An accurate two-phase approximate solution to the acute viral infection model
Perelson, Alan S [Los Alamos National Laboratory
2009-01-01
During an acute viral infection, virus levels rise, reach a peak and then decline. Data and numerical solutions suggest the growth and decay phases are linear on a log scale. While viral dynamic models are typically nonlinear with analytical solutions difficult to obtain, the exponential nature of the solutions suggests approximations can be found. We derive a two-phase approximate solution to the target cell limited influenza model and illustrate the accuracy using data and previously established parameter values of six patients infected with influenza A. For one patient, the subsequent fall in virus concentration was not consistent with our predictions during the decay phase and an alternate approximation is derived. We find expressions for the rate and length of initial viral growth in terms of the parameters, the extent each parameter is involved in viral peaks, and the single parameter responsible for virus decay. We discuss applications of this analysis in antiviral treatments and investigating host and virus heterogeneities.
On the Stable Numerical Approximation of Two-Phase Flow with Insoluble Surfactant
Barrett, John W; Nürnberg, Robert
2013-01-01
We present a parametric finite element approximation of two-phase flow with insoluble surfactant. This free boundary problem is given by the Navier--Stokes equations for the two-phase flow in the bulk, which are coupled to the transport equation for the insoluble surfactant on the interface that separates the two phases. We combine the evolving surface finite element method with an approach previously introduced by the authors for two-phase Navier--Stokes flow, which maintains good mesh properties. The derived finite element approximation of two-phase flow with insoluble surfactant can be shown to be stable. Several numerical simulations demonstrate the practicality of our numerical method.
Xiao-Ying Qin
2014-01-01
Full Text Available An Adomian decomposition method (ADM is applied to solve a two-phase Stefan problem that describes the pure metal solidification process. In contrast to traditional analytical methods, ADM avoids complex mathematical derivations and does not require coordinate transformation for elimination of the unknown moving boundary. Based on polynomial approximations for some known and unknown boundary functions, approximate analytic solutions for the model with undetermined coefficients are obtained using ADM. Substitution of these expressions into other equations and boundary conditions of the model generates some function identities with the undetermined coefficients. By determining these coefficients, approximate analytic solutions for the model are obtained. A concrete example of the solution shows that this method can easily be implemented in MATLAB and has a fast convergence rate. This is an efficient method for finding approximate analytic solutions for the Stefan and the inverse Stefan problems.
Finite Element Approximation for the Dynamics of Fluidic Two-Phase Biomembranes
Barrett, John W; Nürnberg, Robert
2016-01-01
Biomembranes and vesicles consisting of multiple phases can attain a multitude of shapes, undergoing complex shape transitions. We study a Cahn--Hilliard model on an evolving hypersurface coupled to Navier--Stokes equations on the surface and in the surrounding medium to model these phenomena. The evolution is driven by a curvature energy, modelling the elasticity of the membrane, and by a Cahn--Hilliard type energy, modelling line energy effects. A stable semidiscrete finite element approximation is introduced and, with the help of a fully discrete method, several phenomena occurring for two-phase membranes are computed.
Huff, B. D.; Warren, P. B. [CalResources LLC (Canada); Whorff, F. [ITT Barton (Canada)
1995-11-01
The development of a two phase steam measurement system was documented. The system consists of a `V` cone differential pressure device and a vortex meter velocity device in series through which the steam flows. Temperature and pressure sensors are electronically interfaced with a data logging system. The design was described as being very simple and rugged, consequently, well suited to monitoring in the field.. Steam quality measurements were made in the Kern River Field and the Coalinga Field thermal projects using a surface steam separator. In steam flood operations, steam cost is very high, hence appropriate distribution of the steam can result in significant cost reduction. This technology allows the measurement of steam flow and quality at any point in the steam distribution system. The metering system`s orifice meter was found to have a total average error of 45%, with 25% of that attributable to `cold leg` problem. Installation of the metering system was expected to result in a steam use reduction of 8%, without any impact on production. Steam re-distribution could result in a potential oil production increase of 10%. 12 refs., 8 tabs., 9 figs.
Calvo Bernad Esteban
2014-03-01
Full Text Available This paper provides an experimental study of an acoustically forced two-phase air jet generated by a convergent nozzle. The used particles are transparent glass spheres with diameters between 2 and 50 μm (which gives Stokes number of order 1 and the selected forcing frequency (f=400 Hz induces a powerful nearly periodic flow pattern. Measurements were done by a two-colour Phase-Doppler Anemometer. The experimental setup is computer-controlled to provide an accurate control with a high long-term stability. Measurements cover the whole forcing signal cycle. Raw measurements were carefully post-processed to avoid bias induced by the forcing and the instrument setup, as well as obtain right mean values of the dispersed flow. The effect of the forcing and the particle load allows authors to establish the effect of the acoustic forcing and the particle load on the jet.
Accurate Period Approximation for Any Simple Pendulum Amplitude
XUE De-Sheng; ZHOU Zhao; GAO Mei-Zhen
2012-01-01
Accurate approximate analytical formulae of the pendulum period composed of a few elementary functions for any amplitude are constructed.Based on an approximation of the elliptic integral,two new logarithmic formulae for large amplitude close to 180° are obtained.Considering the trigonometric function modulation results from the dependence of relative error on the amplitude,we realize accurate approximation period expressions for any amplitude between 0 and 180°.A relative error less than 0.02％ is achieved for any amplitude.This kind of modulation is also effective for other large-amplitude logarithmic approximation expressions.%Accurate approximate analytical formulae of the pendulum period composed of a few elementary functions for any amplitude are constructed. Based on an approximation of the elliptic integral, two new logarithmic formulae for large amplitude close to 180° are obtained. Considering the trigonometric function modulation results from the dependence of relative error on the amplitude, we realize accurate approximation period expressions for any amplitude between 0 and 180°. A relative error less than 0.02% is achieved for any amplitude. This kind of modulation is also effective for other large-amplitude logarithmic approximation expressions.
Xuemiao Xu
2016-04-01
Full Text Available Exterior orientation parameters’ (EOP estimation using space resection plays an important role in topographic reconstruction for push broom scanners. However, existing models of space resection are highly sensitive to errors in data. Unfortunately, for lunar imagery, the altitude data at the ground control points (GCPs for space resection are error-prone. Thus, existing models fail to produce reliable EOPs. Motivated by a finding that for push broom scanners, angular rotations of EOPs can be estimated independent of the altitude data and only involving the geographic data at the GCPs, which are already provided, hence, we divide the modeling of space resection into two phases. Firstly, we estimate the angular rotations based on the reliable geographic data using our proposed mathematical model. Then, with the accurate angular rotations, the collinear equations for space resection are simplified into a linear problem, and the global optimal solution for the spatial position of EOPs can always be achieved. Moreover, a certainty term is integrated to penalize the unreliable altitude data for increasing the error tolerance. Experimental results evidence that our model can obtain more accurate EOPs and topographic maps not only for the simulated data, but also for the real data from Chang’E-1, compared to the existing space resection model.
Drift flux model as approximation of two fluid model for two phase dispersed and slug flow in tube
Nigmatulin, R.I.
1995-09-01
The analysis of one-dimensional schematizing for non-steady two-phase dispersed and slug flow in tube is presented. Quasi-static approximation, when inertia forces because of the accelerations of the phases may be neglected, is considered. Gas-liquid bubbly and slug vertical upward flows are analyzed. Non-trivial theoretical equations for slip velocity for these flows are derived. Juxtaposition of the derived equations for slip velocity with the famous Zuber-Findlay correlation as cross correlation coefficients is criticized. The generalization of non-steady drift flux Wallis theory taking into account influence of wall friction on the bubbly or slug flows for kinematical waves is considered.
Toumi, I.; Kumbaro, A.; Paillere, H
1999-07-01
These course notes, presented at the 30. Von Karman Institute Lecture Series in Computational Fluid Dynamics, give a detailed and through review of upwind differencing methods for two-phase flow models. After recalling some fundamental aspects of two-phase flow modelling, from mixture model to two-fluid models, the mathematical properties of the general 6-equation model are analysed by examining the Eigen-structure of the system, and deriving conditions under which the model can be made hyperbolic. The following chapters are devoted to extensions of state-of-the-art upwind differencing schemes such as Roe's Approximate Riemann Solver or the Characteristic Flux Splitting method to two-phase flow. Non-trivial steps in the construction of such solvers include the linearization, the treatment of non-conservative terms and the construction of a Roe-type matrix on which the numerical dissipation of the schemes is based. Extension of the 1-D models to multi-dimensions in an unstructured finite volume formulation is also described; Finally, numerical results for a variety of test-cases are shown to illustrate the accuracy and robustness of the methods. (authors)
Abu-Al-Saud, Moataz O.; Riaz, Amir; Tchelepi, Hamdi A.
2017-03-01
We developed a multiscale sharp-interface level-set method for immiscible two-phase flow with a pre-existing thin film on solid surfaces. The lubrication approximation theory is used to model the thin-film equation efficiently. The incompressible Navier-Stokes, level-set, and thin-film evolution equations are coupled sequentially to capture the dynamics occurring at multiple length scales. The Hamilton-Jacobi level-set reinitialization is employed to construct the signed-distance function, which takes into account the deposited thin-film on the solid surface. The proposed multiscale method is validated and shown to match the augmented Young-Laplace equation for a static meniscus in a capillary tube. Viscous bending of the advancing interface over the precursor film is captured by the proposed level-set method and agrees with the Cox-Voinov theory. The advancing bubble surrounded by a wetting film inside a capillary tube is considered, and the predicted film thickness compares well with both theory and experiments. We also demonstrate that the multiscale level-set approach can model immiscible two-phase flow with a capillary number as low as 10-6.
Ahmed, Mahmoud; Eslamian, Morteza
2015-07-01
Laminar natural convection in differentially heated ( β = 0°, where β is the inclination angle), inclined ( β = 30° and 60°), and bottom-heated ( β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation. The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors. Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect. Here we show that thermophoresis has a considerable effect on heat transfer augmentation in laminar natural convection. Our non-homogenous modeling approach shows that heat transfer in nanofluids is a function of the inclination angle and Ra number. It also reveals some details of flow behavior which cannot be captured by single-phase models. The minimum heat transfer rate is associated with β = 90° (bottom-heated) and the maximum heat transfer rate occurs in an inclination angle which varies with the Ra number.
Ahmed, Mahmoud; Eslamian, Morteza
2015-12-01
Laminar natural convection in differentially heated (β = 0°, where β is the inclination angle), inclined (β = 30° and 60°), and bottom-heated (β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation. The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors. Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect. Here we show that thermophoresis has a considerable effect on heat transfer augmentation in laminar natural convection. Our non-homogenous modeling approach shows that heat transfer in nanofluids is a function of the inclination angle and Ra number. It also reveals some details of flow behavior which cannot be captured by single-phase models. The minimum heat transfer rate is associated with β = 90° (bottom-heated) and the maximum heat transfer rate occurs in an inclination angle which varies with the Ra number.
Ashok Sahai
2010-06-01
Full Text Available This paper aims at constructing a two-phase iterative computerizable numerical algorithm for an improved approximation by ‘Modified Lupas’operator. The algorithm uses the ‘statistical perspectives’ for exploiting the information about the unknown function ‘f’ available in terms of its known values at the ‘equidistant-knots’ in C[0,1] more fully. The improvement, achieved by an aposteriori use of this information, happens iteratively. Any typical iteration uses the concepts of ‘Mean Square Error (MSE’ and ‘Bias’ ; the application of the former being preceded by that of the latter in the algorithm.At any iteration, the statistical concept of ‘MSE’ is used in “Phase II”, after that of the ‘Bias’ in “Phase I”. Like a ‘Sandwich’, the top and bottom-breads are the operations of ‘Bias-Reduction’ per the “Phase I” of our algorithm, and the operation of ‘MSEReduction’per the “Phase II” is the stuffing in the sandwich. The algorithm is an iterative one amounting to a desired-height ‘Docked-Pile’ ofsandwiches with the bottom–bread of the first iteration serving as the top-bread for the seconditeration sandwich, and so-on-and-so forth. The potential of the achievable improvements through the proposed ‘computerizable numerical iterative algorithm’ is illustrated per an ‘empirical study’ for which the function ‘f’ is assumed to be known in the sense of simulation. The illustration has been confined to “Three Iterations” only, for the sake of simplicity of the illustration.
Ahmed, Mahmoud; Eslamian, Morteza
2015-01-01
Laminar natural convection in differentially heated (β = 0°, where β is the inclination angle), inclined (β = 30° and 60°), and bottom-heated (β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and th...
Accurate and efficient computation of nonlocal potentials based on Gaussian-sum approximation
Exl, Lukas; Mauser, Norbert J.; Zhang, Yong
2016-12-01
We introduce an accurate and efficient method for the numerical evaluation of nonlocal potentials, including the 3D/2D Coulomb, 2D Poisson and 3D dipole-dipole potentials. Our method is based on a Gaussian-sum approximation of the singular convolution kernel combined with a Taylor expansion of the density. Starting from the convolution formulation of the nonlocal potential, for smooth and fast decaying densities, we make a full use of the Fourier pseudospectral (plane wave) approximation of the density and a separable Gaussian-sum approximation of the kernel in an interval where the singularity (the origin) is excluded. The potential is separated into a regular integral and a near-field singular correction integral. The first is computed with the Fourier pseudospectral method, while the latter is well resolved utilizing a low-order Taylor expansion of the density. Both parts are accelerated by fast Fourier transforms (FFT). The method is accurate (14-16 digits), efficient (O (Nlog N) complexity), low in storage, easily adaptable to other different kernels, applicable for anisotropic densities and highly parallelizable.
Du, Qiang; Yang, Jiang
2017-03-01
This work is concerned with the Fourier spectral approximation of various integral differential equations associated with some linear nonlocal diffusion and peridynamic operators under periodic boundary conditions. For radially symmetric kernels, the nonlocal operators under consideration are diagonalizable in the Fourier space so that the main computational challenge is on the accurate and fast evaluation of their eigenvalues or Fourier symbols consisting of possibly singular and highly oscillatory integrals. For a large class of fractional power-like kernels, we propose a new approach based on reformulating the Fourier symbols both as coefficients of a series expansion and solutions of some simple ODE models. We then propose a hybrid algorithm that utilizes both truncated series expansions and high order Runge-Kutta ODE solvers to provide fast evaluation of Fourier symbols in both one and higher dimensional spaces. It is shown that this hybrid algorithm is robust, efficient and accurate. As applications, we combine this hybrid spectral discretization in the spatial variables and the fourth-order exponential time differencing Runge-Kutta for temporal discretization to offer high order approximations of some nonlocal gradient dynamics including nonlocal Allen-Cahn equations, nonlocal Cahn-Hilliard equations, and nonlocal phase-field crystal models. Numerical results show the accuracy and effectiveness of the fully discrete scheme and illustrate some interesting phenomena associated with the nonlocal models.
How accurate is the Pearson r-from-Z approximation? A Monte Carlo simulation study.
Hittner, James B; May, Kim
2012-01-01
The Pearson r-from-Z approximation estimates the sample correlation (as an effect size measure) from the ratio of two quantities: the standard normal deviate equivalent (Z-score) corresponding to a one-tailed p-value divided by the square root of the total (pooled) sample size. The formula has utility in meta-analytic work when reports of research contain minimal statistical information. Although simple to implement, the accuracy of the Pearson r-from-Z approximation has not been empirically evaluated. To address this omission, we performed a series of Monte Carlo simulations. Results indicated that in some cases the formula did accurately estimate the sample correlation. However, when sample size was very small (N = 10) and effect sizes were small to small-moderate (ds of 0.1 and 0.3), the Pearson r-from-Z approximation was very inaccurate. Detailed figures that provide guidance as to when the Pearson r-from-Z formula will likely yield valid inferences are presented.
Montoya-Castillo, Andrés
2016-01-01
The ability to efficiently and accurately calculate equilibrium time correlation functions of many-body condensed phase quantum systems is one of the outstanding problems in theoretical chemistry. The Nakajima-Zwanzig-Mori formalism coupled to the self-consistent solution of the memory kernel has recently proven to be highly successful for the computation of nonequilibrium dynamical averages. Here, we extend this formalism to treat symmetrized equilibrium time correlation functions for the spin-boson model. Following the first paper in this series [A. Montoya-Castillo and D. R. Reichman, J. Chem. Phys. $\\bf{144}$, 184104 (2016)], we use a Dyson-type expansion of the projected propagator to obtain a self-consistent solution for the memory kernel that requires only the calculation of normally evolved auxiliary kernels. We employ the approximate mean-field Ehrenfest method to demonstrate the feasibility of this approach. Via comparison with numerically exact results for the correlation function $\\mathcal{C}_{zz}...
Belendez, A; Gimeno, E; Mendez, D I; Alvarez, M L [Departamento de Fisica, IngenierIa de Sistemas y TeorIa de la Senal, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain); Fernandez, E [Departamento de Optica, FarmacologIa y AnatomIa, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)], E-mail: a.belendez@ua.es
2008-06-15
A modified generalized, rational harmonic balance method is used to construct approximate frequency-amplitude relations for a conservative nonlinear singular oscillator in which the restoring force is inversely proportional to the dependent variable. The procedure is used to solve the nonlinear differential equation approximately. The approximate frequency obtained using this procedure is more accurate than those obtained using other approximate methods and the discrepancy between the approximate frequency and the exact one is lower than 0.40%.
Montoya-Castillo, Andrés; Reichman, David R
2017-02-28
The ability to efficiently and accurately calculate equilibrium time correlation functions of many-body condensed phase quantum systems is one of the outstanding problems in theoretical chemistry. The Nakajima-Zwanzig-Mori formalism coupled to the self-consistent solution of the memory kernel has recently proven to be highly successful for the computation of nonequilibrium dynamical averages. Here, we extend this formalism to treat symmetrized equilibrium time correlation functions for the spin-boson model. Following the first paper in this series [A. Montoya-Castillo and D. R. Reichman, J. Chem. Phys. 144, 184104 (2016)], we use a Dyson-type expansion of the projected propagator to obtain a self-consistent solution for the memory kernel that requires only the calculation of normally evolved auxiliary kernels. We employ the approximate mean-field Ehrenfest method to demonstrate the feasibility of this approach. Via comparison with numerically exact results for the correlation function Czz(t)=Re⟨σz(0)σz(t)⟩, we show that the current scheme affords remarkable boosts in accuracy and efficiency over bare Ehrenfest dynamics. We further explore the sensitivity of the resulting dynamics to the choice of kernel closures and the accuracy of the initial canonical density operator.
Accurate and Approximate Calculations of Raman Scattering in the Atmosphere of Neptune
Sromovsky, Lawrence
2015-01-01
Raman scattering by H$_2$ in Neptune's atmosphere has significant effects on its reflectivity for $\\lambda <$ 0.5 $\\mu$m, producing baseline decreases of $\\sim$ 20% in a clear atmosphere and $\\sim$ 10% in a hazy atmosphere. Here we present the first radiation transfer algorithm that includes both polarization and Raman scattering and facilitates computation of spatially resolved spectra. New calculations show that Cochran and Trafton's (1978, Astrophys. J. 219, 756-762) suggestion that light reflected in the deep CH$_4$ bands is mainly Raman scattered is not valid for current estimates of the CH$_4$vertical distribution, which implies only a 4% Raman contribution. Comparisons with IUE, HST, and groundbased observations confirm that high altitude haze absorption is reducing Neptune's geometric albedo by $\\sim$6% in the 0.22-0.26 $\\mu$m range and by $\\sim$13% in the 0.35-0.45 $\\mu$m range. We used accurate calculations to evaluate several approximations of Raman scattering. The Karkoschka (1994, Icarus 111, ...
Ahmad, Zahoor; Hanif, Muhammad
2013-01-01
The development of estimators of population parameters based on two-phase sampling schemes has seen a dramatic increase in the past decade. Various authors have developed estimators of population using either one or two auxiliary variables. The present volume is a comprehensive collection of estimators available in single and two phase sampling. The book covers estimators which utilize information on single, two and multiple auxiliary variables of both quantitative and qualitative nature. Th...
Higher accurate approximate solutions for the simple pendulum in terms of elementary functions
Belendez, Augusto; Frances, Jorge; Ortuno, Manuel; Gallego, Sergi; Guillermo Bernabeu, Jose, E-mail: a.belendez@ua.e [Departamento de Fisica, IngenierIa de Sistemas y TeorIa de la Senal, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)
2010-05-15
A closed-form approximate expression for the solution of a simple pendulum in terms of elementary functions is obtained. To do this, the exact expression for the maximum tension of the string of the pendulum is first considered and a trial approximate solution depending on some parameters is used, which is substituted in the tension equation. We obtain the parameters for the approximate by means of a term-by-term comparison of the power series expansion for the approximate maximum tension with the corresponding series for the exact one. We believe that this letter may be a suitable and fruitful exercise for teaching and better understanding nonlinear oscillations of a simple pendulum in undergraduate courses on classical mechanics. (letters and comments)
Mishra, Siddhartha
2011-01-01
Solutions of initial-boundary value problems for systems of conservation laws depend on the underlying viscous mechanism, namely different viscosity operators lead to different limit solutions. Standard numerical schemes for approximating conservation laws do not take into account this fact and converge to solutions that are not necessarily physically relevant. We design numerical schemes that incorporate explicit information about the underlying viscosity mechanism and approximate the physically relevant solution. Numerical experiments illustrating the robust performance of these schemes are presented.
王路; 徐江荣
2015-01-01
统一色噪声近似方法对简单一维色噪声问题研究较为充分，本文将统一色噪声法应用到高度复杂的多维气固两相湍流系统之中。首先从颗粒运动Langevin方程出发，利用统一色噪声法获得两相湍流Fokker-Planck方程，然后以此为基础建立颗粒轨道两阶矩模型。文中建立的新模型成功应用于后台阶两相湍流流场的数值模拟，预报合理正确。研究表明，对于多维两相湍流系统，统一色噪声法仍然行之有效。%A unified colored-noise approximation (UCNA) method has been widely used to solve the simple one-dimensional problem, and this paper attempts to extend this method to multi-dimensional systems. Firstly, a Fokker-Planck equation is obtained by UCNA method based on the Langevin equation for particle motion, then a two-order moment trajectory model is established on this basis. The new model can be successfully used to predict the backward-facing step two-phase flow, and the simulation results agree well with the measurements. This study shows that the UCNA method is still effective in dealing with multi-dimensional two-phase turbulent systems.
A method for the accurate and smooth approximation of standard thermodynamic functions
Coufal, O.
2013-01-01
A method is proposed for the calculation of approximations of standard thermodynamic functions. The method is consistent with the physical properties of standard thermodynamic functions. This means that the approximation functions are, in contrast to the hitherto used approximations, continuous and smooth in every temperature interval in which no phase transformations take place. The calculation algorithm was implemented by the SmoothSTF program in the C++ language which is part of this paper. Program summaryProgram title:SmoothSTF Catalogue identifier: AENH_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AENH_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 3807 No. of bytes in distributed program, including test data, etc.: 131965 Distribution format: tar.gz Programming language: C++. Computer: Any computer with gcc version 4.3.2 compiler. Operating system: Debian GNU Linux 6.0. The program can be run in operating systems in which the gcc compiler can be installed, see http://gcc.gnu.org/install/specific.html. RAM: 256 MB are sufficient for the table of standard thermodynamic functions with 500 lines Classification: 4.9. Nature of problem: Standard thermodynamic functions (STF) of individual substances are given by thermal capacity at constant pressure, entropy and enthalpy. STF are continuous and smooth in every temperature interval in which no phase transformations take place. The temperature dependence of STF as expressed by the table of its values is for further application approximated by temperature functions. In the paper, a method is proposed for calculating approximation functions which, in contrast to the hitherto used approximations, are continuous and smooth in every temperature interval. Solution method: The approximation functions are
Precise and accurate train run data: Approximation of actual arrival and departure times
Richter, Troels; Landex, Alex; Andersen, Jonas Lohmann Elkjær
trains have come to a halt nor when trains have set in motion again. Thus the measurements are inaccurate and do not express the experience of the passengers. A commonly accepted method to make this measurement possible is to construct a correction function to the track circuit based measurement....... This function estimates the inaccuracy or bias of the measurement and thus which offset is needed to approximate the actual arrival and departure times. The development of such a function is described in this paper. The development is based on international best practices combined with what is technically...
DePrince A
2010-01-01
Full Text Available Abstract We model the response of nanoscale Ag prolate spheroids to an external uniform static electric field using simulations based on the discrete dipole approximation, in which the spheroid is represented as a collection of polarizable subunits. We compare the results of simulations that employ subunit polarizabilities derived from the Clausius–Mossotti relation with those of simulations that employ polarizabilities that include a local environmental correction for subunits near the spheroid’s surface [Rahmani et al. Opt Lett 27: 2118 (2002]. The simulations that employ corrected polarizabilities give predictions in very good agreement with exact results obtained by solving Laplace’s equation. In contrast, simulations that employ uncorrected Clausius–Mossotti polarizabilities substantially underestimate the extent of the electric field “hot spot” near the spheroid’s sharp tip, and give predictions for the field enhancement factor near the tip that are 30 to 50% too small.
Gu, Ming; Wu, Cinna Julie
2009-01-01
In this article we propose an algorithm, PARNES, for the basis pursuit denoise problem which approximately finds a minimum one-norm solution to an underdetermined least squares problem. PARNES, (1) combines what we think are the best features of currently available methods SPGL1 and NESTA, and (2) incorporates a new improvement that exhibits linear convergence under the assumption of the restricted isometry property (RIP). As with SPGL1, our approach 'probes the Pareto frontier' and determines a solution to the BPDN problem by exploiting its relation between the LASSO problem as given by their Pareto curve. As with NESTA we rely on the accelerated proximal gradient method proposed by Yu. Nesterov that takes a remarkable O((L/e)^1/2) iterations to come within e > 0 of the optimal value, where L is the Lipschitz constant of the gradient of the objective function. Furthermore we introduce an 'outer loop' that regularly updates the prox center. Nesterov's accelerated proximal gradient method then becomes the 'inn...
Two-phase viscoelastic jetting
Yu, J-D; Sakai, S.; Sethian, J.A.
2008-12-10
A coupled finite difference algorithm on rectangular grids is developed for viscoelastic ink ejection simulations. The ink is modeled by the Oldroyd-B viscoelastic fluid model. The coupled algorithm seamlessly incorporates several things: (1) a coupled level set-projection method for incompressible immiscible two-phase fluid flows; (2) a higher-order Godunov type algorithm for the convection terms in the momentum and level set equations; (3) a simple first-order upwind algorithm for the convection term in the viscoelastic stress equations; (4) central difference approximations for viscosity, surface tension, and upper-convected derivative terms; and (5) an equivalent circuit model to calculate the inflow pressure (or flow rate) from dynamic voltage.
Tao, Jianmin; Mo, Yuxiang; Tian, Guocai; Ruzsinszky, Adrienn
2016-08-01
Long-range van der Waals (vdW) interaction is critically important for intermolecular interactions in molecular complexes and solids. However, accurate modeling of vdW coefficients presents a great challenge for nanostructures, in particular for fullerene clusters, which have huge vdW coefficients but also display very strong nonadditivity. In this work, we calculate the coefficients between fullerenes, fullerene and sodium clusters, and fullerene and alkali atoms with the hollow-sphere model within the modified single-frequency approximation (MSFA). In the MSFA, we assume that the electron density is uniform in a molecule and that only valence electrons in the outmost subshell of atoms contribute. The input to the model is the static multipole polarizability, which provides a sharp cutoff for the plasmon contribution outside the effective vdW radius. We find that the model can generate C6 in excellent agreement with expensive wave-function-based ab initio calculations, with a mean absolute relative error of only 3 % , without suffering size-dependent error. We show that the nonadditivities of the coefficients C6 between fullerenes and C60 and sodium clusters Nan revealed by the model agree remarkably well with those based on the accurate reference values. The great flexibility, simplicity, and high accuracy make the model particularly suitable for the study of the nonadditivity of vdW coefficients between nanostructures, advancing the development of better vdW corrections to conventional density functional theory.
Zhang, Du; Yang, Weitao
2016-10-01
An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and double excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K4), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.
Hadzi-Velkov, Zoran; Karagiannidis, George K; 10.1109/ICC.2009.5198714
2009-01-01
We present a novel and accurate approximation for the distribution of the sum of equally correlated Nakagami-m variates. Ascertaining on this result we study the performance of Equal Gain Combining (EGC) receivers, operating over equally correlating fading channels. Numerical results and simulations show the accuracy of the proposed approximation and the validity of the mathematical analysis.
Thomas Philipp
2012-05-01
Full Text Available Abstract Background It is well known that the deterministic dynamics of biochemical reaction networks can be more easily studied if timescale separation conditions are invoked (the quasi-steady-state assumption. In this case the deterministic dynamics of a large network of elementary reactions are well described by the dynamics of a smaller network of effective reactions. Each of the latter represents a group of elementary reactions in the large network and has associated with it an effective macroscopic rate law. A popular method to achieve model reduction in the presence of intrinsic noise consists of using the effective macroscopic rate laws to heuristically deduce effective probabilities for the effective reactions which then enables simulation via the stochastic simulation algorithm (SSA. The validity of this heuristic SSA method is a priori doubtful because the reaction probabilities for the SSA have only been rigorously derived from microscopic physics arguments for elementary reactions. Results We here obtain, by rigorous means and in closed-form, a reduced linear Langevin equation description of the stochastic dynamics of monostable biochemical networks in conditions characterized by small intrinsic noise and timescale separation. The slow-scale linear noise approximation (ssLNA, as the new method is called, is used to calculate the intrinsic noise statistics of enzyme and gene networks. The results agree very well with SSA simulations of the non-reduced network of elementary reactions. In contrast the conventional heuristic SSA is shown to overestimate the size of noise for Michaelis-Menten kinetics, considerably under-estimate the size of noise for Hill-type kinetics and in some cases even miss the prediction of noise-induced oscillations. Conclusions A new general method, the ssLNA, is derived and shown to correctly describe the statistics of intrinsic noise about the macroscopic concentrations under timescale separation conditions
Yan, Zidan; Perdew, John P.; Kurth, Stefan
2000-03-01
Within a density functional context, the random phase approximation (RPA) for the correlation emergy makes a short-range error which is well-suited for correction by a local spin density or generalized gradient approximation (GGA). Here we construct a GGA for the short-range correction, following the same reliable procedure used earlier to construct the GGA for the whole exchange-correlation energy: real-space cutoff of the spurious long-range contribution to the gradient expansion of the hole around an electron. The resulting density functional is nearly local, and predicts a substantial correction to the RPA correlation energy of an atom but \\underlinevery small corrections to the RPA atomization energy of a molecule, which may by itself come close to "chemical accuracy", and to the RPA surface energy of a metal. A by-product of this work is a density functional for the system-averaged correlation hole within RPA.
Froese, Brittany D
2012-01-01
The theory of viscosity solutions has been effective for representing and approximating weak solutions to fully nonlinear Partial Differential Equations (PDEs) such as the elliptic Monge-Amp\\`ere equation. The approximation theory of Barles-Souganidis [Barles and Souganidis, Asymptotic Anal., 4 (1999) 271-283] requires that numerical schemes be monotone (or elliptic in the sense of [Oberman, SIAM J. Numer. Anal, 44 (2006) 879-895]. But such schemes have limited accuracy. In this article, we establish a convergence result for nearly monotone schemes. This allows us to construct finite difference discretizations of arbitrarily high-order. We demonstrate that the higher accuracy is achieved when solutions are sufficiently smooth. In addition, the filtered scheme provides a natural detection principle for singularities. We employ this framework to construct a formally second-order scheme for the Monge-Amp\\`ere equation and present computational results on smooth and singular solutions.
Patricio Orio
Full Text Available BACKGROUND: The phenomena that emerge from the interaction of the stochastic opening and closing of ion channels (channel noise with the non-linear neural dynamics are essential to our understanding of the operation of the nervous system. The effects that channel noise can have on neural dynamics are generally studied using numerical simulations of stochastic models. Algorithms based on discrete Markov Chains (MC seem to be the most reliable and trustworthy, but even optimized algorithms come with a non-negligible computational cost. Diffusion Approximation (DA methods use Stochastic Differential Equations (SDE to approximate the behavior of a number of MCs, considerably speeding up simulation times. However, model comparisons have suggested that DA methods did not lead to the same results as in MC modeling in terms of channel noise statistics and effects on excitability. Recently, it was shown that the difference arose because MCs were modeled with coupled gating particles, while the DA was modeled using uncoupled gating particles. Implementations of DA with coupled particles, in the context of a specific kinetic scheme, yielded similar results to MC. However, it remained unclear how to generalize these implementations to different kinetic schemes, or whether they were faster than MC algorithms. Additionally, a steady state approximation was used for the stochastic terms, which, as we show here, can introduce significant inaccuracies. MAIN CONTRIBUTIONS: We derived the SDE explicitly for any given ion channel kinetic scheme. The resulting generic equations were surprisingly simple and interpretable--allowing an easy, transparent and efficient DA implementation, avoiding unnecessary approximations. The algorithm was tested in a voltage clamp simulation and in two different current clamp simulations, yielding the same results as MC modeling. Also, the simulation efficiency of this DA method demonstrated considerable superiority over MC methods
Adaptive moving grid methods for two-phase flow in porous media
Dong, Hao
2014-08-01
In this paper, we present an application of the moving mesh method for approximating numerical solutions of the two-phase flow model in porous media. The numerical schemes combine a mixed finite element method and a finite volume method, which can handle the nonlinearities of the governing equations in an efficient way. The adaptive moving grid method is then used to distribute more grid points near the sharp interfaces, which enables us to obtain accurate numerical solutions with fewer computational resources. The numerical experiments indicate that the proposed moving mesh strategy could be an effective way to approximate two-phase flows in porous media. © 2013 Elsevier B.V. All rights reserved.
Liu, Jie; Herbert, John M.
2015-07-01
A novel formulation of time-dependent density functional theory (TDDFT) is derived, based on non-orthogonal, absolutely-localized molecular orbitals (ALMOs). We call this approach TDDFT(MI), in reference to ALMO-based methods for describing molecular interactions (MI) that have been developed for ground-state applications. TDDFT(MI) is intended for efficient excited-state calculations in systems composed of multiple, weakly interacting chromophores. The efficiency is based upon (1) a local excitation approximation; (2) monomer-based, singly-excited basis states; (3) an efficient localization procedure; and (4) a one-step Davidson method to solve the TDDFT(MI) working equation. We apply this methodology to study molecular dimers, water clusters, solvated chromophores, and aggregates of naphthalene diimide that form the building blocks of self-assembling organic nanotubes. Absolute errors of 0.1-0.3 eV with respect to supersystem methods are achievable for these systems, especially for cases involving an excited chromophore that is weakly coupled to several explicit solvent molecules. Excited-state calculations in an aggregate of nine naphthalene diimide monomers are ˜40 times faster than traditional TDDFT calculations.
Neese, Frank; Wennmohs, Frank; Hansen, Andreas
2009-03-01
Coupled-electron pair approximations (CEPAs) and coupled-pair functionals (CPFs) have been popular in the 1970s and 1980s and have yielded excellent results for small molecules. Recently, interest in CEPA and CPF methods has been renewed. It has been shown that these methods lead to competitive thermochemical, kinetic, and structural predictions. They greatly surpass second order Møller-Plesset and popular density functional theory based approaches in accuracy and are intermediate in quality between CCSD and CCSD(T) in extended benchmark studies. In this work an efficient production level implementation of the closed shell CEPA and CPF methods is reported that can be applied to medium sized molecules in the range of 50-100 atoms and up to about 2000 basis functions. The internal space is spanned by localized internal orbitals. The external space is greatly compressed through the method of pair natural orbitals (PNOs) that was also introduced by the pioneers of the CEPA approaches. Our implementation also makes extended use of density fitting (or resolution of the identity) techniques in order to speed up the laborious integral transformations. The method is called local pair natural orbital CEPA (LPNO-CEPA) (LPNO-CPF). The implementation is centered around the concepts of electron pairs and matrix operations. Altogether three cutoff parameters are introduced that control the size of the significant pair list, the average number of PNOs per electron pair, and the number of contributing basis functions per PNO. With the conservatively chosen default values of these thresholds, the method recovers about 99.8% of the canonical correlation energy. This translates to absolute deviations from the canonical result of only a few kcal mol-1. Extended numerical test calculations demonstrate that LPNO-CEPA (LPNO-CPF) has essentially the same accuracy as parent CEPA (CPF) methods for thermochemistry, kinetics, weak interactions, and potential energy surfaces but is up to 500
Two Phase Technology Development Initiatives
Didion, Jeffrey R.
1999-01-01
Three promising thermal technology development initiatives, vapor compression thermal control system, electronics cooling, and electrohydrodynamics applications are outlined herein. These technologies will provide thermal engineers with additional tools to meet the thermal challenges presented by increased power densities and reduced architectural options that will be available in future spacecraft. Goddard Space Flight Center and the University of Maryland are fabricating and testing a 'proto- flight' vapor compression based thermal control system for the Ultra Long Duration Balloon (ULDB) Program. The vapor compression system will be capable of transporting approximately 400 W of heat while providing a temperature lift of 60C. The system is constructed of 'commercial off-the-shelf' hardware that is modified to meet the unique environmental requirements of the ULDB. A demonstration flight is planned for 1999 or early 2000. Goddard Space Flight Center has embarked upon a multi-discipline effort to address a number of design issues regarding spacecraft electronics. The program addressed the high priority design issues concerning the total mass of standard spacecraft electronics enclosures and the impact of design changes on thermal performance. This presentation reviews the pertinent results of the Lightweight Electronics Enclosure Program. Electronics cooling is a growing challenge to thermal engineers due to increasing power densities and spacecraft architecture. The space-flight qualification program and preliminary results of thermal performance tests of copper-water heat pipes are presented. Electrohydrodynamics (EHD) is an emerging technology that uses the secondary forces that result from the application of an electric field to a flowing fluid to enhance heat transfer and manage fluid flow. A brief review of current EHD capabilities regarding heat transfer enhancement of commercial heat exchangers and capillary pumped loops is presented. Goddard Space Flight
Gradient Augmented Level Set Method for Two Phase Flow Simulations with Phase Change
Anumolu, C. R. Lakshman; Trujillo, Mario F.
2016-11-01
A sharp interface capturing approach is presented for two-phase flow simulations with phase change. The Gradient Augmented Levelset method is coupled with the two-phase momentum and energy equations to advect the liquid-gas interface and predict heat transfer with phase change. The Ghost Fluid Method (GFM) is adopted for velocity to discretize the advection and diffusion terms in the interfacial region. Furthermore, the GFM is employed to treat the discontinuity in the stress tensor, velocity, and temperature gradient yielding an accurate treatment in handling jump conditions. Thermal convection and diffusion terms are approximated by explicitly identifying the interface location, resulting in a sharp treatment for the energy solution. This sharp treatment is extended to estimate the interfacial mass transfer rate. At the computational cell, a d-cubic Hermite interpolating polynomial is employed to describe the interface location, which is locally fourth-order accurate. This extent of subgrid level description provides an accurate methodology for treating various interfacial processes with a high degree of sharpness. The ability to predict the interface and temperature evolutions accurately is illustrated by comparing numerical results with existing 1D to 3D analytical solutions.
Moerk, J. Steven (Inventor); Youngquist, Robert C. (Inventor); Werlink, Rudy J. (Inventor)
1999-01-01
A quality and/or flow meter employs a capacitance probe assembly for measuring the dielectric constant of flow stream, particularly a two-phase flow stream including liquid and gas components.ne dielectric constant of the flow stream varies depending upon the volume ratios of its liquid and gas components, and capacitance measurements can therefore be employed to calculate the quality of the flow, which is defined as the volume ratio of liquid in the flow to the total volume ratio of gas and liquid in the flow. By using two spaced capacitance sensors, and cross-correlating the time varying capacitance values of each, the velocity of the flow stream can also be determined. A microcontroller-based processing circuit is employed to measure the capacitance of the probe sensors.The circuit employs high speed timer and counter circuits to provide a high resolution measurement of the time interval required to charge each capacitor in the probe assembly. In this manner, a high resolution, noise resistant, digital representation of each of capacitance value is obtained without the need for a high resolution A/D converter, or a high frequency oscillator circuit. One embodiment of the probe assembly employs a capacitor with two ground plates which provide symmetry to insure that accurate measurements are made thereby.
Two-Phase flow instrumentation for nuclear accidents simulation
Monni, G.; De Salve, M.; Panella, B.
