Mixture Flow Research Articles

A thermodynamic framework for heat‐conducting flows of mixtures of two interacting fluids

AbstractWithin the theory of interacting continua, we develop a model for a heat conducting mixture of two interacting fluids described in terms of the densities and the velocities for each fluid and the temperature field for the mixture as a whole. We use a general thermodynamic framework that determines the response of the material from the knowledge of two pieces of information, namely how the material stores the energy and how the entropy is produced. This information is expressed in the form of the constitutive equations for two scalars: the Helmholtz free energy and the entropy production. Additionally, we follow the goal to determine the response of a mixture from a small (minimal) set of material parameters, including shear viscosity, bulk viscosity and heat conductivity associated with the mixture as a whole and the drag coefficient connected with the interaction force between the constituents. The same thermodynamic approach is used to obtain the model when the mixture as a whole responses as an incompressible material. For both the compressible and incompressible mixtures, we investigate three variants stemming from different definitions of the (averaged) velocity associated with the mixture as a whole. We also address the issue of identification of boundary conditions for the individual constituents from the standard boundary conditions formulated in terms of the quantities associated with the mixture as a whole.

Visualization experiments and seepage characteristics of water–solid mixture flow through a rough fracture of silty mudstone under low hydraulic head

Visualization experiments and seepage characteristics of water–solid mixture flow through a rough fracture of silty mudstone under low hydraulic head

Significant Effect of Rugosity on Transport of Hydrocarbon Liquids in Carbonaceous Nanopores

We report the results of modeling the transport of n-octane and n-hexadecane and their mixtures through carbonaceous nanopores at high-pressure conditions. Pores are modeled as smooth slit sheets with perturbations added as ridges and steps and a version of the statistical associating fluid theory (SAFT-γ Mie) is used both as equation of state and as a coarse-grained force field to account for fluid–fluid and fluid–solid molecular interactions. Molecular simulation allowed the description of transport diffusivities in terms of molecular flow, using boundary driven nonequilibrium molecular dynamics (BD-NEMD). Transport diffusivities are also independently calculated using equilibrium and external force nonequilibrium molecular dynamics (EF-NEMD) simulations, after accounting for the adsorption on the pores. We show consistency between the approaches for quantifying transport in terms of permeabilities (Darcy flows) and transport diffusivities. We find that smooth slit carbon pore models, which are commonly employed in the literature as surrogates for kerogen regions in shale, are an inadequate representation of ultraconfined natural pores. For slit pores, the flow patterns are characterized by a fully mutualized pluglike flow and fast transport. However, by incorporating even a small amount of rugosity (roughness) into the solid walls, the diffusion coefficients decrease dramatically, with surface roughness significantly affecting the characteristic transport and velocity profiles inside the pores. In all cases, it is seen that there are important cross-correlation effects, influencing the way components of the mixture flow together. Calculated self-diffusivities are orders of magnitude smaller than the observed transport diffusivities for liquid mixtures. This work has a direct impact on the understanding and modeling of unconventional hydrocarbon recovery and flow in organic shale rocks.

Segregation patterns in three-dimensional granular flows.

Flow of size-bidisperse particle mixtures in a spherical tumbler rotating alternately about two perpendicular axes produces segregation patterns that track the location of nonmixing islands predicted by a dynamical systems approach. To better understand the paradoxical accumulation of large particles in regions defined by barriers to transport, we perform discrete element method (DEM) simulations to visualize the three-dimensional structure of the segregation patterns and track individual particles. Our DEM simulations and modeling results indicate that segregation pattern formation in the biaxial spherical tumbler is due to the interaction of size-driven radial segregation with the weak spanwise component of the advective surface flow. Specifically, we find that after large particles segregate to the surface, slow axial drift in the flowing layer, which is inherent to spherical tumblers, is sufficient to drive large particles across nominal transport barriers and into nonmixing islands predicted by an advective flow model in the absence of axial drift. Axial drift alters the periodic dynamics of nonmixing islands, turning them into "sinks" where large particles accumulate even in the presence of collisional diffusion. Overall, our results indicate that weak perturbation of chaotic flow has the potential to alter key dynamical system features (e.g., transport barriers), which ultimately can result in unexpected physical phenomena.

