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The present comment concerns some doubtful results included in the above papers. [ABSTRACT FROM AUTHOR]

• Turbulent flow is presented as a heterogeneous mixture of two fluids with different velocities and temperatures. • A closed system of equations for turbulent thermodynamics is derived. • It is shown that the new model is able to describe complex anisotropic turbulent processes of thermodynamics. A new approach to modeling turbulent heat transfer based on the thermodynamics of two fluids is presented in the paper. This study is a development of a two-fluid turbulence model. It was shown that the temperature fluctuation in a turbulent flow is due to the temperature difference of these fluids. A mathematical model of turbulent heat transfer was built on the basis of the two-fluid approach. The obtained mathematical model of turbulence was used to study turbulent heat propagation when flowing past a plane plate, in round and plane jets, and between two rotating cylinders. To verify the model, numerical results were compared with known experimental data. The results obtained showed that the two-fluid model of turbulent transfer describes the thermodynamic properties of the turbulent flow with great accuracy. [ABSTRACT FROM AUTHOR]

Two-phase bubble columns are equipment used to bring one or several gases into contact with a liquid phase. Despite the simple system design, bubble columns are characterized by complex fluid dynamic phenomena at different scales; for this reason, their correct design, operation and scale-up rely on the precise estimation of global and local fluid dynamics properties. In this respect, multi-phase Computational Fluid Dynamics (CFD), in the Eulerian multi-fluid framework, is particularly useful to study the fluid dynamics in multi-phase reactors. Within this approach, the accurate prediction of the fluid dynamics depends on the correct modeling of (a) the momentum exchange between the phases, (b) the effects of the dispersed phase on the turbulence of the continuous phase, and (c) the bubble coalescence and break-up phenomena. Furthermore, the global and the local fluid dynamic properties are related to the prevailing flow regime, i.e., the homogeneous flow regime and the heterogeneous flow regime. This paper mainly focuses on the homogeneous flow regime, which can be classified as “ pseudo-homogeneous ” or “ mono-dispersed homogeneous ”, depending on the prevailing bubble size distribution. The numerical modeling of the “ pseudo-homogeneous ” flow regime has been discussed in our previous papers (i.e., modeling closures and suitable boundary conditions); conversely, this paper contributes to the existing discussion on the modeling closures by investigating the “ mono-dispersed homogeneous ” flow regime in “ small-scale ” and “ large-scale ” bubble columns. To this end, two test cases have been considered: (a) a “ small-scale ” bubble column (a test case taken from the previous literature); (b) a large-scale bubble column (a test case experimentally studied within this paper by image analysis, optical probe and gas holdup techniques). In particular, this paper studies the effects of the interfacial forces and bubble induced turbulence modeling within the Eulerian two-fluid approach. Three-dimensional transient simulations have been performed and the numerical results were compared with experimental data (both local and global fluid dynamics parameters). The results have been critically analyzed and the reasons for the discrepancies between the numerical results and the experimental data have been identified and may serve as a basis for future studies. Likewise, recommendations on suitable closures as well as guidelines for future studies have been provided. In conclusion, this paper extends the validation of a previously proposed set of closure relations (validated for the “ pseudo-homogeneous ” flow regime in a “ large-scale ” annular gap bubble column) to the “ mono-dispersed homogeneous ” flow regime in “ small-scale ” and large-scale bubble columns. [ABSTRACT FROM AUTHOR]

• Three-dimensional finite element simulation of flood discharge atomization process was carried out by the numerical method. • The compressible fluid dynamics equation is solved by the finite element method with a suitable solution strategy. • The numerical simulation results of flood discharge atomization agree well with the measured results. Flood discharge atomization is a phenomenon of water fog diffusion caused by the discharge of water from a spillway structure, which brings strong wind and heavy rainfall. These unnatural winds and rainfall are harmful for the safe operation of hydropower stations with high water heads. Compared to the method of prototype observations, physical models and mathematical models, which are semi-theoretical and semi-empirical, numerical simulation methods have the advantage of being not limited by a similar scale and are more economical. A finite element model is presented to simulate flood discharge atomization based on water–air two-phase flow in this paper. Equations governing flood discharge atomization are composed of partial differential equations of mass and momentum conservation laws with unknowns for pressure, velocity and the water concentration. The finite element method is used to solve the governing equations by adopting appropriate solution strategies to increase the convergence and numerical stability. Then, the finite element model is applied to a practical project, the Shuibuya hydropower station, which experienced a flood discharge in 2016. Simulation results show that the proposed model can simulate flood discharge atomization with efficient convergence and numerical stability in three dimensions, and good agreement was observed between numerical simulations and prototype observational data. Based on the simulation results, the mechanism of flood discharge atomization was analyzed. [ABSTRACT FROM AUTHOR]

This paper attempts to fill the gap in the literature by introducing and discussing an enhanced physical model of the MR damper. The essence of the presented model is to combine the effect of compressibility of the MR fluid enclosed in each chamber with the effect of blocking the flow between the chambers in the case of a low pressure difference. As it will be shown, the concurrence of both considered phenomena significantly affects mechanical behaviour of the damper, influences its dissipative characteristics, and in particular, it is the reason behind the distinctive ‘z-shaped’ force–velocity hysteresis loops observed in experiments. The paper presents explanation of the observed phenomena, detailed derivation of the thermodynamic equations governing response of the damper, their implementation for various constitutive models of the magnetorheological fluid and, finally, formulation of the corresponding reduced and parametric models. Experimental validation shows that proper identification of physical parameters of the proposed mathematical model yields the correct shapes of force–velocity hysteresis loops. [ABSTRACT FROM AUTHOR]