2014-11-01
The paper presents the research work performed at the Energy Department of the Politecnico di Torino, concerning the development of two-phase flow instrumentation and of models, based on the analysis of experimental data, that are able to interpret the measurement signals. The study has been performed with particular reference to the design of power plants, such as nuclear water reactors, where the two-phase flow thermal fluid dynamics must be accurately modeled and predicted. In two-phase flow typically a set of different measurement instruments (Spool Piece - SP) must be installed in order to evaluate the mass flow rate of the phases in a large range of flow conditions (flow patterns, pressures and temperatures); moreover, an interpretative model of the SP need to be developed and experimentally verified. The investigated meters are: Turbine, Venturi, Impedance Probes, Concave sensors, Wire mesh sensor, Electrical Capacitance Probe. Different instrument combinations have been tested, and the performance of each one has been analyzed.
Two-phase flow in refrigeration systems
Gu, Junjie; Gan, Zhongxue
2013-01-01
Two-Phase Flow in Refrigeration Systems presents recent developments from the authors' extensive research programs on two-phase flow in refrigeration systems. This book covers advanced mass and heat transfer and vapor compression refrigeration systems and shows how the performance of an automotive air-conditioning system is affected through results obtained experimentally and theoretically, specifically with consideration of two-phase flow and oil concentration. The book is ideal for university postgraduate students as a textbook, researchers and professors as an academic reference book, and b
Advanced numerical methods for three dimensional two-phase flow calculations
Toumi, I. [Laboratoire d`Etudes Thermiques des Reacteurs, Gif sur Yvette (France); Caruge, D. [Institut de Protection et de Surete Nucleaire, Fontenay aux Roses (France)
1997-07-01
This paper is devoted to new numerical methods developed for both one and three dimensional two-phase flow calculations. These methods are finite volume numerical methods and are based on the use of Approximate Riemann Solvers concepts to define convective fluxes versus mean cell quantities. The first part of the paper presents the numerical method for a one dimensional hyperbolic two-fluid model including differential terms as added mass and interface pressure. This numerical solution scheme makes use of the Riemann problem solution to define backward and forward differencing to approximate spatial derivatives. The construction of this approximate Riemann solver uses an extension of Roe`s method that has been successfully used to solve gas dynamic equations. As far as the two-fluid model is hyperbolic, this numerical method seems very efficient for the numerical solution of two-phase flow problems. The scheme was applied both to shock tube problems and to standard tests for two-fluid computer codes. The second part describes the numerical method in the three dimensional case. The authors discuss also some improvements performed to obtain a fully implicit solution method that provides fast running steady state calculations. Such a scheme is not implemented in a thermal-hydraulic computer code devoted to 3-D steady-state and transient computations. Some results obtained for Pressurised Water Reactors concerning upper plenum calculations and a steady state flow in the core with rod bow effect evaluation are presented. In practice these new numerical methods have proved to be stable on non staggered grids and capable of generating accurate non oscillating solutions for two-phase flow calculations.
Lundegaard, Claus; Lund, Ole; Nielsen, Morten
2008-01-01
Several accurate prediction systems have been developed for prediction of class I major histocompatibility complex (MHC):peptide binding. Most of these are trained on binding affinity data of primarily 9mer peptides. Here, we show how prediction methods trained on 9mer data can be used for accurate...
Numerical modeling of two-phase binary fluid mixing using mixed finite elements
Sun, Shuyu
2012-07-27
Diffusion coefficients of dense gases in liquids can be measured by considering two-phase binary nonequilibrium fluid mixing in a closed cell with a fixed volume. This process is based on convection and diffusion in each phase. Numerical simulation of the mixing often requires accurate algorithms. In this paper, we design two efficient numerical methods for simulating the mixing of two-phase binary fluids in one-dimensional, highly permeable media. Mathematical model for isothermal compositional two-phase flow in porous media is established based on Darcy\\'s law, material balance, local thermodynamic equilibrium for the phases, and diffusion across the phases. The time-lag and operator-splitting techniques are used to decompose each convection-diffusion equation into two steps: diffusion step and convection step. The Mixed finite element (MFE) method is used for diffusion equation because it can achieve a high-order and stable approximation of both the scalar variable and the diffusive fluxes across grid-cell interfaces. We employ the characteristic finite element method with moving mesh to track the liquid-gas interface. Based on the above schemes, we propose two methods: single-domain and two-domain methods. The main difference between two methods is that the two-domain method utilizes the assumption of sharp interface between two fluid phases, while the single-domain method allows fractional saturation level. Two-domain method treats the gas domain and the liquid domain separately. Because liquid-gas interface moves with time, the two-domain method needs work with a moving mesh. On the other hand, the single-domain method allows the use of a fixed mesh. We derive the formulas to compute the diffusive flux for MFE in both methods. The single-domain method is extended to multiple dimensions. Numerical results indicate that both methods can accurately describe the evolution of the pressure and liquid level. © 2012 Springer Science+Business Media B.V.
Hybrid flux splitting schemes for numerical resolution of two-phase flows
Flaatten, Tore
2003-07-01
This thesis deals with the construction of numerical schemes for approximating. solutions to a hyperbolic two-phase flow model. Numerical schemes for hyperbolic models are commonly divided in two main classes: Flux Vector Splitting (FVS) schemes which are based on scalar computations and Flux Difference Splitting (FDS) schemes which are based on matrix computations. FVS schemes are more efficient than FDS schemes, but FDS schemes are more accurate. The canonical FDS schemes are the approximate Riemann solvers which are based on a local decomposition of the system into its full wave structure. In this thesis the mathematical structure of the model is exploited to construct a class of hybrid FVS/FDS schemes, denoted as Mixture Flux (MF) schemes. This approach is based on a splitting of the system in two components associated with the pressure and volume fraction variables respectively, and builds upon hybrid FVS/FDS schemes previously developed for one-phase flow models. Through analysis and numerical experiments it is demonstrated that the MF approach provides several desirable features, including (1) Improved efficiency compared to standard approximate Riemann solvers, (2) Robustness under stiff conditions, (3) Accuracy on linear and nonlinear phenomena. In particular it is demonstrated that the framework allows for an efficient weakly implicit implementation, focusing on an accurate resolution of slow transients relevant for the petroleum industry. (author)
Two-Phase Cavitating Flow in Turbomachines
Sandor I. Bernad
2012-11-01
Full Text Available Cavitating flows are notoriously complex because they are highly turbulent and unsteady flows involving two species (liquid/vapor with a large density difference. These features pose a unique challenge to numerical modeling works. The study briefly reviews the methodology curently employed for industrial cavitating flow simulations using the two-phase mixture model. The two-phase mixture model is evaluated and validated using benchmark problem where experimental data are available. A 3D cavitating flow computation is performed for the GAMM Francis runner. The model is able to qualitatively predict the location and extent of the 3D cavity on the blade, but further investigation are needed to quatitatively assess the accuracy for real turbomachinery cavitating flows.
Pumped two-phase heat transfer loop
Edelstein, Fred
1988-01-01
A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Review of two-phase instabilities
Kang, Han Ok; Seo, Han Ok; Kang, Hyung Suk; Cho, Bong Hyun; Lee, Doo Jeong
1997-06-01
KAERI is carrying out a development of the design for a new type of integral reactors. The once-through helical steam generator is important design features. The study on designs and operating conditions which prevent flow instability should precede the introduction of one-through steam generator. Experiments are currently scheduled to understand two-phase instability, evaluate the effect of each design parameter on the critical point, and determine proper inlet throttling for the prevention of instability. This report covers general two-phase instability with review of existing studies on this topics. The general classification of two phase flow instability and the characteristics of each type of instability are first described. Special attention is paid to BWR core flow instability and once-through steam generator instability. The reactivity feedback and the effect of system parameters are treated mainly for BWR. With relation to once-through steam generators, the characteristics of convective heating and dryout point oscillation are first investigated and then the existing experimental studies are summarized. Finally chapter summarized the proposed correlations for instability boundary conditions. (author). 231 refs., 5 tabs., 47 figs
Critical thinking: a two-phase framework.
Edwards, Sharon L
2007-09-01
This article provides a comprehensive review of how a two-phase framework can promote and engage nurses in the concepts of critical thinking. Nurse education is required to integrate critical thinking in their teaching strategies, as it is widely recognised as an important part of student nurses becoming analytical qualified practitioners. The two-phase framework can be incorporated in the classroom using enquiry-based scenarios or used to investigate situations that arise from practice, for reflection, analysis, theorising or to explore issues. This paper proposes a two-phase framework for incorporation in the classroom and practice to promote critical thinking. Phase 1 attempts to make it easier for nurses to organise and expound often complex and abstract ideas that arise when using critical thinking, identify more than one solution to the problem by using a variety of cues to facilitate action. Phase 2 encourages nurses to be accountable and responsible, to justify a decision, be creative and innovative in implementing change.
Coupling two-phase fluid flow with two-phase darcy flow in anisotropic porous media
Chen, J.
2014-06-03
This paper reports a numerical study of coupling two-phase fluid flow in a free fluid region with two-phase Darcy flow in a homogeneous and anisotropic porous medium region. The model consists of coupled Cahn-Hilliard and Navier-Stokes equations in the free fluid region and the two-phase Darcy law in the anisotropic porous medium region. A Robin-Robin domain decomposition method is used for the coupled Navier-Stokes and Darcy system with the generalized Beavers-Joseph-Saffman condition on the interface between the free flow and the porous media regions. Obtained results have shown the anisotropic properties effect on the velocity and pressure of the two-phase flow. 2014 Jie Chen et al.
Sun, Zhigang
2016-01-01
We proposed a distributed approximating functional method for efficiently describing the electronic dynamics in atoms and molecules in the presence of the Coulomb singularities, using the kernel of a grid representation derived by using the solutions of the Coulomb differential equation based upon the Schwartz's interpolation formula, and a grid representation using the Lobatto/Radau shape functions. The elements of the resulted Hamiltonian matrix are confined in a narrow diagonal band, which is similar to that using the (higher order) finite difference methods. However, the spectral convergence properties of the original grid representations are retained in the proposed distributed approximating functional method for solving the Schr\\"odinger equation involving the Coulomb singularity. Thus the method is effective for solving the electronic Schr\\"odinger equation using iterative methods where the action of the Hamiltonian matrix on the wave function need to evaluate many times. The method is investigated by ...
Microgravity Two-Phase Flow Transition
Parang, M.; Chao, D.
1999-01-01
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
Two-Phase Algorithm for Optimal Camera Placement
Jun-Woo Ahn
2016-01-01
Full Text Available As markers for visual sensor networks have become larger, interest in the optimal camera placement problem has continued to increase. The most featured solution for the optimal camera placement problem is based on binary integer programming (BIP. Due to the NP-hard characteristic of the optimal camera placement problem, however, it is difficult to find a solution for a complex, real-world problem using BIP. Many approximation algorithms have been developed to solve this problem. In this paper, a two-phase algorithm is proposed as an approximation algorithm based on BIP that can solve the optimal camera placement problem for a placement space larger than in current studies. This study solves the problem in three-dimensional space for a real-world structure.
New results in gravity dependent two-phase flow regime mapping
Kurwitz, Cable; Best, Frederick
2002-01-01
Accurate prediction of thermal-hydraulic parameters, such as the spatial gas/liquid orientation or flow regime, is required for implementation of two-phase systems. Although many flow regime transition models exist, accurate determination of both annular and slug regime boundaries is not well defined especially at lower flow rates. Furthermore, models typically indicate the regime as a sharp transition where data may indicate a transition space. Texas A&M has flown in excess of 35 flights aboard the NASA KC-135 aircraft with a unique two-phase package. These flights have produced a significant database of gravity dependent two-phase data including visual observations for flow regime identification. Two-phase flow tests conducted during recent zero-g flights have added to the flow regime database and are shown in this paper with comparisons to selected transition models. .
Two phase decision algorithm of replica allocation
Zuo Chaoshu; Liu Xinsong; Wang Zheng; Li Yi
2006-01-01
In distributed parallel server system, location and redundancy of replicas have great influence on availability and efficiency of the system. In order to improve availahility and efficiency of the system, two phase decision algorithm of replica allocation is proposed. The algorithm which makes use of auto-regression model dynamically predicts the future count of READ and WRITE operation, and then determines location and redundancy of replicas by considering availability, CPU and bands of the network. The algorithm can not only ensure the requirement of availability, but also reduce the system resources consumed by all the operations in a great scale. Analysis and test show that communication complexity and time complexity of the algorithm satisfy O( n ), resource optimizing scale increases with the increase of READ count.
Droplet Manipulations in Two Phase Flow Microfluidics
Arjen M. Pit
2015-11-01
Full Text Available Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of the emergence of new techniques, whose potential has not been fully realized. This review summarizes the currently existing techniques for manipulating droplets in two-phase flow microfluidics. Specifically, very recent developments like the use of acoustic waves, magnetic fields, surface energy wells, and electrostatic traps and rails are discussed. The physical principles are explained, and (potential advantages and drawbacks of different methods in the sense of versatility, flexibility, tunability and durability are discussed, where possible, per technique and per droplet operation: generation, transport, sorting, coalescence and splitting.
Phase appearance or disappearance in two-phase flows
Cordier, Floraine; Kumbaro, Anela
2011-01-01
This paper is devoted to the treatment of specific numerical problems which appear when phase appearance or disappearance occurs in models of two-phase flows. Such models have crucial importance in many industrial areas such as nuclear power plant safety studies. In this paper, two outstanding problems are identified: first, the loss of hyperbolicity of the system when a phase appears or disappears and second, the lack of positivity of standard shock capturing schemes such as the Roe scheme. After an asymptotic study of the model, this paper proposes accurate and robust numerical methods adapted to the simulation of phase appearance or disappearance. Polynomial solvers are developed to avoid the use of eigenvectors which are needed in usual shock capturing schemes, and a method based on an adaptive numerical diffusion is designed to treat the positivity problems. An alternate method, based on the use of the hyperbolic tangent function instead of a polynomial, is also considered. Numerical results are presente...
Estimation of the sugar cane cultivated area from LANDSAT images using the two phase sampling method
Parada, N. D. J. (Principal Investigator); Cappelletti, C. A.; Mendonca, F. J.; Lee, D. C. L.; Shimabukuro, Y. E.
1982-01-01
A two phase sampling method and the optimal sampling segment dimensions for the estimation of sugar cane cultivated area were developed. This technique employs visual interpretations of LANDSAT images and panchromatic aerial photographs considered as the ground truth. The estimates, as a mean value of 100 simulated samples, represent 99.3% of the true value with a CV of approximately 1%; the relative efficiency of the two phase design was 157% when compared with a one phase aerial photographs sample.
Pressure Loss across Tube Bundles in Two-phase Flow
Sim, Woo Gun; Banzragch, Dagdan [Hannam Univ., Daejon (Korea, Republic of)
2016-03-15
An analytical model was developed by Sim to estimate the two-phase damping ratio for upward two-phase flow perpendicular to horizontal tube bundles. The parameters of two-phase flow, such as void fraction and pressure loss evaluated in the model, were calculated based on existing experimental formulations. However, it is necessary to implement a few improvements in the formulations for the case of tube bundles. For the purpose of the improved formulation, we need more information about the two-phase parameters, which can be found through experimental test. An experiment is performed with a typical normal square array of cylinders subjected to the two-phase flow of air-water in the tube bundles, to calculate the two-phase Euler number and the two-phase friction multiplier. The pitch-to-diameter ratio is 1.35 and the diameter of cylinder is 18mm. Pressure loss along the flow direction in the tube bundles is measured with a pressure transducer and data acquisition system to calculate the two-phase Euler number and the two-phase friction multiplier. The void fraction model by Feenstra et al. is used to estimate the void fraction of the two-phase flow in tube bundles. The experimental results of the two phase friction multiplier and two-phase Euler number for homogeneous and non-homogeneous two-phase flows are compared and evaluated against the analytical results given by Sim's model.
A TWO-PHASE APPROACH TO FUZZY SYSTEM IDENTIFICATION
Ta-Wei HUNG; Shu-Cherng FANG; Henry L.W.NUTTLE
2003-01-01
A two-phase approach to fuzzy system identification is proposed. The first phase produces a baseline design to identify a prototype fuzzy system for a target system from a coIlection of input-output data pairs. It uses two easily implemented clustering techniques: the subtractive clustering method and the fuzzy c-means (FCM) clustering algorithm. The second phase (fine tuning)is executed to adjust the parameters identified in the baseline design. This phase uses the steepest descent and recursive least-squares estimation methods. The proposed approach is validated by applying it to both a function approximation type of problem and a classification type of problem. An analysis of the learning behavior of the proposed approach for the two test problems is conducted for further confirmation.
Vapor Compressor Driven Hybrid Two-Phase Loop Project
National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project will demonstrate a vapor compressor driven hybrid two-phase loop technology. The hybrid two-phase loop...
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries.
Dong, S; Wang, X
2016-01-01
Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries.
A Stable Parametric Finite Element Discretization of Two-Phase Navier--Stokes Flow
Barrett, John W; Nürnberg, Robert
2013-01-01
We present a parametric finite element approximation of two-phase flow. This free boundary problem is given by the Navier--Stokes equations in the two phases, which are coupled via jump conditions across the interface. Using a novel variational formulation for the interface evolution gives rise to a natural discretization of the mean curvature of the interface. The parametric finite element approximation of the evolving interface is then coupled to a standard finite element approximation of the two-phase Navier--Stokes equations in the bulk. Here enriching the pressure approximation space with the help of an XFEM function ensures good volume conservation properties for the two phase regions. In addition, the mesh quality of the parametric approximation of the interface in general does not deteriorate over time, and an equidistribution property can be shown for a semidiscrete continuous-in-time variant of our scheme in two space dimensions. Moreover, our finite element approximation can be shown to be uncondit...
Reynolds transport theorem for a two-phase flow
Collado, Francisco J.
2007-01-01
Transport equations for one-dimensional (1d), steady, two-phase flow have been proposed based on the fact that if the phases have different velocities, they cannot cover the same distance (the control volume length) in the same time. Thus, working in the same control volume for the two phases, the time scales of the phases have to be different. From this approach, transport balances for 1D, steady, two-phase flow have been already derived, supplying acceptable correlations for two-phase flow. Here, based on the strict application of the Reynolds transport theorem, general transport balances for two-phase flow are suggested.
Emerging Two-Phase Cooling Technologies for Power Electronic Inverters
Hsu, J.S.
2005-08-17
In order to meet the Department of Energy's (DOE's) FreedomCAR and Vehicle Technologies (FVCT) goals for volume, weight, efficiency, reliability, and cost, the cooling of the power electronic devices, traction motors, and generators is critical. Currently the power electronic devices, traction motors, and generators in a hybrid electric vehicle (HEV) are primarily cooled by water-ethylene glycol (WEG) mixture. The cooling fluid operates as a single-phase coolant as the liquid phase of the WEG does not change to its vapor phase during the cooling process. In these single-phase systems, two cooling loops of WEG produce a low temperature (around 70 C) cooling loop for the power electronics and motor/generator, and higher temperature loop (around 105 C) for the internal combustion engine. There is another coolant option currently available in automobiles. It is possible to use the transmission oil as a coolant. The oil temperature exists at approximately 85 C which can be utilized to cool the power electronic and electrical devices. Because heat flux is proportional to the temperature difference between the device's hot surface and the coolant, a device that can tolerate higher temperatures enables the device to be smaller while dissipating the same amount of heat. Presently, new silicon carbide (SiC) devices and high temperature direct current (dc)-link capacitors, such as Teflon capacitors, are available but at significantly higher costs. Higher junction temperature (175 C) silicon (Si) dies are gradually emerging in the market, which will eventually help to lower hardware costs for cooling. The development of high-temperature devices is not the only way to reduce device size. Two-phase cooling that utilizes the vaporization of the liquid to dissipate heat is expected to be a very effective cooling method. Among two-phase cooling methods, different technologies such as spray, jet impingement, pool boiling and submersion, etc. are being developed. The
袁益让
2002-01-01
For compressible two-phase displacement problem, a kind of upwind operator splitting finite difference schemes is put forward and make use of operator splitting, of calculus of variations, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estinates in L2 norm are derived to determine the error in the approximate solution.
Two-Phase Flow in Geothermal Wells: Development and Uses of a Good Computer Code
Ortiz-Ramirez, Jaime
1983-06-01
A computer code is developed for vertical two-phase flow in geothermal wellbores. The two-phase correlations used were developed by Orkiszewski (1967) and others and are widely applicable in the oil and gas industry. The computer code is compared to the flowing survey measurements from wells in the East Mesa, Cerro Prieto, and Roosevelt Hot Springs geothermal fields with success. Well data from the Svartsengi field in Iceland are also used. Several applications of the computer code are considered. They range from reservoir analysis to wellbore deposition studies. It is considered that accurate and workable wellbore simulators have an important role to play in geothermal reservoir engineering.
Estimation of flow velocity for a debris flow via the two-phase fluid model
S. Guo
2014-06-01
Full Text Available The two-phase fluid model is applied in this study to calculate the steady velocity of a debris flow along a channel bed. By using the momentum equations of the solid and liquid phases in the debris flow together with an empirical formula to describe the interaction between two phases, the steady velocities of the solid and liquid phases are obtained theoretically. The comparison of those velocities obtained by the proposed method with the observed velocities of two real-world debris flows shows that the proposed method can estimate accurately the velocity for a debris flow.
Two-Phase Technology at NASA/Johnson Space Center
Ungar, Eugene K.; Nicholson, Leonard S. (Technical Monitor)
1999-01-01
Since the baseline International Space Station (ISS) External Active Thermal Control System (EATCS) was changed from a two-phase mechanically pumped system to a single phase cascade system in the fall of 1993, two-phase EATCS research has continued at a low level at JSC. One of-the lessons of the ISS EATCS selection was that two-phase thermal control systems must have significantly lower power than comparable single phase systems to overcome their larger radiator area, larger line and fluid mass, and perceived higher technical risk. Therefore, research at JSC has concentrated on low power mechanically pumped two-phase EATCSs. In the presentation, the results of a study investigating the trade of single and two-phase mechanically pumped EATCSs for space vehicles will be summarized. The low power two-phase mechanically pumped EATCS system under development at JSC will be described in detail and the current design status of the subscale test unit will be reviewed. Also, performance predictions for a full size EATCS will be presented. In addition to the discussion of two-phase mechanically pumped EATCS development at JSC, two-phase technologies under development for biological water processing will be discussed. These biological water processor technologies are being prepared for a 2001 flight experiment and subsequent usage on the TransHab module on the International Space Station.
Two Phases of Coherent Structure Motions in Turbulent Boundary Layer
LIU Jian-Hua; JIANG Nan
2007-01-01
Two phases of coherent structure motion are acquired after obtaining conditional phase-averaged waveforms for longitudinal velocity of coherent structures in turbulent boundary layer based on Harr wavelet transfer. The correspondences of the two phases to the two processes (i.e. ejection and sweep) during a burst are determined.
DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS
X. Wang; X. Sun; H. Zhao
2011-09-01
In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in
Multi-needle capacitance probe for non-conductive two-phase flows
Monrós-Andreu, G.; Martinez-Cuenca, R.; Torró, S.; Escrig, J.; Hewakandamby, B.; Chiva, S.
2016-07-01
Despite its variable degree of application, intrusive instrumentation is the most accurate way to obtain local information in a two-phase flow system, especially local interfacial velocity and local interfacial area parameters. In this way, multi-needle probes, based on conductivity or optical principles, have been extensively used in the past few decades by many researchers in two-phase flow investigations. Moreover, the signal processing methods used to obtain the time-averaged two-phase flow parameters in this type of sensor have been thoroughly discussed and validated by many experiments. The objective of the present study is to develop a miniaturized multi-needle probe, based on capacitance measurements applicable to a wide range of non-conductive two-phase flows and, thus, to extend the applicability of multi-needle sensor whilst also maintaining a signal processing methodology provided in the literature for conductivity probes. Results from the experiments performed assess the applicability of the proposed sensor measurement principle and signal processing method for the bubbly flow regime. These results also provide an insight into the sensor application for more complex two-phase flow regimes.
An ALE Finite Element Approach for Two-Phase Flow with Phase Change
Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team
2016-11-01
In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.
Critical transport velocity in two-phase, horizontal pipe flow
Sommerville, D. (U.S. Army Chemical Research, Development and Engineering Center, Aberdeen Proving Grounds, MD (US))
1991-02-01
This paper reports on the suspension of solid particles or entrainment of liquid droplets in two- phase flow. Theoretical and empirical relationships have been derived for both instances without any consideration to the similarities between the two. However, a general relation for two-phase flow is desirable since there are systems that cannot be readily defined due to the dual (solid/liquid) nature of the transported material, such as colloids, pulp, slurries, and sludge. Using turbulence theory, one general equation can be derived to predict critical transport velocities for two-phase horizontal flow.
Thermo-Fluid Dynamics of Two-Phase Flow
Ishii, Mamrou
2011-01-01
"Thermo-fluid Dynamics of Two-Phase Flow, Second Edition" is focused on the fundamental physics of two-phase flow. The authors present the detailed theoretical foundation of multi-phase flow thermo-fluid dynamics as they apply to: Nuclear reactor transient and accident analysis; Energy systems; Power generation systems; Chemical reactors and process systems; Space propulsion; Transport processes. This edition features updates on two-phase flow formulation and constitutive equations and CFD simulation codes such as FLUENT and CFX, new coverage of the lift force model, which is of part
Tunable two-phase coexistence in half-doped manganites
P Chaddah; A Banerjee
2008-02-01
We discuss our very interesting experimental observation that the low-temperature two-phase coexistence in half-doped manganites is multi-valued (at any field) in that we can tune the coexisting antiferromagnetic-insulating (AF-I) and the ferromagnetic-metallic (FM-M) phase fractions by following different paths in (; ) space. We have shown experimentally that the phase fraction, in this two-phase coexistence, can take continuous infinity of values. All but one of these are metastable, and two-phase coexistence is not an equilibrium state.
Yousaf, Masood [Department of Physics, Ulsan National Institute of Science and Technology, Ulsan 689-798 (Korea, Republic of); Physics Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia); Dalhatu, S.A. [Physics Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia); Murtaza, G. [Department of Physics, Islamia College, Peshawar, KPK (Pakistan); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria); Sajjad, M. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Musa, A. [Physics Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia); Rahnamaye Aliabad, H.A. [Department of Physics, Hakim Sabzevari University (Iran, Islamic Republic of); Saeed, M.A., E-mail: saeed@utm.my [Physics Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Johor (Malaysia)
2015-03-15
Highlights: • Highly accurate all-electron FP-LAPW+lo method is used. • New physical parameters are reported, important for the fabrication of optoelectronic devices. • A comparative study that involves FP-LAPW+lo method and modified approximations. • Computed band gap values have good agreement with the experimental values. • Optoelectronic results of fundamental importance can be utilized for the fabrication of devices. - Abstract: We report the structural, electronic and optical properties of the thiospinels XIn{sub 2}S{sub 4} (X = Cd, Mg), using highly accurate all-electron full potential linearized augmented plane wave plus local orbital method. In order to calculate the exchange and correlation energies, the method is coupled with modified techniques such as GGA+U and mBJ-GGA, which yield improved results as compared to the previous studies. GGA+SOC approximation is also used for the first time on these compounds to examine the spin orbit coupling effect on the band structure. From the analysis of the structural parameters, robust character is predicted for both materials. Energy band structures profiles are fairly the same for GGA, GGA+SOC, GGA+U and mBJ-GGA, confirming the indirect and direct band gap nature of CdIn{sub 2}S{sub 4} and MgIn{sub 2}S{sub 4} materials, respectively. We report the trend of band gap results as: (mBJ-GGA) > (GGA+U) > (GGA) > (GGA+SOC). Localized regions appearing in the valence bands for CdIn{sub 2}S{sub 4} tend to split up nearly by ≈1 eV in the case of GGA+SOC. Many new physical parameters are reported that can be important for the fabrication of optoelectronic devices. Optical spectra namely, dielectric function (DF), refractive index n(ω), extinction coefficient k(ω), reflectivity R(ω), optical conductivity σ(ω), absorption coefficient α(ω) and electron loss function are discussed. Optical’s absorption edge is noted to be 1.401 and 1.782 for CdIn{sub 2}S{sub 4} and MgIn{sub 2}S{sub 4}, respectively. The
Particle modulations to turbulence in two-phase round jets
Bing Wang; Huiqiang Zhang; Yi Liu; Xiaofen Yan; Xilin Wang
2009-01-01
The particle modulations to turbulence in round jets were experimentally studied by means of two-phase velocity measurements with Phase Doppler Anemometer (PDA). Laden with very large particles, no significant attenuations of turbulence intensities were measured in the far-fields, due to small two-phase slip velocities and particle Reynolds number. The gas-phase turbulence is enhanced by particles in the near-fields, but it is significantly attenuated by the small particles in the far-fields. The smaller particles have a more profound effect on the attenuation of turbulence intensities. The enhancements or attenuations of turbulence intensities in the far-fields depends on the energy production, transport and dissipation mechanisms between the two phases, which are determined by the particle prop-erties and two-phase velocity slips. The non-dimensional parameter CTI is introduced to represent the change of turbulence intensity.
Gravity Independence of Microchannel Two-Phase Flow Project
National Aeronautics and Space Administration — Most of the amassed two-phase flow and heat transfer knowledge comes from experiments conducted in Earth’s gravity. Space missions span varying gravity levels,...
Vapor Compressor Driven Hybrid Two-Phase Loop Project
National Aeronautics and Space Administration — The Phase I project successfully demonstrated the feasibility of the vapor compression hybrid two-phase loop (VCHTPL). The test results showed the high...
Scaling of Two-Phase Systems Across Gravity Levels Project
National Aeronautics and Space Administration — There is a defined need for long term earth based testing for the development and deployment of two-phase flow systems in reduced-gravity, including lunar gravity,...
Two-phase cooling fluids; Les fluides frigoporteurs diphasiques
Lallemand, A. [Institut National des Sciences Appliquees (INSA), 69 - Lyon (France)
1997-12-31
In the framework of the diminution of heat transfer fluid consumption, the concept of indirect refrigerating circuits, using cooling intermediate fluids, is reviewed and the fluids that are currently used in these systems are described. Two-phase cooling fluids advantages over single-phase fluids are presented with their thermophysical characteristics: solid fraction, two-phase mixture enthalpy, thermal and rheological properties, determination of heat and mass transfer characteristics, and cold storage through ice slurry
An acoustic-convective splitting-based approach for the Kapila two-phase flow model
ten Eikelder, M. F. P.; Daude, F.; Koren, B.; Tijsseling, A. S.
2017-02-01
In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions.
Numerical method for nonlinear two-phase displacement problem and its application
YUAN Yi-rang; LIANG Dong; RUI Hong-xing; DU Ning; WANG Wen-qia
2008-01-01
For the three-dimensional nonlinear two-phase displacement problem, the modified upwind finite difference fractional steps schemes were put forward. Some techniques, such as calculus of variations, induction hypothesis, decomposition of high order difference operators, the theory of prior estimates and techniques were used. Optimal order estimates were derived for the error in the approximation solution. These methods have been successfully used to predict the consequences of seawater intrusion and protection projects.
袁益让
1999-01-01
For compressible two-phase displacement problem, a kind of characteristic finite difference fractional steps schemes is put forward and thick and thin grids are used to form a complete set. Some techniques, such as piecewise biquadratic interpolation, of calculus of variations, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estimates in L~2 norm are derived to determine the error in the approximate solution.
Study of two-phase flows in reduced gravity
Roy, Tirthankar
Study of gas-liquid two-phase flows under reduced gravity conditions is extremely important. One of the major applications of gas-liquid two-phase flows under reduced gravity conditions is in the design of active thermal control systems for future space applications. Previous space crafts were characterized by low heat generation within the spacecraft which needed to be redistributed within the craft or rejected to space. This task could easily have been accomplished by pumped single-phase loops or passive systems such as heat pipes and so on. However with increase in heat generation within the space craft as predicted for future missions, pumped boiling two-phase flows are being considered. This is because of higher heat transfer co-efficients associated with boiling heat transfer among other advantages. Two-phase flows under reduced gravity conditions also find important applications in space propulsion as in space nuclear power reactors as well as in many other life support systems of space crafts. Two-fluid model along with Interfacial Area Transport Equation (IATE) is a useful tool available to predict the behavior of gas-liquid two-phase flows under reduced gravity conditions. It should be noted that considerable differences exist between two-phase flows under reduced and normal gravity conditions especially for low inertia flows. This is because due to suppression of the gravity field the gas-liquid two-phase flows take a considerable time to develop under reduced gravity conditions as compared to normal gravity conditions. Hence other common methods of analysis applicable for fully developed gas-liquid two-phase flows under normal gravity conditions, like flow regimes and flow regime transition criteria, will not be applicable to gas-liquid two-phase flows under reduced gravity conditions. However the two-fluid model and the IATE need to be evaluated first against detailed experimental data obtained under reduced gravity conditions. Although lot of studies
A mechanical erosion model for two-phase mass flows
Pudasaini, Shiva P
2016-01-01
Erosion, entrainment and deposition are complex and dominant, but yet poorly understood, mechanical processes in geophysical mass flows. Here, we propose a novel, process-based, two-phase, erosion-deposition model capable of adequately describing these complex phenomena commonly observed in landslides, avalanches, debris flows and bedload transport. The model is based on the jump in the momentum flux including changes of material and flow properties along the flow-bed interface and enhances an existing general two-phase mass flow model (Pudasaini, 2012). A two-phase variably saturated erodible basal morphology is introduced and allows for the evolution of erosion-deposition-depths, incorporating the inherent physical process including momentum and rheological changes of the flowing mixture. By rigorous derivation, we show that appropriate incorporation of the mass and momentum productions or losses in conservative model formulation is essential for the physically correct and mathematically consistent descript...
Simulating confined swirling gas-solid two phase jet
金晗辉; 夏钧; 樊建人; 岑可法
2002-01-01
A k-ε-kp multi-fluid model was used to simulate confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. After considering the drag force between the two phases and gravity, a series of numerical simulations of the two-phase flow of 30μm, 45μm, 60μm diameter particles were performed on a x×r＝50×50 mesh grid respectively. The results showed that the k-ε-kp multi-fluid model can be applied to predict moderate swirling multi-phase flow. When the particle diameter is large, the collision of the particles with the wall will influence the prediction accuracy. The bigger the diameter of the particles, the stronger the collision with the wall, and the more obvious the difference between measured and calculated results.
Mathematical modeling of disperse two-phase flows
Morel, Christophe
2015-01-01
This book develops the theoretical foundations of disperse two-phase flows, which are characterized by the existence of bubbles, droplets or solid particles finely dispersed in a carrier fluid, which can be a liquid or a gas. Chapters clarify many difficult subjects, including modeling of the interfacial area concentration. Basic knowledge of the subjects treated in this book is essential to practitioners of Computational Fluid Dynamics for two-phase flows in a variety of industrial and environmental settings. The author provides a complete derivation of the basic equations, followed by more advanced subjects like turbulence equations for the two phases (continuous and disperse) and multi-size particulate flow modeling. As well as theoretical material, readers will discover chapters concerned with closure relations and numerical issues. Many physical models are presented, covering key subjects including heat and mass transfers between phases, interfacial forces and fluid particles coalescence and breakup, a...
Velocity and energy relaxation in two-phase flows
Meyapin, Yannick; Gisclon, Marguerite
2009-01-01
In the present study we investigate analytically the process of velocity and energy relaxation in two-phase flows. We begin our exposition by considering the so-called six equations two-phase model [Ishii1975, Rovarch2006]. This model assumes each phase to possess its own velocity and energy variables. Despite recent advances, the six equations model remains computationally expensive for many practical applications. Moreover, its advection operator may be non-hyperbolic which poses additional theoretical difficulties to construct robust numerical schemes |Ghidaglia et al, 2001]. In order to simplify this system, we complete momentum and energy conservation equations by relaxation terms. When relaxation characteristic time tends to zero, velocities and energies are constrained to tend to common values for both phases. As a result, we obtain a simple two-phase model which was recently proposed for simulation of violent aerated flows [Dias et al, 2010]. The preservation of invariant regions and incompressible li...
Two-dimensional Rarefaction Waves in the High-speed Two-phase Flow
Nakagawa, Masafumi; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. The purpose of the present study is to elucidate theoretically the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. Two-dimensional basic equations for the compressible two-phase flow are introduced considering the inter-phase momentum transfer. Sound velocities are obtained from these equations by using monochromatic wave approximation. Those depend on the relaxation time that determines the momentum transfer. The two-phase flow with large relaxation times has a frozen sound velocity, and with small one has an equilibrium sound velocity. Rarefaction waves which occurred behind the two-phase flow nozzle are calculated by the CIP method. Although the frozen Mach number, below one, controls these basic equations, the rarefaction waves appeared for small relaxation time. The Mach line behind which the expansion starts depends on the inlet velocity and the relaxation time. Those relationships are shown in this paper. The pressure expansion curves are only a function of the revolution angle around the corner of the nozzle outlet for the relaxation time less than 0.1. For the larger relaxation time, the pressure decays because of internal friction caused by inter phase momentum transfer, and the expansion curves are a function of not only the angle but also the flow direction. The calculated expansion curves are compared with the experimental ones
Forced Two-Phase Helium Cooling Scheme for the Mu2e Transport Solenoid
Tatkowski, G. [Fermilab; Cheban, S. [Fermilab; Dhanaraj, N. [Fermilab; Evbota, D. [Fermilab; Lopes, M. [Fermilab; Nicol, T. [Fermilab; Sanders, R. [Fermilab; Schmitt, R. [Fermilab; Voirin, E. [Fermilab
2015-01-01
The Mu2e Transport Solenoid (TS) is an S-shaped magnet formed by two separate but similar magnets, TS-u and TS-d. Each magnet is quarter-toroid shaped with a centerline radius of approximately 3 m utilizing a helium cooling loop consisting of 25 to 27 horizontal-axis rings connected in series. This cooling loop configuration has been deemed adequate for cooling via forced single phase liquid helium; however it presents major challenges to forced two-phase flow such as “garden hose” pressure drop, concerns of flow separation from tube walls, difficulty of calculation, etc. Even with these disadvantages, forced two-phase flow has certain inherent advantages which make it a more attractive option than forced single phase flow. It is for this reason that the use of forced two-phase flow was studied for the TS magnets. This paper will describe the analysis using helium-specific pressure drop correlations, conservative engineering approach, helium properties calculated and updated at over fifty points, and how the results compared with those in literature. Based on the findings, the use of forced-two phase helium is determined to be feasible for steady-state cooling of the TS solenoids
Effects of a two-phase oil-water mouthwash on halitosis.
Yaegaki, K; Sanada, K
1992-01-01
Many oral microorganisms possess hydrophobic outer surfaces. A two-phase, oil-water mouthwash has, therefore, recently been developed to remove such oral microorganisms. The oil phase consists of olive oil and other essential oils. The aqueous phase includes cetylpyridinium chloride, which is a disinfectant that promotes the adhesion of microorganisms to oil droplets. This study determined the effects of this mouthwash on the production of volatile sulfide in vivo and in vitro. Neither rinsing with water nor brushing teeth decreased the concentration of sulfide in mouth air at 3.5 h after treatment. A reduction of only 30% of sulfide was observed when a commercial mouthwash was used. However, this study demonstrated that use of the two-phase mouthwash led to approximately 80% reduction of sulfide. Furthermore, volatile sulfide and 2-ketobutyrate productions from methionine in a saliva putrefaction system were completely inhibited by the two-phase mouthwash; and consumption of methionine was decreased by 65 percent. It is concluded that the two-phase mouthwash strongly inhibits the production of volatile sulfide.
Pressure Buildup Analysis for Two-Phase Geothermal Wells: Application to the Baca Geothermal Field
Riney, T. D.; Garg, S. K.
1985-03-01
The recently published pressure transient analysis methods for two-phase geothermal wells are employed to analyze the pressure buildup data for several wells located in the Redondo Creek area of the Baca geothermal field in New Mexico. The downhole drilling information and pressure/temperature surveys are first interpreted to locate zones at which fluid enters the well bore from the formation and to estimate the initial reservoir temperature and pressure in these zones. All of the Baca wells considered here induced flashing in the formation upon production. Interpretation of the buildup data for each well considers well bore effects (e.g., phase change in the well bore fluid and location of the pressure sensor with respect to the permeable horizon) and the carbon dioxide content of the fluid and its effects on the phase behavior of the reservoir fluids and differentiates between the single- and two-phase portions of the pressure buildup data. Different straight-line approximations to the two portions (i.e., single- and two-phase) of the data on the Homer plot are used to obtain corresponding estimates for the single- and two-phase mobilities. Estimates for the formation permeability-thickness (kH) product are also given.
Shock wave of vapor-liquid two-phase flow
Liangju ZHAO; Fei WANG; Hong GAO; Jingwen TANG; Yuexiang YUAN
2008-01-01
The shock wave of vapor-liquid two-phase flow in a pressure-gain steam injector is studied by build-ing a mathematic model and making calculations. The results show that after the shock, the vapor is nearly com-pletely condensed. The upstream Mach number and the volume ratio of vapor have a great effect on the shock. The pressure and Mach number of two-phase shock con-form to the shock of ideal gas. The analysis of available energy shows that the shock is an irreversible process with entropy increase.