Numerical analysis of evaporation from a falling film in a vertical parallel plate channel

A detailed numerical analysis is performed of evaporation from a laminar falling liquid film with a co-current laminar gas-vapour mixture flow in a vertical parallel plate channel. A finite volume method is used to obtain a fully coupled implicit solution of a complete set of parabolic two-phase two-dimensional governing equations. Comparisons with the previous numerical and experimental studies are made to demonstrate the accuracy and capability of the present numerical model. Water-air and ethanol-air mixtures are used to examine the effects of buoyancy forces on the flow and the thermal characteristics of the evaporation process. The effects on the heat and mass transfer of the system of the wall heat flux, the relative humidity, and the inlet pressure are investigated.

Dynamics and runout distance of saturated particle-fluid mixture flow on a horizontal plane: A coupled VOF-DEM study

This study investigates the dynamics and runout of particle-water mixture column collapse using a modelling method coupling Discrete Element Method (DEM) and Volume of Fluid (VOF). From the numerical results, we observe similar and distinct responses between the dry and saturated mixture flows. Both exhibit two different flow behaviours for low and high column collapse. However, the presence of water reduces dissipative interactions between particles, hence increasing the mobility of mixture flows compared to their dry counterparts. The reduction of particle interaction forces also weakens the transition from sliding-dominant to inertial-dominant flows with increasing column aspect ratio. Therefore, the runout distance of mixture flows can be described by a single scaling law rather than by two different functions as for the dry flows. Additionally, the impacts of particle density on mixture flows become more significant in which the flows run out less and retain greater height with increasing particle density.

Effect of hydrogen addition on the dynamics of premixed C1–C4 alkane-air flames in a microchannel with a wall temperature gradient

The effect of hydrogen (H2) addition on the flame dynamics of premixed C1–C4 alkane/air mixtures in a microchannel is investigated using a detailed-chemistry model through two-dimensional numerical computations. A detailed computational study have been performed in a 2 mm diameter tube with 120 mm length and a wall temperature gradient along the axial direction of the channel. The numerical simulations are carried out for various stoichiometric hydrocarbon (HC)/H2 mixtures at 0.15 m/s mixture inlet velocity. Flame repetitive extinction and ignition (FREI) flame pattern has been identified for all the fuel mixtures at these channel wall and mixture flow conditions. CH4/air mixture shows a higher HRR than C3–C4 alkane/air mixtures. Flame residence time in microchannel increases with increase in hydrogen addition percentage for all the three hydrocarbon/air mixtures considered in the present study. A non-monotonic behavior of FREI frequency is identified for CH4/air mixture, whereas it decreases monotonically for C3H8/air and C4H10/air mixtures with H2 addition. The amount of HRR and flame propagation velocity decreases with increase in H2 addition for lower-alkanes/air mixtures. The flame bifurcation effect is observed for CH4/air mixture, which disappears due to H2 addition in the mixture. The bifurcation effect is not present for other hydrocarbon/air mixtures investigated in the present study. The addition of H2 in the mixture enhances the flame stability of hydrocarbon/air mixtures in the microchannel.

Mixed convection MHD boundary layer flow, heat, and mass transfer past an exponential stretching sheet in porous medium with temperature-dependent fluid properties

The mixed convection MHD boundary layer flow, heat and mass transfer of a Newtonian fluid mixture across an exponentially stretched permeable sheet in porous medium with Soret and Dufour effects subject to temperature-dependent fluid properties have been investigated numerically. The distribution of temperature and concentration at the surface is supposed to grow exponentially. Temperature is considered to affect fluid viscosity and thermal conductivity. The guiding partial differential equations with appropriate boundary conditions are converted into coupled, nonlinear ordinary differential equations with variable coefficients via a similarity transformation. Matlab's built in solver bvp4c is used to find numerical solutions. Using a graphical approach, the effects of several emerging physical parameters on velocity, temperature and concentration distributions on a flow field of a chemically nonreacting fluid mixture are examined and discussed. Results are compared to earlier literature available and found to be in good agreement. Furthermore, this research demonstrates that flow, heat and mass transmission are greatly influenced by mixed convection parameters, magnetic field, Prandtl number, viscosity, conductivity, permeability, and Schmidt number. Skin friction grows for mixed convection parameter, magnetic, viscosity. Highest growths of wall temperature and wall concentration gradients are observed for Prandtl number and Schmidt number, respectively. HIGHLIGHTS Heat and mass transfer rates increase with higher values of mixed convection parameters and Darcy parameter. To reduce heat transfer rate magnetic field may be used. Fluid with lower thermal conductivity and with higher Prandtl number may be employed to boost the cooling rate in conducting flows. Higher Schmidt enhances mass transfer rates. Suction stabilizes boundary layer growth. Soret effect can be used to separate light and medium molecular weight components from a fluid mixture and hence can be used for control of air pollution.