Abstract In traditional hydrodynamic theories for ionic fluids, conservation of mass and linear momentum is not properly taken care of. In this paper, we develop hydrodynamic theories for viscous, ionic fluids of N ionic species enforcing mass and momentum conservation as well as considering the size effect of the ionic particles. The theories developed are quasi-incompressible in that the mass-average velocity is no longer divergence-free whenever there exists variability in densities of the fluid components, and the theories are dissipative. We present several ways to derive the transport equations for the ions, which lead to different rates of energy dissipation. The theories can be formulated in either number densities, volume fractions or mass densities of the ionic fluid components. We show that the theory with the Cahn-Hilliard transport equation for ionic species reduces to the classical Poisson-Nernst-Planck (PNP) model with the size effect for ionic fluids when the densities of the fluid components are equal and the entropy of the solvent is neglected. It further reduces to the PNP model when the size effect is neglected. A linear stability analysis of the model together with two of its limits, which are the extended PNP model (EPNP defined in the text) and the classical PNP model (CPNP) with the finite size effect, on a constant state and a comparison among the three models in 1D space are presented to highlight the similarity and the departure of this model from the EPNP and the CPNP model. Highlights • A quasi-incompressible hydrodynamic model of N-species ionic fluid flows is presented. • The model reduces to well-known ionic fluid models in selected time and length scales. • A three-component model is analyzed to showcase effects of quasi-incompressibility. [ABSTRACT FROM AUTHOR]

There are no published mathematical models that combine the dynamics of the returned fluid flow to the active mud pit (top side drilling) and the dynamics of the bottom side of the well being drilled. In this paper a simple dynamic model that combines the top and the bottom side drilling operations is provided. The model has been simulated for various operational scenarios during drilling including pipe connection, movements of drill string and reservoir influx. This combined model can be used for studying not only the pressure dynamics but also to estimate the return fluid flow rate and hence to detect kicks and losses occurring in the well. [ABSTRACT FROM AUTHOR]

The research and design of liquid-cooled integrated circuits (IC) relies heavily on accurate simulation. Ideally, finite-element-method (FEM) based tools should be used for this purpose. However, in most cases a fully coupled thermo-fluidic simulation of complex ICs is very long, mostly due to the fact that the simulation of fluid dynamics is very time consuming. Therefore, in this paper we propose a novel model for thermal simulation of ICs cooled by integrated microchannels which significantly reduces the simulation time. The new approach is based on removing the fluid from the model and treating the solid-liquid boundary as a convective boundary, described by the convection equation. It is shown that the proposed model offers very good accuracy in steady-state, with errors below 3 °C in every chip point. In transient domain the results are equally good, with the maximum error around 3.3 °C (6% relative error). Moreover, the simulation times have been reduced by about two orders of magnitude with respect to fully coupled FEM simulation. However, the proposed model has also important limitations: currently ICs with only one layer of straight microchannels are supported and the model requires recalculation if some chip parameters are changed. [ABSTRACT FROM AUTHOR]

This paper investigates a new drag model for the simulation of the fluidization of fluid catalytic cracking (FCC) particles with air in a fluidized bed using the two-fluid model (TFM) within the Multiphase Flow with Interphase Exchanges (MFIX) code. A cohesion index parameter based on the interparticle cohesive forces has been implemented in the MFIX-TFM code. This index is used as a switching criterion between a particle resolved drag model developed by Tenneti et al. (2011), and some of the drag models available in the MFIX for homogeneous particles, namely the Gidaspow, Syam–O'brien, and Wen–Yu models. The proposed drag correlation in this paper implements an indirect method of introducing interparticle cohesive forces to our TFM simulations. Significant improvement in the solid volume fraction profile along the riser was obtained for all of the drag law combinations, depending on the conditions set in the switching procedures. In the best case, the utilization of the Gidaspow and TGS models resulted in a 60% improvement in maximum deviation of numerical results from the available experimental data. The proposed model can be used in simulations of fluidized beds, where standard models fail to produce accurate results even on extremely refined computational grid, especially for Geldart A type particles that may exhibit strong clustering behavior. [ABSTRACT FROM AUTHOR]

This paper presents a review of the state-of-the-art on interphase mass transfer between immiscible fluids in porous media with focus on the factors that have significant influence on this process. In total close to 300 papers were reviewed focusing to a large extent on the literature relating to NAPL contamination of the subsurface. The large body of work available on this topic was organized according to the length scale of the conducted studies, namely the pore, meso and field scales. The interrelation of interphase mass transfer at these different scales is highlighted. To gain further insight into interphase mass transfer, published studies were discussed and evaluated in terms of the governing flow configurations defined in terms of the wettability and mobility of the different phases. Such organization of the existing literature enables the identification of the interfacial domains that would have significant impact on interphase mass transfer. Available modeling approaches at the various length scales are discussed with regard to current knowledge on the physics of this process. Future research directions are also suggested. [ABSTRACT FROM AUTHOR]

In this paper, a new approach is presented to find the optimum catalyst loading distribution along the flow field. The optimization is performed by integrating a computational fluid dynamic (CFD) model and genetic algorithm optimization method. The CFD model is two-dimensional, steady state and two-phase. Multiphase mixture model (M 2 ) is used to model two-phase transport in porous media of a Polymer Electrolyte Membrane Fuel Cell (PEMFC). Numerical domain includes channel, gas diffusion layer (GDL) and catalyst layer (CL) in the cathode side. In the next step, current density is assumed to be proportional with catalyst loading. Catalyst loading is considered as polynomial functions with unknown coefficients. Genetic algorithm optimization method is applied to find the unknown coefficients and as a result the optimum catalyst loading function along the flow field. The results indicate that catalyst loading distribution has a significant effect on the fuel cell performance and it is seen that in the optimum case, maximum PEMFC power density is increased by about 14%. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new frequency domain method to model the heat transfer between the injected/extracted heat and the temperature of the fluid exiting a borehole heat exchanger. The method is based on in situ measurements and focuses particularly on the short-term borehole heat transfer. It uses a rational function of the Warburg variable in the Laplace domain to model the borehole heat transfer. The rational model is transformed to a time domain model using inverse Laplace transformation. This time domain model makes it possible to calculate the temperature response on a random heat variation signal. The paper also demonstrates a new way to perform the classical thermal response test. Instead of injecting a constant amount of heat, the experiments have been performed using multiple short-duration heat injections. In this way, the obtained rational heat transfer model contains information about both the short- and the long-term heat transfer. The results obtained using the proposed modeling method are compared with those obtained from a state-of-the-art analytical method. The time domain model can be used to design a controller to optimize the performance of a Ground Source Heat Pump system, the efficiency of which depends strongly on the temperature of the fluid exiting the borehole. [Copyright &y& Elsevier]