Dynamic Modeling of Phase Crossings in Two-Phase Flow
Madsen, Søren; Veje, Christian; Willatzen, Morten
2012-01-01
of the variables and are usually very slow to evaluate. To overcome these challenges, we use an interpolation scheme with local refinement. The simulations show that the method handles crossing of the saturation lines for both liquid to two-phase and two-phase to gas regions. Furthermore, a novel result obtained...... in this work, the method is stable towards dynamic transitions of the inlet/outlet boundaries across the saturation lines. Results for these cases are presented along with a numerical demonstration of conservation of mass under dynamically varying boundary conditions. Finally we present results...
Pumped, Two-Phase Heat-Transfer Loop
Edelstein, F.
1986-01-01
Two-phase heat-transfer system delivers coolant to equipment as liquid and removes it as vapor. Alternatively, system heats equipment by delivering vapor and removing condensed liquid. Two-phase scheme effective for heat transfer over long distances. Heat-transfer plates remove heat from or supply heat to equipment. If temperature of plate is high, valve opens liquid-supply line to plate, and cooling results. If plate temperature is low, valve opens liquid-suction line to plate, and heating ensues.
Two Phase Flow and Space-Based Applications
McQuillen, John
1999-01-01
A reduced gravity environment offers the ability to remove the effect of buoyancy on two phase flows whereby density differences that normally would promote relative velocities between the phases and also alter the shape of the interface are removed. However, besides being a potent research tool, there are also many space-based technologies that will either utilize or encounter two-phase flow behavior, and as a consequence, several questions must be addressed. This paper presents some of these technologies missions. Finally, this paper gives a description of web-sites for some funding.
Modelling of two-phase flow based on separation of the flow according to velocity
Narumo, T. [VTT Energy, Espoo (Finland). Nuclear Energy
1997-12-31
The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors. 45 refs. The thesis includes also five previous publications by author.
TWO-PHASE EJECTOR of CARBON DIOXIDE HEAT PUMP CALCULUS
Sit B.M.
2010-12-01
Full Text Available It is presented the calculus of the two-phase ejector for carbon dioxide heat pump. The method of calculus is based on the method elaborated by S.M. Kandil, W.E. Lear, S.A. Sherif, and is modified taking into account entrainment ratio as the input for the calculus.
Numerical simulation of two-phase flow in offshore environments
Wemmenhove, Rik
2008-01-01
Numerical Simulation of Two-Phase Flow in Offshore Environments Rik Wemmenhove Weather conditions on full sea are often violent, leading to breaking waves and lots of spray and air bubbles. As high and steep waves may lead to severe damage on ships and offshore structures, there is a great need for
Two-phase alkali-metal experiments in reduced gravity
Antoniak, Z.I.
1986-06-01
Future space missions envision the use of large nuclear reactors utilizing either a single or a two-phase alkali-metal working fluid. The design and analysis of such reactors require state-of-the-art computer codes that can properly treat alkali-metal flow and heat transfer in a reduced-gravity environment. A literature search of relevant experiments in reduced gravity is reported on here, and reveals a paucity of data for such correlations. The few ongoing experiments in reduced gravity are noted. General plans are put forth for the reduced-gravity experiments which will have to be performed, at NASA facilities, with benign fluids. A similar situation exists regarding two-phase alkali-metal flow and heat transfer, even in normal gravity. Existing data are conflicting and indequate for the task of modeling a space reactor using a two-phase alkali-metal coolant. The major features of past experiments are described here. Data from the reduced-gravity experiments with innocuous fluids are to be combined with normal gravity data from the two-phase alkali-metal experiments. Analyses undertaken here give every expectation that the correlations developed from this data base will provide a valid representation of alkali-metal heat transfer and pressure drop in reduced gravity.
Coal-Face Fracture With A Two-Phase Liquid
Collins, E. R., Jr.
1985-01-01
In new method for mining coal without explosive, two-phase liquid such as CO2 and water, injected at high pressure into deeper ends of holes drilled in coal face. Liquid permeates coal seam through existing microfractures; as liquid seeps back toward face, pressure eventually drops below critical value at which dissolved gas flashvaporizes, breaking up coal.
Two-phase flow in micro and nanofluidic devices
Shui, Lingling
2009-01-01
This thesis provides experimental data and theoretical analysis on two-phase flow in devices with different layouts of micrometer or nanometer-size channels. A full flow diagram is presented for oil and water flow in head-on microfluidic devices. Morphologically different flow regimes (dripping, jet
Modelling two-phase transport of 3H/3He
Visser, A.; Schaap, J.D.; Leijnse, T.; Broers, H.P.; Bierkens, M.F.P.
2008-01-01
Degassing of groundwater by excess denitrification of agricultural pollution complicates the interpretation of 3H/3He data and hinders the estimation of travel times in nitrate pollution studies. In this study we used a two-phase flow and transport model (STOMP) to evaluate the method presented by V
ESTIMATION OF MEAN IN PRESENCE OF MISSING DATA UNDER TWO-PHASE SAMPLING SCHEME
Narendra Singh Thakur
2011-01-01
Full Text Available To estimate the population mean with imputation i.e. the technique of substitutingmissing data, there are a number of techniques available in literature like Ratio method ofimputation, Compromised method of imputation, Mean method of imputation, Ahmed method ofimputation, F-T method of imputation, and so on. If population mean of auxiliary information isunknown then these methods are not useful and the two-phase sampling is used to obtain thepopulation mean. This paper presents some imputation methods of for missing values in twophasesampling. Two different sampling designs in two-phase sampling are compared underimputed data. The bias and m.s.e of suggested estimators are derived in the form of populationparameters using the concept of large sample approximation. Numerical study is performed overtwo populations using the expressions of bias and m.s.e and efficiency compared with Ahmedestimators.
Two-phase velocity measurements around cylinders using particle image velocimetry
Hassan, Y.A.; Philip, O.G.; Schmidl, W.D. [Texas A& M Univ., College Station, TX (United States)] [and others
1995-09-01
The particle Image Velocimetry flow measurement technique was used to study both single-phase flow and two-phase flow across a cylindrical rod inserted in a channel. First, a flow consisting of only a single-phase fluid was studied. The experiment consisted of running a laminar flow over four rods inserted in a channel. The water flow rate was 126 cm{sup 3}/s. Then a two-phase flow was studied. A mixture of water and small air bubbles was used. The water flow rate was 378 cm{sup 3}/s and the air flow rate was approximately 30 cm{sup 3}/s. The data are analyzed to obtain the velocity fields for both experiments. After interpretation of the velocity data, forces acting on a bubble entrained by the vortex were calculated successfully. The lift and drag coefficients were calculated using the velocity measurements and the force data.
Kou, Jisheng
2013-01-01
A class of discontinuous Galerkin methods with interior penalties is presented for incompressible two-phase flow in heterogeneous porous media with capillary pressures. The semidiscrete approximate schemes for fully coupled system of two-phase flow are formulated. In highly heterogeneous permeable media, the saturation is discontinuous due to different capillary pressures, and therefore, the proposed methods incorporate the capillary pressures in the pressure equation instead of saturation equation. By introducing a coupling approach for stability and error estimates instead of the conventional separate analysis for pressure and saturation, the stability of the schemes in space and time and a priori hp error estimates are presented in the L2(H 1) for pressure and in the L∞(L2) and L2(H1) for saturation. Two time discretization schemes are introduced for effectively computing the discrete solutions. © 2013 Societ y for Industrial and Applied Mathematics.
Investigations of two-phase flame propagation under microgravity conditions
Gokalp, Iskender
2016-07-01
Investigations of two-phase flame propagation under microgravity conditions R. Thimothée, C. Chauveau, F. Halter, I Gökalp Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France This paper presents and discusses recent results on two-phase flame propagation experiments we carried out with mono-sized ethanol droplet aerosols under microgravity conditions. Fundamental studies on the flame propagation in fuel droplet clouds or sprays are essential for a better understanding of the combustion processes in many practical applications including internal combustion engines for cars, modern aircraft and liquid rocket engines. Compared to homogeneous gas phase combustion, the presence of a liquid phase considerably complicates the physico-chemical processes that make up combustion phenomena by coupling liquid atomization, droplet vaporization, mixing and heterogeneous combustion processes giving rise to various combustion regimes where ignition problems and flame instabilities become crucial to understand and control. Almost all applications of spray combustion occur under high pressure conditions. When a high pressure two-phase flame propagation is investigated under normal gravity conditions, sedimentation effects and strong buoyancy flows complicate the picture by inducing additional phenomena and obscuring the proper effect of the presence of the liquid droplets on flame propagation compared to gas phase flame propagation. Conducting such experiments under reduced gravity conditions is therefore helpful for the fundamental understanding of two-phase combustion. We are considering spherically propagating two-phase flames where the fuel aerosol is generated from a gaseous air-fuel mixture using the condensation technique of expansion cooling, based on the Wilson cloud chamber principle. This technique is widely recognized to create well-defined mono-size droplets
Computer simulation of two-phase flow in nuclear reactors
Wulff, W.
1992-09-01
Two-phase flow models dominate the economic resource requirements for development and use of computer codes for analyzing thermohydraulic transients in nuclear power plants. Six principles are presented on mathematical modeling and selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited for two-phase flow analysis in nuclear reactors than the two-fluid model, because of the latter`s closure problem. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost.
Computer simulation of two-phase flow in nuclear reactors
Wulff, W.
1992-01-01
Two-phase flow models dominate the economic resource requirements for development and use of computer codes for analyzing thermohydraulic transients in nuclear power plants. Six principles are presented on mathematical modeling and selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited for two-phase flow analysis in nuclear reactors than the two-fluid model, because of the latter's closure problem. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost.
Recent advances in two-phase flow numerics
Mahaffy, J.H.; Macian, R. [Pennsylvania State Univ., University Park, PA (United States)
1997-07-01
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques.
Viscosity Solutions for the two-phase Stefan Problem
Kim, Inwon C
2010-01-01
We introduce a notion of viscosity solutions for the two-phase Stefan problem, which incorporates possible existence of a mushy region generated by the initial data. We show that a comparison principle holds between viscosity solutions, and investigate the coincidence of the viscosity solutions and the weak solutions defined via integration by parts. In particular, in the absence of initial mushy region, viscosity solution is the unique weak solution with the same boundary data.
Computational methods for two-phase flow and particle transport
Lee, Wen Ho
2013-01-01
This book describes mathematical formulations and computational methods for solving two-phase flow problems with a computer code that calculates thermal hydraulic problems related to light water and fast breeder reactors. The physical model also handles the particle and gas flow problems that arise from coal gasification and fluidized beds. The second part of this book deals with the computational methods for particle transport.
Two-phase Flow Distribution in Heat Exchanger Manifolds
Vist, Sivert
2004-01-01
The current study has investigated two-phase refrigerant flow distribution in heat exchange manifolds. Experimental data have been acquired in a heat exchanger test rig specially made for measurement of mass flow rate and gas and liquid distribution in the manifolds of compact heat exchangers. Twelve different manifold designs were used in the experiments, and CO2 and HFC-134a were used as refrigerants.
Estimating disease prevalence in two-phase studies.
Alonzo, Todd A; Pepe, Margaret Sullivan; Lumley, Thomas
2003-04-01
Disease prevalence is ideally estimated using a 'gold standard' to ascertain true disease status on all subjects in a population of interest. In practice, however, the gold standard may be too costly or invasive to be applied to all subjects, in which case a two-phase design is often employed. Phase 1 data consisting of inexpensive and non-invasive screening tests on all study subjects are used to determine the subjects that receive the gold standard in the second phase. Naive estimates of prevalence in two-phase studies can be biased (verification bias). Imputation and re-weighting estimators are often used to avoid this bias. We contrast the forms and attributes of the various prevalence estimators. Distribution theory and simulation studies are used to investigate their bias and efficiency. We conclude that the semiparametric efficient approach is the preferred method for prevalence estimation in two-phase studies. It is more robust and comparable in its efficiency to imputation and other re-weighting estimators. It is also easy to implement. We use this approach to examine the prevalence of depression in adolescents with data from the Great Smoky Mountain Study.
A 3D moving mesh Finite Element Method for two-phase flows
Anjos, G. R.; Borhani, N.; Mangiavacchi, N.; Thome, J. R.
2014-08-01
A 3D ALE Finite Element Method is developed to study two-phase flow phenomena using a new discretization method to compute the surface tension forces. The computational method is based on the Arbitrary Lagrangian-Eulerian formulation (ALE) and the Finite Element Method (FEM), creating a two-phase method with an improved model for the liquid-gas interface. An adaptive mesh update procedure is also proposed for effective management of the mesh to remove, add and repair elements, since the computational mesh nodes move according to the flow. The ALE description explicitly defines the two-phase interface position by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The proposed methodology for computing the curvature leads to accurate results with moderate programming effort and computational cost. Static and dynamic tests have been carried out to validate the method and the results have compared well to analytical solutions and experimental results found in the literature, demonstrating that the new proposed methodology provides good accuracy to describe the interfacial forces and bubble dynamics. This paper focuses on the description of the proposed methodology, with particular emphasis on the discretization of the surface tension force, the new remeshing technique, and the validation results. Additionally, a microchannel simulation in complex geometry is presented for two elongated bubbles.
A Novel Hyperbolization Procedure for The Two-Phase Six-Equation Flow Model
Samet Y. Kadioglu; Robert Nourgaliev; Nam Dinh
2011-10-01
We introduce a novel approach for the hyperbolization of the well-known two-phase six equation flow model. The six-equation model has been frequently used in many two-phase flow applications such as bubbly fluid flows in nuclear reactors. One major drawback of this model is that it can be arbitrarily non-hyperbolic resulting in difficulties such as numerical instability issues. Non-hyperbolic behavior can be associated with complex eigenvalues that correspond to characteristic matrix of the system. Complex eigenvalues are often due to certain flow parameter choices such as the definition of inter-facial pressure terms. In our method, we prevent the characteristic matrix receiving complex eigenvalues by fine tuning the inter-facial pressure terms with an iterative procedure. In this way, the characteristic matrix possesses all real eigenvalues meaning that the characteristic wave speeds are all real therefore the overall two-phase flowmodel becomes hyperbolic. The main advantage of this is that one can apply less diffusive highly accurate high resolution numerical schemes that often rely on explicit calculations of real eigenvalues. We note that existing non-hyperbolic models are discretized mainly based on low order highly dissipative numerical techniques in order to avoid stability issues.
Gurung, Arati; Poelma, Christian
2016-11-01
Ultrasound imaging velocimetry (UIV) has received considerable interest as a tool to measure in non-transparent flows. So far, studies have only reported statistics for steady flows or used a qualitative approach. In this study, we demonstrate that UIV has matured to a level where accurate turbulence statistics can be obtained. The technique is first validated in laminar and fully developed turbulent pipe flow (single-phase, with water as fluid) at a Reynolds number of 5300. The flow statistics agree with the literature data. Subsequently, we obtain similar statistics in turbulent two-phase flows at the same Reynolds number, by adding solid particles up to volume fraction of 3 %. In these cases, the medium is completely opaque, yet UIV provides useable data. The error in the measurements is estimated using an ad hoc approach at a volume load up to 10 %. For this case, the errors are approximately 1.9 and 0.3 % of the centerline velocity for the streamwise and radial velocity components, respectively. Additionally, it is demonstrated that it is possible to estimate the local concentration in stratified flows.
Preparative crystallization of a single chain antibody using an aqueous two-phase system.
Huettmann, Hauke; Berkemeyer, Matthias; Buchinger, Wolfgang; Jungbauer, Alois
2014-11-01
A simultaneous crystallization and aqueous two-phase extraction of a single chain antibody was developed, demonstrating process integration. The process conditions were designed to form an aqueous two-phase system, and to favor crystallization, using sodium sulfate and PEG-2000. At sufficiently high concentrations of PEG, a second phase was generated in which the protein crystallization occurred simultaneously. The single chain antibody crystals were partitioned to the top, polyethylene glycol-rich phase. The crystal nucleation took place in the sodium sulfate-rich phase and at the phase boundary, whereas crystal growth was progressing mainly in the polyethylene glycol-rich phase. The crystals in the polyethylene glycol-rich phase grew to a size of >50 µm. Additionally, polyethylene glycol acted as an anti-solvent, thus, it influenced the crystallization yield. A phase diagram with an undersaturation zone, crystallization area, and amorphous precipitation zone was established. Only small differences in polyethylene glycol concentration caused significant shifts of the crystallization yield. An increase of the polyethylene glycol content from 2% (w/v) to 4% (w/v) increased the yield from approximately 63-87%, respectively. Our results show that crystallization in aqueous two-phase systems is an opportunity to foster process integration.
Central upwind scheme for a compressible two-phase flow model.
Munshoor Ahmed
Full Text Available In this article, a compressible two-phase reduced five-equation flow model is numerically investigated. The model is non-conservative and the governing equations consist of two equations describing the conservation of mass, one for overall momentum and one for total energy. The fifth equation is the energy equation for one of the two phases and it includes source term on the right-hand side which represents the energy exchange between two fluids in the form of mechanical and thermodynamical work. For the numerical approximation of the model a high resolution central upwind scheme is implemented. This is a non-oscillatory upwind biased finite volume scheme which does not require a Riemann solver at each time step. Few numerical case studies of two-phase flows are presented. For validation and comparison, the same model is also solved by using kinetic flux-vector splitting (KFVS and staggered central schemes. It was found that central upwind scheme produces comparable results to the KFVS scheme.
Influence of lactic acid on the two-phase anaerobic digestion of kitchen wastes
ZHANG Bo; CAI Wei-min; HE Pin-jing
2007-01-01
To evaluate the influence of lactic acid on the methanogenesis, anaerobic digestion of kitchen wastes was firstly conducted in a two-phase anaerobic digestion process, and performance of two digesters fed with lactic acid and glucose was subsequently compared.The results showed that the lactic acid was the main fermentation products of hydrolysis-acidification stage in the two-phase anaerobic digestion process for kitchen wastes. The lactic acid concentration constituted approximately 50% of the chemical oxygen demand (COD) concentration in the hydrolysis-acidification liquid. The maximum organic loading rate was lower in the digester fed with lactic acid than that fed with glucose. Volatile fatty acids (VFAs) and COD removal were deteriorated in the methanogenic reactor fed with to the high concentration of lactic acid fed. It could be concluded that avoiding the presence of the lactic acid is necessary in the hydrolysis-acidification process for the improvement of the two-phase anaerobic digestion process of kitchen wastes.
Yi-rang Yuan
2004-01-01
For compressible two-phase displacement problem,the modified upwind finite difference fractional steps schemes are put forward.Some techniques,such as calculus of variations,commutative law of multiplication of difference operators,decomposition of high order difference operators,the theory of prior estimates and techniques are used.Optimal order estimates in L 2 norm are derived for the error in the approximate solution.This method has already been applied to the numerical simulation of seawater intrusion and migration-accumulation of oil resources.
A two-phase solid/fluid model for dense granular flows including dilatancy effects
Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Koné, El-Hadj; Narbona-Reina, Gladys
2016-04-01
account for this transfer of fluid into and out of the mixture, a two-layer model is proposed with a fluid layer on top of the two-phase mixture layer. Mass and momentum conservation are satisfied for the two phases, and mass and momentum are transferred between the two layers. A thin-layer approximation is used to derive average equations. Special attention is paid to the drag friction terms that are responsible for the transfer of momentum between the two phases and for the appearance of an excess pore pressure with respect to the hydrostatic pressure. We present several numerical tests of two-phase granular flows over sloping topography that are compared to the results of the model proposed by {Pitman and Le} [2005]. In particular, we quantify the role of the fluid and compression/dilatation processes on granular flow velocity field and runout distance. F. Bouchut, E.D. Fernandez-Nieto, A. Mangeney, G. Narbona-Reina, A two-phase shallow debris flow model with energy balance, {ESAIM: Math. Modelling Num. Anal.}, 49, 101-140 (2015). F. Bouchut, E. D. Fernandez-Nieto, A. Mangeney, G. Narbona-Reina, A two-phase two-layer model for fluidized granular flows with dilatancy effects, {J. Fluid Mech.}, submitted (2016). R.M. Iverson, M. Logan, R.G. LaHusen, M. Berti, The perfect debris flow? Aggregated results from 28 large-scale experiments, {J. Geophys. Res.}, 115, F03005 (2010). R. Jackson, The Dynamics of Fluidized Particles, {Cambridges Monographs on Mechanics} (2000). E.B. Pitman, L. Le, A two-fluid model for avalanche and debris flows, {Phil.Trans. R. Soc. A}, 363, 1573-1601 (2005). S. Roux, F. Radjai, Texture-dependent rigid plastic behaviour, {Proceedings: Physics of Dry Granular Media}, September 1997. (eds. H. J. Herrmann et al.). Kluwer. Cargèse, France, 305-311 (1998).
Fraser, D.W.H. [Univ. of British Columbia (Canada); Abdelmessih, A.H. [Univ. of Toronto, Ontario (Canada)
1995-09-01
A general unified model is developed to predict one-component critical two-phase pipe flow. Modelling of the two-phase flow is accomplished by describing the evolution of the flow between the location of flashing inception and the exit (critical) plane. The model approximates the nonequilibrium phase change process via thermodynamic equilibrium paths. Included are the relative effects of varying the location of flashing inception, pipe geometry, fluid properties and length to diameter ratio. The model predicts that a range of critical mass fluxes exist and is bound by a maximum and minimum value for a given thermodynamic state. This range is more pronounced at lower subcooled stagnation states and can be attributed to the variation in the location of flashing inception. The model is based on the results of an experimental study of the critical two-phase flow of saturated and subcooled water through long tubes. In that study, the location of flashing inception was accurately controlled and adjusted through the use of a new device. The data obtained revealed that for fixed stagnation conditions, the maximum critical mass flux occurred with flashing inception located near the pipe exit; while minimum critical mass fluxes occurred with the flashing front located further upstream. Available data since 1970 for both short and long tubes over a wide range of conditions are compared with the model predictions. This includes test section L/D ratios from 25 to 300 and covers a temperature and pressure range of 110 to 280{degrees}C and 0.16 to 6.9 MPa. respectively. The predicted maximum and minimum critical mass fluxes show an excellent agreement with the range observed in the experimental data.
Study of two-phase flows in reduced gravity using ground based experiments
Vasavada, S.; Ishii, M. [Purdue University, School of Nuclear Engineering, West Lafayette, IN (United States); Sun, X. [Ohio State University, Department of Mechanical Engineering, Columbus, OH (United States); Duval, W. [NASA Glenn Research Center, Fluid Physics and Transport Branch, Cleveland, OH (United States)
2007-07-15
Experimental studies have been carried out to support the development of a framework of the two-fluid model along with an interfacial area transport equation applicable to reduced gravity two-phase flows. The experimental study simulates the reduced gravity condition in ground based facilities by using two immiscible liquids of similar density namely, water as the continuous phase and Therminol 59 {sup registered} as the dispersed phase. We have acquired a total of eleven data sets in the bubbly flow and bubbly to slug flow transition regimes. These flow conditions have area-averaged void (volume) fractions ranging from 3 to 30% and channel Reynolds number for the continuous phase between 2,900 and 8,800. Flow visualization has been performed and a flow regime map developed which is compared with relevant bubbly to slug flow regime transition criteria. The comparison shows that the transition boundary is well predicted by the criterion based on critical void fraction. The value of the critical void fraction at transition was experimentally determined to be approximately 25%. In addition, important two-phase flow local parameters, including the void fraction, interfacial area concentration, droplet number frequency and droplet velocity, have been acquired at two axial locations using state-of-the-art multi-sensor conductivity probe. The radial profiles and axial development of the two-phase flow parameters show that the coalescence mechanism is enhanced by either increasing the continuous or dispersed phase Reynolds number. Evidence of turbulence induced particle interaction mechanism is highlighted. The data presented in this paper clearly show the marked differences in terms of bubble (droplet) size, phase distribution and phase interaction in two-phase flow between normal and reduced gravity conditions. (orig.)
A real two-phase submarine debris flow and tsunami
Pudasaini, Shiva P.; Miller, Stephen A. [Department of Geodynamics and Geophysics, Steinmann Institute, University of Bonn Nussallee 8, D-53115, Bonn (Germany)
2012-09-26
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
Two algorithms for two-phase Stefan type problems
LIAN Xiao-peng; CHENG Xiao-liang; HAN Wei-min
2009-01-01
In this paper, the relaxation algorithm and two Uzawa type algorithms for solving discretized variational inequalities arising from the two-phase Stefan type problem are proposed. An analysis of their convergence is presented and the upper bounds of the convergence rates are derived. Some numerical experiments are shown to demonstrate that for the second Uzawa algorithm which is an improved version of the first Uzawa algorithm, the convergence rate is uniformly bounded away from 1 if τh-2 is kept bounded, where τ is the time step size and h the space mesh size.
Recurrent pyogenic cholangitis : efficacy of two-phase helical CT
Jeong, Ki Ho; Cho, June Sik; Shin, Kyung Sook; Lee, Se Hyo; Yu, Ho Jun; Park, Jin Yong; Kim, Young Min [College of Medicine, Chungnam National University, Taejon (Korea, Republic of)
2000-01-01
To evaluate the usefulness of two-phase helical CT in patients with recurrent pyogenic cholangitis (RPC) for the detection of acute inflammation and assessment of the degree of portal vein (PV) stenosis as a cause of hepatic parenchymal atrophy. We retrospectively reviewed two-phase CT findings in 30 patients with RPC diagnosed by CT, ERCP (endoscopic retrograde cholangiopancreatography), and surgery. Two-phase helical CT scans were obtained 30 sec (arterial phase, AP) and 70 sec (portal phase, PP) after the start of IV administration of contrast material. Without prior information, we analyzed periductal parenchymal and ductal wall enhancement during the AP and PP, and the degree of PV stenosis during the PP. Acute inflammation was diagnosed on the basis of symptoms and laboratory findings. To evaluate the relationship between parenchymal a trophy and PV stenosis, the degree of PV stenosis in affected parenchyma was classified as one of three types (mild, less than 25%; moderate, 25-75%; severe, greater than 75%), as compared with the diameter of normal PV in unaffected parenchyma. Ten of the 30 patients underwent CT during the acute inflammatory stage and 20 during the remission stage. Of the ten patients with acute inflammation, eight (80%) showed transient periductal parenchymal enhancement during the AP (p less than 0.05), which correlated closely with acute inflammation. Only three (15%) of the 20 patients with remission, however, showed transient parenchymal enhancement during this phase, at which time ductal wall enhancement was seen in three (30%) of the ten patients with acute inflammation and in seven (35%) of the 20 who showed remission (p greater than 0.05). There was no significant difference in parenchymal and ductal wall enhancement during the PP between patients with acute inflammation and those who showed remission (p greater than 0.05). Hepatic parenchymal atrophy of the lesion was seen in 24 patients. Among these, PV stenosis was mild in five
Stochastic analysis of particle-fluid two-phase flows
无
2000-01-01
This paper is devoted to exploring approaches to understanding the stochastic characteristics of particle-fluid two-phase flow. By quantifying the forces dominating the particle motion and modelling the less important and/or unclear forces as random forces, a stochastic differential equation is proposed to describe the complex behavior of a particle motion. An exploratory simulation has shown satisfactory agreement with phase doppler particle analyzer (PDPA) measurements, which indicates that stochastic analysis is a potential approach for revealing the details of particle-fluid flow phenomena.
Experimental Two-Phase Liquid-Metal Magnetohydrodynamic Generator Program
1979-04-01
efficiencies in excess of 0.8 are attainable. Initial measurements of local flow parameters in a NaK -nitrogen two-phase liquid - metal MHD generator...hot liquid metals . Thus, the concept of using surface-active aaents in MHD generators can be evaluated more rapidly and inexpensively with NaK , the...describe this aggregation of bchbles as a foam. When the Ba- NaK solution was transferred, helium was blown under the surface of the liquid metal with the
Two-phase nozzle flow and the subcharacteristic condition
Linga, Gaute; Aursand, Peder; Flåtten, Tore
2015-01-01
We consider nozzle flow models for two-phase flow with phase transfer. Such models are based on energy considerations applied to the frozen and equilibrium limits of the underlying relaxation models. In this paper, we provide an explicit link between the mass flow rate predicted by these models a...... leakage of CO2 is presented, indicating that the frozen and equilibrium models provide significantly different predictions. This difference is comparable in magnitude to the modeling error introduced by applying simple ideal-gas/incompressible-liquid equations-of-state for CO2....
Experimental and numerical investigation on two-phase flow instabilities
Ruspini, Leonardo Carlos
2013-03-01
Two-phase flow instabilities are experimentally and numerically studied within this thesis. In particular, the phenomena called Ledinegg instability, density wave oscillations and pressure drop oscillations are investigated. The most important investigations regarding the occurrence of two-phase flow instabilities are reviewed. An extensive description of the main contributions in the experimental and analytical research is presented. In addition, a critical discussion and recommendations for future investigations are presented. A numerical framework using a hp-adaptive method is developed in order to solve the conservation equations modelling general thermo-hydraulic systems. A natural convection problem is analysed numerically in order to test the numerical solver. Moreover, the description of an adaptive strategy to solve thermo-hydraulic problems is presented. In the second part of this dissertation, a homogeneous model is used to study Ledinegg, density wave and pressure drop oscillations phenomena numerically. The dynamic characteristics of the Ledinegg (flow excursion) phenomenon are analysed through the simulation of several transient examples. In addition, density wave instabilities in boiling and condensing systems are investigated. The effects of several parameters, such as the fluid inertia and compressibility volumes, on the stability limits of Ledinegg and density wave instabilities are studied, showing a strong influence of these parameters. Moreover, the phenomenon called pressure drop oscillations is numerically investigated. A discussion of the physical representation of several models is presented with reference to the obtained numerical results. Finally, the influence of different parameters on these phenomena is analysed. In the last part, an experimental investigation of these phenomena is presented. The designing methodology used for the construction of the experimental facility is described. Several simulations and a non
Hou, Jiangyong
2016-02-05
In this paper, we present a hybrid method, which consists of a mixed-hybrid finite element method and a penalty discontinuous Galerkin method, for the approximation of a fractional flow formulation of a two-phase flow problem in heterogeneous media with discontinuous capillary pressure. The fractional flow formulation is comprised of a wetting phase pressure equation and a wetting phase saturation equation which are coupled through a total velocity and the saturation affected coefficients. For the wetting phase pressure equation, the continuous mixed-hybrid finite element method space can be utilized due to a fundamental property that the wetting phase pressure is continuous. While it can reduce the computational cost by using less degrees of freedom and avoiding the post-processing of velocity reconstruction, this method can also keep several good properties of the discontinuous Galerkin method, which are important to the fractional flow formulation, such as the local mass balance, continuous normal flux and capability of handling the discontinuous capillary pressure. For the wetting phase saturation equation, the penalty discontinuous Galerkin method is utilized due to its capability of handling the discontinuous jump of the wetting phase saturation. Furthermore, an adaptive algorithm for the hybrid method together with the centroidal Voronoi Delaunay triangulation technique is proposed. Five numerical examples are presented to illustrate the features of proposed numerical method, such as the optimal convergence order, the accurate and efficient velocity approximation, and the applicability to the simulation of water flooding in oil field and the oil-trapping or barrier effect phenomena.
Gautschi, Walter; Rassias, Themistocles M
2011-01-01
Approximation theory and numerical analysis are central to the creation of accurate computer simulations and mathematical models. Research in these areas can influence the computational techniques used in a variety of mathematical and computational sciences. This collection of contributed chapters, dedicated to renowned mathematician Gradimir V. Milovanovia, represent the recent work of experts in the fields of approximation theory and numerical analysis. These invited contributions describe new trends in these important areas of research including theoretic developments, new computational alg
Acute cholecystitis: two-phase spiral CT finding
Oh, Eung Young; Yoon, Myung Hwan; Yang, Dal Mo; Chun Seok; Bae, Jun Gi; Kim, Hak Soo; Kim, Hyung Sik [Chungang Ghil Hospital, Incheon (Korea, Republic of)
1998-07-01
To describe the two-phase spiral CT findings of acute cholecystitis. Materials and Methods : CT scans of nine patients with surgically-proven acute cholecystitis were retrospectively reviewed for wall thickening, enhancement pattern of the wall, attenuation of the liver adjacent to the gallbladder, gallstones,gallbladder distension, gas collection within the gallbladder, pericholecystic fluid and infiltration of pericholecystic fat. Results : In all cases, wall thickening of the gallbladder was seen, though this was more distinct on delayed images, Using high-low-high attenuation, one layer was seen in five cases, nd three layers in four. On arterial images, eight cases showed transient focal increased attenuation of the liver adjacent to the gall bladder;four of these showed curvilinear attenuation and four showed subsegmental attenuation. One case showed curvilinear decreased attenuation between increased attenuation of the liver and the gallbladder, and during surgery, severe adhesion between the liver and gallbladder was confirmed. Additional CT findings were infiltration of pericholecystic fat (n=9), gallstones (n=7), gallbladder distension (n=6), pericholecystic fluid(n=3), and gas collection within the gallbladder (n=2). Conclusion : In patients with acute cholecystitis,two-phase spiral CT revealed wall thickening in one or three layers ; on delayed images this was more distinct. In many cases, arterial images showed transient focal increased attenuation of the liver adjacent to the gallbladder.
Experimental study of two-phase natural circulation circuit
Lemos, Wanderley Freitas; Su, Jian, E-mail: wlemos@lasme.coppe.ufrj.br, E-mail: sujian@nuclear.ufrj.br [Coordenacao dos Programas de Pos-Graduacao em Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Faccini, Jose Luiz Horacio, E-mail: faccini@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), RIo de Janeiro, RJ (Brazil). Lab. de Termo-Hidraulica Experimental
2012-07-01
This paper reports an experimental study on the behavior of fluid flow in natural circulation under single-and two-phase flow conditions. The natural circulation circuit was designed based on concepts of similarity and scale in proportion to the actual operating conditions of a nuclear reactor. This test equipment has similar performance to the passive system for removal of residual heat presents in Advanced Pressurized Water Reactors (A PWR). The experiment was carried out by supplying water to primary and secondary circuits, as well as electrical power resistors installed inside the heater. Power controller has available to adjust the values for supply of electrical power resistors, in order to simulate conditions of decay of power from the nuclear reactor in steady state. Data acquisition system allows the measurement and control of the temperature at different points by means of thermocouples installed at several points along the circuit. The behavior of the phenomenon of natural circulation was monitored by a software with graphical interface, showing the evolution of temperature measurement points and the results stored in digital format spreadsheets. Besides, the natural circulation flow rate was measured by a flowmeter installed on the hot leg. A flow visualization technique was used the for identifying vertical flow regimes of two-phase natural circulation. Finally, the Reynolds Number was calculated for the establishment of a friction factor correlation dependent on the scale geometrical length, height and diameter of the pipe. (author)
Two-phase electrochemical lithiation in amorphous silicon.
Wang, Jiang Wei; He, Yu; Fan, Feifei; Liu, Xiao Hua; Xia, Shuman; Liu, Yang; Harris, C Thomas; Li, Hong; Huang, Jian Yu; Mao, Scott X; Zhu, Ting
2013-02-13
Lithium-ion batteries have revolutionized portable electronics and will be a key to electrifying transport vehicles and delivering renewable electricity. Amorphous silicon (a-Si) is being intensively studied as a high-capacity anode material for next-generation lithium-ion batteries. Its lithiation has been widely thought to occur through a single-phase mechanism with gentle Li profiles, thus offering a significant potential for mitigating pulverization and capacity fade. Here, we discover a surprising two-phase process of electrochemical lithiation in a-Si by using in situ transmission electron microscopy. The lithiation occurs by the movement of a sharp phase boundary between the a-Si reactant and an amorphous Li(x)Si (a-Li(x)Si, x ~ 2.5) product. Such a striking amorphous-amorphous interface exists until the remaining a-Si is consumed. Then a second step of lithiation sets in without a visible interface, resulting in the final product of a-Li(x)Si (x ~ 3.75). We show that the two-phase lithiation can be the fundamental mechanism underpinning the anomalous morphological change of microfabricated a-Si electrodes, i.e., from a disk shape to a dome shape. Our results represent a significant step toward the understanding of the electrochemically driven reaction and degradation in amorphous materials, which is critical to the development of microstructurally stable electrodes for high-performance lithium-ion batteries.
Droplets formation and merging in two-phase flow microfluidics.
Gu, Hao; Duits, Michel H G; Mugele, Frieder
2011-01-01
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Droplets Formation and Merging in Two-Phase Flow Microfluidics
Hao Gu
2011-04-01
Full Text Available Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i the emulsification step should lead to a very well controlled drop size (distribution; and (ii the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Experimental study of two phase flow in inclined channel
Park, Goon Cherl; Lee, Tae Ho; Lee, Sang Won [Seoul National University, Seoul (Korea, Republic of)
1997-07-01
Local two-phase flow parameters were measured to investigate the internal flow structures of steam-water boiling flow in an inclined channel. The vapor phase local flow parameters, such as void fraction, bubble frequency, vapor velocity, interfacial area concentration and chord length, were measured, using two conductivity probe method, and local liquid phase velocity was measured by pitot tube. In order to investigate the effects of channel inclination on two phase flow structure, the experiments were conducted for three angles of inclination; 0 degree(vertical), 30 degree and 60 degree. The experimental flow conditions were confined to the liquid superficial velocities less than 1.4 m/sec and nearly atmospheric pressure, and the flow regime was limited to the subcooled boiling. Using the measured distributions of the local phasic parameters, correlations for the drift-flux parameters such as distribution parameter and drift velocity were proposed. Those correlations were compared with the available correlation applicable to the inclined channel by the calculation of average void fraction using the present data. 44 refs., 4 tabs., 88 figs. (author)
无
2000-01-01
In the investigation of effect of KSCN on the partitioning of lysozyme in PEG2000/ammonium sulfate aqueous two-phase system, it was found that the KSCN could alter the pH difference between the two phases, and thus affect the partition of lysozyme. The relationship between partition coefficients of lysozyme and pH differences between two phases was discussed.
Thirty-two phase sequences design with good autocorrelation properties
S P Singh; K Subba Rao
2010-02-01
Polyphase Barker Sequences are ﬁnite length, uniform complex sequences; the magnitude of their aperiodic autocorrelation sidelobes are bounded by 1. Such sequences have been used in numerous real-world applications such as channel estimation, radar and spread spectrum communication. In this paper, thirty-two phase Barker sequences up to length 24 with an alphabet size of only 32 are presented. The sequences from length 25 to 289 have autocorrelation properties better than well-known Frank codes. Because of the complex structure the sequences are very difﬁcult to detect and analyse by an enemy’s electronic support measures (ESMs). The synthesized sequences are promising for practical application to radar and spread spectrum communication systems. These sequences are found using the Modiﬁed Simulated Annealing Algorithm (MSAA). The convergence rate of the algorithm is good.
Flooding in counter-current two-phase flow
Ragland, W.A.; Ganic, E.N.
1982-01-01
Flooding is a phenomenon which is best described as the transition from counter-current to co-current flow. Early notice was taken of this phenomenon in the chemical engineering industry. Flooding also plays an important role in the field of two-phase heat transfer since it is a limit for many systems involving counter-current flow. Practical applications of flooding limited processes include wickless thermosyphons and the emergency core cooling system (ECCS) of pressurized water nuclear reactors. The phenomenon of flooding also is involved in the behavior of nuclear reactor core materials during severe accident conditions where flooding is one of the mechanisms governing the motion of the molten fuel pin cladding.
Transient thermohydraulic modeling of two-phase fluid systems
Blet, N.; Delalandre, N.; Ayel, V.; Bertin, Y.; Romestant, C.; Platel, V.
2012-11-01
This paper presents a transient thermohydraulic modeling, initially developed for a capillary pumped loop in gravitational applications, but also possibly suitable for all kinds of two-phase fluid systems. Using finite volumes method, it is based on Navier-Stokes equations for transcribing fluid mechanical aspects. The main feature of this 1D-model is based on a network representation by analogy with electrical. This paper also proposes a parametric study of a counterflow condenser following the sensitivity to inlet mass flow rate and cold source temperature. The comparison between modeling results and experimental data highlights a good numerical evaluation of temperatures. Furthermore, the model is able to represent a pretty good dynamic evolution of hydraulic variables.
Stability of stratified two-phase flows in horizontal channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima; Vitoshkin, Helen
2016-01-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems the stratified flow with smooth interface is stable only in confined zone of relatively lo...
Two-phase flow instabilities in a vertical annular channel
Babelli, I.; Nair, S.; Ishii, M. [Purdue Univ., West Lafayette, IN (United States)
1995-09-01
An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.