Dimensionless Profiles of Temperature and Steam Mass Fraction in Flows of Steam-Air Mixtures on a Flat Plate

Abstract Wall functions are generally used in a turbulent analysis with a computational fluid dynamics (CFD) code and large computation cells. The logarithmic law based on the analogy between momentum, energy, and mass transfer is widely used in wall functions for turbulent flows, but its validity in the turbulent boundary layer has not been confirmed for dimensionless profiles of temperature and steam mass fraction in flows of steam and noncondensable gases. In this article, therefore, we evaluated dimensionless profiles of temperature and steam mass fraction in flows of steam and air on a flat plate by using existing data. From the heat and mass transfer equations at the condensation surface based on the gradient of temperature or steam mass fraction, we showed that the convection heat flux qconv (which is used for the definition of the dimensionless temperature T+) should include the term of condensate mass flux ms and that the dimensionless steam mass fraction Ys+ should be a function of the dimensionless distance y+ (= uτ y/ν where uτ is the friction velocity), the Schmidt number Sc and the air mass fraction (1−Xs). Values obtained from the newly defined T+ and Ys+ and the existing data agreed relatively well with the linear function near the viscous sublayer (a few data points were there) but were much smaller than the existing logarithmic law due to condensation in the turbulent boundary layer (i.e., mist generation). On the other hand, the T+ and Ys+ values obtained by using the local Nusselt number Nuy and the local Sherwood number Shy (which were proposed in our previous study), respectively, agreed well with the logarithmic law.

Thermal performance of water‐based brines as a heat carrier for ground heat exchanger under severely cold environments

AbstractThe aim of the present study is to investigate the performance of water‐based brine solutions in the ground heat exchanger (GHX) for space heating applications under severely cold climate conditions. The conventional ethylene glycol (EG) and propylene glycol (PG)‐based water solutions have been considered for investigation. For the closed‐loop vertical U‐tube GHX, a mathematically built model is developed for ambient temperature below 0°C. The thermal performance analysis of GHX is carried out for the variation in fluid flow rate and brine solutions for different mixture percentages of water in EG and PG. The percentage of the mixture and fluid flow rate varied from 25% to 60% and 0.2 to 0.6 LPS, respectively. GHX performance parameters, namely convective coefficient, pressure drop, borehole resistance, and GHX effectiveness are determined for both EG and PG brines. Better performance of GHX is noticed with EG brines as compared to PG brines for similar operating conditions. The drop in convective coefficient from 22% to 44% in the case of PG brines as compared to EG brines with the increase in mixture percentage from 25% to 60%, for the same operating conditions. The pressure drops decreased from 15% to 74% for EG mixture as compared to PG mixture at considered flow rate and mixture percentage. The effectiveness and overall borehole resistance were higher for EG as compared to the PG solution.

Research on size segregation dynamics and processes of a binary mixture dense granular flow

This study employed an experimental approach to investigate the effects of various filling degrees of the granular bed and the rotation speed on size-induced particle segregation behavior in an almost fully filled double-walled rotating drum. The distributions of the concentrations of bicolor particles in the system were obtained via image processing to determine the segregation state. The dynamics of the mixture flow including the statistical distribution, the azimuthal angle and radial direction granular temperature profiles were measured and calculated via particle-tracking velocimetry (PTV). The results were similar for the Brazil-nut effect and its reverse in the radial direction at high or low rotation speeds. When the rotation speed or filling degree was changed, the effect on two different particle sizes in the binary mixture system was inconsistent, and different flow mechanisms led to different segregation patterns. Two phase diagrams with the rotation speed and filling degree and the magnitude and position of the maximum granular temperature as the space enabled the prediction of segregation states.