Abstract: Fluid or mean-field methods are approximate analytical techniques which have proven effective in tackling the infamous state-space explosion problem which typically arises when modelling large-scale concurrent systems based on interleaving semantics. These methods are particularly suitable in situations which present large populations of simple interacting objects characterised by small local state spaces, since they require the analysis of a problem which is insensitive to the population sizes but is dependent only on the size of the local state spaces. This paper studies the case when the replicated objects are best described as composites which consist of smaller simple objects. A congenial formal modelling framework for situations of this kind may be given by stochastic process algebra. Using PEPA as a representative case, we find that fluid models with replicated copies of composite processes do not scale well with increasing population sizes, thus rendering intractable the analysis of the underlying system of ordinary differential equations (ODEs). We call this problem continuous state-space explosion, by analogy with its counterpart phenomenon in discrete state spaces. The main contribution of this paper is a result of equivalence that simplifies, in an exact way, the potentially massive ODE system arising in those circumstances to one whose size is independent from all the multiplicities in the model. As a byproduct, we find that these simplified ODEs turn out to characterise the fluid behaviour of a family of PEPA models whose elements cannot be related to each other through any known equivalence relation. A substantial numerical assessment investigates the relationship between the different underlying Markov chains and their unique fluid limit, demonstrating its generally good accuracy for all practical purposes. [Copyright &y& Elsevier]

Abstract: Along with the developments of lattice-Boltzmann method in simulation of fluid flow, its thermal features should be also improved. An important problem which is encountered in many cases is the conjugate heat transfer or heat transfer at the fluid–solid interface. In this case, a strict technique is required to calculate the heat exchange between fluid and solid. Only a few works have been published regarding this phenomenon. In this paper, we have presented a model for analysis of the conjugate heat transfer. The model has been validated by two benchmarks: (I) Fluid flow and heat transfer in a backward-facing step channel with heated thick wall, and (II) Fluid flow and heat transfer in a channel with infinite number of heated obstacles mounted on the wall. The numerical tips concerned in the simulation of these problems by lattice-Boltzmann method have been also represented in the paper. [Copyright &y& Elsevier]

The last paper of A. Fronczak presents a new, combinatorial approach to the model of perfect gas of clusters of interacting fluids. In the paper the enumerative properties and combinatorial meaning of Bell polynomials have been used to reveal some properties of systems described by grand canonical ensemble. In this paper, an exact proof of one of the important assertions from the work mentioned above is given. The assertion states that for the system in which one can distinguish k non interacting clusters the canonical partition function is given by Bell polynomial of the derivatives of the grand-thermodynamic potential with respect to the fugacity. Some possible applications of the considered theorem are presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a coupling of Discrete Element Method (DEM) and Constrained Interpolation Profile (CIP) mainly designed for simulations of the nucleation process in wet granulation. The governing equations for fluid (liquid and gas) phases are the volume averaged form of the Navier–Stokes equation, continuity and colour function equations. These equations are solved by use of a meso-scale fixed Cartesian grid whose cell is larger than individual particles. The solid–liquid–gas interfacial effects on both fluid and particle phases are taken into account in the simulation. The surface tension effect on the fluid motion was modelled in three different ways depending on the relative position of the liquid–gas interfaces to powder beds: the models outside, inside, and on the surface of powder beds correspond to a free surface, capillary action and bed surface wetting. A new model for the surface tension effect on the solid (particle) motion, i.e. the capillary force effect, is proposed in this paper. This capillary force model is particularly useful when using a meso-scale fixed grid, and it can be used with various types of multi-fluid scheme such as CIP, Volume of Fluid (VoF) and Level Set methods. The proposed models are validated by comparing the simulation results with theoretical and experimental results. It is also revealed that the capillary force model is crucial to obtain reasonable simulation results for nucleation process. [Copyright &y& Elsevier]

Abstract: Steam circulation in SAGD start-up processes has significant impacts on the whole SAGD process. The start-up aims to heat the fluid sufficiently to improve oil mobility to establish communication between the injector and the producer. An efficient and economic approach is needed by the industry to identify the communication between the well-pair and to minimize the steam-circulation period. Knowing the hot-zone size and shape distribution formed by steam circulation along the horizontal wellbore can also help better understand the start-up process and obtain a long-term SAGD performance. This paper proposes a new technique called Transient Temperature Analysis (TTA) to estimate the hot-zone size and shape by interpreting the temperature falloff data in the injector and the producer obtained from fiber optics after the wells are shut in. Both forward and inverse mathematical models are presented to facilitate the application of this technique. Three forward mathematic models, two-system model with a hot-zone and a cold-zone, three-system model with an additional transition zone, and superposition of multiple two-systems model for irregular hot-zone shape were developed to model the temperature falloff. An inverse model is proposed to automatically interpret the hot-zone size through matching the temperature falloff. Sensitivity analysis shows that the hot-zone size and shape and observing location strongly affect the temperature falloff behaviors. Synthetic case studies suggest that the proposed models can be used to identify the hot-zone size and shape around the producer and the injector, and then to identify whether those hot-zones have established communication. Because of the ready-to-use temperature data and the semi-analytic solutions presented in this paper, the TTA technology can provide fast and economical estimation of the hot-zone size. [Copyright &y& Elsevier]