Equations of two-phase flow in spray chamber
李新禹; 张志红; 金星; 徐杰
2009-01-01
The downstream water-air heat and moisture transfer system in a moving coordinate was studied. The relationship between the diameter of the misted droplets and the spray pressure was determined. Based on the theory of the relative velocity,the two-phase flow mode of the spray chamber and the efficiency equation for heat and moisture exchange were established. Corrections were carried out for the efficiency equation with spray pressure of 157 kPa. The results show that the pressure plays an important part in determining the efficiency of heat and moisture exchange. When the spray pressure is less than 157 kPa,better coincidence is noticed between the theoretical analysis and the test results with the error less than 6%. Greater error will be resulted in the case when the spray pressure is beyond 157 kPa. After the correction treatment,the coincidence between the theoretical and the experimental results is greatly improved.
Response of two-phase droplets to intense electromagnetic radiation
Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.
1993-01-01
The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii of 37, 55, and 80 microns) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.
Two-phase microfluidics: thermophysical fundamentals and engineering concepts
Kuznetsov, V. V.
2016-10-01
Thermophysical fundamentals and engineering concepts of the two-phase microfluidic devises based on controlled liquid decay are discussed in this paper. The results of an experimental study of the explosive evaporation at a thin film heater of the MEMS devise in application to thermal inkjet printing are presented. The peculiarities of homogeneous nucleation and bubble growth in the liquid subjected to pulse heating are discussed. Using experimental data a simple equation suitable for predicting the growth rate of a vapor bubble in a non-uniformly superheated liquid was obtained and used to complete a mathematical model of the self-consistent nucleation and vapor bubbles growth in the induced pressure field. The results of numerical calculations according to the proposed model showed good agreement with the experimental data on a time of nucleation and duration of the initial stage of an explosive evaporation of water.
Two phase coexistence for the hydrogen-helium mixture
Fantoni, Riccardo
2015-01-01
We use our newly constructed quantum Gibbs ensemble Monte Carlo algorithm to perform computer experiments for the two phase coexistence of a hydrogen-helium mixture. Our results are in quantitative agreement with the experimental results of C. M. Sneed, W. B. Streett, R. E. Sonntag, and G. J. Van Wylen. The difference between our results and the experimental ones is in all cases less than 15% relative to the experiment, reducing to less than 5% in the low helium concentration phase. At the gravitational inversion between the vapor and the liquid phase, at low temperatures and high pressures, the quantum effects become relevant. At extremely low temperature and pressure the first component to show superfluidity is the helium in the vapor phase.
Solutal Marangoni instability in layered two-phase flows
Picardo, Jason R; Pushpavanam, S
2015-01-01
In this paper, the instability of layered two-phase flows caused by the presence of a soluble surfactant (or a surface active solute) is studied. The fluids have different viscosities, but are density matched to focus on Marangoni effects. The fluids flow between two flat plates, which are maintained at different solute concentrations. This establishes a constant flux of solute from one fluid to the other in the base state. A linear stability analysis is performed, using a combination of asymptotic and numerical methods. In the creeping flow regime, Marangoni stresses destabilize the flow, provided a concentration gradient is maintained across the fluids. One long wave and two short wave Marangoni instability modes arise, in different regions of parameter space. A well-defined condition for the long wave instability is determined in terms of the viscosity and thickness ratios of the fluids, and the direction of mass transfer. Energy budget calculations show that the Marangoni stresses that drive long and shor...
Two-phase flow instability in a parallel multichannel system
HOU Suxia
2009-01-01
The two-phase flow instabilities observed in through parallel multichannel can be classified into three types, of which only one is intrinsic to parallel multichannel systems. The intrinsic instabilities observed in parallel multichannel system have been studied experimentally. The stable boundary of the flow in such a parallel-channel system are sought, and the nature of inlet flow oscillation in the unstable region has been examined experimentally under various conditions of inlet velocity, heat flux, liquid temperature, cross section of channel and entrance throttling. The results show that parallel multichannel system possess a characteristic oscillation that is quite independent of the magnitude and duration of the initial disturbance, and the stable boundary is influenced by the characteristic frequency of the system as well as by the exit quality when this is low, and upon raising the exit quality and reducing the characteristic frequency, the system increases its instability, and entrance throttling effectively contributes to stabilization of the system.
Two-phase flow simulation of aeration on stepped spillway
CHENG Xiangju; LUO Lin; ZHAO Wenqian; LI Ran
2004-01-01
Stepped spillways have existed as escape works for a very long time. It is found that water can trap a lot of air when passing through steps and then increasing oxygen content in water body, so stepped spillways can be used as a measure of re-aeration and to improve water quality of water body. However, there is no reliable theoretical method on quantitative calculation of re-aeration ability for the stepped spillways. By introducing an air-water two-phase flow model, this paper used k-ε turbulence model to calculate the characteristic variables of free-surface aeration on stepped spillway. The calculated results fit with the experimental results well. It supports that the numerical modeling method is reasonable and offers firm foundation on calculating re-aeration ability of stepped spillways. The simulation approach can provide a possible optimization tool for designing stepped spillways of more efficient aeration capability.
Note on Two-Phase Phenomena in Financial Markets
JIANG Shi-Mei; CAI Shi-Min; ZHOU Wao; ZHOU Pei-Ling
2008-01-01
The two-phase behaviour in financial markets actually means the bifurcation phenomenon, which represents the change of the conditional probability from an unimodal to a bimodal distribution. We investigate the bifurcation phenomenon in Hang-Seng index. It is observed that the bifurcation phenomenon in financial index is not universal, but specific under certain conditions. For Hang-Seng index and randomly generated time series, the phenomenon just emerges when the power-law exponent of absolute increment distribution is between i and 2 with appropriate period. Simulations on a randomly generated time series suggest the bifurcation phenomenon itself is subject to the statistics of absolute increment, thus it may not be able to reflect essential financial behaviours. However, even under the same distribution of absolute increment, the range where bifurcation phenomenon occurs is far different from real market to artificial data, which may reflect certain market information.
Tomei, M Concetta; Annesini, M Cristina; Rita, Sara; Daugulis, Andrew J
2008-10-01
The objectives of this work were to demonstrate the potential of a two-phase sequencing batch reactor in degrading xenobiotics and to evaluate the kinetic parameters leading to a mathematical model of the system. 4-Nitrophenol (4NP), a typical representative of substituted phenols, was selected as the target xenobiotic; this compound has never been remediated in a two-phase bioreactor before. Partition tests were conducted to determine the most appropriate partitioning solvent, and among the three investigated solvents (1-undecanol, 2-undecanone and oleyl alcohol), 2-undecanone was chosen because of its favourable partition coefficient and its negligible emulsion-forming tendencies. Moreover, the selected solvent showed satisfactory biocompatibility characteristics with respect to the biomass, with only minor effects on the intrinsic microbial kinetics. Kinetic tests were then performed in a sequencing batch reactor (2-l volume) operated in both conventional one- and two-phase configurations, with the two-phase system showing a significant improvement in the process kinetics in terms of reduced inhibition and increased maximum removal rate. The obtained kinetic parameters suggest that the two-phase sequencing batch system may find full-scale application, as the maximum removal rate k(max) (approximately 3 mg 4NP mgVSS(-1) day(-1)) is of the same order of magnitude of heterotrophic bacteria operating in wastewater treatment plants.
Two-phase methanization of food wastes in pilot scale.
Lee, J P; Lee, J S; Park, S C
1999-01-01
A 5 ton/d pilot scale two-phase anaerobic digester was constructed and tested to treat Korean food wastes in Anyang city near Seoul. The easily degradable presorted food waste was efficiently treated in the two-phase anaerobic digestion process. The waste contained in plastic bags was shredded and then screened for the removal of inert materials such as fabrics and plastics, and subsequently put into the two-stage reactors. Heavy and light inerts such as bones, shells, spoons, and plastic pieces were again removed by gravity differences. The residual organic component was effectively hydrolyzed and acidified in the first reactor with 5 d space time at pH of about 6.5. The second, methanization reactor converted the acids into methane with pH between 7.4 and 7.8. The space time for the second reactor was 15 d. The effluent from the second reactor was recycled to the first reactor to provide alkalinities. The process showed stable steady-state operation with the maximum organic loading rate of 7.9 kg volatile solid (VS)/m3/d and the volatile solid reduction efficiency of about 70%. The total of 3.6 tons presorted MSW containing 2.9 tons of food organic was treated to produce about 230 m3 of biogas with 70% (v/v) of methane and 80 kg of humus. This process is extended to full-scale treating 15 tons of food waste a day in Euiwang city and the produced biogas is utilized for the heating/cooling of adjacent buildings.
Supporting universal prevention programs: a two-phased coaching model.
Becker, Kimberly D; Darney, Dana; Domitrovich, Celene; Keperling, Jennifer Pitchford; Ialongo, Nicholas S
2013-06-01
Schools are adopting evidence-based programs designed to enhance students' emotional and behavioral competencies at increasing rates (Hemmeter et al. in Early Child Res Q 26:96-109, 2011). At the same time, teachers express the need for increased support surrounding implementation of these evidence-based programs (Carter and Van Norman in Early Child Educ 38:279-288, 2010). Ongoing professional development in the form of coaching may enhance teacher skills and implementation (Noell et al. in School Psychol Rev 34:87-106, 2005; Stormont et al. 2012). There exists a need for a coaching model that can be applied to a variety of teacher skill levels and one that guides coach decision-making about how best to support teachers. This article provides a detailed account of a two-phased coaching model with empirical support developed and tested with coaches and teachers in urban schools (Becker et al. 2013). In the initial universal coaching phase, all teachers receive the same coaching elements regardless of their skill level. Then, in the tailored coaching phase, coaching varies according to the strengths and needs of each teacher. Specifically, more intensive coaching strategies are used only with teachers who need additional coaching supports, whereas other teachers receive just enough support to consolidate and maintain their strong implementation. Examples of how coaches used the two-phased coaching model when working with teachers who were implementing two universal prevention programs (i.e., the PATHS curriculum and PAX Good Behavior Game [PAX GBG]) provide illustrations of the application of this model. The potential reach of this coaching model extends to other school-based programs as well as other settings in which coaches partner with interventionists to implement evidence-based programs.
Two phase continuous digestion of solid manure on-farm
Schaefer, W.; Lehto, M. [MTT Agrifood Research Finland, Vihti (Finland). Animal Production Research; Evers, L.; Granstedt, A. [Biodynamic Research Inst., Jaerna (Sweden)
2007-07-01
Present commercially available biogas plants are mainly suitable for slurry and co-substrates. Cattle, horse and poultry farms using a solid manure chain experience a crucial competitive disadvantage, because conversion to slurry technology requires additional investments. Based on the technological progress of anaerobic digestion of municipal solid waste, so called 'dry fermentation' prototype plants were developed for anaerobic digestion of organic material containing 15-50% total solids (Hoffman, 2001). These plants show added advantages compared to slurry digestion plants: Less reactor volume, less process energy, less transport capacity, less odour emissions. On-farm research (Gronauer and Aschmann, 2004; Kusch and Oechsner, 2004) and prototype research (Linke, 2004) on dry fermentation in batch reactors show that loading and discharging of batch reactors remains difficult and/or time-consuming compared to slurry reactors. Additionally a constant level of gas generation requires offset operation of several batch reactors. Baserga et al. (1994) developed a pilot plant of 9.6 m{sup 3} capacity for continuous digestion of solid beef cattle manure on-farm. However, on-farm dry fermentation plants are not common and rarely commercially available. We assume that lack of tested technical solutions and scarceness of on-farm research results are the main reason for low acceptance of dry fermentation technology on-farm. We report about an innovative two phase farm-scale biogas plant. The plant continuously digests dairy cattle manure and organic residues of the farm and the surrounding food processing units. The two phase reactor technology was chosen for two reasons: first it offers the separation of a liquid fraction and a solid fraction for composting after hydrolysis and secondly the methanation of the liquid fraction using fixed film technology results in a very short hydraulic retention time, reduction in reactor volume, and higher methane content of the
Correct numerical simulation of a two-phase coolant
Kroshilin, A. E.; Kroshilin, V. E.
2016-02-01
Different models used in calculating flows of a two-phase coolant are analyzed. A system of differential equations describing the flow is presented; the hyperbolicity and stability of stationary solutions of the system is studied. The correctness of the Cauchy problem is considered. The models' ability to describe the following flows is analyzed: stable bubble and gas-droplet flows; stable flow with a level such that the bubble and gas-droplet flows are observed under and above it, respectively; and propagation of a perturbation of the phase concentration for the bubble and gas-droplet media. The solution of the problem about the breakdown of an arbitrary discontinuity has been constructed. Characteristic times of the development of an instability at different parameters of the flow are presented. Conditions at which the instability does not make it possible to perform the calculation are determined. The Riemann invariants for the nonlinear problem under consideration have been constructed. Numerical calculations have been performed for different conditions. The influence of viscosity on the structure of the discontinuity front is studied. Advantages of divergent equations are demonstrated. It is proven that a model used in almost all known investigating thermohydraulic programs, both in Russia and abroad, has significant disadvantages; in particular, it can lead to unstable solutions, which makes it necessary to introduce smoothing mechanisms and a very small step for describing regimes with a level. This does not allow one to use efficient numerical schemes for calculating the flow of two-phase currents. A possible model free from the abovementioned disadvantages is proposed.
Modeling of fluidelastic instability in tube bundle subjected to two-phase cross-flow
Sawadogo, T.P.; Mureithi, N.W.; Azizian, R.; Pettigrew, M.J. [Ecole Polytechnique, Dept. of Mechanical Engineering, BWC/AECL/NSERC Chair of Fluid-Structure Interaction, Montreal, Quebec (Canada)
2009-07-01
Tube arrays in steam generators and heat exchangers operating in two-phase cross-flow are subjected sometimes to strong vibration due mainly to turbulence buffeting and fluidelastic forces. This can lead to tube damage by fatigue or fretting wear. A computer implementation of a fluidelastic instability model is proposed to determine with improved accuracy the fluidelastic forces and hence the critical instability flow velocity. Usually the fluidelastic instability is 'predicted', using the Connors relation with K=3. While the value of K can be determined experimentally to get an accurate prediction of the instability, the Connors relation does not allow good estimation of the fluid forces. Consequently the RMS value of the magnitude of vibration of the tube bundle, necessary to evaluate the work rate and the tube wear is only poorly estimated. The fluidelastic instability analysis presented here is based on the quasi-steady model, originally developed for single phase flow. The fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives which are determined experimentally. The forces also depend on the tube displacement and velocity. In the computer code ABAQUS, the fluid forces are provided in the user subroutines VDLOAD or VUEL. A typical simulation of the vibration of a single flexible tube within an array in two phase cross-flow is done in ABAQUS and the results are compared with the experimental measurements for a tube with similar physical properties. For a cantilever tube, in two phase cross-flow of void fraction 60%, the numerical critical flow velocity was 2.0 m/s compared to 1.8 m/s obtained experimentally. The relative error was 5% compared to 26.6% for the Connors relation with K=3. The simulation of the vibration of a typical tube in a steam generator is also presented. The numerical results show good agreement with experimental measurements. (author)
Identification of two-phase flow regimes under variable gravity conditions
Kamiel S Gabriel [University of Ontario Institute of Technology 2000 Simcoe Street North, Oshawa, ON L1H 7K4 (Canada); Huawei Han [Mechanical Engineering Department, University of Saskatchewan 57 Campus Dr., Saskatoon, Saskatchewan, S7N 5A9 (Canada)
2005-07-01
Full text of publication follows: Two-phase flow is becoming increasingly important as we move into new and more aggressive technologies in the twenty-first century. Some of its many applications include the design of efficient heat transport systems, the transfer and storage of cryogenic fluids, and condensation and flow boiling processes in heat exchangers and energy transport systems. Two-phase flow has many applications in reduced gravity environments experienced in orbiting spacecraft and earth observation satellites. Examples are heat transport systems, the transfer and storage of cryogenic fluids, and condensation and flow boiling processes in heat exchangers. A concave parallel plate capacitance sensor has been developed to measure void fraction for the purpose of objectively identifying flow regimes. The sensor has been used to collect void-fraction data at microgravity conditions aboard the NASA and ESA zero-gravity aircraft. It is shown that the flow regimes can be objectively determined from the probability density functions of the void fraction signals. It was shown that under microgravity conditions four flow regimes exist: bubbly flow, characterized by discrete gas bubbles flowing in the liquid; slug flow, consisting of Taylor bubbles separated by liquid slugs which may or may not contain several small gas bubbles; transitional flow, characterized by the liquid flowing as a film at the tube wall, and the gas phase flowing in the center with the frequent appearance of chaotic, unstable slugs; and annular flow in which the liquid flows as a film along the tube wall and the gas flows uninterrupted through the center. Since many two-phase flow models are flow regime dependent, a method that can accurately and objectively determine flow regimes is required. (authors)
Two-phase micro- and macro-time scales in particle-laden turbulent channel flows
Bing Wang; Michael Manhart
2012-01-01
The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct numerical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases,respectively.Lagrangian and Eulerian time scales of both phases are calculated using velocity correlation functions.Due to flow anisotropy,micro-time scales are not the same with the theoretical estimations in large Reynolds number (isotropic) turbulence.Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number.The fluid-phase Lagrangian integral time scales increase with distance from the wall,longer than those time scales seen by particles.The Eulerian integral macro-time scales increase in near-wall regions but decrease in out-layer regions.The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales,and in good agreement with previous measurements and numerical predictions.For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions,while away from the walls the micro Lagrangian time scales are longer.The Lagrangian integral time scales are longer than the Eulerian ones.The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.
Creep of Two-Phase Microstructures for Microelectronic Applications
Reynolds, Heidi Linch [Univ. of California, Berkeley, CA (United States)
1998-12-01
The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructure.” The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructure found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructure in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from O°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ageutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dom: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructure, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a
Cheng, Lixin; Bandarra Filho, Enio P; Thome, John R
2008-07-01
Nanofluids are a new class of fluids engineered by dispersing nanometer-size solid particles in base fluids. As a new research frontier, nanofluid two-phase flow and thermal physics have the potential to improve heat transfer and energy efficiency in thermal management systems for many applications, such as microelectronics, power electronics, transportation, nuclear engineering, heat pipes, refrigeration, air-conditioning and heat pump systems. So far, the study of nanofluid two-phase flow and thermal physics is still in its infancy. This field of research provides many opportunities to study new frontiers but also poses great challenges. To summarize the current status of research in this newly developing interdisciplinary field and to identify the future research needs as well, this paper focuses on presenting a comprehensive review of nucleate pool boiling, flow boiling, critical heat flux, condensation and two-phase flow of nanofluids. Even for the limited studies done so far, there are some controversies. Conclusions and contradictions on the available nanofluid studies on physical properties, two-phase flow, heat transfer and critical heat flux (CHF) are presented. Based on a comprehensive analysis, it has been realized that the physical properties of nanofluids such as surface tension, liquid thermal conductivity, viscosity and density have significant effects on the nanofluid two-phase flow and heat transfer characteristics but the lack of the accurate knowledge of these physical properties has greatly limited the study in this interdisciplinary field. Therefore, effort should be made to contribute to the physical property database of nanofluids as a first priority. Secondly, in particular, research on nanofluid two-phase flow and heat transfer in microchannels should be emphasized in the future.
Numerical modeling of immiscible two-phase flow in micro-models using a commercial CFD code
Crandall, Dustin; Ahmadia, Goodarz; Smith, Duane H.
2009-01-01
Off-the-shelf CFD software is being used to analyze everything from flow over airplanes to lab-on-a-chip designs. So, how accurately can two-phase immiscible flow be modeled flowing through some small-scale models of porous media? We evaluate the capability of the CFD code FLUENT{trademark} to model immiscible flow in micro-scale, bench-top stereolithography models. By comparing the flow results to experimental models we show that accurate 3D modeling is possible.
A modified Rusanov scheme for shallow water equations with topography and two phase flows
Mohamed, Kamel; Benkhaldoun, F.
2016-06-01
In this work, we introduce a finite volume method for numerical simulation of shallow water equations with source terms in one and two space dimensions, and one-pressure model of two-phase flows in one space dimension. The proposed method is composed of two steps. The first, called predictor step, depends on a local parameter allowing to control the numerical diffusion. A strategy based on limiters theory enables to control this parameter. The second step recovers the conservation equation. The scheme can thus be turned to order 1 in the regions where the flow has a strong variation, and order 2 in the regions where the flow is regular. The numerical scheme is applied to several test cases in one and two space dimensions. This scheme demonstrates its well-balanced property, and that it is an efficient and accurate approach for solving shallow water equations with and without source terms, and water faucet problem.
Mathematical modeling of a gas jet impinging on a two phase bath
Delgado-Álvárez, J.; Ramírez-Argáez, Marco A.; González-Rivera, C.
2012-09-01
In this work a three phase 3D mathematical model was developed using the Volume Of Fluid (VOF) algorithm, which is able to accurately describe the cavity geometry and size as well as the liquid flow patterns created when a gas jet impinges on a two phase liquid free surface. These phenomena are commonly found in steelmaking operations such as in the Electric Arc Furnace (EAF) and the Basic Oxygen Furnace (BOF) where oxygen jets impinge on a steel bath and they control heat, momentum and mass transfer. The cavity formed in the liquids by the impinging jet depends on a force balance at the free surface where the inertial force of the jet governs these phenomena. The inertial force of the jet and its angle play important roles, being the lowest angle the best choice to shear the bath and promote stronger circulation and better mixing in the liquids.
Simulation of heterogeneous two-phase media using random fields and level sets
George STEFANOU[1,2
2015-01-01
The accurate and efficient simulation of random heterogeneous media is important in the framework of modeling and design of complex materials across multiple length scales. It is usually assumed that the morphology of a random microstructure can be described as a non-Gaussian random field that is completely defined by its multivariate distribution. A particular kind of non-Gaussian random fields with great practical importance is that of translation fields resulting from a simple memory-less transformation of an underlying Gaussian field with known second-order statistics. This paper provides a critical examination of existing random field models of heterogeneous two-phase media with emphasis on level-cut random fields which are a special case of translation fields. The case of random level sets, often used to represent the geometry of physical systems, is also examined. Two numerical examples are provided to illustrate the basic features of the different approaches.
Microporous silica gels from alkylsilicate-water two phase hydrolysis
Chu, L.; Tejedor-Tejedor, M.I.; Anderson, M.A. [Univ. of Wisconsin, Madison, WI (United States). Water Chemistry Program
1994-12-31
Microporous silica gels have been synthesized through a nano-particulate sol-gel route. These gels have uniformly distributed and extremely small pores(< 15 {angstrom} in diameter). Hydrolysis and condensation reactions leading to these gels were carried out in an alkyl silicate-water (ammonia) two phase system. These reactions took place at the alkyl silicate droplet-water interfacial boundary. No alcohol was added. A clear, stable and uniformly distributed colloidal silica suspension having an average particle size less than 6 nm was prepared by this method. Fast hydrolysis, slow condensation and low solubility all contribute to a high supersaturation level and result in the formation of small particles. This process is consistent with classic nucleation theory. When the particles are produced under acidic rather than under basic reaction conditions, smaller particles are formed due to the slower condensation rate and lower solubility of these silica particles in acidic conditions. At the same pH, alkylsilicates having smaller alkyl groups react faster with water leading to smaller primary particles. Homogeneous nucleation conditions are achieved when the water/alkylsilicate ratio is high.
Stability of stratified two-phase flows in horizontal channels
Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.
2016-04-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.
Aqueous Nanofluid as a Two-Phase Coolant for PWR
Pavel N. Alekseev
2012-01-01
Full Text Available Density fluctuations in liquid water consist of two topological kinds of instant molecular clusters. The dense ones have helical hydrogen bonds and the nondense ones are tetrahedral clusters with ice-like hydrogen bonds of water molecules. Helical ordering of protons in the dense water clusters can participate in coherent vibrations. The ramified interface of such incompatible structural elements induces clustering impurities in any aqueous solution. These additives can enhance a heat transfer of water as a two-phase coolant for PWR due to natural forming of nanoparticles with a thermal conductivity higher than water. The aqueous nanofluid as a new condensed matter has a great potential for cooling applications. It is a mixture of liquid water and dispersed phase of extremely fine quasi-solid particles usually less than 50 nm in size with the high thermal conductivity. An alternative approach is the formation of gaseous (oxygen or hydrogen nanoparticles in density fluctuations of water. It is possible to obtain stable nanobubbles that can considerably exceed the molecular solubility of oxygen (hydrogen in water. Such a nanofluid can convert the liquid water in the nonstoichiometric state and change its reduction-oxidation (RedOx potential similarly to adding oxidants (or antioxidants for applying 2D water chemistry to aqueous coolant.
Two-Phase Flow Hydrodynamics in Superhydrophobic Channels
Stevens, Kimberly; Crockett, Julie; Maynes, Daniel; Iverson, Brian
2015-11-01
Superhydrophobic surfaces promote drop-wise condensation and droplet removal leading to the potential for increased thermal transport. Accordingly, great interest exists in using superhydrophobic surfaces in flow condensing environments, such as power generation and desalination. Adiabatic air-water mixtures were used to gain insight into the effect of hydrophobicity on two-phase flows and the hydrodynamics present in flow condensation. Pressure drop and onset of various flow regimes in hydrophilic, hydrophobic, and superhydrophobic mini (0.5 x 10 mm) channels were explored. Data for air/water mixtures with superficial Reynolds numbers from 20-200 and 250-1800, respectively, were obtained. Agreement between experimentally obtained pressure drops and correlations in literature for the conventional smooth control surfaces was better than 20 percent. Transitions between flow regimes for the hydrophobic and hydrophilic channels were similar to commonly recognized flow types. However, the superhydrophobic channel demonstrated significantly different flow regime behavior from conventional surfaces including a different shape of the air slugs, as discussed in the presentation.
An automated two-phase system for hydrogel microbead production.
Coutinho, Daniela F; Ahari, Amir F; Kachouie, Nezamoddin N; Gomes, Manuela E; Neves, Nuno M; Reis, Rui L; Khademhosseini, Ali
2012-09-01
Polymeric beads have been used for protection and delivery of bioactive materials, such as drugs and cells, for different biomedical applications. Here, we present a generic two-phase system for the production of polymeric microbeads of gellan gum or alginate, based on a combination of in situ polymerization and phase separation. Polymer droplets, dispensed using a syringe pump, formed polymeric microbeads while passing through a hydrophobic phase. These were then crosslinked, and thus stabilized, in a hydrophilic phase as they crossed through the hydrophobic-hydrophilic interface. The system can be adapted to different applications by replacing the bioactive material and the hydrophobic and/or the hydrophilic phases. The size of the microbeads was dependent on the system parameters, such as needle size and solution flow rate. The size and morphology of the microbeads produced by the proposed system were uniform, when parameters were kept constant. This system was successfully used for generating polymeric microbeads with encapsulated fluorescent beads, cell suspensions and cell aggregates proving its ability for generating bioactive carriers that can potentially be used for drug delivery and cell therapy.
Unsteady flow analysis of a two-phase hydraulic coupling
Hur, N.; Kwak, M.; Lee, W. J.; Moshfeghi, M.; Chang, C.-S.; Kang, N.-W.
2016-06-01
Hydraulic couplings are being widely used for torque transmitting between separate shafts. A mechanism for controlling the transmitted torque of a hydraulic system is to change the amount of working fluid inside the system. This paper numerically investigates three-dimensional turbulent flow in a real hydraulic coupling with different ratios of charged working fluid. Working fluid is assumed to be water and the Realizable k-ɛ turbulence model together with the VOF method are used to investigate two-phase flow inside the wheels. Unsteady simulations are conducted using the sliding mesh technique. The primary wheel is rotating at a fixed speed of 1780 rpm and the secondary wheel rotates at different speeds for simulating different speed ratios. Results are investigated for different blade angles, speed ratios and also different water volume fractions, and are presented in the form of flow patterns, fluid average velocity and also torques values. According to the results, blade angle severely affects the velocity vector and the transmitted torque. Also in the partially-filled cases, air is accumulated in the center of the wheel forming a toroidal shape wrapped by water and the transmitted torque sensitively depends on the water volume fraction. In addition, in the fully-filled case the transmitted torque decreases as the speed ration increases and the average velocity associated with lower speed ratios are higher.
Particle migration in two-phase, viscoelastic flows
Jaensson, Nick; Hulsen, Martien; Anderson, Patrick
2014-11-01
Particles suspended in creeping, viscoelastic flows can migrate across stream lines due to gradients in normal stresses. This phenomenon has been investigated both numerically and experimentally. However, particle migration in the presence of fluid-fluid interfaces is hardly studied. We present results of simulations in 2D and 3D of rigid spherical particles in two-phase flows, where either one or both of the fluids are viscoelastic. The fluid-fluid interface is assumed to be diffuse and is described using Cahn-Hilliard theory. The particle boundary is assumed to be sharp and is described by a boundary-fitted, moving mesh. The governing equations are solved using the finite element method. We show that differences in normal stresses between the two fluids can induce a migration of the particle towards the interface in a shear flow. Depending on the magnitude of the surface tension and the properties of the fluids, particle migration can be halted due to the induced Laplace pressure, the particle can be adsorbed at the interface, or the particle can cross the interface into the other fluid. Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
Pressure transient analysis of two-phase flow problems
Chu, W.C.; Reynolds, A.C.; Raghavan, R.
1986-04-01
This paper considers the analysis of pressure drawdown and buildup data for two-phase flow problems. Of primary concern is the analysis of data influenced by saturation gradients that exist within the reservoir. Wellbore storage effects are assumed to be negligible. The pressure data considered are obtained from a two-dimensional (2D) numerical coning model for an oil/water system. The authors consider constant-rate production followed by a buildup period and assume that the top, bottom, and outer boundaries of the reservoir are sealed. First, they consider the case where the producing interval is equal to the total formation thickness. Second, they discuss the effect of partial penetration. In both cases, they show that average pressure can be estimated by the Matthews-Brons-Hazebroek method and consider the computation of the skin factor. They also show that a reservoir limit test can estimate reservoir PV only if the total mobility adjacent to the wellbore does not vary with time.
Thermal performance of closed two-phase thermosyphon using nanofluids
Khandekar, Sameer; Mehta, Balkrishna [Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Joshi, Yogesh M. [Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016 (India)
2008-06-15
Nanofluids, stabilized suspensions of nanoparticles typically <100 nm in conventional fluids, are evolving as potential enhanced heat transfer fluids due to their improved thermal conductivity, increase in single phase heat transfer coefficient and significant increase in critical boiling heat flux. In the present paper, we investigate the overall thermal resistance of closed two-phase thermosyphon using pure water and various water based nanofluids (of Al{sub 2}O{sub 3}, CuO and laponite clay) as working fluids. We observe that all these nanofluids show inferior thermal performance than pure water. Furthermore, we observe that the wettability of all nanofluids on copper substrate, having the same average roughness as that of the thermosyphon container pipe, is better than that of pure water. A scaling analysis is presented which shows that the increase in wettability and entrapment of nanoparticles in the grooves of the surface roughness cause decrease in evaporator side Peclet number that finally leads to poor thermal performance. (author)
Diagnosing Traffic Anomalies Using a Two-Phase Model
Bin Zhang; Jia-Hai Yang; Jian-Ping Wu; Ying-Wu Zhu
2012-01-01
Network traffic anomalies are unusual changes in a network,so diagnosing anomalies is important for network management.Feature-based anomaly detection models (ab)normal network traffic behavior by analyzing packet header features. PCA-subspace method (Principal Component Analysis) has been verified as an efficient feature-based way in network-wide anomaly detection.Despite the powerful ability of PCA-subspace method for network-wide traffic detection,it cannot be effectively used for detection on a single link.In this paper,different from most works focusing on detection on flow-level traffic,based on observations of six traffc features for packet-level traffic,we propose a new approach B6SVM to detect anomalies for packet-level traffic on a single link.The basic idea of B6-SVM is to diagnose anomalies in a multi-dimensional view of traffic features using Support Vector Machine (SVM).Through two-phase classification,B6-SVM can detect anomalies with high detection rate and low false alarm rate.The test results demonstrate the effectiveness and potential of our technique in diagnosing anomalies.Further,compared to previous feature-based anomaly detection approaches,B6-SVM provides a framework to automatically identify possible anomalous types.The framework of B6-SVM is generic and therefore,we expect the derived insights will be helpful for similar future research efforts.
Passive Two-Phase Cooling of Automotive Power Electronics: Preprint
Moreno, G.; Jeffers, J. R.; Narumanchi, S.; Bennion, K.
2014-08-01
Experiments were conducted to evaluate the use of a passive two-phase cooling strategy as a means of cooling automotive power electronics. The proposed cooling approach utilizes an indirect cooling configuration to alleviate some reliability concerns and to allow the use of conventional power modules. An inverter-scale proof-of-concept cooling system was fabricated, and tests were conducted using the refrigerants hydrofluoroolefin HFO-1234yf and hydrofluorocarbon HFC-245fa. Results demonstrated that the system can dissipate at least 3.5 kW of heat with 250 cm3 of HFC-245fa. An advanced evaporator design that incorporates features to improve performance and reduce size was conceived. Simulation results indicate its thermal resistance can be 37% to 48% lower than automotive dual side cooled power modules. Tests were also conducted to measure the thermal performance of two air-cooled condensers--plain and rifled finned tube designs. The results combined with some analysis were then used to estimate the required condenser size per operating conditions and maximum allowable system (i.e., vapor and liquid) temperatures.
Two Phase Compressible Flow Fields in One Dimensional and Eulerian Grid Framework
Lee, Sungsu; Park, Chan Wook
2008-11-01
Numerical investigation for two phase compressible flow fields of air-water in one dimensional tube are performed in the fixed Eulerian grid framework. Using an equation of states of Tait's type for a multiphase cell, the two phase compressible flow is modeled as equivalent single phase which is discretized using the Roe`s approximate Riemann solver, while the phase interface is captured via volume fractions of each phase. The most common problem found in the computational approaches in compressible multiphase flow is occurrence of the pressure oscillation at the phase interface. In order to suppress that phenomenon, tried are two approaches; a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The results show that the direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. This work was supported by a research fund granted from Agency for Defense Development, South Korea
Optical Readout of a Two Phase Liquid Argon TPC using CCD Camera and TGEMs
Mavrokoridis, K; Carroll, J; Lazos, M; McCormick, K J; Smith, N A; Touramanis, C; Walker, J
2014-01-01
This paper presents a preliminary study into the use of CCDs to image secondary scintillation light generated by Thick Gas Electron Multipliers (TGEMs) in a two phase LAr TPC. A Sony ICX285AL CCD chip was mounted above a double TGEM in the gas phase of a 40 litre two-phase LAr TPC with the majority of the camera electronics positioned externally via a feedthrough. An Am-241 source was mounted on a rotatable motion feedthrough allowing the positioning of the alpha source either inside or outside of the field cage. Developed for and incorporated into the TPC design was a novel high voltage feedthrough featuring LAr insulation. Furthermore, a range of webcams were tested for operation in cryogenics as an internal detector monitoring tool. Of the range of webcams tested the Microsoft HD-3000 (model no:1456) webcam was found to be superior in terms of noise and lowest operating temperature. In ambient temperature and atmospheric pressure 1 ppm pure argon gas, the TGEM gain was approximately 1000 and using a 1 msec...
A Hydrodynamic Model for Slug Frequency in Horizontal Gas-Liquid Two-Phase Flow
刘磊; 孙贺东; 胡志华; 周芳德
2003-01-01
The prediction of slug frequency has important significance on gas-liquid two-phase flow. A hydrodynamic model was put forward to evaluate slug frequency for horizontal two-phase flow, based on the dependence of slug frequency on the frequency of unstable interfacial wave. Using air and water, experimental verification of the model was carried out in a large range of flow parameters. Six electrical probes were installed at different positions of a horizontal plexiglass pipe to detect slug frequency development. The pipe is 30 m long and its inner diameter is 24 ram. It is observed experimentally that the interracial wave frequency at the inlet is about i to 3 times the frequency of stable slug. The slug frequencies predicted by the model fit well with Tronconi (1990) model and the experimental data. The combination of the hydrodynamic model and the experimental data results in a conclusion that the frequency of equilibrium liquid slug is approximately half the minimum frequency of interfacial wave.
Approximate Representations and Approximate Homomorphisms
Moore, Cristopher
2010-01-01
Approximate algebraic structures play a defining role in arithmetic combinatorics and have found remarkable applications to basic questions in number theory and pseudorandomness. Here we study approximate representations of finite groups: functions f:G -> U_d such that Pr[f(xy) = f(x) f(y)] is large, or more generally Exp_{x,y} ||f(xy) - f(x)f(y)||^2$ is small, where x and y are uniformly random elements of the group G and U_d denotes the unitary group of degree d. We bound these quantities in terms of the ratio d / d_min where d_min is the dimension of the smallest nontrivial representation of G. As an application, we bound the extent to which a function f : G -> H can be an approximate homomorphism where H is another finite group. We show that if H's representations are significantly smaller than G's, no such f can be much more homomorphic than a random function. We interpret these results as showing that if G is quasirandom, that is, if d_min is large, then G cannot be embedded in a small number of dimensi...
Chalons, Christophe; Girardin, Mathieu; Kokh, Samuel
2017-04-01
We propose an all regime Lagrange-Projection like numerical scheme for 2D homogeneous models for two-phase flows. By all regime, we mean that the numerical scheme is able to compute accurate approximate solutions with an under-resolved discretization, i.e. a mesh size and time step much bigger than the Mach number M of the mixture. The key idea is to decouple acoustic, transport and phase transition phenomenon using a Lagrange-Projection decomposition in order to treat implicitly (fast) acoustic and phase transition phenomenon and explicitly the (slow) transport phenomena. Then, extending a strategy developed in the case of the usual gas dynamics equations, we alter the numerical flux in the acoustic approximation to obtain a uniform truncation error in terms of M. This modified scheme is conservative and endowed with good stability properties with respect to the positivity of the density and preserving the mass fraction within the interval (0 , 1). Numerical evidences are proposed and show the ability of the scheme to deal with cases where the flow regime may vary from low to high Mach values.
STUDIES OF TWO-PHASE PLUMES IN STRATIFIED ENVIRONMENTS
Scott A. Socolofsky; Brian C. Crounse; E. Eric Adams
1998-11-18
Two-phase plumes play an important role in the more practical scenarios for ocean sequestration of CO{sub 2}--i.e. dispersing CO{sub 2} as a buoyant liquid from either a bottom-mounted or ship-towed pipeline. Despite much research on related applications, such as for reservoir destratification using bubble plumes, our understanding of these flows is incomplete, especially concerning the phenomenon of plume peeling in a stratified ambient. To address this deficiency, we have built a laboratory facility in which we can make fundamental measurements of plume behavior. Although we are using air, oil and sediments as our sources of buoyancy (rather than CO{sub 2}), by using models, our results can be directly applied to field scale CO{sub 2} releases to help us design better CO{sub 2} injection systems, as well as plan and interpret the results of our up-coming international field experiment. The experimental facility designed to study two-phase plume behavior similar to that of an ocean CO{sub 2} release includes the following components: 1.22 x 1.22 x 2.44 m tall glass walled tank; Tanks and piping for the two-tank stratification method for producing step- and linearly-stratified ambient conditions; Density profiling system using a conductivity and temperature probe mounted to an automated depth profiler; Lighting systems, including a virtual point source light for shadowgraphs and a 6 W argon-ion laser for laser induced fluorescence (LIF) imaging; Imaging system, including a digital, progressive scanning CCD camera, computerized framegrabber, and image acquisition and analysis software; Buoyancy source diffusers having four different air diffusers, two oil diffusers, and a planned sediment diffuser; Dye injection method using a Mariotte bottle and a collar diffuser; and Systems integration software using the Labview graphical programming language and Windows NT. In comparison with previously reported experiments, this system allows us to extend the parameter range of
Numerical methods for two-phase flow with contact lines
Walker, Clauido
2012-07-01
This thesis focuses on numerical methods for two-phase flows, and especially flows with a moving contact line. Moving contact lines occur where the interface between two fluids is in contact with a solid wall. At the location where both fluids and the wall meet, the common continuum descriptions for fluids are not longer valid, since the dynamics around such a contact line are governed by interactions at the molecular level. Therefore the standard numerical continuum models have to be adjusted to handle moving contact lines. In the main part of the thesis a method to manipulate the position and the velocity of a contact line in a two-phase solver, is described. The Navier-Stokes equations are discretized using an explicit finite difference method on a staggered grid. The position of the interface is tracked with the level set method and the discontinuities at the interface are treated in a sharp manner with the ghost fluid method. The contact line is tracked explicitly and its dynamics can be described by an arbitrary function. The key part of the procedure is to enforce a coupling between the contact line and the Navier-Stokes equations as well as the level set method. Results for different contact line models are presented and it is demonstrated that they are in agreement with analytical solutions or results reported in the literature.The presented Navier-Stokes solver is applied as a part in a multiscale method to simulate capillary driven flows. A relation between the contact angle and the contact line velocity is computed by a phase field model resolving the micro scale dynamics in the region around the contact line. The relation of the microscale model is then used to prescribe the dynamics of the contact line in the macro scale solver. This approach allows to exploit the scale separation between the contact line dynamics and the bulk flow. Therefore coarser meshes can be applied for the macro scale flow solver compared to global phase field simulations
Two Phase Flow Mapping and Transition Under Microgravity Conditions
Parang, Masood; Chao, David F.
