a different reinitiation mode was obtained, whereby the development of intrinsic instabilities resonates with the reflection on the bottom wall, rendering the Mach reflection randomly occurring or even absent. The critical limit of detonation failure is characterized by the radius of the half-cylinder and the cell size. In addition, the transition length from regular to Mach reflection was measured to reveal the length-scale effect on the process. • Two re-initiation mechanisms are proposed for stable and unstable mixtures respectively. • The detonation failure limit is dominated by the radius and detonation cell size. • The transition from regular to Mach reflection shows the existence of length-scale effect.

Modeling of viscosity of unstable crude oil–water mixture by characterization of energy consumption and crude oil physical properties

When oilfield development enters the middle and late stages, the crude oil–water mixture (COWM) produced from oil wells often has a high water cut and cannot form a stable emulsion. The traditional viscosity model of an emulsion is not suitable for this unstable mixture. Mastering the viscosity characteristics of the unstable crude oil–water mixture with high water cut (UCMH) for pipeline transportation of such mixtures is important. The apparent viscosities of UCMH (water cut of mixture ranging from 0.70 to 0.90) for 16 crude oils were determined via the stirring viscometric method. The results showed that the apparent viscosity of UCMH decreased with increasing shear rate, water cut of mixture, and temperature, demonstrating the property of shear thinning. The apparent viscosity of UCMH did not depend on the content of single surfactants such as resins, asphaltenes, waxes, and mechanical impurities but was closely related to the content of the above-mentioned combinatorial surfactants. The parameter exergy loss rate of shear that describes energy consumption was determined to characterize the external shear action on UCMH, which can fully reflect the essence of the mechanical energy consumption in the emulsifying process under different shearing conditions. A new viscosity model for UCMH was established by the quantitative characterization of the energy consumption and crude oil physical properties (i.e., saturate content, aromatic content, surfactant content, acid value, and crude oil viscosity). In light of the statistical results of 336 groups of validation experimental data from four crude oils, the average relative deviation between the apparent viscosity calculated by the new model and the measured apparent viscosity of UCMH was 5.3%, which is considerably better than the traditional emulsion viscosity models, that is, the Einstein, Vand, Taylor, and Richardson models.

Voltage-controlled precision electronic power regulator.

The architecture of a novel electronic power regulator, which allows a set value of constant power on a wire probe to be maintained, is presented. A gain in the negative feedback loop of ≈2 · 103 allows the set power value in the series of pulses to be accurately maintained at the level of 99.95% (proximity 0.05). In order to study short term processes, the response time of the described regulator is in the order of 2 μs. The created architecture is easily scalable for various tasks, ranging from the well-known transient hot-wire method to other applications, examples of which are given in this article (unsteady heat transfer in supercritical-pressure fluids and unstable mixtures having lower critical solution temperature). A comparison of the presented controller architecture with the previously described solutions from the pointof view of operational stability is given.

Two-Phase Liquid–Liquid Flow in the Aspect of Reduction of Pumping Power of Hydrophobic Substances with High Viscosity

The paper reports the results of a study into a method of estimating the level of power/energy reduction needed for pumping highly viscous hydrophobic liquids. The effect of reducing the flow resistance resulting from feeding an adequate volume of water into the flow tube is considered. The polar parameters of water selected for analysis are different than oil. Experimental studies were not carried out in this regard, since the commonly accessible equation expressing the resistance of two-phase liquid–liquid flow was utilized to develop the method discussed in this study. On its basis, simulations were carried out to determine the conditions and level of reduction of the two-phase flow resistance in comparison to the single-phase flow resistance of a highly viscous oily liquid. The analysis of the results provided means for determination of such ranges of variations in the flow parameters of the two-phase liquid–liquid system, in which the total power of pumps applied to pump both liquids is smaller than the power of one pump feeding oil into the pipeline in the conditions of single-phase flow. Calculations were performed for selected constant mass flux densities of oil with various viscosities as well as for water. The proposed method can be applied in the procedure of optimization calculations for pipeline installations and their feed systems. The given example of its use was preceded by a description of the reasons and effects associated with the reduction of flow resistance in liquid–liquid systems and a detailed presentation of how to use the equation that forms the essence of the described calculation method. Attention was also paid to other phenomena accompanying two-phase liquid–liquid flows, i.e., interfacial slip, phase inversion, specific flow structures, and the viscosity of the unstable mixture of two liquids flowing in the pipe.