Abstract: The fluid channeling during hydraulic fracturing has been seriously restricting the efficient development of low permeability oilfield and CBM Field. The occurrence of fluid channeling after hydraulic fracturing is hinged on shear strength at cement–interlayer interface (CII) and hydraulic fracturing pressure. Interface defects are key factors that influence the shear strength at CII. In view of this, the influence of interface defects on shear strength at CII and fluid channeling is discussed in this paper. The formation reasons of interface defects are analyzed firstly. Based on analysis of the essence of shear strength at CII, it is concluded that all interface defects amount to the missing amount of mud cake ring. Then a mathematical model between missing amount of mud cake ring and shear strength at CII is developed. In order to verify the accuracy of the model, a simulated experimental system is built. Based on the model and fluid channeling coefficient equation, a modified version of the fluid channeling coefficient is derived and the influence of interface defects on interlayer fluid channeling during hydraulic fracturing is evaluated quantitatively. The results revealed that the shear strength at CII decreases linearly with the increase of interface defects, and verification results show that the relative errors between calculated values by the model and experimental values are less than 10%. From the modified equation of the fluid channeling coefficient, this paper established a typical exponential relationship between missing amount of mud cake ring and fluid channeling coefficient, which indicates that interface defects drastically affect fluid channeling at CII. [Copyright &y& Elsevier]

In this paper we evaluate the performance of Unified Parallel C (which implements the partitioned global address space programming model) using a numerical method that is widely used in fluid dynamics. In order to evaluate the incremental approach to parallelization (which is possible with UPC) and its performance characteristics, we implement different levels of optimization of the UPC code and compare it with an MPI parallelization on four different clusters of the Austrian HPC infrastructure (LEO3, LEO3E, VSC2, VSC3) and on an Intel Xeon Phi. We find that UPC is significantly easier to develop in compared to MPI and that the performance achieved is comparable to MPI in most situations. The obtained results show worse performance (on VSC2), competitive performance (on LEO3, LEO3E and VSC3), and superior performance (on the Intel Xeon Phi) compared with MPI. [ABSTRACT FROM AUTHOR]

The paper presents the results on modelling high pressure phase behaviour of the systems consisting of refrigerant, trifluoromethane (R23) and 1-phenylpropane. There were used cubic equations of state (GEOS, SRK and PR) coupled with van der Waals mixing rules in a semi-predictive approach (SPA). Based on the experimental VLE isothermal data in the range 300–330 K, binary interaction parameters (BIPs) were optimized, through regression of bubble pressure type. Unique sets of interaction parameters were estimated for each EoS, and used in the SPA to calculate the critical, subcritical and supercritical behaviour of the system. The SPA calculations are comparatively discussed with the available experimental data in the temperature range (250–400) K and pressures up to 12 MPa. The calculations of critical line and of vapour-liquid, liquid-liquid, vapour-liquid-liquid phase equilibria, and of critical endpoints indicate a good modelling capacity of the tested EoSs and an accurate representation of the complex critical and subcritical behaviour of the investigated system. [ABSTRACT FROM AUTHOR]

Flotation in mechanically agitated cells has been the workhorse of the mining industry, but our quantitative understanding of the effect of microturbulence generated by agitation on flotation is still very limited. This paper aims to review the literature on quantifying the microturbulence effects on bubble-particle interactions in flotation. The particular focus is on the stochastic description of bubble-particle interactions in the turbulent flow which is a random field. We briefly review the stochastic description of microturbulence and motions of particles of micrometre sizes and bubbles of millimetre sizes in the isotropic turbulence of mechanical flotation cells. The key starting point is the generic equation of motion, which can be decomposed into the mean turbulent variables and fluctuating turbulent variables. The turbulent flow of the carrying liquid is characterised using isotropic turbulence theory. The next focus is on reviewing bubble-particle turbulent collision and detachment interactions. Bubble-particle turbulent collision is poorly quantified; no quantitative models of the bubble-particle turbulent collision efficiency relevant for flotation are available. Current theories on bubble-particle turbulent detachment face some deficiencies. In assessing the microturbulence effect on bubble-particle detachment, the majority of studies only considers the particle acceleration in the centrifugal direction but ignore the transverse acceleration of particles, which is due to turbulent shear flow. Critically, contact angle required in quantifying the detachment is not constant, single-valued as considered in the theories, but can vary from receding to advancing value during the relaxation of the triple contact line on the particle surface. The latest experiments show that multiple-valued contact angle can significantly affect stability and detachment of floating particles. Finally, quantifying the microturbulence effect on flotation requires further research. [ABSTRACT FROM AUTHOR]

Under investigation in this paper is a generalized (3+1)-dimensional variable-coefficient B-type Kadomtsev–Petviashvili equation, which describes the propagation of nonlinear waves in fluid dynamics. Bilinear form and Bäcklund transformation are derived by virtue of the Bell polynomials. Besides, the one- and two-soliton solutions are constructed via the Hirota method. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a lattice Boltzmann method (LBM) based study aimed at numerical simulation of highly turbulent and largely inclined flow around obstacles of curved geometry using non-body-fitted Cartesian meshes. The approach features (1) combining the interpolated bounce-back scheme with the LBM of multi-relaxation-time (MRT) type to enable the use of simple Cartesian mesh for the flow cases even with complex geometries; and (2) incorporating the Spalart–Allmaras (SA) turbulence model into LBM in order to represent the turbulent flow effect. The numerical experiments are performed corresponding to flows around an NACA0012 airfoil at Re=5×105 and around a flat plate at Re=2×104, respectively. The agreement between all simulation results obtained from this study and the data provided by other literature demonstrates the reliability of the enhanced LBM proposed in this paper for simulating, simply on Cartesian meshes, complex flows that may involve bodies of curved boundary, high Reynolds number, and large angle of attack. [Copyright &y& Elsevier]

Abstract: This paper presents a dynamic model of a counter flow water to oil heat exchanger when all inputs (inlet temperatures of the fluids and the mass flow rates) are simultaneously varying. Although interesting results about modeling of heat exchanger by linear parameter varying (LPV) can be found in , several problems remain to be solved such as the structure estimation or a proper initial MISO model for the optimization algorithms. This paper introduces a new model structure called quasi LPV model which simulates accurately the temperature and flow transients in a counter flow heat exchanger (COFHX). The quasi LPV model is compared to a realistic numerical model of a counter flow heat exchanger adjusted with the test rig heat exchanger of the University of Valenciennes in France. Comparisons indicate that the developed quasi LPV model is capable of predicting the transient performance of the heat exchangers satisfactorily. [Copyright &y& Elsevier]