1998-01-01
In this paper, recent microgravity two-phase flow data for air-water, air-water-glycerin, and air- water-Zonyl FSP mixtures are analyzed for transition from bubbly to slug and from slug to annular flow. It is found that Weber number-based maps are inadequate to predict flow-pattern transition, especially over a wide range of liquid flow rates. It is further shown that slug to annular flow transition is dependent on liquid phase Reynolds number at high liquid flow rate. This effect may be attributed to growing importance of liquid phase inertia in the dynamics of the phase flow and distribution. As a result a new form of scaling is introduced to present data using liquid Weber number based on vapor and liquid superficial velocities and Reynolds number based on liquid superficial velocity. This new combination of the dimensionless parameters seem to be more appropriate for the presentation of the microgravity data and provides a better flow pattern prediction and should be considered for evaluation with data obtained in the future. Similarly, the analysis of bubble to slug flow transition indicates a strong dependence on both liquid inertia and turbulence fluctuations which seem to play a significant role on this transition at high values of liquid velocity. A revised mapping of data using a new group of dimensionless parameters show a better and more consistent description of flow transition over a wide range of liquid flow rates. Further evaluation of the proposed flow transition mapping will have to be made after a wider range of microgravity data become available.
Analysis of Fractional Flow for Transient Two-Phase Flow in Fractal Porous Medium
Lu, Ting; Duan, Yonggang; Fang, Quantang; Dai, Xiaolu; Wu, Jinsui
2016-03-01
Prediction of fractional flow in fractal porous medium is important for reservoir engineering and chemical engineering as well as hydrology. A physical conceptual fractional flow model of transient two-phase flow is developed in fractal porous medium based on the fractal characteristics of pore-size distribution and on the approximation that porous medium consist of a bundle of tortuous capillaries. The analytical expression for fractional flow for wetting phase is presented, and the proposed expression is the function of structural parameters (such as tortuosity fractal dimension, pore fractal dimension, maximum and minimum diameters of capillaries) and fluid properties (such as contact angle, viscosity and interfacial tension) in fractal porous medium. The sensitive parameters that influence fractional flow and its derivative are formulated, and their impacts on fractional flow are discussed.
THE NONLINEAR BEHAVIOR OF INTERFACE BETWEEN TWO-PHASE SHEAR FLOW WITH LARGE DENSITY RATIOS
DONG Yu-hong
2006-01-01
The Navier-Stokes equations for the two-dimensional incompressible flow are used to investigate the effects of the Reynolds number and the Weber number on the behavior of interface between liquid-gas shear flow.In the present study, the density ratios are fixed at approximately 100-103.The interface between the two phases is resolved using the level-set approach.The Reynolds number and the Weber number, based on the gas, are selected as 400-10000 and 40-5000, respectively.In the past, simulations reappeared the amplitude of interface growth predicted by viscous Orr-Sommerfeld linear theory, verifying the applicability and accuracy of the numerical method over a wide range of density and viscosity ratios; now, the simulations show that the nonlinear development of ligament elongated structures and resulted in the subsequent breakup of the heavier fluid into drops.
EFFECTS OF PHASE CONTINUITY ON RHEOLOGY OF TWO-PHASE ROCKS:A CONTINUUM MECHANICL MODEL
JI Shao-cheng
2001-01-01
Based on continuum mechanics,we have developed a model for semi-quantitative estimating effects of phase continuity on flow strength of two-phase rocks including partially melted or crystallized rocks.Calculations of the bulk flow strength of composite rocks as functions of the volume fraction,geometrical shape and continuity of the constitutive phases involve in numerically solving two non-linear equations and thus are easy to be performed.The model has been justified by a good agreement between the predicted and measured results on diabase (64% clinopyroxene and 36% plagioclase) in the range of experimental temperatures and strain-rates.It is believed that the present model could provide an approximate estimate for the rheological evolution of magmatic rocks during their life cycle of melting-crystallization-deformation.
CERN. Geneva
2015-01-01
Most physics results at the LHC end in a likelihood ratio test. This includes discovery and exclusion for searches as well as mass, cross-section, and coupling measurements. The use of Machine Learning (multivariate) algorithms in HEP is mainly restricted to searches, which can be reduced to classification between two fixed distributions: signal vs. background. I will show how we can extend the use of ML classifiers to distributions parameterized by physical quantities like masses and couplings as well as nuisance parameters associated to systematic uncertainties. This allows for one to approximate the likelihood ratio while still using a high dimensional feature vector for the data. Both the MEM and ABC approaches mentioned above aim to provide inference on model parameters (like cross-sections, masses, couplings, etc.). ABC is fundamentally tied Bayesian inference and focuses on the “likelihood free” setting where only a simulator is available and one cannot directly compute the likelihood for the dat...
Two-Phase Algorithm for Optimal Camera Placement
Jun-Woo Ahn; Tai-Woo Chang; Sung-Hee Lee; Yong Won Seo
2016-01-01
As markers for visual sensor networks have become larger, interest in the optimal camera placement problem has continued to increase. The most featured solution for the optimal camera placement problem is based on binary integer programming (BIP). Due to the NP-hard characteristic of the optimal camera placement problem, however, it is difficult to find a solution for a complex, real-world problem using BIP. Many approximation algorithms have been developed to solve this problem. In this pape...
Two-phase analysis in consensus genetic mapping.
Ronin, Y; Mester, D; Minkov, D; Belotserkovski, R; Jackson, B N; Schnable, P S; Aluru, S; Korol, A
2012-05-01
Numerous mapping projects conducted on different species have generated an abundance of mapping data. Consequently, many multilocus maps have been constructed using diverse mapping populations and marker sets for the same organism. The quality of maps varies broadly among populations, marker sets, and software used, necessitating efforts to integrate the mapping information and generate consensus maps. The problem of consensus genetic mapping (MCGM) is by far more challenging compared with genetic mapping based on a single dataset, which by itself is also cumbersome. The additional complications introduced by consensus analysis include inter-population differences in recombination rate and exchange distribution along chromosomes; variations in dominance of the employed markers; and use of different subsets of markers in different labs. Hence, it is necessary to handle arbitrary patterns of shared sets of markers and different level of mapping data quality. In this article, we introduce a two-phase approach for solving MCGM. In phase 1, for each dataset, multilocus ordering is performed combined with iterative jackknife resampling to evaluate the stability of marker orders. In this phase, the ordering problem is reduced to the well-known traveling salesperson problem (TSP). Namely, for each dataset, we look for order that gives minimum sum of recombination distances between adjacent markers. In phase 2, the optimal consensus order of shared markers is selected from the set of allowed orders and gives the minimal sum of total lengths of nonconflicting maps of the chromosome. This criterion may be used in different modifications to take into account the variation in quality of the original data (population size, marker quality, etc.). In the foregoing formulation, consensus mapping is considered as a specific version of TSP that can be referred to as "synchronized TSP." The conflicts detected after phase 1 are resolved using either a heuristic algorithm over the
48 CFR 36.301 - Use of two-phase design-build selection procedures.
2010-10-01
... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Use of two-phase design... ACQUISITION REGULATION SPECIAL CATEGORIES OF CONTRACTING CONSTRUCTION AND ARCHITECT-ENGINEER CONTRACTS Two-Phase Design-Build Selection Procedures 36.301 Use of two-phase design-build selection procedures....
48 CFR 570.105-2 - Two-phase design-build selection procedures.
2010-10-01
... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false Two-phase design-build..., you must use the two-phase design-build selection procedures in section 303M of the Federal Property... use of the two-phase selection procedures. (v) The capability of the agency to manage the...
24 CFR 115.201 - The two phases of substantial equivalency certification.
2010-04-01
... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false The two phases of substantial... ENFORCEMENT AGENCIES Certification of Substantially Equivalent Agencies § 115.201 The two phases of.... The Department has developed a two-phase process of substantial equivalency certification....
Prestack wavefield approximations
Alkhalifah, Tariq
2013-09-01
The double-square-root (DSR) relation offers a platform to perform prestack imaging using an extended single wavefield that honors the geometrical configuration between sources, receivers, and the image point, or in other words, prestack wavefields. Extrapolating such wavefields, nevertheless, suffers from limitations. Chief among them is the singularity associated with horizontally propagating waves. I have devised highly accurate approximations free of such singularities which are highly accurate. Specifically, I use Padé expansions with denominators given by a power series that is an order lower than that of the numerator, and thus, introduce a free variable to balance the series order and normalize the singularity. For the higher-order Padé approximation, the errors are negligible. Additional simplifications, like recasting the DSR formula as a function of scattering angle, allow for a singularity free form that is useful for constant-angle-gather imaging. A dynamic form of this DSR formula can be supported by kinematic evaluations of the scattering angle to provide efficient prestack wavefield construction. Applying a similar approximation to the dip angle yields an efficient 1D wave equation with the scattering and dip angles extracted from, for example, DSR ray tracing. Application to the complex Marmousi data set demonstrates that these approximations, although they may provide less than optimal results, allow for efficient and flexible implementations. © 2013 Society of Exploration Geophysicists.
Experimental Investigation of Two-Phase Flow in Rock Salt
Malama, Bwalya; Howard, Clifford L.
2014-07-01
This Test Plan describes procedures for conducting laboratory scale flow tests on intact, damaged, crushed, and consolidated crushed salt to measure the capillary pressure and relative permeability functions. The primary focus of the tests will be on samples of bedded geologic salt from the WIPP underground. However, the tests described herein are directly applicable to domal salt. Samples being tested will be confined by a range of triaxial stress states ranging from atmospheric pressure up to those approximating lithostatic. Initially these tests will be conducted at room temperature, but testing procedures and equipment will be evaluated to determine adaptability to conducting similar tests under elevated temperatures.
Experimental investigation of two-phase flow in rock salt
Malama, Bwalya [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Howard, Clifford L. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2014-07-01
This Test Plan describes procedures for conducting laboratory scale flow tests on intact, damaged, crushed, and consolidated crushed salt to measure the capillary pressure and relative permeability functions. The primary focus of the tests will be on samples of bedded geologic salt from the WIPP underground. However, the tests described herein are directly applicable to domal salt. Samples being tested will be confined by a range of triaxial stress states ranging from atmospheric pressure up to those approximating lithostatic. Initially these tests will be conducted at room temperature, but testing procedures and equipment will be evaluated to determine adaptability to conducting similar tests under elevated temperatures.
Bubble Dynamics in a Two-Phase Medium
Jayaprakash, Arvind; Chahine, Georges
2010-01-01
The spherical dynamics of a bubble in a compressible liquid has been studied extensively since the early work of Gilmore. Numerical codes to study the behavior, including when large non-spherical deformations are involved, have since been developed and have been shown to be accurate. The situation is however different and common knowledge less advanced when the compressibility of the medium surrounding the bubble is provided mainly by the presence of a bubbly mixture. In one of the present works being carried out at DYNAFLOW, INC., the dynamics of a primary relatively large bubble in a water mixture including very fine bubbles is being investigated experimentally and the results are being provided to several parallel on-going analytical and numerical approaches. The main/primary bubble is produced by an underwater spark discharge from two concentric electrodes placed in the bubbly medium, which is generated using electrolysis. A grid of thin perpendicular wires is used to generate bubble distributions of vary...
Effect of large-scale parameters for two-phase flow in heterogeneous porous media
Girgrah, B.
1994-01-01
Important problems in environmental protection and resource management require quantification of parameters at field (large) scale. A numerical model is utilized to construct large-scale capillary pressure (CP) and relative permeability (RP) curves for two-phase flow in heterogeneous porous media. Two-phase flow simulations were performed over a two-dimensional, numerically generated, heterogeneous permeability field. CP and RP curves were constructed for each simulation. The fields ranged in size from 1.25x1.25 m to 5x10 m and had a mean overall log-hydraulic conductivity of [minus]4.6. Flow was vertically downward with the left and right boundaries of the domain remaining impermeable. Following the simulations on heterogeneous fields, homogeneous equivalents were determined and run for sample simulations. The heterogeneous simulations included investigations into the representative elementary volume (REV) for two permeability fields, the effects of fluid properties on CP and RP, and the effects of correlation structure. The equivalent homogeneous simulations explored the feasibility of homogeneous solutions to predict heterogeneous behavior. Results showed that the REVs for fields one and two were a domain size of 50x50 nodes. Fluid property investigations showed that CP decreased when interfacial tension decreased. Structural explorations showed vertical bedding caused an increase in both CP and RP results. A decrease in log-hydraulic conductivity variance caused slight increases in RP and CP. No direct correlation was obtained between homogeneous and heterogeneous flow behavior. A modification could be made to the homogeneous model to allow it to accurately predict heterogeneous flow. 49 refs., 28 figs., 10 tabs.
Accurately approximating algebraic tomographic reconstruction by filtered backprojection
Pelt, D.M.; Batenburg, K.J.; King, M.; Glick, S.; Mueller, K.
2015-01-01
In computed tomography, algebraic reconstruction methods tend to produce reconstructions with higher quality than analytical methods when presented with limited and noisy projection data. The high computational requirements of algebraic methods, however, limit their usefulness in
On the Two-Phase Structure of Protogalactic Clouds
Lin, D N C
2000-01-01
Within protogalaxies, thermal instability leads to the formation of a population of cool fragments, confined by the pressure of residual hot gas. The hot gas remains in quasi-hydrostatic equilibrium, at approximately the virial temperature of the dark matter halo. It is heated by compression and shock dissipation and is cooled by bremsstrahlung emission and conductive losses into the cool clouds. The cool fragments are photoionized and heated by the extragalactic UV background and nearby massive stars. The smallest clouds are evaporated due to conductive heat transfer from the hot gas. All are subject to disruption due to hydrodynamic instabilities. They also gain mass due to collisions and mergers and condensation from the hot gas due to conduction. The size distribution of the fragments in turn determines the rate and efficiency of star formation during the early phase of galactic evolution. We have performed one-dimensional hydrodynamic simulations of the evolution of the hot and cool gas. The cool clouds ...
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2014-01-01
Accurate multi-phase flow solvers at low Reynolds number are of particular interest for the simulation of interface instabilities in the co-processing of multilayered material. We present a two-phase flow solver for incompressible viscous fluids which uses the streamfunction as the primary variab...
Syntrophic acetate oxidation in two-phase (acid-methane) anaerobic digesters.
Shimada, T; Morgenroth, E; Tandukar, M; Pavlostathis, S G; Smith, A; Raskin, L; Kilian, R E
2011-01-01
The microbial processes involved in two-phase anaerobic digestion were investigated by operating a laboratory-scale acid-phase (AP) reactor and analyzing two full-scale, two-phase anaerobic digesters operated under mesophilic (35 °C) conditions. The digesters received a blend of primary sludge and waste activated sludge (WAS). Methane levels of 20% in the laboratory-scale reactor indicated the presence of methanogenic activity in the AP. A phylogenetic analysis of an archaeal 16S rRNA gene clone library of one of the full-scale AP digesters showed that 82% and 5% of the clones were affiliated with the orders Methanobacteriales and Methanosarcinales, respectively. These results indicate that substantial levels of aceticlastic methanogens (order Methanosarcinales) were not maintained at the low solids retention times and acidic conditions (pH 5.2-5.5) of the AP, and that methanogenesis was carried out by hydrogen-utilizing methanogens of the order Methanobacteriales. Approximately 43, 31, and 9% of the archaeal clones from the methanogenic phase (MP) digester were affiliated with the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales, respectively. A phylogenetic analysis of a bacterial 16S rRNA gene clone library suggested the presence of acetate-oxidizing bacteria (close relatives of Thermacetogenium phaeum, 'Syntrophaceticus schinkii,' and Clostridium ultunense). The high abundance of hydrogen consuming methanogens and the presence of known acetate-oxidizing bacteria suggest that acetate utilization by acetate oxidizing bacteria in syntrophic interaction with hydrogen-utilizing methanogens was an important pathway in the second-stage of the two-phase digestion, which was operated at high ammonium-N concentrations (1.0 and 1.4 g/L). A modified version of the IWA Anaerobic Digestion Model No. 1 (ADM1) with extensions for syntrophic acetate oxidation and weak-acid inhibition adequately described the dynamic profiles of volatile acid production
Optical Measurement of Mass Flow of a Two-Phase Fluid
Wiley, John; Pedersen, Kevin; Koman, Valentin; Gregory, Don
2008-01-01
An optoelectronic system utilizes wavelength-dependent scattering of light for measuring the density and mass flow of a two-phase fluid in a pipe. The apparatus was invented for original use in measuring the mass flow of a two-phase cryogenic fluid (e.g., liquid hydrogen containing bubbles of hydrogen gas), but underlying principles of operation can readily be adapted to non-cryogenic two-phase fluids. The system (see figure) includes a laser module, which contains two or more laser diodes, each operating at a different wavelength. The laser module also contains beam splitters that combine the beams at the various wavelengths so as to produce two output beams, each containing all of the wavelengths. One of the multiwavelength output beams is sent, via a multimode fiberoptic cable, to a transmitting optical coupler. The other multiwavelength output beam is sent, via another multimode fiber-optic cable, to a reference detector module, wherein fiber-optic splitters split the light into several multiwavelength beams, each going to a photodiode having a spectral response that is known and that differs from the spectral responses of the other photodiodes. The outputs of these photodiodes are digitized and fed to a processor, which executes an algorithm that utilizes the known spectral responses to convert the photodiode outputs to obtain reference laser-power levels for the various wavelengths. The transmitting optical coupler is mounted in (and sealed to) a hole in the pipe and is oriented at a slant with respect to the axis of the pipe. The transmitting optical coupler contains a collimating lens and a cylindrical lens that form the light emerging from the end of the fiber-optic cable into a fan-shaped beam in a meridional plane of the pipe. Receiving optical couplers similar to the transmitting optical couplers are mounted in the same meridional plane at various longitudinal positions on the opposite side of the pipe, approximately facing the transmitting optical
Vertex centred Discretization of Two-Phase Darcy flows on General Meshes
Herbin Raphaèle
2012-04-01
Full Text Available This paper concerns the discretization of multiphase Darcy flows, in the case of heterogeneous anisotropic porous media and general 3D meshes used in practice to represent reservoir and basin geometries. An unconditionally coercive and symmetric vertex centred approach is introduced in this paper. This scheme extends the Vertex Approximate Gradient scheme (VAG, already introduced for single phase diffusive problems in [9], to multiphase Darcy flows. The convergence of the VAG scheme is proved for a simplified two-phase Darcy flow model, coupling an elliptic equation for the pressure and a linear hyperbolic equation for the saturation. The ability for the VAG scheme to efficiently deal with highly heterogeneous media and complex meshes is exhibited on immiscible and miscible two phase Darcy flow models. Cet article porte sur la discrétisation des flux de Darcy polyphasiques au sein de milieux poreux hétérogènes et anisotropes, dans des maillages tridimensionnels généraux utilisés dans le contexte de la simulation de réservoir ou de bassin. Un schéma avec inconnues aux sommets [9], qui a l’avantage d’être inconditionnellement coercif et symétrique, est généralisé au cas des écoulements de Darcy polyphasiques. La convergence du schéma est démontrée sur un modèle diphasique simplifié, couplant une équation elliptique pour la pression à une équation hyperbolique linéaire pour la saturation. On illustre ensuite la capacité du schéma à prendre en compte efficacement les fortes hétérogénéités et les maillages complexes sur des exemples d’écoulements diphasiques immiscibles et miscibles.
Rehmann, Lars; Prpich, George P; Daugulis, Andrew J
2008-10-01
The feasibility of a two-step treatment process has been assessed at laboratory scale for the remediation of soil contaminated with a model mixture of polycyclic aromatic hydrocarbons (PAHs) (phenanthrene, pyrene, and fluoranthene). The initial step of the process involved contacting contaminated soil with thermoplastic, polymeric pellets (polyurethane). The ability of three different mobilizing agents (water, surfactant (Biosolve) and isopropyl alcohol) to enhance recovery of PAHs from soil was investigated and the results were compared to the recovery of PAHs from dry soil. The presence of isopropyl alcohol had the greatest impact on PAH recovery with approximately 80% of the original mass of PAHs in the soil being absorbed by the polymer pellets in 48 h. The second stage of the suggested treatment involved regeneration of the PAH loaded polymers via PAH biodegradation, which was carried out in a solid-liquid two-phase partitioning bioreactor. In addition to the PAH containing polymer pellets, the bioreactor contained a microbial consortium that was pre-selected for its ability to degrade the model PAHs and after a 14 d period approximately 78%, 62% and 36% of phenanthrene, pyrene, and fluoranthene, respectively, had been desorbed from the polymer and degraded. The rate of phenanthrene degradation was shown to be limited by mass transfer of phenanthrene from the polymer pellets. In case of pyrene and fluoranthene a combination of mass transfer and biodegradation rate might have been limiting.
Mathematical models for two-phase stratified pipe flow
Biberg, Dag
2005-06-01
The simultaneous transport of oil, gas and water in a single multiphase flow pipe line has for economical and practical reasons become common practice in the gas and oil fields operated by the oil industry. The optimal design and safe operation of these pipe lines require reliable estimates of liquid inventory, pressure drop and flow regime. Computer simulations of multiphase pipe flow have thus become an important design tool for field developments. Computer simulations yielding on-line monitoring and look ahead predictions are invaluable in day-to-day field management. Inaccurate predictions may have large consequences. The accuracy and reliability of multiphase pipe flow models are thus important issues. Simulating events in large pipelines or pipeline systems is relatively computer intensive. Pipe-lines carrying e.g. gas and liquefied gas (condensate) may cover distances of several hundred km in which transient phenomena may go on for months. The evaluation times associated with contemporary 3-D CFD models are thus not compatible with field applications. Multiphase flow lines are therefore normally simulated using specially dedicated 1-D models. The closure relations of multiphase pipe flow models are mainly based on lab data. The maximum pipe inner diameter, pressure and temperature in a multiphase pipe flow lab is limited to approximately 0.3 m, 90 bar and 60{sup o}C respectively. The corresponding field values are, however, much higher i.e.: 1 m, 1000 bar and 200{sup o}C respectively. Lab data does thus not cover the actual field conditions. Field predictions are consequently frequently based on model extrapolation. Applying field data or establishing more advanced labs will not solve this problem. It is in fact not practically possible to acquire sufficient data to cover all aspects of multiphase pipe flow. The parameter range involved is simply too large. Liquid levels and pressure drop in three-phase flow are e.g. determined by 13 dimensionless parameters
Gradient-augmented hybrid interface capturing method for incompressible two-phase flow
Zheng, Fu; Shi-Yu, Wu; Kai-Xin, Liu
2016-06-01
Motivated by inconveniences of present hybrid methods, a gradient-augmented hybrid interface capturing method (GAHM) is presented for incompressible two-phase flow. A front tracking method (FTM) is used as the skeleton of the GAHM for low mass loss and resources. Smooth eulerian level set values are calculated from the FTM interface, and are used for a local interface reconstruction. The reconstruction avoids marker particle redistribution and enables an automatic treatment of interfacial topology change. The cubic Hermit interpolation is employed in all steps of the GAHM to capture subgrid structures within a single spacial cell. The performance of the GAHM is carefully evaluated in a benchmark test. Results show significant improvements of mass loss, clear subgrid structures, highly accurate derivatives (normals and curvatures) and low cost. The GAHM is further coupled with an incompressible multiphase flow solver, Super CE/SE, for more complex and practical applications. The updated solver is evaluated through comparison with an early droplet research. Project supported by the National Natural Science Foundation of China (Grant Nos. 10972010, 11028206, 11371069, 11372052, 11402029, and 11472060), the Science and Technology Development Foundation of China Academy of Engineering Physics (CAEP), China (Grant No. 2014B0201030), and the Defense Industrial Technology Development Program of China (Grant No. B1520132012).
Determination of volume fractions in two-phase flows from sound speed measurement
Chaudhuri, Anirban [Los Alamos National Laboratory; Sinha, Dipen N. [Los Alamos National Laboratory; Osterhoudt, Curtis F. [University of Alaska
2012-08-15
Accurate measurement of the composition of oil-water emulsions within the process environment is a challenging problem in the oil industry. Ultrasonic techniques are promising because they are non-invasive and can penetrate optically opaque mixtures. This paper presents a method of determining the volume fractions of two immiscible fluids in a homogenized two-phase flow by measuring the speed of sound through the composite fluid along with the instantaneous temperature. Two separate algorithms are developed by representing the composite density as (i) a linear combination of the two densities, and (ii) a non-linear fractional formulation. Both methods lead to a quadratic equation with temperature dependent coefficients, the root of which yields the volume fraction. The densities and sound speeds are calibrated at various temperatures for each fluid component, and the fitted polynomial is used in the final algorithm. We present results when the new algorithm is applied to mixtures of crude oil and process water from two different oil fields, and a comparison of our results with a Coriolis meter; the difference between mean values is less than 1%. Analytical and numerical studies of sensitivity of the calculated volume fraction to temperature changes and calibration errors are also presented.
Apparent and Actual Dynamic Contact Angles in Confined Two-Phase Flows
Omori, Takeshi; Kajishima, Takeo
2016-11-01
To accurately predict the fluid flow with moving contact lines, it has a crucial importance to use a model for the dynamic contact angle which gives contact angles on the length scale corresponding to the spacial resolution of the fluid solver. The angle which a moving fluid interface forms to a solid surface deviates from an actual (microscopic) dynamic contact angle depending on the distance from the contact line and should be called an apparent (macroscopic) dynamic contact angle. They were, however, often undistinguished especially in the experimental works, on which a number of empirical correlations between a contact angle and a contact line velocity have been proposed. The present study is the first attempt to measure both apparent and actual contact angles from the identical data sets to discuss the difference and the relationship between these two contact angles of difference length scales. The study is conducted by means of numerical simulation, solving the Navier-Stokes equation and the Cahn-Hilliard equation under the generalized Navier boundary condition for the immiscible two-phase flow in channels. The present study also illustrates how the system size and the physical properties of the adjoining fluid affect the apparent and the actual dynamic contact angles. JSPS KAKENHI Grant No. 15K17974.
Experimental investigation of two-phase pressure drop in rough minichannels
Paweł Wacławczyk
2014-01-01
Full Text Available Following the general tendency of miniaturization of devices in many branches of industry, smaller and smaller components are used. Mini channels are used to construct mini heat exchangers and mini reactors. Because of this fact, predicting two-phase pressure drops along the mini tube plays an important role already at the design stage. It defines the proper and safe operating conditions of such devices. It was decided to research this phenomena in five single mini channels and undertake a comparison of various correlations models reported in literature and check how the process of changing critical Reynolds value affects the conformity of the experimental data and results reported in literature. It was found that the Mishima-Hibiki model derived from literature offers the possibility of most accurate mathematical modelling. It was also found that changing critical Reynolds value because of mini channel roughness can significantly improve the accuracy of the existing correlations models e.g. for Lee-Lee model the improvement is equal to almost 9%.
Efficient and robust compositional two-phase reservoir simulation in fractured media
Zidane, A.; Firoozabadi, A.
2015-12-01
Compositional and compressible two-phase flow in fractured media has wide applications including CO2 injection. Accurate simulations are currently based on the discrete fracture approach using the cross-flow equilibrium model. In this approach the fractures and a small part of the matrix blocks are combined to form a grid cell. The major drawback is low computational efficiency. In this work we use the discrete-fracture approach to model the fractures where the fracture entities are described explicitly in the computational domain. We use the concept of cross-flow equilibrium in the fractures (FCFE). This allows using large matrix elements in the neighborhood of the fractures. We solve the fracture transport equations implicitly to overcome the Courant-Freidricks-Levy (CFL) condition in the small fracture elements. Our implicit approach is based on calculation of the derivative of the molar concentration of component i in phase (cαi ) with respect to the total molar concentration (ci ) at constant volume V and temperature T. This contributes to significant speed up of the code. The hybrid mixed finite element method (MFE) is used to solve for the velocity in both the matrix and the fractures coupled with the discontinuous Galerkin (DG) method to solve the species transport equations in the matrix, and a finite volume (FV) discretization in the fractures. In large scale problems the proposed approach is orders of magnitude faster than the existing models.
Solution of the equations for one-dimensional, two-phase, immiscible flow by geometric methods
Ivan, Boronin; Andrey, Shevlyakov
2016-12-01
Buckley-Leverett equations describe non viscous, immiscible, two-phase filtration, which is often of interest in modelling of oil production. For many parameters and initial conditions, the solutions of these equations exhibit non-smooth behaviour, namely discontinuities in form of shock waves. In this paper we obtain a novel method for the solution of Buckley-Leverett equations, which is based on geometry of differential equations. This method is fast, accurate, stable, and describes non-smooth phenomena. The main idea of the method is that classic discontinuous solutions correspond to the continuous surfaces in the space of jets - the so-called multi-valued solutions (Bocharov et al., Symmetries and conservation laws for differential equations of mathematical physics. American Mathematical Society, Providence, 1998). A mapping of multi-valued solutions from the jet space onto the plane of the independent variables is constructed. This mapping is not one-to-one, and its singular points form a curve on the plane of the independent variables, which is called the caustic. The real shock occurs at the points close to the caustic and is determined by the Rankine-Hugoniot conditions.
Zeng, Chao-Xi; Xin, Rui-Pu; Qi, Sui-Jian; Yang, Bo; Wang, Yong-Hua
2016-02-01
Aqueous two-phase systems, based on the use of natural quaternary ammonium compounds, were developed to establish a benign biotechnological route for efficient protein separation. In this study, aqueous two-phase systems of two natural resources betaine and choline with polyethyleneglycol (PEG400/600) or inorganic salts (K2 HPO4 /K3 PO4 ) were formed. It was shown that in the K2 HPO4 -containing aqueous two-phase system, hydrophobic interactions were an important driving force of protein partitioning, while protein size played a vital role in aqueous two-phase systems that contained polyethylene glycol. An extraction efficiency of more than 90% for bovine serum albumin in the betaine/K2 HPO4 aqueous two-phase system can be obtained, and this betaine-based aqueous two-phase system provided a gentle and stable environment for the protein. In addition, after investigation of the cluster phenomenon in the betaine/K2 HPO4 aqueous two-phase systems, it was suggested that this phenomenon also played a significant role for protein extraction in this system. The development of aqueous two-phase systems based on natural quaternary ammonium compounds not only provided an effective and greener method of aqueous two-phase system to meet the requirements of green chemistry but also may help to solve the mystery of the compartmentalization of biomolecules in cells.
Clive R McMahon
Full Text Available Generally, sigmoid curves are used to describe the growth of animals over their lifetime. However, because growth rates often differ over an animal's lifetime a single curve may not accurately capture the growth. Broken-stick models constrained to pass through a common point have been proposed to describe the different growth phases, but these are often unsatisfactory because essentially there are still two functions that describe the lifetime growth. To provide a single, converged model to age animals with disparate growth phases we developed a smoothly joining two-phase nonlinear function (SJ2P, tailored to provide a more accurate description of lifetime growth of the macropod, the Tasmanian pademelon Thylogale billardierii. The model consists of the Verhulst logistic function, which describes pouch-phase growth--joining smoothly to the Brody function, which describes post-pouch growth. Results from the model demonstrate that male pademelons grew faster and bigger than females. Our approach provides a practical means of ageing wild pademelons for life history studies but given the high variability of the data used to parametrise the second growth phase of the model, the accuracy of ageing of post-weaned animals is low: accuracy might be improved with collection of longitudinal growth data. This study provides a unique, first robust method that can be used to characterise growth over the lifespan of pademelons. The development of this method is relevant to collecting age-specific vital rates from commonly used wildlife management practices to provide crucial insights into the demographic behaviour of animal populations.
Dahms, Rainer N.
2016-04-01
A generalized framework for multi-component liquid injections is presented to understand and predict the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions. The analysis focuses on the thermodynamic structure and the immiscibility state of representative gas-liquid interfaces. The most modern form of Helmholtz energy mixture state equation is utilized which exhibits a unique and physically consistent behavior over the entire two-phase regime of fluid densities. It is combined with generalized models for non-linear gradient theory and for liquid injections to quantify multi-component two-phase interface structures in global thermal equilibrium. Then, the Helmholtz free energy is minimized which determines the interfacial species distribution as a consequence. This minimal free energy state is demonstrated to validate the underlying assumptions of classic two-phase theory and spray atomization. However, under certain engine-relevant conditions for which corroborating experimental data are presented, this requirement for interfacial thermal equilibrium becomes unsustainable. A rigorously derived probability density function quantifies the ability of the interface to develop internal spatial temperature gradients in the presence of significant temperature differences between injected liquid and ambient gas. Then, the interface can no longer be viewed as an isolated system at minimal free energy. Instead, the interfacial dynamics become intimately connected to those of the separated homogeneous phases. Hence, the interface transitions toward a state in local equilibrium whereupon it becomes a dense-fluid mixing layer. A new conceptual view of a transitional liquid injection process emerges from a transition time scale analysis. Close to the nozzle exit, the two-phase interface still remains largely intact and more classic two-phase processes prevail as a consequence. Further downstream, however, the transition to dense-fluid mixing
Housila P. Singh
2013-05-01
Full Text Available In this paper a double (or two-phase sampling version of (Singh and Tailor, 2005 estimator has been suggested along with its properties under large sample approximation. It is shown that the estimator due to (Kawathekar and Ajgaonkar, 1984 is a member of the proposed class of estimators. Realistic conditions have been obtained under which the proposed estimator is better than usual unbiased estimator, usual double sampling ratio ( tRd product ( tPd estimators and (Kawathekar and Ajgaonkar, 1984 estimator. This fact has been shown also through an empirical study.
Multi-scale diffuse interface modeling of multi-component two-phase flow with partial miscibility
Kou, Jisheng
2016-05-10
In this paper, we introduce a diffuse interface model to simulate multi-component two-phase flow with partial miscibility based on a realistic equation of state (e.g. Peng-Robinson equation of state). Because of partial miscibility, thermodynamic relations are used to model not only interfacial properties but also bulk properties, including density, composition, pressure, and realistic viscosity. As far as we know, this effort is the first time to use diffuse interface modeling based on equation of state for modeling of multi-component two-phase flow with partial miscibility. In numerical simulation, the key issue is to resolve the high contrast of scales from the microscopic interface composition to macroscale bulk fluid motion since the interface has a nanoscale thickness only. To efficiently solve this challenging problem, we develop a multi-scale simulation method. At the microscopic scale, we deduce a reduced interfacial equation under reasonable assumptions, and then we propose a formulation of capillary pressure, which is consistent with macroscale flow equations. Moreover, we show that Young-Laplace equation is an approximation of this capillarity formulation, and this formulation is also consistent with the concept of Tolman length, which is a correction of Young-Laplace equation. At the macroscopical scale, the interfaces are treated as discontinuous surfaces separating two phases of fluids. Our approach differs from conventional sharp-interface two-phase flow model in that we use the capillary pressure directly instead of a combination of surface tension and Young-Laplace equation because capillarity can be calculated from our proposed capillarity formulation. A compatible condition is also derived for the pressure in flow equations. Furthermore, based on the proposed capillarity formulation, we design an efficient numerical method for directly computing the capillary pressure between two fluids composed of multiple components. Finally, numerical tests
Multi-scale diffuse interface modeling of multi-component two-phase flow with partial miscibility
Kou, Jisheng; Sun, Shuyu
2016-08-01
In this paper, we introduce a diffuse interface model to simulate multi-component two-phase flow with partial miscibility based on a realistic equation of state (e.g. Peng-Robinson equation of state). Because of partial miscibility, thermodynamic relations are used to model not only interfacial properties but also bulk properties, including density, composition, pressure, and realistic viscosity. As far as we know, this effort is the first time to use diffuse interface modeling based on equation of state for modeling of multi-component two-phase flow with partial miscibility. In numerical simulation, the key issue is to resolve the high contrast of scales from the microscopic interface composition to macroscale bulk fluid motion since the interface has a nanoscale thickness only. To efficiently solve this challenging problem, we develop a multi-scale simulation method. At the microscopic scale, we deduce a reduced interfacial equation under reasonable assumptions, and then we propose a formulation of capillary pressure, which is consistent with macroscale flow equations. Moreover, we show that Young-Laplace equation is an approximation of this capillarity formulation, and this formulation is also consistent with the concept of Tolman length, which is a correction of Young-Laplace equation. At the macroscopical scale, the interfaces are treated as discontinuous surfaces separating two phases of fluids. Our approach differs from conventional sharp-interface two-phase flow model in that we use the capillary pressure directly instead of a combination of surface tension and Young-Laplace equation because capillarity can be calculated from our proposed capillarity formulation. A compatible condition is also derived for the pressure in flow equations. Furthermore, based on the proposed capillarity formulation, we design an efficient numerical method for directly computing the capillary pressure between two fluids composed of multiple components. Finally, numerical tests
DRAG FORCE IN DENSE GAS-PARTICLE TWO-PHASE FLOW
由长福; 祁海鹰; 徐旭常
2003-01-01
Numerical simulations of flow over a stationary particle in a dense gas-particle two-phase flow have been carried out for small Reynolds numbers (less than 100).In order to study the influence of the particles interaction on the drag force,three particle arrangements have been tested:a single particle,two particles placed in the flow direction and many particles located regularly in the flow field.The Navier-Stokes equations are discretized in the three-dimensional space using finite volume method.For the first and second cases,the numerical results agree reasonably well with the data in literature.For the third case,i.e.,the multiparticle case,the influence of the particle volume fraction and Reynolds numbers on the drag force has been investigated.The results show that the computational values of the drag ratio agree approximately with the published results at higher Reynolds numbers (from 34.2 to 68.4),but there is a large difference between them at small Reynolds numbers.
On Internet Traffic Classification: A Two-Phased Machine Learning Approach
Taimur Bakhshi
2016-01-01
Full Text Available Traffic classification utilizing flow measurement enables operators to perform essential network management. Flow accounting methods such as NetFlow are, however, considered inadequate for classification requiring additional packet-level information, host behaviour analysis, and specialized hardware limiting their practical adoption. This paper aims to overcome these challenges by proposing two-phased machine learning classification mechanism with NetFlow as input. The individual flow classes are derived per application through k-means and are further used to train a C5.0 decision tree classifier. As part of validation, the initial unsupervised phase used flow records of fifteen popular Internet applications that were collected and independently subjected to k-means clustering to determine unique flow classes generated per application. The derived flow classes were afterwards used to train and test a supervised C5.0 based decision tree. The resulting classifier reported an average accuracy of 92.37% on approximately 3.4 million test cases increasing to 96.67% with adaptive boosting. The classifier specificity factor which accounted for differentiating content specific from supplementary flows ranged between 98.37% and 99.57%. Furthermore, the computational performance and accuracy of the proposed methodology in comparison with similar machine learning techniques lead us to recommend its extension to other applications in achieving highly granular real-time traffic classification.
A new treatment of capillarity to improve the stability of IMPES two-phase flow formulation
Kou, Jisheng
2010-12-01
In this paper, we present an efficient numerical method for two-phase immiscible flow in porous media with different capillarity pressures. In highly heterogeneous permeable media, the saturation is discontinuous due to different capillary pressure functions. One popular scheme is to split the system into a pressure and a saturation equation, and to apply IMplicit Pressure Explicit Saturation (IMPES) approach for time stepping. One disadvantage of IMPES is instability resulting from the explicit treatment for capillary pressure. To improve stability, the capillary pressure is usually incorporated in the saturation equation which gradients of saturation appear. This approach, however, does not apply to the case of different capillary pressure functions for multiple rock-types, because of the discontinuity of saturation across rock interfaces. In this paper, we present a new treatment of capillary pressure, which appears implicitly in the pressure equation. Using an approximation of capillary function, we substitute the implicit saturation equation into the pressure equation. The coupled pressure equation will be solved implicitly and followed by the explicit saturation equation. Five numerical examples are provided to demonstrate the advantages of our approach. Comparison shows that our proposed method is more efficient and stable than the classical IMPES approach. © 2010 Elsevier Ltd.
A splitting method for the isentropic Baer-Nunziato two-phase flow model
Coquel Frédéric
2013-01-01
Full Text Available In the present work, we propose a fractional step method for computing approximate solutions of the isentropic Baer-Nunziato two-phase flow model. The scheme relies on an operator splitting method corresponding to a separate treatment of fast propagation phenomena due to the acoustic waves on the one hand and slow propagation phenomena due to the fluid motion on the other. The scheme is proved to preserve positive values of the statistical fractions and densities. We also provide two test-cases that assess the convergence of the method. Nous proposons ici une méthode à pas fractionnaires pour le calcul de solutions approchées pour la version isentropique du modèle diphasique de Baer-Nunziato. Le schéma s’appuie sur un splitting de l’opérateur temporel correspondant à la prise en compte différenciée des phéno-mènes de propagation rapide dus aux ondes acoustiques et des phénomènes de propagation lente dus aux ondes matérielles. On prouve que le schéma permet de préserver des valeurs positives pour les taux statistiques de présence des phases ainsi que pour les densités. Deux cas tests numériques permettent d’illustrer la convergence de la méthode.