Numerical Research of Spontaneous Condensation of Boron Oxide Vapor in Flat Nozzles

A model of spontaneous condensation of boron oxide vapor in chemically reacting gas mixtures is proposed, based on the classical theory of nucleation and one-speed and one-temperature approximation for the equations of two-phase mixture flow. The model considers nucleation, condensational growth, coagulation, and gas-phase chemical reactions of molten boron oxide droplets. Numerical research of the spontaneous condensation of boron oxide in flat nozzles of different sizes and geometries was carried out using the model. The condensation shock wave is shown to occur immediately behind the nozzle throat. The highest nucleation rates (up to ) are characteristic of a zone adjacent to the sidewall of the nozzle, where the rate of expansion of combustion products is maximum. In nozzles with similar geometries, the position of the front of the condensation shock wave does not depend on the linear dimensions of the nozzle; and only the Mach number in front of the condensation shock wave determines its position. In flat nozzles with geometrically similar inlet regions, the front of the condensation shock wave position does not depend on the nozzle linear dimensions because the condensation shock wave is formed in the field that is independent of the expansion angle of the nozzle. The effect of gas-phase chemical reactions on the spontaneous condensation of boron oxide vapor development is estimated. This effect is weak and tangible only in large nozzles.

Optimization of the gas-air path system parameters for trapping automotive fuel vapors

Introduction (statement of the problem and parameters relevance). The composition of the mixture of air and gasoline vapors differs in air and vapors ratio when purging the absorber at different time of the car operation. Therefore, the air-fuel mixture entering the engine for afterburning can create uncertainties in lambda control.The purposeof the research was to determine the main features of lambda regulation in an unstable fuel-air mixture.Methodology and research methods. An analysis of the mixed air and fuel vapor flows entering the engine during absorber purge was made. The composition and quantity effect of this mixture on the excess air coefficient was determined. The main parameters of air and gasoline vapor mixture in the fuel tank vapor space were established.Scientific novelty and results. An equation obtained testifies that the excess air coefficients in the flows of the fuel-air mixture relate to the mixture flow rate during absorber purge. The requirements for the composition of the fuel-air mixture leaving the absorber have been formulated. In order not to exceed these values the threshold values of short-term fuel supply were corrected and the relative mass flow value rate of gasoline vapors from the tank in relation to the air flow rate purge was determined.Practical significance. The factors limiting the flow sections of the absorber gas-air paths and the optimal ratios of the flow sections were determined on the example of a two-chamber absorber to exclude excessive enrichment of the fuel-air mixture entering the engine during purge.

Dynamic behavior of miscible binary fluid mixtures in nanopores: Implications for CO2-enhanced oil flow in shale reservoirs

Dynamic behavior of miscible CO2-oil mixtures is the heart of CO2 enhanced oil recovery (EOR) and CO2 storage in shale reservoirs. However, the omnipresent nanopores not only raise the difference in CO2-reduced oil viscosity through thermodynamic effect from that of bulk condition but also add additional kinetic resistance resulting from a pore surface. In this work, a novel thermo-kinetic model is proposed to characterize the miscible mixtures flow in nanopores with involving changes in activation free energy induced by thermodynamic effect and kinetic effect, where the former is correlated with Helmholtz free energy by a modified Soave-Redlich-Kwong equation of state, while the latter is determined by a solid–fluid potential model with assuming a miscible mixture as a single pseudo-fluid. Subsequently, CO2-enhanced oil flow in nanopores and its deviation from bulk results are demonstrated. Moreover, the roles of different microscopic interactions are clarified, and the effects of a pore size, CO2 content as well as the strength of fluid-wall interactions are discussed. It is found that CO2 can simultaneously weaken the fluid–fluid interactions and fluid-wall interactions, jointly leading to a reduction in local fluid viscosity and an enhancement in oil flow. The increase in wall-oil affinity and CO2 content can strengthen the enhancement effect. Moreover, our results indicate that the relationship between enhancement effect and pore size strongly depends on the strength of interfacial interactions. For a nanopore with low wall energy (εs/kb < 10 K), a reduction in the enhancement factor is obtained with a decrease in pore size, while the opposite phenomenon is observed for a pore wall with a strong affinity to the oil. Our study lay a theoretical foundation for the reservoir simulation of CO2-EOR and CO2 storage in shale reservoirs.