Abstract: This paper examined the features of three typical thermal storage systems including: 1) direct storage of heat transfer fluid in containers, 2) storage of thermal energy in a packed bed of solid filler material, with energy being carried in/out by a flowing heat transfer fluid which directly contacts the packed bed, and 3) a system in which heat transfer fluid flows through tubes that are imbedded into a thermal storage material which may be solid, liquid, or a mixture of the two. The similarity of the three types of thermal storage systems was discussed, and generalized energy storage governing equations were introduced in both dimensional and dimensionless forms. The temperatures of the heat transfer fluid during energy charge and discharge processes and the overall energy storage efficiencies were studied through solution of the energy storage governing equations. Finally, provided in the paper are a series of generalized charts bearing curves for energy storage effectiveness against four dimensionless parameters grouped up from many of the thermal storage system properties including dimensions, fluid and thermal storage material properties, as well as the operational conditions including mass flow rate of the fluid, and the ratio of energy charge and discharge time periods. Engineers can conveniently look up the charts to design and calibrate the size of thermal storage tanks and operational conditions without doing complicated individual modeling and computations. It is expected that the charts will serve as standard tools for thermal storage system design and calibration. [Copyright &y& Elsevier]

Abstract: A mathematical model based on the Lucas–Washburn equation has been developed to address the relations of the capillary height, capillary radius and the heat flux in a capillary column and the equation is extended to a capillary loop for investigating the stability of the condensing interface with phase change by some simplifications in the paper. The stability of the condensing interface is studied by introducing a small disturbance into capillary height. The dynamics performances of the condensing interface under three different operating conditions are discussed in this paper. The results show that the condensing interface presents high instability under non-gravitational condition, while the stability can be enhanced in gravitational condition with a certain gravitational height, moreover, regular vibration can be formed on the condensing interface due to the periodic oscillation of the pressure in the system. [Copyright &y& Elsevier]

Abstract: Two categories of fields can be defined for the application of flow modeling workflows: green fields, and brown fields. In its most fundamental form, a green field is an undeveloped field, while a brown field is a developed field. The main difference between a green field and a brown field is the availability of applicable historical production and/or injection data for the brown field. This difference has a significant impact on reservoir flow modeling workflows. A workflow for green fields is presented in this paper, and workflows for brown fields are presented in the companion paper (Fanchi, 2011). [Copyright &y& Elsevier]

Abstract: Obstacles considerably influence boundary layer processes. Their influences have been included in mesoscale models (MeM) for a long time. Methods used to parameterise obstacle effects in a MeM are summarised in this paper using results of the mesoscale model METRAS as examples. Besides the parameterisation of obstacle influences it is also possible to use a joint modelling approach to describe obstacle induced and mesoscale changes. Three different methods may be used for joint modelling approaches: The first method is a time-slice approach, where steady basic state profiles are used in an obstacle resolving microscale model (MiM, example model MITRAS) and diurnal cycles are derived by joining steady-state MITRAS results. The second joint modelling approach is one-way nesting, where the MeM results are used to initialise the MiM and to drive the boundary values of the MiM dependent on time. The third joint modelling approach is to apply multi-scale models or two-way nesting approaches, which include feedbacks from the MiM to the MeM. The advantages and disadvantages of the different approaches and remaining problems with joint Reynolds-averaged Navier–Stokes modelling approaches are summarised in the paper. [Copyright &y& Elsevier]

Abstract: This paper presents results from seven experimental facilities on the co-current flow of air and water in downward sloping pipes. As a function of the air flow rate, pipe diameter and pipe slope, the required water discharge to prevent air accumulation was determined. In case the water discharge was less than the required water discharge, the air accumulation and additional gas pocket head loss were measured. Results show that volumetric air discharge as small as 0.1% of the water discharge accumulate in a downward sloping section. The experimental data cover all four flow regimes of water-driven air transport: stratified, blow-back, plug and dispersed bubble flow. The analysis of the experimental results shows that different dimensionless numbers characterise certain flow regimes. The pipe Froude number determines the transition from blow-back to plug flow. The gas pocket head loss in the blow-back flow regime follows a pipe Weber number scaling. A numerical model for the prediction of the air discharge as a function of the relevant system parameters is proposed. The novelty of this paper is the presentation of experimental data and a numerical model that cover all flow regimes on air transport by flowing water in downward inclined pipes. [Copyright &y& Elsevier]

Abstract: In this paper, a fully coupled numerical model is presented for the finite element analysis of the deforming porous medium interacting with the flow of two immiscible compressible wetting and non-wetting pore fluids. The governing equations involving coupled fluid flow and deformation processes in unsaturated soils are derived within the framework of the generalized Biot theory. The displacements of the solid phase, the pressure of the wetting phase and the capillary pressure are taken as the primary unknowns of the present formulation. The other variables are incorporated into the model using the experimentally determined functions that define the relationship between the hydraulic properties of the porous medium, i.e. saturation, relative permeability and capillary pressure. It is worth mentioning that the imposition of various boundary conditions is feasible notwithstanding the choice of the primary variables. The modified Pastor–Zienkiewicz generalized constitutive model is introduced into the mathematical formulation to simulate the mechanical behavior of the unsaturated soil. The accuracy of the proposed mathematical model for analyzing coupled fluid flows in porous media is verified by the resolution of several numerical examples for which previous solutions are known. Finally, the performance of the computational algorithm in modeling of large-scale porous media problems including the large elasto-plastic deformations is demonstrated through the fully coupled analysis of the failure of two earth and rockfill dams. Furthermore, the three-phase model is compared to its simplified one which simulates the unsaturated porous medium as a two-phase one with static air phase. The paper illustrates the shortcomings of the commonly used simplified approach in the context of seismic analysis of two earth and rockfill dams. It is shown that accounting the pore air as an independent phase significantly influences the unsaturated soil behavior. [Copyright &y& Elsevier]