Non-isothermal two-phase flow in low-permeable porous media
Kolditz, O.; De Jonge, J.
In this paper, we consider non-isothermal two-phase flow of two components (air and water) in gaseous and liquid phases in extremely low-permeable porous media through the use of the finite element method (FEM). Interphase mass transfer of the components between any of the phases is evaluated by assuming local thermodynamic equilibrium between the phases. Heat transfer occurs by conduction and multiphase advection. General equations of state for phase changes (Clausius-Clapeyron and Henry law) as well as multiphase properties for the low-permeable bentonites are implemented in the code. Additionally we consider the impact of swelling/shrinking processes on porosity and permeability changes. The numerical model is implemented in the context of the simulator RockFlow/RockMech (RF/RM), which is based on object-oriented programming techniques. The finite element formulations are written in terms of dimensionless quantities. This has proved to be advantageous for preconditioning composite system matrices of coupled multi-field problems. Three application examples are presented. The first one examines differences between the Richards' approximation and the multicomponent/multiphase approach, and between two numerical coupling schemes. The second example serves as partial verification against experimental results and to demonstrate coherence between different element types. The last example shows simultaneous desaturation and resaturation in one system.
Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity
Pais, S. C.; Kamotani, Y.; Bhunia, A.; Ostrach, S.
1999-01-01
The present investigation reports a study of bubble generation under reduced gravity conditions, using both a co-flow and a cross-flow configuration. This study may be used in the conceptual design of a space-based thermal management system. Ensuing two-phase flow void fraction can be accurately monitored using a single nozzle gas injection system within a continuous liquid flow conduit, as utilized in the present investigation. Accurate monitoring of void fraction leads to precise control of heat and mass transfer coefficients related to a thermal management system; hence providing an efficient and highly effective means of removing heat aboard spacecraft or space stations. Our experiments are performed in parabolic flight aboard the modified DC-9 Reduced Gravity Research Aircraft at NASA Lewis Research Center, using an air-water system. For the purpose of bubble dispersion in a flowing liquid, we use both a co-flow and a cross-flow configuration. In the co-flow geometry, air is introduced through a nozzle in the same direction with the liquid flow. On the other hand, in the cross-flow configuration, air is injected perpendicular to the direction of water flow, via a nozzle protruding inside the two-phase flow conduit. Three different flow conduit (pipe) diameters are used, namely, 1.27 cm, 1.9 cm and 2.54 cm. Two different ratios of nozzle to pipe diameter (D(sub N))sup * are considered, namely (D(sub N))sup * = 0.1 and 0.2, while superficial liquid velocities are varied from 8 to 70 cm/s depending on flow conduit diameter. It is experimentally observed that by holding all other flow conditions and geometry constant, generated bubbles decrease in size with increase in superficial liquid velocity. Detached bubble diameter is shown to increase with air injection nozzle diameter. Likewise, generated bubbles grow in size with increasing pipe diameter. Along the same lines, it is shown that bubble frequency of formation increases and hence the time to detachment of a
NUMERICAL SIMULATION OF CHARGED GAS-LIQUID TWO PHASE JET FLOW IN ELECTROSTATIC SPRAYING
无
2001-01-01
Multi-fluid k-ε-kp two phase turbulence model is used to simulate charged gas-liquid two phase coaxial jet, which is the transorting flow field in electrostatic spraying. Compared with the results of experiment, charged gas-liquid twophase turbulence can be well predicted by this model.
CALCULATION ON TWO-PHASE FLOW TRANSIENTS AND THEIR EXPERIMENTAL RESEARCH
无
2002-01-01
From basic equations of gas-liquid, solid-liquid, solid-gas two-phase flow, the calculating method on flowtransients of two-phase flow is developed by means of characteristic method. As one example, a gas-liquid flow transientis calculated and it agrees well with the experimental result. It is shown that the method is satisfactory for engineeringdemand.
Two-phase flow experimental studies in micro-models (Utrecht Studies in Earth Sciences 034)
Karadimitriou, N.K.
2013-01-01
The aim of this research project was to put more physics into theories of two-phase flow. The significance of including interfacial area as a separate variable in two-phase flow and transport models was investigated. In order to investigate experimentally the significance of the inclusion of interfa
Chiaramonte, Francis; Motil, Brian; McQuillen, John
2014-01-01
The Two-phase Heat Transfer International Topical Team consists of researchers and members from various space agencies including ESA, JAXA, CSA, and RSA. This presentation included descriptions various fluid experiments either being conducted by or planned by NASA for the International Space Station in the areas of two-phase flow, flow boiling, capillary flow, and crygenic fluid storage.
Solutions of Green s function for Lamb s problem of a two-phase saturated medium
无
2011-01-01
The solutions of Green's function are significant for simplification of problem on a two-phase saturated medium.Using transformation of axisymmetric cylindrical coordinate and Sommerfeld's integral,superposition of the influence field on a free surface,authors obtained the solutions of a two-phase saturated medium subjected to a concentrated force on the semi-space.
Symmetrical components and power analysis for a two-phase microgrid system
Alibeik, M.; Santos Jr., E. C. dos; Blaabjerg, Frede
2014-01-01
This paper presents a mathematical model for the symmetrical components and power analysis of a new microgrid system consisting of three wires and two voltages in quadrature, which is designated as a two-phase microgrid. The two-phase microgrid presents the following advantages: 1) constant power...
Majhi, Bijoy Kumar; Jash, Tushar
2016-12-01
Biogas production from vegetable market waste (VMW) fraction of municipal solid waste (MSW) by two-phase anaerobic digestion system should be preferred over the single-stage reactors. This is because VMW undergoes rapid acidification leading to accumulation of volatile fatty acids and consequent low pH resulting in frequent failure of digesters. The weakest part in the two-phase anaerobic reactors was the techniques applied for solid-liquid phase separation of digestate in the first reactor where solubilization, hydrolysis and acidogenesis of solid organic waste occur. In this study, a two-phase reactor which consisted of a solid-phase reactor and a methane reactor was designed, built and operated with VMW fraction of Indian MSW. A robust type filter, which is unique in its implementation method, was developed and incorporated in the solid-phase reactor to separate the process liquid produced in the first reactor. Experiments were carried out to assess the long term performance of the two-phase reactor with respect to biogas production, volatile solids reduction, pH and number of occurrence of clogging in the filtering system or choking in the process liquid transfer line. The system performed well and was operated successfully without the occurrence of clogging or any other disruptions throughout. Biogas production of 0.86-0.889m(3)kg(-1)VS, at OLR of 1.11-1.585kgm(-3)d(-1), were obtained from vegetable market waste, which were higher than the results reported for similar substrates digested in two-phase reactors. The VS reduction was 82-86%. The two-phase anaerobic digestion system was demonstrated to be stable and suitable for the treatment of VMW fraction of MSW for energy generation.
Analysis of transient gas-liquid two-phase natural circulation
Kataoka, Isao; Matsumoto, Tadayoshi; Morita, Yu; Kawashima, Atsushi [Department of Mechanophysics Engineering, Osaka University, Suita, Osaka (Japan); Nakayama, Akio
1999-07-01
Analyses were made on the transient behavior of two-phase natural circulation in annular passage. Drift flux model was used in the analyses and several correlations of drift velocity were used and compared. Transient variation of void fraction, inlet liquid flux and length of two-phase region were predicted based on simplified model. It was revealed that in transient two-phase natural circulation, the condition for pressure difference between inlet and outlet is quite important and difficult to be specified. A simplified model for inlet pressure condition was assumed and transient two-phase natural circulation was reasonably predicted. The correlation of drift velocity was shown to have important effect on the flow behavior particularly for the transient variation of two-phase length. (author)
A MODEL FOR PREDICTING PHASE INVERSION IN OIL-WATER TWO-PHASE PIPE FLOW
GONG Jing; LI Qing-ping; YAO Hai-yuan; YU Da
2006-01-01
Experiments of phase inversion characteristics for horizontal oil-water two-phase flow in a stainless steel pipe loop (25.7 mm inner diameter,52 m long) are conducted. A new viewpoint is brought forward about the process of phase inversion in oil-water two-phase pipe flow. Using the relations between the total free energies of the pre-inversion and post-inversion dispersions, a model for predicting phase inversion in oil-water two-phase pipe flow has been developed that considers the characteristics of pipe flow. This model is compared against other models with relevant data of phase inversion in oil-water two-phase pipe flow. Results indicate that this model is better than other models in terms of calculation precision and applicability. The model is useful for guiding the design for optimal performance and safety in the operation of oil-water two-phase pipe flow in oil fields.
Marrone, Salvatore; Colagrossi, Andrea; Di Mascio, Andrea; Le Touzé, David
2016-05-01
The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.
Validation of Wall Friction Model in SPACE-3D Module with Two-Phase Cross Flow Experiment
Choi, Chi-Jin; Yang, Jin-Hwa; Cho, Hyoung-Kyu; Park, Goon-Cher [Seoul National University, Seoul (Korea, Republic of); Euh, Dong-Jin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-10-15
In this study, SPACE-3D was used to simulate the Yang's experiment, and obtained the local variables. Then, the wall friction model used in SPACE-3D was validated by comparing the two-phase cross flow experimental results with the calculated local variables. In this study, the two-phase cross flow experiment was modeled by SPACE-3D to validate the wall friction model in multi-dimensional module. Considering the realistic phenomena in the reactor, however, recent trends in safety analysis codes have tended to adopt multi-dimensional module to simulate the complex flow more accurately. Even though the module was applied to deal the multi-dimensional phenomena, implemented models in that are one-dimensional empirical models. Therefore, prior to applying the multi-dimensional module, the constitutive models implemented in the codes need to be validated. In the downcomer of Advanced Power Reactor 1400 (APR1400) which has direct vessel injection (DVI) lines as an emergency core cooling system, multi-dimensional two-phase flow may occur due to the Loss-of-Coolant-Accident (LOCA). The accurate prediction about that is high relevance to evaluation of the integrity of the reactor core. For this reason, Yang performed an experiment that was to investigate the two-dimensional film flow which simulated the two-phase cross flow in the upper downcomer, and obtained the local liquid film velocity and thickness data. From these data, it could be possible to validate the friction models in multi-dimensional module of system analysis codes. Compared with the experiment, SPACE-3D underestimated the liquid film velocity and overestimated the liquid film thickness. From these results, it was clarified that the Wallis correlation which is used as a wall friction model in SPACE-3D overestimates the wall friction. On the other hand, H.T.F.S. correlation which is used as the wall friction in MARS-multiD underestimates the wall friction.
Patel, Sonal; Wilding, W Vincent; Rowley, Richard L
2011-01-14
Molecular dynamics simulations were performed to determine two-phase configurations of model propane molecules below the critical point and in the near-critical, two-phase region. A postprocessor that uses a Monte Carlo method for determination of volumes attributable to each molecule was used to obtain density histograms of the particles from which the bulk coexisting equilibrium vapor and liquid densities were determined. This method of analyzing coexisting densities in a two-phase simulation is straightforward and can be easily implemented for complex, multisite models. Various degrees of internal flexibility in the propane models have little effect on the coexisting densities at temperatures 40 K or more below the critical point, but internal flexibility (angle bending and bond vibrations) does affect the saturated liquid densities in the near-critical region, changing the critical temperature by approximately 20 K. Shorter cutoffs were also found to affect the phase dome and the location of the critical point.
Two-phase aqueous micellar systems: an alternative method for protein purification
Rangel-Yagui C. O.
2004-01-01
Full Text Available Two-phase aqueous micellar systems can be exploited in separation science for the extraction/purification of desired biomolecules. This article reviews recent experimental and theoretical work by Blankschtein and co-workers on the use of two-phase aqueous micellar systems for the separation of hydrophilic proteins. The experimental partitioning behavior of the enzyme glucose-6-phosphate dehydrogenase (G6PD in two-phase aqueous micellar systems is also reviewed and new results are presented. Specifically, we discuss very recent work on the purification of G6PD using: i a two-phase aqueous micellar system composed of the nonionic surfactant n-decyl tetra(ethylene oxide (C10E4, and (ii a two-phase aqueous mixed micellar system composed of C10E4 and the cationic surfactant decyltrimethylammonium bromide (C10TAB. Our results indicate that the two-phase aqueous mixed (C10E4/C10TAB micellar system can improve significantly the partitioning behavior of G6PD relative to that observed in the two-phase aqueous C10E4 micellar system.
Numerical investigation on the characteristics of two-phase flow in fuel assemblies with spacer grid
Chen, D.; Yang, Z.; Zhong, Y.; Xiao, Y.; Hu, L. [Chongqing Univ. (China). Key Lab. of Low-grade Energy Utilization Technologies and Systems
2016-07-15
In pressurized water reactors (PWRs), the spacer grids of the fuel assembly has significant impact on the thermal-hydraulic performance of the fuel assembly. Particularly, the spacer grids with the mixing vanes can dramatically enhance the secondary flow and have significant effect on the void distribution in the fuel assembly. In this paper, the CFD study has been carried out to analyze the effects of the spacer grid with the steel contacts, dimples and mixing vanes on the boiling two-phase flow characteristics, such as the two-phase flow field, the void distribution, and so on. Considered the influence of the boiling phase change on two-phase flow, a boiling model was proposed and applied in the CFD simulation by using the UDF (User Defined Function) method. Furthermore, in order to analyze the effects of the spacer grid with mixing vanes, the adiabatic (without boiling) two-phase flow has also been investigated as comparison with the boiling two-phase flow in the fuel assembly with spacer grids. The CFD simulation on two-phase flow in the fuel assembly with the proposed boiling model can predict the characteristics of two-phase flow better.
Interfacial area and two-phase flow structure development measured by a double-sensor probe
Leung, Waihung; Revankar, S.T.; Ishii, Yoshihiko; Ishii, Mamoru
1992-06-01
In this report, we studied the local phasic characters of dispersed flow regime both at the entrance and at the fully developed regions. Since the dispersed phase is distributed randomly in the medium and enclosed in relatively small interfaces, the phasic measurement becomes difficult to obtain. Local probe must be made with a miniaturized sensor in order to reduce the interface distortion. The double-sensor resistivity probe has been widely used in local void fraction and interface velocity measurements because the are small in comparison with the interfaces. It has been tested and proved to be an accurate local phasic measurement tool. In these experiments, a double-sensor probe was employed to measure the local void fraction and interface velocity in an air-water system. The test section was flow regime can be determined by visualization. Furthermore, local phasic measurements can be verified by photographic studies. We concentrated our study on the bubbly flow regime only. The local measurements were conducted at two axial locations, L/D = 8 and 60, in which the first measurement represents the entrance region where the flow develops, and the second measurement represents the fully developed flow region where the radial profile does not change as the flow moves along the axial direction. Four liquid flow rates were chosen in combination with four different gas injection rates. The superficial liquid velocities were j{sub t} = 1.0, 0.6,0.4, and 0.1 m/s and superficial gas velocities were j{sub g} = 0.0965, 0.0696, 0.0384, and 0.0192 m/s. These combinations put the two-phase flow well in the bubbly flow regime. In this sequence of phenomenological studies, the local void fraction, interface area concentration, sauter mean diameter, bubble velocity and bubble frequency were measured.
Investigation of Two-Phase Flow in AxialCentrifugal Impeller by Hydrodynamic Modeling Methods
V. O. Lomakin
2014-01-01
Full Text Available The article provides a methodology to study the flow in the wet part of the pump with fundamentally new axial-centrifugal impeller by methods of hydrodynamic modeling in the software package STAR CCM +. The objective of the study was to determine the normal and cavitation characteristics of the pump with a new type of wet part, as well as optimization of the geometrical parameters of the pump. Authors solved this problem using an example of the hot coolant pump, which should meet high requirements for cavitation quality and efficiency (hydraulic efficiency up to 87%, critical value of NPSH to 2.2 m.Also, the article focuses on the methods of numerical solution of two-phase flow simulation in a pump that are needed for a more accurate simulation of cavitation in the pump and research work in liquids with high gas content.Hydrodynamic modeling was performed on a computing cluster at the department E-10 of BMSTU for pump flow simulation in unsteady statement of problem using the computational grid size to 1.5 million cells. Simultaneously, the experimental model of the pump was made by 3D printing and tested at the stand in the BMSTU. Test results, which were compared with the calculated data are also given in the article. Inaccuracy of the calculation of pump head does not exceed 5%.The simulation results may be of interest to specialists in the field of hydrodynamic modeling, and for designers of such pumps. The authors also report production of a full-length prototype of the pump in order to conduct further testing for the verification of the data in the article, primarily in terms of cavitation characteristics.
Two phase flow bifurcation due to turbulence: transition from slugs to bubbles
Górski, Grzegorz; Litak, Grzegorz; Mosdorf, Romuald; Rysak, Andrzej
2015-09-01
The bifurcation of slugs to bubbles within two-phase flow patterns in a minichannel is analyzed. The two-phase flow (water-air) occurring in a circular horizontal minichannel with a diameter of 1 mm is examined. The sequences of light transmission time series recorded by laser-phototransistor sensor is analyzed using recurrence plots and recurrence quantification analysis. Recurrence parameters allow the two-phase flow patterns to be found. On changing the water flow rate we identified partitioning of slugs or aggregation of bubbles.
Numerical simulation of bubbly two-phase flow using the lattice Boltzmann method
Watanabe, Tadashi; Ebihara, Kenichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2000-09-01
The two-component two-phase lattice Boltzmann method, in which two distribution functions are used to represent two phases, is used to simulate bubbly flows as one of the fundamental two-phase flow phenomena in nuclear application fields. The inlet flow condition is proposed to simulate steady-state flow fields. The time variation and the spatial distribution of the volume fraction and the interfacial area are measured numerically. The simulation program is parallelized in one direction by the domain decomposition method using the MPI (Message Passing Interface) libraries, and parallel computations are performed on a workstation cluster. (author)
Spacecraft Thermal Management using Advanced Hybrid Two-Phase Loop Technology
2007-02-01
HYBRID TWO-PHASE LOOPS The schematic of the Hybrid Two-Phase Loop (HTPL) used for a thermal testing is shown in Figure 3. Main components for the...hybrid two-phase loop with single evaporator. The thermal test starts first by turning on the liquid pump to circulate liquid along the loop. Once the...Vapor Out Evaporator Body (E1) Evaporator Body (E2) Total Heat Input Heat Input (E1) Heat Input (E2) Thermal Resistance (E1) FIGURE 10. Thermal test results
On the nonequilibrium segregation state of a two-phase mixture in a porous column
Shapiro, Alexander; Stenby, Erling Halfdan
1996-01-01
The problem of segregation of a two-phase multicomponent mixture under the action of thermal gradient, gravity and capillary forces is studied with respect to component distribution in a thick oil-gas-condensate reservoir. Governing equations are derived on the basis of nonequilibrium thermodynam...... thermodynamics. A steady state of the two-phase mixture with nonzero diffusion fluxes and exchange between phases is described. In the case of binary mixtures analytical formulae for saturation, component distribution and flow in the two-phase zone are obtained....
Single- and two-phase flow in microfluidic porous media analogs based on Voronoi tessellation
Wu, Mengjie [Colorado School of Mines, Golden; Xiao, Feng [Colorado School of Mines, Golden; Johnson-Paben, Rebecca [Colorado School of Mines, Golden; Retterer, Scott T [ORNL; Yin, Xiaolong [Colorado School of Mines, Golden; Neeves, Keith B [ORNL
2012-01-01
The objective of this study was to create a microfluidic model of complex porous media for studying single and multiphase flows. Most experimental porous media models consist of periodic geometries that lend themselves to comparison with well-developed theoretical predictions. However, most real porous media such as geological formations and biological tissues contain a degree of randomness and complexity that is not adequately represented in periodic geometries. To design an experimental tool to study these complex geometries, we created microfluidic models of random homogeneous and heterogeneous networks based on Voronoi tessellations. These networks consisted of approximately 600 grains separated by a highly connected network of channels with an overall porosity of 0.11 0.20. We found that introducing heterogeneities in the form of large cavities within the network changed the permeability in a way that cannot be predicted by the classical porosity-permeability relationship known as the Kozeny equation. The values of permeability found in experiments were in excellent agreement with those calculated from three-dimensional lattice Boltzmann simulations. In two-phase flow experiments of oil displacement with water we found that the surface energy of channel walls determined the pattern of water invasion, while the network topology determined the residual oil saturation. These results suggest that complex network topologies lead to fluid flow behavior that is difficult to predict based solely on porosity. The microfluidic models developed in this study using a novel geometry generation algorithm based on Voronoi tessellation are a new experimental tool for studying fluid and solute transport problems within complex porous media.
Mapping moveout approximations in TI media
Stovas, Alexey
2013-11-21
Moveout approximations play a very important role in seismic modeling, inversion, and scanning for parameters in complex media. We developed a scheme to map one-way moveout approximations for transversely isotropic media with a vertical axis of symmetry (VTI), which is widely available, to the tilted case (TTI) by introducing the effective tilt angle. As a result, we obtained highly accurate TTI moveout equations analogous with their VTI counterparts. Our analysis showed that the most accurate approximation is obtained from the mapping of generalized approximation. The new moveout approximations allow for, as the examples demonstrate, accurate description of moveout in the TTI case even for vertical heterogeneity. The proposed moveout approximations can be easily used for inversion in a layered TTI medium because the parameters of these approximations explicitly depend on corresponding effective parameters in a layered VTI medium.
Critical Regimes of Two-Phase Flows with a Polydisperse Solid Phase
Barsky, Eugene
2010-01-01
This book brings to light peculiarities of the formation of critical regimes of two-phase flows with a polydisperse solid phase. A definition of entropy is formulated on the basis of statistical analysis of these peculiarities. The physical meaning of entropy and its correlation with other parameters determining two-phase flows are clearly defined. The interrelations and main differences between this entropy and the thermodynamic one are revealed. The main regularities of two-phase flows both in critical and in other regimes are established using the notion of entropy. This parameter serves as a basis for a deeper insight into the physics of the process and for the development of exhaustive techniques of mass exchange estimation in such flows. The book is intended for graduate and postgraduate students of engineering studying two-phase flows, and to scientists and engineers engaged in specific problems of such fields as chemical technology, mineral dressing, modern ceramics, microelectronics, pharmacology, po...
Numerical simulation of multi-dimensional two-phase flow based on flux vector splitting
Staedtke, H.; Franchello, G.; Worth, B. [Joint Research Centre - Ispra Establishment (Italy)
1995-09-01
This paper describes a new approach to the numerical simulation of transient, multidimensional two-phase flow. The development is based on a fully hyperbolic two-fluid model of two-phase flow using separated conservation equations for the two phases. Features of the new model include the existence of real eigenvalues, and a complete set of independent eigenvectors which can be expressed algebraically in terms of the major dependent flow parameters. This facilitates the application of numerical techniques specifically developed for high speed single-phase gas flows which combine signal propagation along characteristic lines with the conservation property with respect to mass, momentum and energy. Advantages of the new model for the numerical simulation of one- and two- dimensional two-phase flow are discussed.
Non-local two phase flow momentum transport in S BWR
Espinosa P, G.; Salinas M, L.; Vazquez R, A., E-mail: gepe@xanum.uam.mx [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Apdo. Postal 55-535, 09340 Ciudad de Mexico (Mexico)
2015-09-15
The non-local momentum transport equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection, diffusion and transport properties for two-phase flow. For instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail. The S BWR was considered to study the non-local effects on the two-phase flow thermal-hydraulic core performance in steady-state, and the results were compared with the classical local averaging volume conservation equations. (Author)
Research of Characteristics of Gas-liquid Two-phase Pressure Drop in Microreactor
Li Dan
2015-01-01
Full Text Available With the research system of nitrogen and deionized water, this paper researches the pressure drop of gas-liquid two-phase flow in the circular microchannel with an inner diameter which is respectively 0.9mm and 0.5mm, analyzes the effect of microchannel diameter on gas-liquid two-phase frictional pressure drop in the microchannel reactor, and compares with the result of frictional pressure drop and the predicting result of divided-phase flow pattern. The result shows that, the gas-liquid two-phase frictional pressure drop in the microchannel significantly increases with the decreasing microchannel diameter; Lockhart-Martinelli relationship in divided-phase flow pattern can preferably predict the gas-liquid two-phase frictional pressure drop in the microchannel, but the Tabular constant needs to be corrected.
Single and two-phase flow pressure drop for CANFLEX bundle
Park, Joo Hwan; Jun, Ji Su; Suk, Ho Chun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Dimmick, G. R.; Bullock, D. E. [Atomic Energy of Canada Limited, Ontario (Canada)
1998-12-31
Friction factor and two-phase flow frictional multiplier for a CANFLEX bundle are newly developed and presented in this paper. CANFLEX as a 43-element fuel bundle has been developed jointly by AECL/KAERI to provide greater operational flexibility for CANDU reactor operators and designers. Friction factor and two-phase flow frictional multiplier have been developed by using the experimental data of pressure drops obtained from two series of Freon-134a (R-134a) CHF tests with a string of simulated CANFLEX bundles in a single phase and a two-phase flow conditions. The friction factor for a CANFLEX bundle is found to be about 20% higher than that of Blasius for a smooth circular pipe. The pressure drop predicted by using the new correlations of friction factor and two-phase frictional multiplier are well agreed with the experimental pressure drop data of CANFLEX bundle within {+-} 5% error. 11 refs., 5 figs. (Author)
Mosdorf Romuald
2015-06-01
Full Text Available The two-phase flow (water-air occurring in square minichannel (3x3 mm has been analysed. In the minichannel it has been observed: bubbly flow, flow of confined bubbles, flow of elongated bubbles, slug flow and semi-annular flow. The time series recorded by laser-phototransistor sensor was analysed using the recurrence quantification analysis. The two coefficients:Recurrence rate (RR and Determinism (DET have been used for identification of differences between the dynamics of two-phase flow patterns. The algorithm which has been used normalizes the analysed time series before calculating the recurrence plots.Therefore in analysis the quantitative signal characteristicswas neglected. Despite of the neglect of quantitative signal characteristics the analysis of its dynamics (chart of DET vs. RR allows to identify the two-phase flow patterns. This confirms that this type of analysis can be used to identify the two-phase flow patterns in minichannels.
Experimental study on transient behavior of semi-open two-phase thermosyphon
朱华; 王建新; 张巧惠; 屠传经
2004-01-01
An experimental system was set up to measure the temperature, pressure, heat transfer rate and mass flow rate in a semi-open two-phase thermosyphon. The behaviors of a semi-open two-phase thermosyphon during startup, shutdown and lack of water were studied to get complete understanding of its thermal characteristics. The variation of wall temperature, heat-exchange condition and pressure fluctuations of semi-open two-phase thermosyphons showed that the startup of SOTPT needs about 60-70 min; the startup speed of SOTPT is determined by the startup speed of the condensation section; the average pressure in the heat pipe is equal to the environmental pressure usually; the shutdown of SOTPT needs about 30-50min; a semi-open two-phase thermosyphon has good response to lack of water accident.
Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary
2014-06-10
A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.
CHOOSING STRUCTURE-DEPENDENT DRAG COEFFICIENT IN MODELING GAS-SOLID TWO-PHASE FLOW
Ning Yang; Wei Wang; Wei Ge; Jinghai Li
2003-01-01
@@ Introduction Gas-solid two-phase flow is often encountered in chemical reactors for the process industry. For industrial users, design, scale-up, control and optimization for these reactors require a good understanding of the hydrodynamics of gas-solid two-phase flow. For researchers, exploration and prediction of the complex phenomena call for a good comprehension of the heterogeneous structure and of the dominant mechanisms of gas-solid and solid-solid interactions.
Bioconversion of apigenin-7-O-β-glucoside in aqueous two-phase system
Ilić Sanja M.; Đaković Sanja D.; Cvejić Jelena H.; Antov Mirjana G.; Zeković Zoran P.
2005-01-01
The study is concerned with the conversion of apigenin-7-O-β-glucoside into apigenin in polyethylene glycol 6000 / dextran 20000 aqueous two-phase system by β-glucosidase. Apigenin was separated from apigenin-7-O-β-glucoside and β-glucosidase by their partition into opposite phases. In 14% PEG / 22.5% DEX aqueous two-phase system obtained yield of apigenin in top phase was 108%.
Scaling analysis of gas-liquid two-phase flow pattern in microgravity
Lee, Jinho
1993-01-01
A scaling analysis of gas-liquid two-phase flow pattern in microgravity, based on the dominant physical mechanism, was carried out with the goal of predicting the gas-liquid two-phase flow regime in a pipe under conditions of microgravity. The results demonstrated the effect of inlet geometry on the flow regime transition. A comparison of the predictions with existing experimental data showed good agreement.
Numerical investigation of confined swirling gas-solid two phase jet
无
2002-01-01
This paper presents a k-ε-kp multi-fluid model for simulating confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two-phase flow of 30 μm, 45 μm, 60 μm diameter particles respectively yielded results fitting well with published experimental data.
Numerical Simulation of Swirling Gas-solid Two Phase Flow through a Pipe Expansion
Jin Hanhui; Xia Jun; Fan Jianren; Cen Kefa
2001-01-01
A k- ε -kp multi-fluid model is stated and adopted to simulate swirling gas-solid two phase flow. A particle-laden flow from a center tube and a swirling air stream from the coaxial annular enter the test section. A series of numerical simulations of the two-phase flow are performed based on 30 μ m, 45 μ m, 60 μ m diameter particles respectively. The results fit well with published experimental data.
Numerical investigation of confined swirling gas-solid two phase jet
金晗辉; 夏钧; 樊建人; 岑可法
2002-01-01
This paper presents a k-e-kp multi-fluid model for simulating confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two-phase flow of 30μm, 45μm, 60μm diameter particles respectively yielded results fitting well with published experimental data.
Bioconversion of apigenin-7-O-β-glucoside in aqueous two-phase system
Ilić Sanja M.
2005-01-01
Full Text Available The study is concerned with the conversion of apigenin-7-O-β-glucoside into apigenin in polyethylene glycol 6000 / dextran 20000 aqueous two-phase system by β-glucosidase. Apigenin was separated from apigenin-7-O-β-glucoside and β-glucosidase by their partition into opposite phases. In 14% PEG / 22.5% DEX aqueous two-phase system obtained yield of apigenin in top phase was 108%.
CURE OF A MICROGEL-EPOXY RESIN TWO-PHASE POLYMER WITH ETHYLENE DIAMINE
SONG Aiteng; HUANG Wei; YU Yunzhao
1992-01-01
The curing of a microgel-epoxy resin two phase polymer prepared by in situ copolymerization of unsaturated polyester with acrylic monomer was studied. The unsaturated unit reacted with N- H during the cure of the resin with ethylene diamine. The Michael type reaction was ten times more rapid than the addition of N -H to epoxide .This was accounted for the lower apparent activation energy of the curing of the two phase resin.
Separated two-phase flow regime parameter measurement by a high speed ultrasonic pulse-echo system.
Masala, Tatiana; Harvel, Glenn; Chang, Jen-Shih
2007-11-01
In this work, a high speed ultrasonic multitransducer pulse-echo system using a four transducer method was used for the dynamic characterization of gas-liquid two-phase separated flow regimes. The ultrasonic system consists of an ultrasonic pulse signal generator, multiplexer, 10 MHz (0.64 cm) ultrasonic transducers, and a data acquisition system. Four transducers are mounted on a horizontal 2.1 cm inner diameter circular pipe. The system uses a pulse-echo method sampled every 0.5 ms for a 1 s duration. A peak detection algorithm (the C-scan mode) is developed to extract the location of the gas-liquid interface after signal processing. Using the measured instantaneous location of the gas/liquid interface, two-phase flow interfacial parameters in separated flow regimes are determined such as liquid level and void fraction for stratified wavy and annular flow. The shape of the gas-liquid interface and, hence, the instantaneous and cross-sectional averaged void fraction is also determined. The results show that the high speed ultrasonic pulse-echo system provides accurate results for the determination of the liquid level within +/-1.5%, and the time averaged liquid level measurements performed in the present work agree within +/-10% with the theoretical models. The results also show that the time averaged void fraction measurements for a stratified smooth flow, stratified wavy flow, and annular flow qualitatively agree with the theoretical predictions.
Lee, Pilhwa; Wolgemuth, Charles W.
2016-01-01
The swimming of microorganisms typically involves the undulation or rotation of thin, filamentary objects in a fluid or other medium. Swimming in Newtonian fluids has been examined extensively, and only recently have investigations into microorganism swimming through non-Newtonian fluids and gels been explored. The equations that govern these more complex media are often nonlinear and require computational algorithms to study moderate to large amplitude motions of the swimmer. Here, we develop an immersed boundary method for handling fluid-structure interactions in a general two-phase medium, where one phase is a Newtonian fluid and the other phase is viscoelastic (e.g., a polymer melt or network). We use this algorithm to investigate the swimming of an undulating, filamentary swimmer in 2D (i.e., a sheet). A novel aspect of our method is that it allows one to specify how forces produced by the swimmer are distributed between the two phases of the fluid. The algorithm is validated by comparing theoretical predictions for small amplitude swimming in gels and viscoelastic fluids. We show how the swimming velocity depends on material parameters of the fluid and the interaction between the fluid and swimmer. In addition, we simulate the swimming of Caenorhabditis elegans in viscoelastic fluids and find good agreement between the swimming speeds and fluid flows in our simulations and previous experimental measurements. These results suggest that our methodology provides an accurate means for exploring the physics of swimming through non-Newtonian fluids and gels.
Living between two worlds: two-phase culture systems for producing plant secondary metabolites.
Malik, Sonia; Hossein Mirjalili, Mohammad; Fett-Neto, Arthur Germano; Mazzafera, Paulo; Bonfill, Mercedes
2013-03-01
The two-phase culture system is an important in vitro strategy to increase the production of secondary metabolites (SMs) by providing an enhanced release of these compounds from plant cells. Whereas the first phase supports cell growth, the second phase provides an additional site or acts as a metabolic sink for the accumulation of SMs and also reduces feedback inhibition. This review is focused on several aspects of the two-phase culture system and aims to show the diverse possibilities of employing this technique for the in vitro production of SMs from plant cells. Depending on the material used in the secondary phase, two-phase culture systems can be broadly categorised as liquid-liquid or liquid-solid. The choice of material for the second phase depends on the type of compound to be recovered and the compatibility with the other phase. Different factors affecting the efficiency of two-phase culture systems include the choice of material for the secondary phase, its concentration, volume, and time of addition. Factors such as cell elicitation, immobilization, and permeabilization, have been suggested as important strategies to make the two-phase culture system practically reliable on a commercial scale. Since there are many possibilities for designing a two-phase system, more detailed studies are needed to broaden the range of secondary phases compatible with the various plant species producing SMs with potential applications, mainly in the food and pharmacology industries.
IMPROVED SUBGRID SCALE MODEL FOR DENSE TURBULENT SOLID-LIQUID TWO-PHASE FLOWS
TANG Xuelin; QIAN Zhongdong; WU Yulin
2004-01-01
The dense solid-phase governing equations for two-phase flows are obtained by using the kinetic theory of gas molecules. Assuming that the solid-phase velocity distributions obey the Maxwell equations, the collision term for particles under dense two-phase flow conditions is also derived.In comparison with the governing equations of a dilute two-phase flow, the solid-particle's governing equations are developed for a dense turbulent solid-liquid flow by adopting some relevant terms from the dilute two-phase governing equations. Based on Cauchy-Helmholtz theorem and Smagorinsky model,a second-order dynamic sub-grid-scale (SGS) model, in which the sub-grid-scale stress is a function of both the strain-rate tensor and the rotation-rate tensor, is proposed to model the two-phase governing equations by applying dimension analyses. Applying the SIMPLEC algorithm and staggering grid system to the two-phase discretized governing equations and employing the slip boundary conditions on the walls, the velocity and pressure fields, and the volumetric concentration are calculated. The simulation results are in a fairly good agreement with experimental data in two operating cases in a conduit with a rectangular cross-section and these comparisons imply that these models are practical.
Mixed Model for Silt-Laden Solid-Liquid Two-Phase Flows
唐学林; 徐宇; 吴玉林
2003-01-01
The kinetic theory of molecular gases was used to derive the governing equations for dense solid-liquid two-phase flows from a microscopic flow characteristics viewpoint by multiplying the Boltzmann equation for each phase by property parameters and integrating over the velocity space. The particle collision term was derived from microscopic terms by comparison with dilute two-phase flow but with consideration of the collisions between particles for dense two-phase flow conditions and by assuming that the particle-phase velocity distribution obeys the Maxwell equations. Appropriate terms from the dilute two-phase governing equations were combined with the dense particle collision term to develop the governing equations for dense solid-liquid turbulent flows. The SIMPLEC algorithm and a staggered grid system were used to solve the discretized two-phase governing equations with a Reynolds averaged turbulence model. Dense solid-liquid turbulent two-phase flows were simulated for flow in a duct. The simulation results agree well with experimental data.
Oppermann, Sebastian; Stein, Florian; Kragl, Udo
2011-02-01
The development of biotechnological processes using novel two-phase systems based on molten salts known as ionic liquids (ILs) got into the focus of interest. Many new approaches for the beneficial application of the interesting solvent have been published over the last years. ILs bring beneficial properties compared to organic solvents like nonflammability and nonvolatility. There are two possible ways to use the ILs: first, the hydrophobic ones as a substitute for organic solvents in pure two-phase systems with water and second, the hydrophilic ones in aqueous two-phase systems (ATPS). To effectively utilise IL-based two-phase systems or IL-based ATPS in biotechnology, extensive experimental work is required to gain the optimal system parameters to ensure selective extraction of the product of interest. This review will focus on the most actual findings dealing with the basic driving forces for the target extraction in IL-based ATPS as well as presenting some selected examples for the beneficial application of ILs as a substitute for organic solvents. Besides the research focusing on IL-based two-phase systems, the "green aspect" of ILs, due to their negligible vapour pressure, is widely discussed. We will present the newest results concerning ecotoxicity of ILs to get an overview of the state of the art concerning ILs and their utilisation in novel two-phase systems in biotechnology.
Michal Prazenica
2011-01-01
Full Text Available This paper deals with the two-stage two-phase electronic systems with orthogonal output voltages and currents - DC/AC/AC. Design of two-stage DC/AC/AC high frequency converter with two-phase orthogonal output using single-phase matrix converter is also introduced. Output voltages of them are strongly nonharmonic ones, so they must be pulse-modulated due to requested nearly sinusoidal currents with low total harmonic distortion. Simulation experiment results of matrix converter for both steady and transient states for IM motors are given in the paper, also experimental verification under R-L load, so far. The simulation results confirm a very good time-waveform of the phase current and the system seems to be suitable for low-cost application in automotive/aerospace industries and application with high frequency voltage sources.
Shin, Y.W.; Wiedermann, A.H.
1984-02-01
A method was published, based on the integral method of characteristics, by which the junction and boundary conditions needed in computation of a flow in a piping network can be accurately formulated. The method for the junction and boundary conditions formulation together with the two-step Lax-Wendroff scheme are used in a computer program; the program in turn, is used here in calculating sample problems related to the blowdown transient of a two-phase flow in the piping network downstream of a PWR pressurizer. Independent, nearly exact analytical solutions also are obtained for the sample problems. Comparison of the results obtained by the hybrid numerical technique with the analytical solutions showed generally good agreement. The good numerical accuracy shown by the results of our scheme suggest that the hybrid numerical technique is suitable for both benchmark and design calculations of PWR pressurizer blowdown transients.
Variant of a volume-of-fluid method for surface tension-dominant two-phase flows
G Biswas
2013-12-01
The capabilities of the volume-of-fluid method for the calculation of surface tension-dominant two-phase flows are explained. The accurate calculation of the interface remains a problem for the volume-of-fluid method if the density ratios of the fluids in different phases are high. The simulations of bubble growth is performed in water at near critical pressure for different degrees of superheat using combined levelset and volume-of fluid (CLSVOF) method. The effect of superheat on the frequency of bubble formation was analyzed. A deviation from the periodic bubble release is observed in the case of superheat of 20 K in water. The vapor-jet-like columnar structure is observed. Effect of heat flux on the slender vapor column has also been explained.
Mohammadi, M. [Petroleum Univ. of Technology, Ahwaz (Iran, Islamic Republic of). Gas Engineering Dept.