Numerical simulation of a thermally enhanced EMHD flow of a heterogeneous micropolar mixture comprising (60%)-ethylene glycol (EG), (40%)-water (W), and copper oxide nanomaterials (CuO)

In the past decades, the thermal and rheological properties of nanofluids have attracted much attention from many investigators due to their numerous applications as promising enhanced working fluids. The present numerical analysis intended to evidence the main hydro-thermal and mass transport appearances featuring the convective flows of an exceptional non-homogeneous micropolar mixture (i.e., 60% of ethylene glycol, 40% of pure water, and copper oxide nanomaterials) over an impermeable horizontal electromagnetic surface (i.e., Riga plate), which is heated convectively in the presence of a particular variable heat source. For this purpose, several admissible physical theories and hypotheses are adopted herein to derive the foremost conservation equations based on the renovated Buongiorno's formulation and some more realistic boundary conditions. Further, the leading partial differential equations (PDEs) are transformed into a system of ordinary differential equations (ODEs), which are tacked thereafter numerically using an efficient GDQNRM procedure. After performing multiple validations with the recent literature results, the aspects of the studied EMHD convective micropolar nanofluid flow are spotted accordingly and then discussed comprehensively via multiple figures and tables. As prominent results, it is found that the micropolarity and electrically conducting trends of the nanofluidic medium play an important role in the hastening of the nanofluid motion. Also, it is explored that the thermally enhancing influence of the thermophoresis diffusive mechanism can be reinforced more by the existence of an internal heat source along with an appropriate convective heating process.

Study on condensation flow and heat transfer characteristics of multicomponent mixture in dimple tube

The flow and heat transfer characteristics of methane/propane and methane/ethane/propane have been numerically investigated in the dimple tube. The effect of mass flux, saturation pressure and composition ratio on the characteristics of flow, heat transfer and void fraction are examined. The results indicate that the heat transfer coefficient, friction pressure drop increase with the increase of mass flux and decrease with the pressure drop increased. The heat transfer coefficient of a binary mixture is higher than that of ternary mixture under the same condition. The friction pressure drop of the ternary mixture is greater than that of the binary mixture at high vapor quality. In addition, the influence of geometric parameters is discussed. Higher dimple depth and lower pitch will result in higher heat transfer efficiency. The dimple tube with r = 0.75 mm, p = 5.08 mm, e = 4.33 mm have the best heat transfer performance, and the surface performance factor PFS and the performance factor enhancement PFE are 1.041–1.304 and 0.885, respectively. Besides, the simulation result of void fraction, heat transfer coefficient and friction pressure drop are compared with some general models. Finally, an improved pressure drop model for the enhanced tube is proposed.

Performance and emission characteristics of a diesel engine with on-board produced hydrogen-oxygen injection

In this research, experimental study is conducted on a generator connected to a diesel engine to enhance the performance and reduce the emissions using on-board produced H2/O2 gas mixture. The H2/O2 gas mixture is generated and supplied by a HYDI unit, which uses electrolysis of water to produce the required H2/O2 mixture. It is found that through the addition of the H2/O2 mixture via the inlet air there is significant reductions in the exhaust emissions of PM concentrations. The average reductions in PM concentrations are 10.34%, 24.77% and 41.05% across the load range at H2/O2 mixture flow rates of 0.42 LPM, 0.84 LPM and 1.25 LPM, which are equivalent to 0.022%, 0.045% and 0.067% hydrogen energy substitution (HES), respectively. The maximum reduction in exhaust emission of PM concentrations is 56% at 115.4% of the rated load with H2/O2 mixture flow rate of 0.067% HES. It is also found that there are slight reductions in the exhaust emission of CO. The average reductions in CO emissions are 5.50%, 3.40% and 2.32% across the load range at H2/O2 mixture flow rates of 0.022% HES, 0.045% HES and 0.067% HES, respectively. Since the maximum flow rate of H2/O2 gas mixture is only 0.067% HES, there is little or no change of fuel mass flowrate, thermal efficiency and bsfc. The power needed to produce H2/O2 gas mixture is provided by the battery/alternator. It only uses a little amount power of 360 W and there is no issue to start the generator after overnight shutdown. The storage and consumption of water do not possess any issue as it only consumes 0.974 L of water for 24-hours operation.