Abstract: In a previous paper Lucas and Mishra (2005) a local four-sensor conductance probe was introduced to measure the velocity vectors of dispersed bubbles in bubbly two-phase flow in which the continuous phase is water. There are a very limited number of alternative methods available for bubble velocity vector measurement with which results from, for example, computational fluid dynamic models can be compared and so the four-sensor probe technique is of interest to the multiphase flow community. In the previous paper  a mathematical model was presented to calculate the velocity vector of each gas bubble from seven time intervals which were measured using the output signals from each of four ‘needle’ conductance sensors located within the probe. In the present paper, a new technique for making the local four-sensor probe is introduced to minimise interference with the measured bubbles. A new signal processing method is presented using criteria to ensure that (i) the group of sensor signals from which the bubble velocity vector is to be determined are all produced by the same bubble and (ii) bubbles which contact the local four-sensor probe in an ambiguous manner are ignored. The accuracy with which the locations of each of the rear sensors in the probe relative to the lead sensor can be measured influences the accuracy with which the bubble velocity vector can be measured. However, the degree to which the accuracy of the measured velocity vector is affected by errors in the measured probe dimensions is dependent upon the geometrical arrangement of the four sensors within the probe. Experimental results and an error analysis are presented which show that the susceptibility of the velocity vector measurement technique to errors in the measured probe dimensions is reduced if the geometrical arrangement of the four sensors is optimised. As a result of this initial work, an optimised probe, known as the P30 probe, was designed and built and results obtained from the P30 probe in swirling oil-in-water bubbly flow are presented. A probe calibration factor is defined in this paper which can be interpreted as a measure of the interference of a probe with the motion of the bubbles with which it interacts. For the probes described in this paper the calibration factor was found to be much closer to unity than for previous four-sensor probes described in the literature (e.g. ) suggesting that these new probes have a much smaller effect on the bubbles’ motion than previous probes. [Copyright &y& Elsevier]

Abstract: Mathematical modeling of the convective processes caused by impact of various forces on the fluid and gas media is rather important nowadays. The increased interest to these problems is caused also by the preparation of experiments on the International Space Station in the frame of the scientific project “Convection and Interfacial Mass Exchange” (CIMEX) of the European Space Agency. They are the experiments to investigate the convective flows of the fluids with a thermocapillary interface between liquid and gas phases. In the case, when a gas flow generates the tangential stresses on a free boundary of liquid, the additional characteristics of the convective flows should be identified. In this paper a stationary coupled problem of gravitational, thermocapillary convection in a horizontal layer with free boundary under conditions of a co-current gas flow is studied. The kinematic and dynamic conditions are fulfilled exactly on the gas–liquid interface. The exact solutions for different types of thermal boundary conditions have been obtained. An evaporation effect through the gas–liquid interface is modeled qualitatively with the help of a heat transfer condition. It has been found that the direction of the velocity at the gas–liquid interface is determined by the governing parameters. The equal-zero condition for the interface velocity has been found, as well. The paper presents the velocity and temperature profiles in the conditions, which correspond qualitatively to the CIMEX experiments. [Copyright &y& Elsevier]

Abstract: Squeeze flow theory has been used as an effective tool to clarify how and which process conditions determine cavity-filling behavior in nanoimprint lithography (NIL). Conventional squeeze flow models used in NIL research fields have assumed no-slip conditions at the solid-to-liquid boundaries, that is, at the stamp-to-polymer or polymer-to-substrate boundaries. The no-slip assumptions are often violated, however, in micrometer- to nanometer-scale fluid flow. It is therefore necessary to adopt slip or partial slip boundary conditions. In this paper, an analytical mathematical model for the cavity-filling process of NIL that takes into account slip or partial slip boundary conditions is derived using squeeze flow theory. Velocity profiles, pressure distributions, imprinting forces, and evolutions of residual thickness can be predicted using this analytical model. This paper also aims to elucidate how far the slip phenomenon is able to promote the process rate. [Copyright &y& Elsevier]

Abstract: This paper addresses computational models for dilute gas-particle multiphase flow in which the three dimensional, time-dependent fluid motion is calculated in an Eulerian frame, and a large number of particles are tracked in a Lagrangian frame. Point forces are used to represent the back effect of the particles on the turbulence. The paper describes the early development of the technique, summarizes several experiments which show how dilute particle loadings can significantly alter the turbulence, and demonstrates how the point-particle method fails when the particles are comparable in scale to the small scale turbulence. High-resolution simulations and experiments which demonstrate the importance of the flow details around individual particles are described. Finally, opinions are stated on how future model development should proceed. [Copyright &y& Elsevier]

Abstract: Polydisperse suspensions consist of particles differing in size or density that are dispersed in a viscous fluid. During sedimentation, the different particle species segregate and create areas of different composition. Spatially one-dimensional mathematical models of this process can be expressed as strongly coupled, nonlinear systems of first-order conservation laws. The solution of this system is the vector of volume fractions of each species as a function of depth and time, which will in general be discontinuous. It is well known that this system is strictly hyperbolic provided that the Masliyah–Lockett–Bassoon (MLB) flux vector is chosen, the particles have the same density, and the hindered-settling factor (a multiplicative algebraic expression appearing in the flux vector) does not depend on the particle size but is the same for all species. It is the purpose of this paper to prove that this hyperbolicity result remains valid in a fairly general class of cases where the hindered-settling factor does depend on particle size. This includes the common power-law type hindered-settling factor in which the exponent, sometimes called Richardson–Zaki exponent, is determined individually for each species, and is a decreasing function of particle size. The importance of this paper is two-fold: it proves stability for a class of polydisperse suspensions that was not covered in previous work, and it offers a new analysis of real data. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical model for the simulation of a swash-plate axial piston pump, focusing on the characterization of fluid properties. As it is well known, the reduction of flow oscillations (which generates pressure ripples and produces vibration and noise in the entire circuit) and the avoidance of cavitation are the major problems in the design of these pumps. Developing a simulation code can be very useful for component optimisation in order to predict and reduce the undesired phenomena. The paper first gives a quick overview on a previously developed pump model; afterwards four different models of the fluid are presented: they take into account cavitation in different ways. Their aim at characterizing as well as possible the unsteady and erratic cavitation features in a simplified manner, in order to apply the models to the simulation of hydraulic components. In the second part of the paper an application is shown of these models to an axial piston pump: a few results are presented and compared with available test data. The effects of the fluid models on the predicted pump performance are shown and commented. [Copyright &y& Elsevier]