2006-07-01
Liquid holdup in pipelines refers to the fraction of pipe that is occupied by liquid. Accurate prediction of liquid holdup associated with multiphase flow is important for the design and operation of modern petroleum production systems. Multiphase flow refers to the concurrent flow of 2 or more phases, liquid, solid or gas, where motion affects the interface between the phases. The ability to predict liquid holdup makes it possible to calculate a pressure gradient based on a two-phase friction factor. However, this approach is dependent on the accuracy of flow pattern predictions and is subject to discontinuities in predictions made across flow pattern transition boundaries. Artificial neural networks (ANN) are computing tools that can recognize complex patterns within available data. ANN has been used successfully to solve many difficult engineering problems including multiphase flow problems that involve pressure drop, flow pattern identification and liquid holdup. This study used a 3-layer backpropagation ANN model for predicting the liquid holdup in gas-liquid two-phase flow at all ranges of pipe inclinations. Five independent sets of experimental data were used, covering a wide range of variables such as inclination from horizontal, pipe diameter, gas and liquid superficial velocity, liquid viscosity, density and surface tension. The model is independent of flow pattern determination and uses an individual method for all conditions. Experimental results have shown that the newly developed model can accurately predict liquid holdup in terms of the lowest absolute average percent error, the lowest standard deviation and the highest correlation coefficient. This study confirmed the power of ANN models in solving complicated engineering problems. 28 refs., 5 tabs., 4 figs., 1 appendix.
Marios S. Valavanides
2016-02-01
Full Text Available Steady-state two-phase flow in porous media is a process whereby a wetting phase displaces a non-wetting phase within a pore network. It is an off-equilibrium stationary process—in the sense that it is maintained in dynamic equilibrium at the expense of energy supplied to the system. The efficiency of the process depends on its spontaneity, measurable by the rate of global entropy production. The latter has been proposed to comprise two components: the rate of mechanical energy dissipation at constant temperature (a thermal entropy component, Q/T, in the continuum mechanics scale and the configurational entropy (a Boltzmann–Gibbs entropy component, klnW, due to the existence of a canonical ensemble of flow configurations, physically admissible to the externally imposed macrostate conditions. Here, we propose an analytical model to account the number of microstates, lnW, in two-phase flows in pore networks. Combinatorial analysis is implemented to evaluate the number of identified microstates per physically admissible internal flow arrangement, compatible with the imposed steady-state flow conditions. Then, Stirling’s approximation is applied to downscale the large factorial numbers. Finally, the number of microstates is estimated by contriving an appropriate mixing scheme over the canonical ensemble of the physically admissible flow configurations. Indicative computations are furnished.
Hejranfar, Kazem; Ezzatneshan, Eslam
2015-11-01
A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is extended and applied to accurately simulate two-phase liquid-vapor flows with high density ratios. Herein, the He-Shan-Doolen-type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting equations are discretized by using the fourth-order compact finite-difference scheme and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient two-phase flow solver. A high-order spectral-type low-pass compact nonlinear filter is used to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions and at the same time to remove the numerical oscillations in the interfacial region between the two phases. Three discontinuity-detecting sensors for properly switching between a second-order and a higher-order filter are applied and assessed. It is shown that the filtering technique used can be conveniently adopted to reduce the spurious numerical effects and improve the numerical stability of the CFDLBM implemented. A sensitivity study is also conducted to evaluate the effects of grid size and the filtering procedure implemented on the accuracy and performance of the solution. The accuracy and efficiency of the proposed solution procedure based on the compact finite-difference LBM are examined by solving different two-phase systems. Five test cases considered herein for validating the results of the two-phase flows are an equilibrium state of a planar interface in a liquid-vapor system, a droplet suspended in the gaseous phase, a liquid droplet located between two parallel wettable surfaces, the coalescence of two droplets, and a phase separation in a liquid-vapor system at different conditions. Numerical results are also presented for the coexistence curve and the verification of the Laplace law. Results obtained are in good agreement with the analytical solutions and also
Dynamic behavior of pipes conveying gas–liquid two-phase flow
An, Chen, E-mail: anchen@cup.edu.cn [Offshore Oil/Gas Research Center, China University of Petroleum-Beijing, Beijing 102249 (China); Su, Jian, E-mail: sujian@lasme.coppe.ufrj.br [Nuclear Engineering Program, COPPE, Universidade Federal do Rio de Janeiro, CP 68509, Rio de Janeiro 21941-972 (Brazil)
2015-10-15
Highlights: • Dynamic behavior of pipes conveying gas–liquid two-phase flow was analyzed. • The generalized integral transform technique (GITT) was applied. • Excellent convergence behavior and long-time stability were shown. • Effects of volumetric quality and volumetric flow rate on dynamic behavior were studied. • Normalized volumetric-flow-rate stability envelope of dynamic system was determined. - Abstract: In this paper, the dynamic behavior of pipes conveying gas–liquid two-phase flow was analytically and numerically investigated on the basis of the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the transverse vibration equation lead to a coupled system of second order differential equations in the dimensionless temporal variable. The Mathematica's built-in function, NDSolve, was employed to numerically solve the resulting transformed ODE system. The characteristics of gas–liquid two-phase flow were represented by a slip-ratio factor model that was devised and used for similar problems. Good convergence behavior of the proposed eigenfunction expansions is demonstrated for calculating the transverse displacement at various points of pipes conveying air–water two-phase flow. Parametric studies were performed to analyze the effects of the volumetric gas fraction and the volumetric flow rate on the dynamic behavior of pipes conveying air–water two-phase flow. Besides, the normalized volumetric-flow-rate stability envelope for the dynamic system was obtained.
New Results in Two-Phase Pressure Drop Calculations at Reduced Gravity Conditions
Braisted, Jon; Kurwitz, Cable; Best, Frederick
2004-02-01
The mass, power, and volume energy savings of two-phase systems for future spacecraft creates many advantages over current single-phase systems. Current models of two-phase phenomena such as pressure drop, void fraction, and flow regime prediction are still not well defined for space applications. Commercially available two-phase modeling software has been developed for a large range of acceleration fields including reduced-gravity conditions. Recently, a two-phase experiment has been flown to expand the two-phase database. A model of the experiment was created in the software to determine how well the software could predict the pressure drop observed in the experiment. Of the simulations conducted, the computer model shows good agreement of the pressure drop in the experiment to within 30%. However, the software does begin to over-predict pressure drop in certain regions of a flow regime map indicating that some models used in the software package for reduced-gravity modeling need improvement.
DSMC simulation of two-phase plume flow with UV radiation
Li, Jie; Liu, Ying; Wang, Ning; Jin, Ling [College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, Hunan, 410073 (China)
2014-12-09
Rarefied gas-particle two-phase plume in which the phase of particles is liquid or solid flows from a solid propellant rocket of hypersonic vehicle flying at high altitudes, the aluminum oxide particulates not only impact the rarefied gas flow properties, but also make a great difference to plume radiation signature, so the radiation prediction of the rarefied gas-particle two-phase plume flow is very important for space target detection of hypersonic vehicles. Accordingly, this project aims to study the rarefied gas-particle two-phase flow and ultraviolet radiation (UV) characteristics. Considering a two-way interphase coupling of momentum and energy, the direct simulation Monte Carlo (DSMC) method is developed for particle phase change and the particle flow, including particulate collision, coalescence as well as separation, and a Monte Carlo ray trace model is implemented for the particulate UV radiation. A program for the numerical simulation of the gas-particle two-phase flow and radiation in which the gas flow nonequilibrium is strong is implemented as well. Ultraviolet radiation characteristics of the particle phase is studied based on the calculation of the flow field coupled with the radiation calculation, the radiation model for different size particles is analyzed, focusing on the effects of particle emission, absorption, scattering as well as the searchlight emission of the nozzle. A new approach may be proposed to describe the rarefied gas-particle two-phase plume flow and radiation transfer characteristics in this project.
Performance characteristics of two-phase-flow turbo-expanders used in water-cooled chillers
Brasz, J.J. [United Technologies Carrier, New York, NY (United States)
1999-07-01
Use of two-phase-flow throttle loss recovery devices in water-cooled chillers requires satisfactory part-load operation. This paper describes the results of two-phase-flow impulse turbine testing and the data reduction of the test results into a two-phase-flow turbine off-design performance model. It was found that the main parameter controlling the efficiency of two-phase-flow turbine is the ratio of the nozzle spouting velocity to the rotor speed. The turbine mass flow rate is mainly controlled by inlet subcooling of the entering liquid. The strong sensitivity of turbine mass flow rate on inlet subcooling allows the use of a conventional float valve upstream of the turbine as an effective means of controlling the turbine during part-load operation. For a well-designed two-phase-flow turbine, nozzle spouting velocity and therefore turbine efficiency is hardly affected by the amount of inlet subcooling. Also, capacity can be substantially reduced by a reduction in the amount of inlet subcooling entering the turbine nozzles. Hence, turbine part-load efficiency equals its full-load efficiency over a wide range of flow rates using this control concept. (Author)
Gas-liquid two-phase flow across a bank of micropillars
Krishnamurthy, Santosh; Peles, Yoav
2007-04-01
Adiabatic nitrogen-water two-phase flow across a bank of staggered circular micropillars, 100μm long with a diameter of 100μm and a pitch-to-diameter ratio of 1.5, was investigated experimentally for Reynolds number ranging from 5 to 50. Flow patterns, void fraction, and pressure drop were obtained, discussed, and compared to large scale as well as microchannel results. Two-phase flow patterns were determined by flow visualization, and a flow map was constructed as a function of gas and liquid superficial velocities. Significant deviations from conventional scale systems, with respect to flow patterns and trend lines, were observed. A unique flow pattern, driven by surface tension, was observed and termed bridge flow. The applicability of conventional scale models to predict the void fraction and two-phase frictional pressure drop was also assessed. Comparison with a conventional scale void fraction model revealed good agreement, but was found to be in a physically wrong form. Thus, a modified physically based model for void fraction was developed. A two-phase frictional multiplier was found to be a strong function of mass flux, unlike in previous microchannel studies. It was observed that models from conventional scale systems did not adequately predict the two-phase frictional multiplier at the microscale, thus, a modified model accounting for mass flux was developed.
A new two-phase erosion-deposition model for mass flows
Pudasaini, Shiva P.; Fischer, Jan-Thomas
2016-04-01
Erosion, entrainment and deposition are complex and dominant, but yet poorly understood, mechanical processes in geophysical mass flows. Here, we propose a novel, two-phase, erosion-deposition model capable of adequately describing these complex phenomena commonly observed in landslides, avalanches, debris flows and bedload transports. The model enhances an existing general two-phase mass flow model (Pudasaini, 2012) by introducing a two-phase variably saturated erodible basal morphology. The adaptive basal morphology allows for the evolution of erosion-deposition-depths, incorporating the inherent physical process and rheological changes of the flowing mixture. With rigorous derivation, we show that appropriate incorporation of the mass and momentum productions and losses in conservative model formulation is essential for the physically correct and mathematically consistent description of erosion-entrainment-deposition processes. Simulation indicates a sharp erosion-front and steady-state-rear erosion depth. The model appropriately captures the emergence and propagation of complex frontal surge dynamics associated with the frontal ambient-drag which is a new hypothesis associated with erosion. The novel enhanced real two-phase model also allows for simulating fluid-run-off during the deposition process. The model resembles laboratory experiments for particle-fluid mixture flows and reveals some major aspects of the mechanics associated with erosion, entrainment and deposition. Reference: Shiva P. Pudasaini (2012): A general two-phase debris flow model. J. Geophys. Res., 117, F03010, doi: 10.1029/2011JF002186.
A Derivation of the Nonlocal Volume-Averaged Equations for Two-Phase Flow Transport
Gilberto Espinosa-Paredes
2012-01-01
Full Text Available In this paper a detailed derivation of the general transport equations for two-phase systems using a method based on nonlocal volume averaging is presented. The local volume averaging equations are commonly applied in nuclear reactor system for optimal design and safe operation. Unfortunately, these equations are limited to length-scale restriction and according with the theory of the averaging volume method, these fail in transition of the flow patterns and boundaries between two-phase flow and solid, which produce rapid changes in the physical properties and void fraction. The non-local volume averaging equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection diffusion and transport properties for two-phase flow; for instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail.
Two phase convective heat transfer augmentation in swirl flow with non-boiling
Cha, K.O. [Myong Ji University, Kyonggi-do (Korea, Republic of); Kim, J.G. [Myongji University Graduate School, Kyonggi-do (Korea, Republic of)
1995-10-01
Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased. (author). 13 refs., 15 figs.
Design and evaluation of a two-phase turbine for low quality steam--water mixtures
Comfort, W.J. III
1977-05-16
A new two-phase turbine was designed and built for testing in the laboratory, using a low quality steam-water mixture as a working fluid. The measured performance compares well with performance predictions of a numerical model of the expander. Details of the selection of the type of expander are given. The design of an experimental expander for use in a clean two-phase flow laboratory experiment and the development of a numerical model for performance analysis and extrapolations are described. Experiments including static cascade performance with two-phase fluid, disk friction and windage measurements, and two-phase performance measurements of the experimental expander are reported. Comparisons of the numerical model and experimental results, and the prediction of the performance of an advanced design, indicating how performance improvements can be achieved, are also included. An engine efficiency of 23 percent for a single-nozzle test was measured. Full admission performance, based upon the numerical model and achievable nozzle thrust coefficients indicate that an engine efficiency of between 38 and 48 percent can be realized with present technology. If maximum liquid removal loss is assumed, this performance range is predicted to be 38 to 41 percent. Droplet size reduction and the development and implementation of enhanced two-phase flow analysis techniques should make it possible to achieve the research goal of 70 percent engine efficiency.
Evaluation of Gaussian approximations for data assimilation in reservoir models
Iglesias, Marco A.
2013-07-14
implementation of the MCMC method provides the gold standard against which the aforementioned Gaussian approximations are assessed. We present numerical synthetic experiments where we quantify the capability of each of the ad hoc Gaussian approximation in reproducing the mean and the variance of the posterior distribution (characterized via MCMC) associated to a data assimilation problem. Both single-phase and two-phase (oil-water) reservoir models are considered so that fundamental differences in the resulting forward operators are highlighted. The main objective of our controlled experiments was to exhibit the substantial discrepancies of the approximation properties of standard ad hoc Gaussian approximations. Numerical investigations of the type we present here will lead to the greater understanding of the cost-efficient, but ad hoc, Bayesian techniques used for data assimilation in petroleum reservoirs and hence ultimately to improved techniques with more accurate uncertainty quantification. © 2013 Springer Science+Business Media Dordrecht.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume II. Chapters 6-10)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Entropy analysis on non-equilibrium two-phase flow models
Karwat, H.; Ruan, Y.Q. [Technische Universitaet Muenchen, Garching (Germany)
1995-09-01
A method of entropy analysis according to the second law of thermodynamics is proposed for the assessment of a class of practical non-equilibrium two-phase flow models. Entropy conditions are derived directly from a local instantaneous formulation for an arbitrary control volume of a structural two-phase fluid, which are finally expressed in terms of the averaged thermodynamic independent variables and their time derivatives as well as the boundary conditions for the volume. On the basis of a widely used thermal-hydraulic system code it is demonstrated with practical examples that entropy production rates in control volumes can be numerically quantified by using the data from the output data files. Entropy analysis using the proposed method is useful in identifying some potential problems in two-phase flow models and predictions as well as in studying the effects of some free parameters in closure relationships.
Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
Brauner, N.; Rovinsky, J.; Maron, D.M. [Tel-Aviv Univ. (Israel)
1995-09-01
The present study represents a complete analytical solution for laminar two-phase flows with curved interfaces. The solution of the Navier-Stokes equations for the two-phases in bipolar coordinates provides the `flow monograms` describe the relation between the interface curvature and the insitu flow geometry when given the phases flow rates and viscosity ratios. Energy considerations are employed to construct the `interface monograms`, whereby the characteristic interfacial curvature is determined in terms of the phases insitu holdup, pipe diameter, surface tension, fluids/wall adhesion and gravitation. The two monograms are then combined to construct the system `operational monogram`. The `operational monogram` enables the determination of the interface configuration, the local flow characteristics, such as velocity profiles, wall and interfacial shear stresses distribution as well as the integral characteristics of the two-phase flow: phases insitu holdup and pressure drop.
The solidification of two-phase heterogeneous materials: Theory versus experiment
ZHANG Bin; KIM Tongbeum; LU TianJian
2009-01-01
The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied. The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model for two selected porosities (ε), ε=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.
Numerical Study of Void Fraction Distribution Propagation in Gas-Liquid Two-Phase Flow
YANG Jianhui; LI Qing; LU Wenqiang
2005-01-01
A dynamic propagation model was developed for waves in two-phase flows by assuming that continuity waves and dynamic waves interact nonlinearly for certain flow conditions. The drift-flux model is solved with the one-dimensional continuity equation for gas-liquid two-phase flows as an initial-boundary value problem solved using the characteristic-curve method. The numerical results give the void fraction distribution propagation in a gas-liquid two-phase flow which shows how the flow pattern transition occurs. The numerical simulations of different flow patterns show that the void fraction distribution propagation is determined by the characteristics of the drift-flux between the liquid and gas flows and the void fraction range. Flow pattern transitions begin around a void fraction of 0.27 and end around 0.58. Flow pattern transitions do not occur for very high void concentrations.
On Riemann Solvers and Kinetic Relations for Isothermal Two-Phase Flows with Surface Tension
Rohde, Christian
2016-01-01
We consider a sharp-interface approach for the inviscid isothermal dynamics of compressible two-phase flow, that accounts for phase transition and surface tension effects. To fix the mass exchange and entropy dissipation rate across the interface kinetic relations are frequently used. The complete uni-directional dynamics can then be understood by solving generalized two-phase Riemann problems. We present new well-posedness theorems for the Riemann problem and corresponding computable Riemann solvers, that cover quite general equations of state, metastable input data and curvature effects. The new Riemann solver is used to validate different kinetic relations on physically relevant problems including a comparison with experimental data. Riemann solvers are building blocks for many numerical schemes that are used to track interfaces in two-phase flow. It is shown that the new Riemann solver enables reliable and efficient computations for physical situations that could not be treated before.
Two-phase application of multi-objective genetic algorithms in green building design
Wang, W.; Zmeureanu, R. [Concordia Univ., Centre for Building Studies, Montreal, PQ (Canada). Dept. of Building, Civil and Environmental Engineering; Rivard, H. [Ecole de Technologie Superieure, Montreal, PQ (Canada). Dept. of Construction Engineering
2005-07-01
The application of multi-objective genetic algorithms for green building design in two phases were presented in order to better help designers in the decision-making process. The purpose is to minimize two conflicting criteria: the life-cycle cost and the life-cycle environmental impact. Environmental impact criteria examined include energy and non-energy natural resources, global warming, and acidification. Variables focus on building envelope-related parameters. The application of multi-objective genetic algorithms is divided into two phases. The first phase intends to help designers in understanding the trade-off relationship between the two conflicting criteria. The second phase intends to refine the performance region that is of the designer's interest. The results after the two-phase application of the multi objective genetic algorithm were then presented. 13 refs., 4 tabs., 3 figs.
Numerical Simulation of Erosion-Corrosion in the Liquid Solid Two-Phase Flow
无
2000-01-01
Erosion-corrosion of liquid-solid two-phase flow occurring in a pipe with sudden expansion in cross section is numerically simulated in this paper. The global model for erosion-corrosion process includes three main components: the liquid-solid two-phase flow model, erosion model and corrosion model. The Euierian-Lagranglan approach is used to simulate liquid-solid two-phase flow, while the stochastic trajectory model was adopted to obtain properties of particle phase. Two-way coupling effect between the fluid and the particle phase is considered in the model. The accuracy of the models is tested by the data in the reference. The comparison shows that the model is basically correct and feasible.
OPTIMIZATION DESIGN OF GAS-PARTICLE TWO-PHASE AXIAL-FLOW FAN
无
2000-01-01
Based on the shaping theory of writhed blade in streamline design, the geometric shape of blade is designed and then computational formulas for the dynamic design of fan with writhed the blades in gas-particle two-phase axial-flow are derived with the two-phase continuum coupling model. Concurrently, the correlation between the structure of impeller and flow-field dynamic functional parameters is presented. Further, the software for the optimization design of gas-particle two-phase axial-flow fan with writhed blades is obtained. By means of the available software, a sample fan is formed with its all dynamic characteristic curves and geometric shape. Finally, the conclusion on the effect of particles on fan running is reached, quantitatively and qualitatively, as is expected in the fan industry.
Investigation of two-phase heat transfer coefficients of argon-freon cryogenic mixed refrigerants
Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon
2014-11-01
Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon-freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.
The Two-Phase Hell-Shaw Flow: Construction of an Exact Solution
Malaikah, K. R.
2013-03-01
We consider a two-phase Hele-Shaw cell whether or not the gap thickness is time-dependent. We construct an exact solution in terms of the Schwarz function of the interface for the two-phase Hele-Shaw flow. The derivation is based upon the single-valued complex velocity potential instead of the multiple-valued complex potential. As a result, the construction is applicable to the case of the time-dependent gap. In addition, there is no need to introduce branch cuts in the computational domain. Furthermore, the interface evolution in a two-phase problem is closely linked to its counterpart in a one-phase problem
Two-Phase Cooling of Targets and Electronics for Particle Physics Experiments
Thome, J R; Park, J E
2009-01-01
An overview of the LTCM lab’s decade of experience with two-phase cooling research for computer chips and power electronics will be described with its possible beneficial application to high-energy physics experiments. Flow boiling in multi-microchannel cooling elements in silicon (or aluminium) have the potential to provide high cooling rates (up to as high as 350 W/cm2), stable and uniform temperatures of targets and electronics, and lightweight construction while also minimizing the fluid inventory. An overview of two-phase flow and boiling research in single microchannels and multi-microchannel test elements will be presented together with video images of these flows. The objective is to stimulate discussion on the use of two-phase cooling in these demanding applications, including the possible use of CO2.
An Implicit Numerical Method for the Simulation of Two-phase Flow
Yoon, Han Young; Lee, Seung-Jun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Jeong, Jae Jun [Pusan National University, Busan (Korea, Republic of)
2015-10-15
An implicit numerical method is presented for the analysis of two-phase flows in PWRs. Numerical stability and efficiency are improved by decoupling energy equations from the pressure equation. All the convection and diffusion terms are calculated implicitly. The proposed numerical method is verified against conceptual two-phase flow problems. An implicit numerical method has been proposed for two-phase calculation where energy equations are decoupled from the pressure equation. Convection and diffusion terms are calculated implicitly. The calculation results are the same for PME-explicit, PM explicit, and PM-implicit. Large time step size has been tested with PM-implicit-c and the results are also the same.
Thermodynamic properties and mixing thermodynamic parameters of two-phase metallic melts
Jian Zhang
2005-01-01
Based on the calculating model of metallic melts involving eutectic, the calculating equations of mixing thermodynamic parameters for two phase metallic melts have been formulated in the light of those equations of homogeneous solutions. Irrespective as to whether the activity deviation relative to Raoultian behavior is positive or negative, or the deviation is symmetrical or unsymmetrical, the evaluated results not only agree well with experimental values, but also strictly obey the mass action law. This testifies that these equations can authentically reflect the structural reality and mixing thermodynamic characteristics of two-phase metallic melts. The calculating equations of mixing thermodynamic parameters for the model of two phase metallic melts offer two practical criteria (activity and mixing thermodynamic parameters) and one theoretical criterion (the mass action law).
Selective separation and enrichment of proteins in aqueous two-phase extraction system
Feng Qu; Hao Qin; Min Dong; Dong Xu Zhao; Xin Ying Zhao; Jing Hua Zhang
2009-01-01
A simple aqueous two-phase extraction system(ATPS)of PEG/phosphate was proposed for selective separation and enrichment of proteins.The combination of ATPE with HPLC was applied to identify the partition of proteins in two phases.Five proteins (bovine serum albumin,Cytochrome C,lysozyme,myoglobin,and trypsin)were used as model proteins to study the effect of phosphate concentration and pH on proteins partition.The PEG/phosphate system was firstly applied to real human saliva and plasma samples,some proteins showed obviously different partition in two phases.The primary results manifest the selective separation and enrichment of proteins in ATPS provided the potential for high abundance proteins depletion in proteomics.
Two-phase pressure drop across a hydrofoil-based micro pin device using R-123
Kosar, Ali [Mechatronics Engineering Program, Sabanci University, Orhanli, Tuzla, 34956 Istanbul (Turkey)
2008-05-15
The two-phase pressure drop in a hydrofoil-based micro pin fin heat sink has been investigated using R-123 as the working fluid. Two-phase frictional multipliers have been obtained over mass fluxes from 976 to 2349 kg/m{sup 2} s and liquid and gas superficial velocities from 0.38 to 1.89 m/s and from 0.19 to 24 m/s, respectively. It has been found that the two-phase frictional multiplier is strongly dependent on flow pattern. The theoretical prediction using Martinelli parameter based on the laminar fluid and laminar gas flow represented the experimental data fairly well for the spray-annular flow. For the bubbly and wavy-intermittent flow, however, large deviations from the experimental data were recorded. The Martinelli parameter was successfully used to determine the flow patterns, which were bubbly, wavy-intermittent, and spray-annular flow in the current study. (author)
Reduced-gravity two-phase flow experiments in the NASA KC-135
Cuta, Judith M.; Michener, Thomas E.; Best, Frederick R.; Kachnik, Leo J.
1988-01-01
An adequate understanding is sought of flow and heat transfer behavior in reduced and zero gravity conditions. Microgravity thermal-hydraulic analysis capabilities were developed for application to space nuclear power systems. A series of reduced gravity two phase flow experiments using the NASA KC-135 were performed. The objective was to supply basic thermal hydraulic information that could be used in development of analytical tools for design of space power systems. The experiments are described. Two main conclusions were drawn. First, the tests demonstrate that the KC-135 is a suitable test environment for obtaining two phase flow and heat transfer data in reduced gravity conditions. Second, the behavior of two phase flow in low gravity is sufficiently different from that obtained in 1 g to warrant intensive investigation of the phenomenon if adequate analytical tools are to be developed for microgravity conditions.
Diophantine approximation and badly approximable sets
Kristensen, S.; Thorn, R.; Velani, S.
2006-01-01
. The classical set Bad of `badly approximable' numbers in the theory of Diophantine approximation falls within our framework as do the sets Bad(i,j) of simultaneously badly approximable numbers. Under various natural conditions we prove that the badly approximable subsets of Omega have full Hausdorff dimension......Let (X,d) be a metric space and (Omega, d) a compact subspace of X which supports a non-atomic finite measure m. We consider `natural' classes of badly approximable subsets of Omega. Loosely speaking, these consist of points in Omega which `stay clear' of some given set of points in X....... Applications of our general framework include those from number theory (classical, complex, p-adic and formal power series) and dynamical systems (iterated function schemes, rational maps and Kleinian groups)....
Numerical investigation of the mechanism of two-phase flow instability in parallel narrow channels
Hu, Lian [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); Chen, Deqi, E-mail: chendeqi@cqu.edu.cn [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Huang, Yanping, E-mail: hyanping007@163.com [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Yuan, Dewen; Wang, Yanling [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Pan, Liangming [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China)
2015-06-15
Highlights: • A mathematical model is proposed to predict the two-phase flow instability. • The mathematical model predicted result agrees well with the experimental result. • Oscillation characteristics of the two-phase flow instability is discussed in detail. - Abstract: In this paper, the mechanism of two-phase flow instability in parallel narrow channels is studied theoretically, and the characteristic of the flow instability is discussed in detail. Due to the significant confining effect of the narrow channel on the vapor–liquid interface, the two-phase flow resistance in the narrow channel is probably different from that in conventional channel. Therefore, the vapor confined number (N{sub conf}), defined by the size of narrow channel and bubble detachment diameter, is considered in the “Chisholm B model” to investigate the two-phase flow pressure drop. The flow instability boundaries are plotted in parameter plane with phase-change-number (N{sub pch}) and subcooling-number (N{sub sub}) under different working conditions. It is found that the predicted result agrees well with the experimental result. According to the predicted result, the oscillation behaviors near the flow instability boundary indicate that the Supercritical Hopf bifurcation appears in high sub-cooled region and the Subcritical Hopf bifurcation appears in low sub-cooled region. Also, a detailed analysis about the effects of key parameters on the characteristic of two-phase flow instability and the flow instability boundary is proposed, including the effects of inlet subcooling, heating power, void distribution parameter and drift velocity.
无
2001-01-01
Based on the Biot's theory about two-phase saturated medium, according to the character of d function, the Green function on two-phase saturated medium by the point source under concentrated force can be derived. By the Betti's theorem for the two-phase saturated medium field, the source vector and static displacement field by elastic dislocation on the two-phase saturated medium were comprehensively discussed.
RESEARCH ON THE FLOW STABILITY IN A CYLINDRICAL PARTICLE TWO-PHASE BOUNDARY LAYER
林建忠; 聂德明
2003-01-01
Based on the momentum and constitutive equations, the modified Orr-Sommerfeld equation describing the flow stability in a cylindrical particle two-phase flow was derived. For a cylindrical particle two-phase boundary layer, the neutral stability curves and critical Reynolds number were given with numerical simulation. The results show that the cylindrical particles have a suppression effect on the flow instability, the larger the particle volume fraction and the particle aspect-ratio are, the more obvious the suppression effect is.
Investigation on two-phase flow instability in steam generator of integrated nuclear reactor
无
1996-01-01
In the pressure range of 3-18MPa,high pressure steam-water two-phase flow density wave instability in vertical upward parallel pipes with inner diameter of 12mm is studied experimentally.The oscillation curves of two-phase flow instability and the effects of several parameters on the oscillation threshold of the system are obtained.Based on the small pertubation linearization method and the stability principles of automatic control system,a mathematical model is developed to predict the characteristics of density wave instability threshold.The predictions of the model are in good agreement with the experimental results.
Research of Characteristics of Gas-liquid Two-phase Pressure Drop in Microreactor
Li Dan
2015-01-01
With the research system of nitrogen and deionized water, this paper researches the pressure drop of gas-liquid two-phase flow in the circular microchannel with an inner diameter which is respectively 0.9mm and 0.5mm, analyzes the effect of microchannel diameter on gas-liquid two-phase frictional pressure drop in the microchannel reactor, and compares with the result of frictional pressure drop and the predicting result of divided-phase flow pattern. The result shows that, the gas-liquid two-...
Problems of heat transfer and hydraulics of two-phase media
Kutateladze, S S
1969-01-01
Problems of Heat Transfer and Hydraulics of Two-Phase Media presents the theory of heat transfer and hydrodynamics. This book discusses the various aspects of heat transfer and the flow of two-phase systems. Organized into two parts encompassing 22 chapters, this book starts with an overview of the laws of similarity for heat transfer to or from a flowing liquid with various physical properties and allowed for variation in viscosity and thermal conductivity. This book then explores the general functional relationship that exists between viscosity and thermal conductivity for thermodynamically
Camomile autofermentation in polyethylene glycol/dextran two-phase system
Đaković Sanja D.
2008-01-01
Full Text Available The objective of this study was the investigation of the extractive bioconversion of apigenin-7-O-β-glucoside in camomile ligulate flowers into apigenin by autofermentation in polyethylene glycol 6000/dextran 200000 two-phase system. In 22.5% polyethylene glycol/14% dextran aqueous two-phase system the obtained yield of apigenin in the top phase was 96.5%. In the presence of plant material that partiotioned to the interphase, the yield of apigenin in the top phase was 3.5 times higher in comparison to the model system.
Two-phase flow stability structure in a natural circulation system
Zhou, Zhiwei [Nuclear Engineering Laboratory Zurich (Switzerland)
1995-09-01
The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.
Characterization of annular two-phase gas-liquid flows in microgravity
Bousman, W. Scott; Mcquillen, John B.
1994-01-01
A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
Thermal Marangoni Convection of Two-phase Dusty Fluid Flow along a Vertical Wavy Surface
S. Siddiqa
2017-01-01
Full Text Available The paper considers the influence of thermal Marangoni convection on boundary layer flow of two-phase dusty fluid along a vertical wavy surface. The dimensionless boundary layer equations for two-phase problem are reduced to a convenient form by primitive variable transformations (PVF and then integrated numerically by employing the implicit finite difference method along with the Thomas Algorithm. The effect of thermal Marangoni convection, dusty water and sinusoidal waveform are discussed in detail in terms of local heat transfer rate, skin friction coefficient, velocity and temperature distributions. This investigation reveals the fact that the water-particle mixture reduces the rate of heat transfer, significantly.
Position Control of Synchronous Motor Drive by Modified Adaptive Two-phase Sliding Mode Controller
Mohamed Said Sayed Ahmed; Ping Zhang; Yun-Jie Wu
2008-01-01
A modified adaptive two-phase sliding mode controller for the synchronous motor drive that is highly robust to uncertain-ties and external disturbances is proposed in this paper. The proposed controller uses two-phase sliding mode control (SMC) where the 1st phase mainly controls the system in steady states and disturbed states-it is a smoothing phase. The 2nd phase is used mainly in the case of disturbed states. Also, it is an autotuning phase and uses a simple adaptive algorithm to tune the gain of conventional variable structure control (VSC). The modified controller is useful in position control of a permanent magnet synchronous drive.
A phenomenological model of two-phase (air/fuel droplet developing and breakup
Pavlović Radomir R.
2013-01-01
Full Text Available Effervescent atomization namely the air-filled liquid atomization comprehends certain complex two-phase phenomenon that are difficult to be modeled. Just a few researchers have found the mathematical expressions for description of the complex atomization model of the two-phase mixture air/diesel fuel. In the following review, developing model of twophase (air/fuel droplet of Cummins spray pump-injector is shown. The assumption of the same diameters of the droplet and the opening of the atomizer is made, while the air/fuel mass ratio inside the droplet varies.
Determination of production-shipment policy using a two-phase algebraic approach
Huei-Hsin Chang
2012-04-01
Full Text Available The optimal production-shipment policy for end products using mathematicalmodeling and a two-phase algebraic approach is investigated. A manufacturing systemwith a random defective rate, a rework process, and multiple deliveries is studied with thepurpose of deriving the optimal replenishment lot size and shipment policy that minimisestotal production-delivery costs. The conventional method uses differential calculus on thesystem cost function to determine the economic lot size and optimal number of shipmentsfor such an integrated vendor-buyer system, whereas the proposed two-phase algebraicapproach is a straightforward method that enables practitioners who may not havesufficient knowledge of calculus to manage real-world systems more effectively.
The performance of a cryogenic pump for the two-phase flow condition
YAMADA, HITOSHI; WATANABE, Mitsuo; Hasegawa, Satoshi; Kamijo, Kenjiro; 山田, 仁; 渡辺, 光男; 長谷川, 敏; 上條, 謙二郎
1985-01-01
An experimental investigation was carried out in order to obtain the performance characteristics of a cryogenic pump under a two-phase flow condition. The experiment used an oxygen pump with an inducer and liquid nitrogen as the test fluid. The vapor volumetric fraction at the pump inlet was calculated with an assumption of a constant enthalpy process across an orifice which was used to generate the two-phase flow at the pump inlet. The results showed that the pump head rise did hardly decrea...
Conceptual design of two-phase fluid mechanics and heat transfer facility for spacelab
North, B. F.; Hill, M. E.
1980-01-01
Five specific experiments were analyzed to provide definition of experiments designed to evaluate two phase fluid behavior in low gravity. The conceptual design represents a fluid mechanics and heat transfer facility for a double rack in Spacelab. The five experiments are two phase flow patterns and pressure drop, flow boiling, liquid reorientation, and interface bubble dynamics. Hardware was sized, instrumentation and data recording requirements defined, and the five experiments were installed as an integrated experimental package. Applicable available hardware was selected in the experiment design and total experiment program costs were defined.
On the peculiarities of LDA method in two-phase flows with high concentrations of particles
Poplavski, S. V.; Boiko, V. M.; Nesterov, A. U.
2016-10-01
Popular applications of laser Doppler anemometry (LDA) in gas dynamics are reviewed. It is shown that the most popular method cannot be used in supersonic flows and two-phase flows with high concentrations of particles. A new approach to implementation of the known LDA method based on direct spectral analysis, which offers better prospects for such problems, is presented. It is demonstrated that the method is suitable for gas-liquid jets. Owing to the progress in laser engineering, digital recording of spectra, and computer processing of data, the method is implemented at a higher technical level and provides new prospects of diagnostics of high-velocity dense two-phase flows.
Prestack traveltime approximations
Alkhalifah, Tariq Ali
2012-05-01
Many of the explicit prestack traveltime relations used in practice are based on homogeneous (or semi-homogenous, possibly effective) media approximations. This includes the multifocusing, based on the double square-root (DSR) equation, and the common reflection stack (CRS) approaches. Using the DSR equation, I constructed the associated eikonal form in the general source-receiver domain. Like its wave-equation counterpart, it suffers from a critical singularity for horizontally traveling waves. As a result, I recasted the eikonal in terms of the reflection angle, and thus, derived expansion based solutions of this eikonal in terms of the difference between the source and receiver velocities in a generally inhomogenous background medium. The zero-order term solution, corresponding to ignoring the lateral velocity variation in estimating the prestack part, is free of singularities and can be used to estimate traveltimes for small to moderate offsets (or reflection angles) in a generally inhomogeneous medium. The higher-order terms include limitations for horizontally traveling waves, however, we can readily enforce stability constraints to avoid such singularities. In fact, another expansion over reflection angle can help us avoid these singularities by requiring the source and receiver velocities to be different. On the other hand, expansions in terms of reflection angles result in singularity free equations. For a homogenous background medium, as a test, the solutions are reasonably accurate to large reflection and dip angles. A Marmousi example demonstrated the usefulness and versatility of the formulation. © 2012 Society of Exploration Geophysicists.
Amrhein, Sven; Schwab, Marie-Luise; Hoffmann, Marc; Hubbuch, Jürgen
2014-11-07
Over the last decade, the use of design of experiment approaches in combination with fully automated high throughput (HTP) compatible screenings supported by robotic liquid handling stations (LHS), adequate fast analytics and data processing has been developed in the biopharmaceutical industry into a strategy of high throughput process development (HTPD) resulting in lower experimental effort, sample reduction and an overall higher degree of process optimization. Apart from HTP technologies, lab-on-a-chip technology has experienced an enormous growth in the last years and allows further reduction of sample consumption. A combination of LHS and lab-on-a-chip technology is highly desirable and realized in the present work to characterize aqueous two phase systems with respect to tie lines. In particular, a new high throughput compatible approach for the characterization of aqueous two phase systems regarding tie lines by exploiting differences in phase densities is presented. Densities were measured by a standalone micro fluidic liquid density sensor, which was integrated into a liquid handling station by means of a developed generic Tip2World interface. This combination of liquid handling stations and lab-on-a-chip technology enables fast, fully automated, and highly accurate density measurements. The presented approach was used to determine the phase diagram of ATPSs composed of potassium phosphate (pH 7) and polyethylene glycol (PEG) with a molecular weight of 300, 400, 600 and 1000 Da respectively in the presence and in the absence of 3% (w/w) sodium chloride. Considering the whole ATPS characterization process, two complete ATPSs could be characterized within 24h, including four runs per ATPS for binodal curve determination (less than 45 min/run), and tie line determination (less than 45 min/run for ATPS preparation and 8h for density determination), which can be performed fully automated over night without requiring man power. The presented methodology provides
A New Method for Ultrasound Detection of Interfacial Position in Gas-Liquid Two-Phase Flow
Fábio Rizental Coutinho
2014-05-01
Full Text Available Ultrasonic measurement techniques for velocity estimation are currently widely used in fluid flow studies and applications. An accurate determination of interfacial position in gas-liquid two-phase flows is still an open problem. The quality of this information directly reflects on the accuracy of void fraction measurement, and it provides a means of discriminating velocity information of both phases. The algorithm known as Velocity Matched Spectrum (VM Spectrum is a velocity estimator that stands out from other methods by returning a spectrum of velocities for each interrogated volume sample. Interface detection of free-rising bubbles in quiescent liquid presents some difficulties for interface detection due to abrupt changes in interface inclination. In this work a method based on velocity spectrum curve shape is used to generate a spatial-temporal mapping, which, after spatial filtering, yields an accurate contour of the air-water interface. It is shown that the proposed technique yields a RMS error between 1.71 and 3.39 and a probability of detection failure and false detection between 0.89% and 11.9% in determining the spatial-temporal gas-liquid interface position in the flow of free rising bubbles in stagnant liquid. This result is valid for both free path and with transducer emitting through a metallic plate or a Plexiglas pipe.
Development of an electrical impedance computed tomographic two-phase flows analyzer. Final report
Ovacik, L.; Jones, O.C.