An investigation of a gas–liquid swirling flow with shear-thinning power-law liquids

A gas–liquid swirling flow with shear-thinning liquid rheology exhibits complex behavior. In order to investigate its flow characteristics, experiments and computational fluid dynamics (CFD) simulations are conducted based on dimensional analysis. A Malvern particle size analyzer and electrical resistance tomography are applied to obtain the bubble size distribution and section void fraction. A Coriolis mass flowmeter is applied to obtain the mixture flow rate and mixture density for an entrance gas volume fraction smaller than 7%. The CFD coupled mixture multiphase model and large eddy simulation model are applied, considering the liquid shear-thinning power-law rheology. The results show that the swirling flow can be divided into developing and decaying sections according to the swirl intensity evolution in the axial direction. A gas–liquid swirl flow with shear-thinning liquid prohibits a core-annulus flow structure. A smaller index n contributes to maintaining the development of the swirl flow field and its core-annulus flow structure so that the swirl flow can form over a shorter distance with a stronger intensity. For a more uniform distribution of the apparent viscosity, the gas column in the pipe center is thinner. On the other hand, a larger consistency k enlarges the stress tensor. The amplitude of the velocity and the pressure of the core-annulus flow structure are reduced. A weaker swirl intensity appears with a wider gas column appearing as a consequence. Furthermore, the swirl number decays with an exponential behavior with parameters sensitive to the consistency k and index n of the decaying section of the swirling flow field. These are beneficial to gas–liquid separator design and optimization when encountering the shear-thinning power-law liquid phase in the petroleum industry.

Numerical Simulations of Laminar Film Condensation of H2O/Air or H2O/CO2 on a Vertical Plate

The liquid film thickness seriously affects the distribution of temperature, velocity, and components near the interface for steam condensation in the presence of small concentration noncondensable gas. The liquid film thickness for H2O/CO2 forced convection condensation separation on vertical plate has not been studied numerically. Thus, volume of fluid model and a phase change model were used to study steam condensation in the presence of noncondensable gases. The calculations studied the effects of velocity, surface subcooling, and noncondensable gas mole fraction on the heat transfer for H2O/air or H2O/CO2 mixtures. The results show that the predicted heat transfer coefficients agree well with previous experimental data. The gas and liquid film thicknesses controlling the condensation heat transfer in the presence of a noncondensable gas become thicker as the mixture flows along the cooled wall. The condensate mass flow rate and the heat transfer coefficient are both seriously reduced by the noncondensable gas. The condensate heat transfer in the presence of noncondensable gases is mainly determined by the diffusion coefficient and the thermal conductivities of the components in the gas film layer.

Effects of scavenging port angle and combustion chamber geometry on combustion and emmission of a high-pressure direct-injection natural gas marine engine

ABSTRACT HPDI natural gas (HPDI-NA) engines can improve nitrogen oxides and PM emissions while getting better in-cylinder combustion in the comparison of the conventional engines fueled with diesel. In this paper, a three-dimensional (3D) of a HPDI natural gas marine engine is set up. The influence of geometry parameters on mixture flow, combustion, and emissions were presented and discussed. The geometry parameters include scavenging port angle (SPA) and three combustion chamber geometries (shallow-basin-shaped (SBC), shallow-ω-shaped (SWC), and deep-pit-shaped combustion chamber (DPC)). The results show that increasing the SPA can significantly swell the swirl ratio, but too large the swirl ratio is not conducive to improving the scavenging effect. As SPA is varied from 30° to 60°, a richer-than-flammable region gets greater, and the penetration distance is shortened by the larger vortex. Then, the mixing and combustion process get worse. With the increase of the SPA, the emissions of soot, carbonic oxide (CO), and unburned hydrocarbons (HC) can be optimized. Also, a larger scavenge port angle is not conducive to improving nitrogen oxides emission and the fuel consumption efficiency. The combustion chamber geometries have fewer effects on the mixture flow and the pressure profiles and temperature than that of SPA. The CO/HC and soot emissions of the three tested combustion chamber geometries are similar. The effect of the shallow basin-shaped combustion chamber (SBC) is much better than that of the other combustion chamber geometries with respect to NOx emission.