In this paper, integral mathematic model of fluid flow and heat transfer of GTAW arc and weld pool was established. This model built in this paper may avoid the assumption which surface temperature of weld pool is constant and at the same time provide reliable boundary conditions for analyzing of weld pool. Using finite element analysis software ANSYS, behavior of welding arc and weld pool was systematically analyzed including welding arc temperature field, current density distribution, fluid flow in weld pool and effects of a few forces on weld pool shape. The calculated results were proved by experiments. [Copyright &y& Elsevier]

In an earlier paper it was shown that the basic one-dimensional transient two-fluid model is capable of capturing horizontal and near-horizontal slug flow automatically. However, that work did not account for the effect of gas entrainment into the liquid slug body which is deemed to be an important phenomenon. In this paper, a mathematical model to account for the entrainment of gas bubbles into liquid slugs is proposed, implemented and validated. The model is cast in the framework of the existing two-fluid model and is incorporated in a computational procedure, which is applied to the prediction of slug flow in horizontal and slightly inclined pipes. The model entails the introduction of a scalar equation for the transport of the dispersed gas bubbles within the liquid. The rate of entrainment of gas at the slug front is supplied as a closure relation, the expression for which is obtained from existing correlations. The model is validated against experimental data and the comparison shows satisfactory agreement. However, the inclusion of the aeration model appears to yield marginal differences when compared to predictions which ignore entrainment in the horizontal pipe flow cases studied. More significant differences are obtained in the case of the flow in a V-section pipeline. [Copyright &y& Elsevier]

The micropiled raft (MPR) offers an efficient foundation system that combines the advantages of micropiles and piled rafts that can be used as primary foundation system or to enhance an existing raft foundation. In this paper, a calibrated and verified finite element model (FEM) with centrifuge tests was used to carry out a numerical investigation on the performance of MPR in sand. A total of 78 different cases were analyzed in this study to assess the behavior of MPR in sand taking into account a number of factors that may influence its behavior such as: the number of micropiles (MPs), the spacing to micropile diameter ( S / D mp ), the raft thickness, type of loading and soil density. The outcomes of this investigation should help in understanding the effect of these factors on the MPR axial stiffness, including; differential settlement; load sharing between the MPs and the raft; and the raft bending moment. Moreover, the ability of the PDR method to evaluate the axial stiffness of a MPR for the preliminary design stage is examined. It was found that the MPR system has the ability to increase the tolerable bearing pressure by 190% compared to an isolated raft system. In addition, an adjustment factor ( ω PR ) for PDR method was introduced to account for the raft flexibility. [ABSTRACT FROM AUTHOR]

The present paper deals with a turbulent dual jet consisting of a wall jet and an offset jet. The flow field has been numerically simulated using two-dimensional unsteady RANS equations. The Reynolds number based on the separation distance between the two jets ( s ) is R e = 10 , 000 . The width of the offset jet nozzle equals the separation distance between the two jets. To examine the influence of the bottom wall, the width of the wall jet nozzle ( h ) has been varied in a range 0.2 ≤ h / s ≤ 2 . According to the computational results, for h / s = 0.2 , the flow field remains to be always steady with two counter-rotating stable vortices in between the two jets. On the contrary, within the range of 0.3 ≤ h / s ≤ 1 , the near flow field demonstrates a periodic vortex shedding phenomenon similar to what would be observed in the near wake region for flow over a two-dimensional bluff body. Within this flow regime, the Strouhal number based on the vortex shedding frequency gradually decreases with the progressive increase in h / s . However, for h / s > 1 , although the periodic vortex shedding phenomenon is still evident in the flow field, the Strouhal number becomes insensitive to the bottom wall similar to the flow behaviour for a flow over an unconfined cylinder. [ABSTRACT FROM AUTHOR]

Two-phase flow modeling is a general problem in science and engineering. Two-phase flow phenomenon is inherently complicated and characterized by a large number of flow variables. It is historically known that the lack of proper dimensionless numbers in two-phase flow is one of the major shortcomings as compared to single-phase flow. A new dimensionless number (Slippage Number) for gas–liquid flow in pipes is proposed in this paper. The number is defined as the ratio of the difference in the gravitational forces between slip and no-slip conditions to the inertial force of the gas. It is found to be a function of Froude number based on the mixture velocity especially in the elongated bubble, slug, churn, bubble, and high film thickness wavy annular flow patterns. The liquid holdup data for a wide range of fluid and flow conditions (different viscosities, densities, pipe diameters, inclination angles, gas and liquid flow rates) can be correlated with a single curve using the Slippage Number. The value of the number varies from highest to lowest for bubble, elongated bubble, slug, churn, stratified and annular flow patterns, respectively. It is close to zero for homogeneous flow patterns like mist and dispersed bubble flows. We also show that this number may be used as a flow pattern identifier. [ABSTRACT FROM AUTHOR]

This paper investigates the flame shape and flame volume of turbulent gaseous fuel jets. Experiments are conducted for turbulent gaseous fuel jet flames produced by nozzles with different diameters of 4, 5, 6 and 8 mm using propane as fuel in both normal-(Hefei city: 100 kPa) and a sub-atmospheric pressure (Lhasa city: 64 kPa). The predicted flame shape outlines by the classic Baron’s model are compared with the experimental results obtained by the Orloff’s image analysis method. It is shown that Baron’s method can well predict the width as well as the shape of the flame, although the predicted flame widths are slightly larger than the experimental results at the bottom and top part of the flame. Then, a mathematical model for the flame volume estimation is deduced by the integration of the Baron’s expression, to provide an explicit and easily applied model to calculate the flame volume based on just the flame height. The proposed model is shown to fairly well predict the flame volume in both pressures although the predictions are a bit larger than the experimental values. [ABSTRACT FROM AUTHOR]

In literature, the diffusion-free residence time distribution (RTD) of laminar flows – the so-called convection model – has been determined for various velocity profiles mostly on a case-by-case basis. In this analytical paper, we derive general mathematical relations which allow computing the diffusion-free differential and cumulative RTD in straight planar, circular and concentric annular channels for arbitrary monotonic and piece-wise monotonic one-dimensional velocity profiles. The theory is used to determine the RTD of plane Couette–Poiseuille flow with non-monotonic velocity profile, and the optimal value of the volumetric flow rate where the RTD becomes most narrow. It is shown that any velocity profile that depends in a sub-layer linearly on the distance from a stationary or moving no-slip wall has a differential RTD which follows a −3 power law as the residence time approaches its maximum. The variance of the RTD is directly associated with the asymptotic behavior of the RTD and can be finite or infinite. [ABSTRACT FROM AUTHOR]

The paper is devoted to the modelling of chemotaxis within continuum physics. The cells are regarded as active (or self-propelled) oriented particles. Cells, extracellular liquid and chemical attractant are modelled as a fluid mixture. The balance of mass and linear momentum follows the standard scheme of fluid mixtures. The balance of angular momentum, instead, is established by ascribing the cells also an orientational momentum and hence the cell constituent is viewed as a micropolar fluid of rigid particles. A more explicit account of the dynamics of the cell constituent is obtained by restricting attention to a plane orientational motion. The orientational motion is determined by a body couple density, which tends to align the director in the direction of the gradient of the attractant density, and an interaction torque between the cells and the extracellular liquid. The balance equations, for the mass density and the velocity of the cells, are shown to provide a hyperbolic equation for the excess mass density. A detailed comparison with other approaches and results is also given. [ABSTRACT FROM AUTHOR]

In the present paper we consider a 1D Poisson model characterized by the presence of an interface, where a transmission condition arises due to jumps of the coefficients. We aim at studying finite element methods with meshes not fitting such an interface. It is well known that when the mesh does not fit the material discontinuities the resulting scheme provides in general lower order accurate solutions. We focus on so-called embedded approaches, frequently adopted to treat fluid–structure interaction problems, with the aim of recovering higher order of approximation also in presence of non fitting meshes; we implement several methods inspired by: the Immersed Boundary method, the Fictitious Domain method, and the Extended Finite Element method. In particular, we present four formulations in a comprehensive and unified format, proposing several numerical tests and discussing their performance. Moreover, we point out issues that may be encountered in the generalization to higher dimensions and we comment on possible solutions. [ABSTRACT FROM AUTHOR]

In this paper, a Three-dimensional Distinct Element Code (3DEC) was used and developed for simulating the initiation and propagation of hydraulically induced fractures in a typical reservoir hosted by a rock mass. Due to the fact that the modeling of the initiation of fracturing through intact rock within the Discrete Element Method (DEM) is not possible, a fictitious joint technique was introduced in order to simulate the process. The analysis results substantiate the previous understanding that the success of the hydraulic fracturing process not only depends on controllable parameters such as fracture fluid properties and injection rate, but also relies on the uncontrollable parameters such as ground in-situ stress regime, orientation of principal stresses, and in-situ rock mass properties. Moreover, a sensitivity study of input variables was carried out to examine the effect of different field conditions which involved the orientation and magnitude of principal stress components, fracture fluid properties, injection rate and rock parameters. Comparing the results with analytical solution indicated that the model provides a reasonable approximation for computing fluid injection pressure. Thus, the proposed modeling procedure can be employed in more complicated cases for further studies, such as interaction between induced hydraulic fractures and natural fractures. [ABSTRACT FROM AUTHOR]

Abstract: The need for an accurate and relatively efficient numerical model to analyse the hydrodynamic aspects of the interaction between a floating structure and surrounding ice has motivated the authors to develop a simulator that incorporates rigid-body dynamics and fluid flow around the structure and ice. A thorough mathematical description of both the model and the adopted numerical method are presented in the paper. An extensive validation study was conducted that included comparisons with other models' solutions and experimental data; for the latter, a number of physical model tests were conducted in a towing tank to investigate the hydrodynamic action of a floating structure on submerged ice masses. A cylindrical structure was towed past a fixed ice mass model at various speeds and separation distances. The surge and sway forces on the ice that occurred in response to the cylinder's passage were measured as the quantifiable indicators of the action. The obtained experimental data are primarily intended for validation purposes, but they can also be used for analyses of bergy bit and ship-collision scenarios in calm waters. The results of the study not only have shown the effectiveness of the numerical model for the considered problems, but also revealed the limits of both its applicability and the underlying theory. [Copyright &y& Elsevier]

Abstract: A generalized finite volume-based model to simulate Microchannel Heat Exchangers (MCHXs) with variable tube and fin geometries using a three-stream UA-AMTD method is presented in this paper. MCHXs with variable geometry can have different port dimensions, tube sizes and fin surfaces within the heat exchanger core and can have single or multiple tube banks. These novel MCHX design can further enhance the heat exchanger performance and improve its material utilization. A comprehensive literature review reveals that there is no experimental or numerical investigation of such innovative designs nor is there a modeling approach that can handle such flexible geometries. The model is validated against 227 experimental data points for eight different fluids, and eighteen MCHX geometries, including four different variable geometry microchannel condensers. This validation effort is the most comprehensive MCHX model validation presented in open literature. The average absolute capacity deviation between predicted and measured values was 2.7%. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional mathematical model for determining the dynamic behavior of a parabolic trough solar concentrator of one degree of freedom, with a water displacement mechanism capable of minimize the angle of incidence (angle between the sun's rays irradiated on a surface and the line normal to this surface). This mathematical model allows the calculation of the angle of inclination of the collecting surface and the forces acting on the system. The validity of the proposed mathematical model is verified experimentally on two solar concentrators of different dimension. [Copyright &y& Elsevier]