1998-08-01
This report summarizes the work on the research project on this cooperative program between DOE and Hitachi, Ltd. Major advances were made in the computational reconstruction of images from electrical excitation and response data with respect to existing capabilities reported in the literature. A demonstration is provided of the imaging of one or more circular objects within the measurement plane with demonstrated linear resolution of six parts in two hundred. At this point it can be said that accurate excitation and measurement of boundary voltages and currents appears adequate to obtain reasonable images of the real conductivity distribution within a body and the outlines of insulating targets suspended within a homogeneous conducting medium. The quality of images is heavily dependent on the theoretical and numerical implementation of imaging algorithms. The overall imaging system described has the potential of being both fast and cost effective in comparison with alternative methods. The methods developed use multiple plate-electrode excitation in conjunction with finite element block decomposition, preconditioned voltage conversion, layer approximation of the third dimension and post processing of boundary measurements to obtain optimal boundary excitations. Reasonably accurate imaging of single and multiple targets of differing size, location and separation is demonstrated and the resulting images are better than any others found in the literature. Recommendations for future effort include the improvement in computational algorithms with emphasis on internal conductivity shape functions and the use of adaptive development of quadrilateral (2-D) or tetrahedral or hexahedral (3-D) elements to coincide with large discrete zone boundaries in the fields, development of a truly binary model and completion of a fast imaging system. Further, the rudimentary methods shown herein for three-dimensional imaging need improving.
Zhou, Yijie [ORNL; Lim, Hyun-Kyung [ORNL; de Almeida, Valmor F [ORNL; Navamita, Ray [State University of New York, Stony Brook; Wang, Shuqiang [State University of New York, Stony Brook; Glimm, James G [ORNL; Li, Xiao-lin [State University of New York, Stony Brook; Jiao, Xiangmin [ORNL
2012-06-01
This progress report describes the development of a front tracking method for the solution of the governing equations of motion for two-phase micromixing of incompressible, viscous, liquid-liquid solvent extraction processes. The ability to compute the detailed local interfacial structure of the mixture allows characterization of the statistical properties of the two-phase mixture in terms of droplets, filaments, and other structures which emerge as a dispersed phase embedded into a continuous phase. Such a statistical picture provides the information needed for building a consistent coarsened model applicable to the entire mixing device. Coarsening is an undertaking for a future mathematical development and is outside the scope of the present work. We present here a method for accurate simulation of the micromixing dynamics of an aqueous and an organic phase exposed to intense centrifugal force and shearing stress. The onset of mixing is the result of the combination of the classical Rayleigh- Taylor and Kelvin-Helmholtz instabilities. A mixing environment that emulates a sector of the annular mixing zone of a centrifugal contactor is used for the mathematical domain. The domain is small enough to allow for resolution of the individual interfacial structures and large enough to allow for an analysis of their statistical distribution of sizes and shapes. A set of accurate algorithms for this application requires an advanced front tracking approach constrained by the incompressibility condition. This research is aimed at designing and implementing these algorithms. We demonstrate verification and convergence results for one-phase and unmixed, two-phase flows. In addition we report on preliminary results for mixed, two-phase flow for realistic operating flow parameters.
Lattice-Boltzmann-based two-phase thermal model for simulating phase change
Kamali, M.R.; Gillissen, J.J.J.; Van den Akker, H.E.A.; Sundaresan, S.
2013-01-01
A lattice Boltzmann (LB) method is presented for solving the energy conservation equation in two phases when the phase change effects are included in the model. This approach employs multiple distribution functions, one for a pseudotemperature scalar variable and the rest for the various species. A
Two-phase (bio)catalytic reactions in a table-top centrifugal contact separator
Kraai, Gerard N.; Zwol, Floris van; Schuur, Boelo; Heeres, Hero J.; Vries, Johannes G. de
2008-01-01
A new spin on catalysis: A table-top centrifugal contact separator allows for fast continuous two-phase reactions to be performed by intimately mixing two immiscible phases and then separating them. Such a device has been used to produce biodiesel from sunflower oil and MeOH/NaOMe. A lipase-catalyze
Kraai, Gerard N.; Schuur, Boelo; van Zwol, Floris; Haak, Robert M.; Minnaard, Adriaan J.; Feringa, Ben L.; Heeres, Hero J.; de Vries, Johannes G.; Prunier, ML
2009-01-01
Production of fine chemicals is mostly performed in batch reactors. Use of continuous processes has many advantages which may reduce the cost of production. We have developed the use of centrifugal contact separators (CCSs) for continuous two-phase catalytic reactions. This equipment has previously
Multi-scale symbolic time reverse analysis of gas-liquid two-phase flow structures
Wang, Hongmei; Zhai, Lusheng; Jin, Ningde; Wang, Youchen
Gas-liquid two-phase flows are widely encountered in production processes of petroleum and chemical industry. Understanding the dynamic characteristics of multi-scale gas-liquid two-phase flow structures is of great significance for the optimization of production process and the measurement of flow parameters. In this paper, we propose a method of multi-scale symbolic time reverse (MSTR) analysis for gas-liquid two-phase flows. First, through extracting four time reverse asymmetry measures (TRAMs), i.e. Euclidean distance, difference entropy, percentage of constant words and percentage of reversible words, the time reverse asymmetry (TRA) behaviors of typical nonlinear systems are investigated from the perspective of multi-scale analysis, and the results show that the TRAMs are sensitive to the changing of dynamic characteristics underlying the complex nonlinear systems. Then, the MSTR analysis is used to study the conductance signals from gas-liquid two-phase flows. It is found that the multi-scale TRA analysis can effectively reveal the multi-scale structure characteristics and nonlinear evolution properties of the flow structures.
Two-Phase Flow in Rotating Hele-Shaw Cells with Coriolis Effects
Escher, Joachim; Walker, Christoph
2011-01-01
The free boundary problem of a two phase flow in a rotating Hele-Shaw cell with Coriolis effects is studied. Existence and uniqueness of solutions near spheres is established, and the asymptotic stability and instability of the trivial solution is characterized in dependence on the fluid densities.
Extraction of peptide tagged cutinase in detergent-based aqueous two-phase systems
Rodenbrock, A.; Selber, K.; Egmond, M.R.; Kula, M.-R.
2010-01-01
Detergent-based aqueous two-phase systems have the advantage to require only one auxiliary chemical to induce phase separation above the cloud point. In a systematic study the efficiency of tryptophan-rich peptide tags was investigated to enhance the partitioning of an enzyme to the detergent-rich p
Effects of Gravity and Inlet Location on a Two-Phase Countercurrent Imbibition in Porous Media
M. F. El-Amin
2012-01-01
Full Text Available We introduce a numerical investigation of the effect of gravity on the problem of two-phase countercurrent imbibition in porous media. We consider three cases of inlet location, namely, from, side, top, and bottom. A 2D rectangular domain is considered for numerical simulation. The results indicate that gravity has a significant effect depending on open-boundary location.
Nonequilibrium capillarity effects in two-phase flow through porous media at different scales
Bottero, S.; Hassanizadeh, S.M.; Kleingeld, P.J.; Heimovaara, T.J.
2011-01-01
A series of primary drainage experiments was carried out in order to investigate nonequilibrium capillarity effects in two-phase flow through porous media. Experiments were performed with tetrachloroethylene (PCE) and water as immiscible fluids in a sand column 21 cm long. Four drainage experiments
THE LINEAR HOMOGENEOUS FLOW MODEL FOR TWO-PHASE FLOW INSTABILITY IN BOILING CHANNELS
无
2002-01-01
This paper presents liner homogeneous model describing two-phase flow instability. Dimensionless parameter η was derived by using the linear homogeneous model. Using parameter η the stability of a system could be easily judged. The calculated results agree with the experimental data well.
Effects of Particles Collision on Separating Gas–Particle Two-Phase Turbulent Flows
Sihao, L. V.
2013-10-10
A second-order moment two-phase turbulence model incorporating a particle temperature model based on the kinetic theory of granular flow is applied to investigate the effects of particles collision on separating gas–particle two-phase turbulent flows. In this model, the anisotropy of gas and solid phase two-phase Reynolds stresses and their correlation of velocity fluctuation are fully considered using a presented Reynolds stress model and the transport equation of two-phase stress correlation. Experimental measurements (Xu and Zhou in ASME-FED Summer Meeting, San Francisco, Paper FEDSM99-7909, 1999) are used to validate this model, source codes and prediction results. It showed that the particles collision leads to decrease in the intensity of gas and particle vortices and takes a larger effect on particle turbulent fluctuations. The time-averaged velocity, the fluctuation velocity of gas and particle phase considering particles colli-sion are in good agreement with experimental measurements. Particle kinetic energy is always smaller than gas phase due to energy dissipation from particle collision. Moreover, axial– axial and radial–radial fluctuation velocity correlations have stronger anisotropic behaviors. © King Fahd University of Petroleum and Minerals 2013
Approaches to myosin modelling in a two-phase flow model for cell motility
Kimpton, L. S.; Whiteley, J. P.; Waters, S. L.; Oliver, J. M.
2016-04-01
A wide range of biological processes rely on the ability of cells to move through their environment. Mathematical models have been developed to improve our understanding of how cells achieve motion. Here we develop models that explicitly track the cell's distribution of myosin within a two-phase flow framework. Myosin is a small motor protein which is important for contracting the cell's actin cytoskeleton and enabling cell motion. The two phases represent the actin network and the cytosol in the cell. We start from a fairly general description of myosin kinetics, advection and diffusion in the two-phase flow framework, then identify a number of sub-limits of the model that may be relevant in practice, two of which we investigate further via linear stability analyses and numerical simulations. We demonstrate that myosin-driven contraction of the actin network destabilizes a stationary steady state leading to cell motion, but that rapid diffusion of myosin and rapid unbinding of myosin from the actin network are stabilizing. We use numerical simulation to investigate travelling-wave solutions relevant to a steadily gliding cell and we consider a reduction of the model in which the cell adheres strongly to the substrate on which it is crawling. This work demonstrates that a number of existing models for the effect of myosin on cell motility can be understood as different sub-limits of our two-phase flow model.
Milking microalga Dunaliella salina for Beta-carotene production in two-phase bioreactors
Hejazi, M.; Holwerda, E.; Wijffels, R.H.
2004-01-01
A new method was developed for production of beta-carotene from Dunaliella salina. Cells were grown in low light intensity and then transferred to a production bioreactor illuminated at a higher light intensity. It was a two-phase bioreactor consisting of an aqueous and a biocompatible organic phase
Generating a Two-Phase Lesson for Guiding Beginners to Learn Basic Dance Movements
Yang, Yang; Leung, Howard; Yue, Lihua; Deng, Liqun
2013-01-01
In this paper, an automated lesson generation system for guiding beginners to learn basic dance movements is proposed. It analyzes the dance to generate a two-phase lesson which can provide a suitable cognitive load thus offering an efficient learning experience. In the first phase, the dance is divided into small pieces which are patterns, and…
Kang, Han-Ok; Han, Hun Sik; Kim, Young-In; Kim, Keung Koo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-05-15
Reduction of installation space for steam generators can lead to much smaller reactor vessel with resultant decrease of overall manufacturing cost for the components. A PCHE(Printed Circuit Heat Exchanger) is one of the compact types of heat exchangers available as an alternative to conventional shell and tube heat exchangers. Its name is derived from the procedure used to manufacture the flat metal plates that form the core of the heat exchanger, which is done by chemical milling. These plates are then stacked and diffusion bonded, converting the plates into a solid metal block containing precisely engineered fluid flow passages. PCSG(Printed Circuit Steam Generator) is a potential candidate to be applied to the integral reactor with its compactness and mechanical robustness. For the introduction of new steam generator, design requirement for the two-phase flow instability should be considered. This paper describes two-phase flow instability characteristics of PCSG for the low pressure condition. PCSG is a potential candidate to be applied to the integral reactor with its compactness and mechanical robustness. Interconnecting flow path was developed to mitigate the two-phase flow instability in the cold side. The flow characteristics of two-phase flow instability at the PCSG is examined experimentally in this study.
A Chebyshev collocation method for solving two-phase flow stability problems
Boomkamp, P.A.M.; Boersma, B.J.; Miesen, R.H.M.; Beijnon, G.V.
1997-01-01
This paper describes a Chebyshev collocation method for solving the eigenvalue problem that governs the stability of parallel two-phase flow. The method is based on the expansion of the eigenfunctions in terms of Chebyshev polynomials, point collocation, and the subsequent solution of the resulting
Measurements of solids concentration and axial solids velocity in gas-solid two-phase flows.
Nieuwland, J.J.; Meijer, R.; Kuipers, J.A.M.; Swaaij, van W.P.M.
1996-01-01
Several techniques reported in the literature for measuring solids concentration and solids velocity in (dense) gas-solid two-phase flow have been briefly reviewed. An optical measuring system, based on detection of light reflected by the suspended particles, has been developed to measure local soli
Affinity partitioning of human antibodies in aqueous two-phase systems
Rosa, P. A. J.; Azevedo, A. M.; Ferreira, I. F.; de Vries, J.; Korporaal, R.; Verhoef, H. J.; Visser, T. J.; Aires-Barros, M. R.
2007-01-01
The partitioning of human immunoglobulin (IgG) in a polymer-polymer and polymer-salt aqueous two-phase system (ATPS) in the presence of several functionalised polyethylene glycols (PEGs) was studied. As a first approach, the partition studies were performed with pure IgG using systems in which the t
A Dual-Stage Two-Phase Model of Selective Attention
Hubner, Ronald; Steinhauser, Marco; Lehle, Carola
2010-01-01
The dual-stage two-phase (DSTP) model is introduced as a formal and general model of selective attention that includes both an early and a late stage of stimulus selection. Whereas at the early stage information is selected by perceptual filters whose selectivity is relatively limited, at the late stage stimuli are selected more efficiently on a…
A FINITE ELEMENT COLLOCATION METHOD FOR TWO-PHASE INCOMPRESSIBLE IMMISCIBLE PROBLEMS
Ma Ning
2007-01-01
Two-phase, incompressible, immiscible flow in porous media is governed by a coupled system of nonlinear partial differential equations. The pressure equation is elliptic,whereas the concentration equation is parabolic, and both are treated by the collocation scheme. Existence and uniqueness of solutions of the algorithm are proved. A optimal convergence analysis is given for the method.
Comparison of two-phase and three-phase methanol synthesis processes
van de Graaf, G.H; Beenackers, A.A C M
1996-01-01
A comparison is made between the ICI (two-phase) methanol synthesis process and a three-phase slurry process based on a multi-stage agitated reactor. The process calculations are based on a complete reactor system consisting of the reactor itself, a recycling system and a gas-liquid separator. The b
Gravity Effect on Two-Phase Immiscible Flows in Communicating Layered Reservoirs
Zhang, Xuan; Shapiro, Alexander; Stenby, Erling Halfdan
2012-01-01
An upscaling method is developed for two-phase immiscible incompressible flows in layered reservoirs with good communication between the layers. It takes the effect of gravity into consideration. Waterflooding of petroleum reservoirs is used as a basic example for application of this method...... for gravity segregation. The effects of gravity are analyzed....
Lamb's integral formulas of two-phase saturated medium for soil dynamic with drainage
Bo-yang DING; Gai-hong DANG; Jin-hua YUAN
2010-01-01
When dynamic force is applied to a saturated porous soil,drainage is common.In this paper,the saturated porous soil with a two-phase saturated medium is simulated,and Lamb's integral formulas with drainage and stress formulas for a two-phase saturated medium are given based on Biot's equation and Betti's theorem(the reciprocal theorem).According to the basic solution to Biot's equation,Green's function Gij and three terms of Green's function G4i,Gi4,and G44 of a two-phase saturated medium subject to a concentrated force on a spherical coordinate are presented.The displacement field with drainage,the magnitude of drainage,and the pore pressure of the center explosion source are obtained in computation.The results of the classical Sharpe's solutions and the solutions of the two-phase saturated medium that decays to a single-phase medium are compared.Good agreement is observed.
Effects of Macroparticle Sizes on Two-phase Mixture Discharge Under DC Voltage
YAO Wenjun; HE Zhenghao; DENG Heming; WANG Guoli; ZHANG Man; MA Jun; LI Jin; YE Qizheng; HU Hui
2012-01-01
The discharge laws of the two-phase mixtures are of significance to the lightning protection and external insulation of HV transmission lines under the influence of severe climatic conditions. The initiation and propagation of discharge and its influence factors are the fundamental problems to be studied.
Effects of gravity and inlet location on a two-phase countercurrent imbibition in porous media
El-Amin, Mohamed
2012-01-01
We introduce a numerical investigation of the effect of gravity on the problem of two-phase countercurrent imbibition in porous media. We consider three cases of inlet location, namely, from, side, top, and bottom. A 2D rectangular domain is considered for numerical simulation. The results indicate that gravity has a significant effect depending on open-boundary location.
Well logging interpretation of production profile in horizontal oil-water two phase flow pipes
Zhai, Lu-Sheng; Jin, Ning-De; Gao, Zhong-Ke; Zheng, Xi-Ke
2012-03-01
Due to the complicated distribution of local velocity and local phase hold up along the radial direction of pipe in horizontal oil-water two phase flow, it is difficult to measure the total flow rate and phase volume fraction. In this study, we carried out dynamic experiment in horizontal oil-water two phases flow simulation well by using combination measurement system including turbine flowmeter with petal type concentrating diverter, conductance sensor and flowpassing capacitance sensor. According to the response resolution ability of the conductance and capacitance sensor in different range of total flow rate and water-cut, we use drift flux model and statistical model to predict the partial phase flow rate, respectively. The results indicate that the variable coefficient drift flux model can self-adaptively tone the model parameter according to the oil-water two phase flow characteristic, and the prediction result of partial phase flow rate of oil-water two phase flow is of high accuracy.
23 CFR 636.202 - When are two-phase design-build selection procedures appropriate?
2010-04-01
... 23 Highways 1 2010-04-01 2010-04-01 false When are two-phase design-build selection procedures appropriate? 636.202 Section 636.202 Highways FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION ENGINEERING AND TRAFFIC OPERATIONS DESIGN-BUILD CONTRACTING Selection Procedures, Award Criteria §...
Approximate Sparse Regularized Hyperspectral Unmixing
Chengzhi Deng
2014-01-01
Full Text Available Sparse regression based unmixing has been recently proposed to estimate the abundance of materials present in hyperspectral image pixel. In this paper, a novel sparse unmixing optimization model based on approximate sparsity, namely, approximate sparse unmixing (ASU, is firstly proposed to perform the unmixing task for hyperspectral remote sensing imagery. And then, a variable splitting and augmented Lagrangian algorithm is introduced to tackle the optimization problem. In ASU, approximate sparsity is used as a regularizer for sparse unmixing, which is sparser than l1 regularizer and much easier to be solved than l0 regularizer. Three simulated and one real hyperspectral images were used to evaluate the performance of the proposed algorithm in comparison to l1 regularizer. Experimental results demonstrate that the proposed algorithm is more effective and accurate for hyperspectral unmixing than state-of-the-art l1 regularizer.
Implementation of the interfacial area transport equation in trace for boiling two-phase flows
Bernard, Matthew S.
Correctly predicting the interfacial area concentration (a i) is vital to the overall accuracy of the two-fluid model because ai describes the amount of surface area that exists between the two-phases, and is therefore directly related to interfacial mass, momentum and energy transfer. The conventional method for specifying ai in the two-fluid model is through flow regime-based empirical correlations coupled with regime transition criteria. However, a more physically consistent approach to predicting ai is through the interfacial area transport equation (IATE), which can address the deficiencies of the flow regime-based approach. Some previous studies have been performed to demonstrate the feasibility of IATE in developmental versions of the nuclear reactor systems analysis code, TRACE. However, a full TRACE version capable of predicting boiling two-phase flows with the IATE has not been established. Therefore, the current work develops a version of TRACE that is capable of predicting boiling two-phase flows using the IATE. The development is carried out in stages. First, a version of TRACE which employs the two-group IATE for adiabatic, vertical upward, air-water conditions is developed. An in-depth assessment on the existing experimental database is performed to select reliable experimental data for code assessment. Then, the implementation is assessed against the qualified air-water two-phase flow experimental data. Good agreement is observed between the experimental data for ai and the TRACE code with an average error of +/-9% for all conditions. Following the initial development, one-group IATE models for vertical downward and horizontal two-phase flows are implemented and assessed against qualified data. Finally, IATE models capable of predicting subcooled boiling two-phase flows are implemented. An assessment of the models shows that TRACE is capable of generating ai in subcooled boiling two-phase flows with the IATE and that heat transfer effects dominate
Two-phase flow and boiling heat transfer in two vertical narrow annuli
Peng Changhong [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China)]. E-mail: pxm321@163.com; Guo Yun [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China); Qiu Suizheng [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China); Jia Dounan [Department of Nuclear and Thermal Power Engineering, Xi' an Jiaotong University, Xian 710049 (China); Nie Changhua [Nuclear Power Institute of China, Chengdu 610041 (China)
2005-07-01
Experimental study associated with two-phase flow and heat transfer during flow boiling in two vertical narrow annuli has been conducted. The parameters examined were: mass flux from 38.8 to 163.1 kg/m{sup 2} s; heat flux from 4.9 to 50.7 kW/m{sup 2} for inside tube and from 4.2 to 78.8 kW/m{sup 2} for outside tube; equilibrium mass quality from 0.02 to 0.88; system pressure from 1.5 to 6.0 MPa. It was found that the boiling heat transfer was strongly influenced by heat flux, while the effect of mass velocity and mass quality were not very significant. This suggested that the boiling heat transfer was mainly via nucleate boiling. The data were used to develop a new correlation for boiling heat transfer in the narrow annuli. In the two-phase flow study, the comparison with the correlation of Chisholm [Chisholm, D., 1967. A theoretical basis for the Lockhart-Martinelli correlation for two-phase flow. Int. J. Heat Mass Transfer 10, 1767-1778] and Mishima and Hibiki [Mishima, K., Hibiki, T., 1996. Some characteristics of air-water two-phase flow in small diameter vertical tubes. Int. J. Multiphase Flow 22, 703-712] indicated that the existing correlations could not predict the two-phase multiplier in the narrow annuli well. Based on the experimental data, a new correlation was developed.
Robust risk prediction with biomarkers under two-phase stratified cohort design.
Payne, Rebecca; Yang, Ming; Zheng, Yingye; Jensen, Majken K; Cai, Tianxi
2016-12-01
Identification of novel biomarkers for risk prediction is important for disease prevention and optimal treatment selection. However, studies aiming to discover which biomarkers are useful for risk prediction often require the use of stored biological samples from large assembled cohorts, and thus the depletion of a finite and precious resource. To make efficient use of such stored samples, two-phase sampling designs are often adopted as resource-efficient sampling strategies, especially when the outcome of interest is rare. Existing methods for analyzing data from two-phase studies focus primarily on single marker analysis or fitting the Cox regression model to combine information from multiple markers. However, the Cox model may not fit the data well. Under model misspecification, the composite score derived from the Cox model may not perform well in predicting the outcome. Under a general two-phase stratified cohort sampling design, we present a novel approach to combining multiple markers to optimize prediction by fitting a flexible nonparametric transformation model. Using inverse probability weighting to account for the outcome-dependent sampling, we propose to estimate the model parameters by maximizing an objective function which can be interpreted as a weighted C-statistic for survival outcomes. Regardless of model adequacy, the proposed procedure yields a sensible composite risk score for prediction. A major obstacle for making inference under two phase studies is due to the correlation induced by the finite population sampling, which prevents standard inference procedures such as the bootstrap from being used for variance estimation. We propose a resampling procedure to derive valid confidence intervals for the model parameters and the C-statistic accuracy measure. We illustrate the new methods with simulation studies and an analysis of a two-phase study of high-density lipoprotein cholesterol (HDL-C) subtypes for predicting the risk of coronary heart
P.A.Nikrityuk; K.Eckert; R.Grundmann; B.Willers; S.Eckert
2003-01-01
The main aim of this work is to study numerically the influence of an external magnetic field on the solidification processes of two-component materials. Based on the continuum model of two-phase flow a mathematical model for the directional solidification of a binary alloy in a magnetic field is presented. The model includes mass,momentum, energy and species mass conservation equations written in compressible form and additional relationships describing the temperature-solute coupling. The geometry under study is a cylindrical mold with adiabatic walls and cooled bottom. The macroscale transport in the solidification of alloys is governed by the progress of the two-phase mushy zone, which is treated by means of a porous medium approach. The volume fraction of liquid and solid phases, respectively, is calculated from a 2D approximation of the phase diagram. The results of calculation are compared with experimental data.
Nikrityuk, P. A.; Eckert, K.; Grundmann, R.; Willers, B.; Eckert, S.
2003-11-01
The main aim of this work is to study numerically the influence of an external magnetic field on the solidification processes of two-component materials. Based on the continuum model of two-phase flow a mathematical model for the directional solidification of a binary alloy in a magnetic field is presented. The model includes mass, momentum, energy and species mass conservation equations written in compressible form and additional relationships describing the temperature-solute coupling. The geometry under study is a cylindrical mold with adiabatic walls and cooled bottom. The macroscale transport in the solidification of alloys is governed by the progress of the two-phase mushy zone, which is treated by means of a porous medium approach. The volume fraction of liquid and solid phases, respectively, is calculated from a 2D approximation of the phase diagram. The results of calculation are compared with experimental data.
Mathematical algorithms for approximate reasoning
Murphy, John H.; Chay, Seung C.; Downs, Mary M.
1988-01-01
Most state of the art expert system environments contain a single and often ad hoc strategy for approximate reasoning. Some environments provide facilities to program the approximate reasoning algorithms. However, the next generation of expert systems should have an environment which contain a choice of several mathematical algorithms for approximate reasoning. To meet the need for validatable and verifiable coding, the expert system environment must no longer depend upon ad hoc reasoning techniques but instead must include mathematically rigorous techniques for approximate reasoning. Popular approximate reasoning techniques are reviewed, including: certainty factors, belief measures, Bayesian probabilities, fuzzy logic, and Shafer-Dempster techniques for reasoning. A group of mathematically rigorous algorithms for approximate reasoning are focused on that could form the basis of a next generation expert system environment. These algorithms are based upon the axioms of set theory and probability theory. To separate these algorithms for approximate reasoning various conditions of mutual exclusivity and independence are imposed upon the assertions. Approximate reasoning algorithms presented include: reasoning with statistically independent assertions, reasoning with mutually exclusive assertions, reasoning with assertions that exhibit minimum overlay within the state space, reasoning with assertions that exhibit maximum overlay within the state space (i.e. fuzzy logic), pessimistic reasoning (i.e. worst case analysis), optimistic reasoning (i.e. best case analysis), and reasoning with assertions with absolutely no knowledge of the possible dependency among the assertions. A robust environment for expert system construction should include the two modes of inference: modus ponens and modus tollens. Modus ponens inference is based upon reasoning towards the conclusion in a statement of logical implication, whereas modus tollens inference is based upon reasoning away
Leike, Reimar H
2016-01-01
In Bayesian statistics probability distributions express beliefs. However, for many problems the beliefs cannot be computed analytically and approximations of beliefs are needed. We seek a ranking function that quantifies how "embarrassing" it is to communicate a given approximation. We show that there is only one ranking under the requirements that (1) the best ranked approximation is the non-approximated belief and (2) that the ranking judges approximations only by their predictions for actual outcomes. We find that this ranking is equivalent to the Kullback-Leibler divergence that is frequently used in the literature. However, there seems to be confusion about the correct order in which its functional arguments, the approximated and non-approximated beliefs, should be used. We hope that our elementary derivation settles the apparent confusion. We show for example that when approximating beliefs with Gaussian distributions the optimal approximation is given by moment matching. This is in contrast to many su...
The 2005 Vazcun Valley Lahar: Evaluation of the TITAN2D Two-Phase Flow Model Using an Actual Event.
Williams, R.; Stinton, A. J.; Sheridan, M. F.
2005-12-01
TITAN2D is a depth-averaged, thin-layer computational fluid dynamics (CFD) code, suitable for simulating a variety of geophysical mass flows. TITAN2D output data include pile thickness and flow momentum at each time step for all cells traversed by the flow during the simulation. From this the flow limit, run-out path, pile velocity, deposit thickness, and travel time can be calculated. Results can be visualized in the open source GRASS GIS software or with the built-in TITAN2D viewer. A new two-phase TITAN2D version allows simulation of flows containing various mixtures of water and solids. The purpose of this study is to compare simulations by the two-phase flow version of TITAN2D with an actual event. The chosen natural flow is a small ash-rich lahar (volume approximately 60,000 m3) that occurred on 12 February 2005 in the Vazcún Valley, located on the north-east flank of Volcán Tungurahua, Ecuador. Lahars and pyroclastic flows along this valley could potentially threaten the 20,000 inhabitants living in and near the city of Baños. A variety of data sources exist for this lahar, including: pre- and post-event meter-scale topography, and photographic, video, seismic and acoustic flow monitoring (AFM) records from during the event. These data permit detailed comparisons between the dynamics of the actual lahar and those of the TITAN2D simulated flow. In particular, detailed comparisons are made between run-up heights, flow velocity, inundation area, and deposit area and thickness. Simulations utilize a variety of data derived from field observations such as lahar volume, solid to pore-fluid ratio and pre-event topography. TITAN2D is important in modeling lahars because it allows assessment of the impact of the flows on buildings and infrastructure lifelines located near drainages that descend from volcanoes.
Interfacial area transport for reduced-gravity two-phase flows
Vasavada, Shilp
An extensive experimental and theoretical study of two-phase flow behavior in reduced-gravity conditions has been performed as part of the current research and the results of the same are presented in this thesis. The research was undertaken to understand the behavior of two-phase flows in an environment where the gravity field is reduced as compared to that on earth. The goal of the study was to develop a model capable of predicting the flow behavior. An experimental program was developed and accomplished which simulated reduced-gravity conditions on earth by using two liquids of similar density, thereby decreasing the body force effect akin to actual reduced-gravity conditions. The justification and validation of this approach has been provided based on physical arguments as well as comparison of acquired data with that obtained aboard parabolic flights by previous researchers. The experimental program produced an extensive dataset of local and averaged two-phase flow parameters using state-of-the-art instrumentation. Such data were acquired for a wide range of flow conditions at different radial and axial locations in a 25 mm inner diameter test facility. The current dataset is, in the author's opinion, the most extensive and detailed dataset available for such conditions at present. Analysis of the data revealed important differences between two-phase flows in normal and reduced-gravity conditions. The data analysis also highlighted key interaction mechanisms between the fluid particles and physical phenomena occurring in two-phase flows under reduced-gravity conditions. The interfacial area transport equation (IATE) for reduced-gravity conditions has been developed by considering two groups of bubbles/drops and mechanistically modeling the interaction mechanisms. The developed model has been benchmarked against the acquired data and the predictions of the model compared favorably against the experimental data. This signifies the success achieved in modeling
Zhang, G; Stillinger, F H; Torquato, S
2016-12-28
Disordered hyperuniform many-particle systems have attracted considerable recent attention, since they behave like crystals in the manner in which they suppress large-scale density fluctuations, and yet also resemble statistically isotropic liquids and glasses with no Bragg peaks. One important class of such systems is the classical ground states of "stealthy potentials." The degree of order of such ground states depends on a tuning parameter χ. Previous studies have shown that these ground-state point configurations can be counterintuitively disordered, infinitely degenerate, and endowed with novel physical properties (e.g., negative thermal expansion behavior). In this paper, we focus on the disordered regime (0 two-phase media by circumscribing each point with a possibly overlapping sphere of a common radius a: the "particle" and "void" phases are taken to be the space interior and exterior to the spheres, respectively. The hyperuniformity of such two-phase media depends on the sphere sizes: While it was previously analytically proven that the resulting two-phase media maintain hyperuniformity if spheres do not overlap, here we show numerically that they lose hyperuniformity whenever the spheres overlap. We study certain transport properties of these systems, including the effective diffusion coefficient of point particles diffusing in the void phase as well as static and time-dependent characteristics associated with diffusion-controlled reactions. Besides these effective transport properties, we also investigate several related structural properties, including pore-size functions, quantizer error, an order metric, and percolation thresholds. We show that these transport, geometrical, and topological properties of our two-phase media derived from decorated stealthy ground states are distinctly different from those of equilibrium hard-sphere systems and spatially uncorrelated overlapping spheres. As the extent of short-range order increases, stealthy disordered
Approximate analytic solutions to the NPDD: Short exposure approximations
Close, Ciara E.; Sheridan, John T.
2014-04-01
There have been many attempts to accurately describe the photochemical processes that take places in photopolymer materials. As the models have become more accurate, solving them has become more numerically intensive and more 'opaque'. Recent models incorporate the major photochemical reactions taking place as well as the diffusion effects resulting from the photo-polymerisation process, and have accurately described these processes in a number of different materials. It is our aim to develop accessible mathematical expressions which provide physical insights and simple quantitative predictions of practical value to material designers and users. In this paper, starting with the Non-Local Photo-Polymerisation Driven Diffusion (NPDD) model coupled integro-differential equations, we first simplify these equations and validate the accuracy of the resulting approximate model. This new set of governing equations are then used to produce accurate analytic solutions (polynomials) describing the evolution of the monomer and polymer concentrations, and the grating refractive index modulation, in the case of short low intensity sinusoidal exposures. The physical significance of the results and their consequences for holographic data storage (HDS) are then discussed.
Strongly coupled dispersed two-phase flows; Ecoulements diphasiques disperses fortement couples
Zun, I.; Lance, M.; Ekiel-Jezewska, M.L.; Petrosyan, A.; Lecoq, N.; Anthore, R.; Bostel, F.; Feuillebois, F.; Nott, P.; Zenit, R.; Hunt, M.L.; Brennen, C.E.; Campbell, C.S.; Tong, P.; Lei, X.; Ackerson, B.J.; Asmolov, E.S.; Abade, G.; da Cunha, F.R.; Lhuillier, D.; Cartellier, A.; Ruzicka, M.C.; Drahos, J.; Thomas, N.H.; Talini, L.; Leblond, J.; Leshansky, A.M.; Lavrenteva, O.M.; Nir, A.; Teshukov, V.; Risso, F.; Ellinsen, K.; Crispel, S.; Dahlkild, A.; Vynnycky, M.; Davila, J.; Matas, J.P.; Guazelli, L.; Morris, J.; Ooms, G.; Poelma, C.; van Wijngaarden, L.; de Vries, A.; Elghobashi, S.; Huilier, D.; Peirano, E.; Minier, J.P.; Gavrilyuk, S.; Saurel, R.; Kashinsky, O.; Randin, V.; Colin, C.; Larue de Tournemine, A.; Roig, V.; Suzanne, C.; Bounhoure, C.; Brunet, Y.; Tanaka, A.T.; Noma, K.; Tsuji, Y.; Pascal-Ribot, S.; Le Gall, F.; Aliseda, A.; Hainaux, F.; Lasheras, J.; Didwania, A.; Costa, A.; Vallerin, W.; Mudde, R.F.; Van Den Akker, H.E.A.; Jaumouillie, P.; Larrarte, F.; Burgisser, A.; Bergantz, G.; Necker, F.; Hartel, C.; Kleiser, L.; Meiburg, E.; Michallet, H.; Mory, M.; Hutter, M.; Markov, A.A.; Dumoulin, F.X.; Suard, S.; Borghi, R.; Hong, M.; Hopfinger, E.; Laforgia, A.; Lawrence, C.J.; Hewitt, G.F.; Osiptsov, A.N.; Tsirkunov, Yu. M.; Volkov, A.N.
2003-07-01
This document gathers the abstracts of the Euromech 421 colloquium about strongly coupled dispersed two-phase flows. Behaviors specifically due to the two-phase character of the flow have been categorized as: suspensions, particle-induced agitation, microstructure and screening mechanisms; hydrodynamic interactions, dispersion and phase distribution; turbulence modulation by particles, droplets or bubbles in dense systems; collective effects in dispersed two-phase flows, clustering and phase distribution; large-scale instabilities and gravity driven dispersed flows; strongly coupled two-phase flows involving reacting flows or phase change. Topic l: suspensions particle-induced agitation microstructure and screening mechanisms hydrodynamic interactions between two very close spheres; normal stresses in sheared suspensions; a critical look at the rheological experiments of R.A. Bagnold; non-equilibrium particle configuration in sedimentation; unsteady screening of the long-range hydrodynamic interactions of settling particles; computer simulations of hydrodynamic interactions among a large collection of sedimenting poly-disperse particles; velocity fluctuations in a dilute suspension of rigid spheres sedimenting between vertical plates: the role of boundaries; screening and induced-agitation in dilute uniform bubbly flows at small and moderate particle Reynolds numbers: some experimental results. Topic 2: hydrodynamic interactions, dispersion and phase distribution: hydrodynamic interactions in a bubble array; A 'NMR scattering technique' for the determination of the structure in a dispersion of non-brownian settling particles; segregation and clustering during thermo-capillary migration of bubbles; kinetic modelling of bubbly flows; velocity fluctuations in a homogeneous dilute dispersion of high-Reynolds-number rising bubbles; an attempt to simulate screening effects at moderate particle Reynolds numbers using an hybrid formulation; modelling the two-phase
On Element SDD Approximability
Avron, Haim; Toledo, Sivan
2009-01-01
This short communication shows that in some cases scalar elliptic finite element matrices cannot be approximated well by an SDD matrix. We also give a theoretical analysis of a simple heuristic method for approximating an element by an SDD matrix.
Approximate iterative algorithms
Almudevar, Anthony Louis
2014-01-01
Iterative algorithms often rely on approximate evaluation techniques, which may include statistical estimation, computer simulation or functional approximation. This volume presents methods for the study of approximate iterative algorithms, providing tools for the derivation of error bounds and convergence rates, and for the optimal design of such algorithms. Techniques of functional analysis are used to derive analytical relationships between approximation methods and convergence properties for general classes of algorithms. This work provides the necessary background in functional analysis a
Experimental study on steam-water two-phase flow frictional pressure drops in helical coils
无
1997-01-01
Experiments of steam-water two-phase flow frictional pressure drop in a vertical helical coil were carried out in the high-pressure water test loop of Xi'an jiaotong University,The coil is made of stainless steel tube with an inner diameter of 16mm,the helix diameter measured from tube axis to tube axis is 1.3m,and helix angle of the coil is 3.65°,The experimental conditions are:pressurep=4-18MPa,mass velocity G=400-1400kg/(m2.s),inner wall heat flux q=100-700kW/m2,Based on these data,a correlation for predicting the steam-water two-phase flow frictional pressure drop was derived,it can be used for the design of steam generator of HTGR.
Tang, Malcolm S. Y.; Ng, Eng-Poh; Juan, Joon Ching; Ooi, Chien Wei; Ling, Tau Chuan; Woon, Kai Lin; Loke Show, Pau
2016-08-01
It is known that carbon nanotubes show desirable physical and chemical properties with a wide array of potential applications. Nonetheless, their potential has been hampered by the difficulties in acquiring high purity, chiral-specific tubes. Considerable advancement has been made in terms of the purification of carbon nanotubes, for instance chemical oxidation, physical separation, and myriad combinations of physical and chemical methods. The aqueous two-phase separation technique has recently been demonstrated to be able to sort carbon nanotubes based on their chirality. The technique requires low cost polymers and salt, and is able to sort the tubes based on their diameter as well as metallicity. In this review, we aim to provide a review that could stimulate innovative thought on the progress of a carbon nanotubes sorting method using the aqueous two-phase separation method, and present possible future work and an outlook that could enhance the methodology.
A continuum theory for two-phase flows of particulate solids: application to Poiseuille flows
Monsorno, Davide; Varsakelis, Christos; Papalexandris, Miltiadis V.
2015-11-01
In the first part of this talk, we present a novel two-phase continuum model for incompressible fluid-saturated granular flows. The model accounts for both compaction and shear-induced dilatancy and accommodates correlations for the granular rheology in a thermodynamically consistent way. In the second part of this talk, we exercise this two-phase model in the numerical simulation of a fully-developed Poiseuille flow of a dense suspension. The numerical predictions are shown to compare favorably against experimental measurements and confirm that the model can capture the important characteristics of the flow field, such as segregation and formation of plug zones. Finally, results from parametric studies with respect to the initial concentration, the magnitude of the external forcing and the width of the channel are presented and the role of these physical parameters is quantified. Financial Support has been provided by SEDITRANS, an Initial Training Network of the European Commission's 7th Framework Programme
Use of two-phase flow heat transfer method in spacecraft thermal system
Hye, A.
1985-01-01
In space applications, weight, volume and power are critical parameters. Presently liquid freon is used in the radiator planels of the Space Shuttle to dissipate heat. This requires a large amount of freon, large power for pumps, large volume and weight. Use of two-phase flow method to transfer heat can reduce them significantly. A modified commercial vapor compression refrigerator/freezer was sucessfully flown in STS-4 to study the effect of zero-gravity on the system. The duty cycle was about 5 percent higher in flight as compared to that on earth due to low flow velocity in condenser. The vapor Reynolds number at exit was about 4000 as compared to about 12,000. Efforts are underway to design a refrigerator/freezer using an oil-free compressor for Spacelab Mission 4 scheduled to fly in January 1986. A thermal system can be designed for spacecraft using the two-phase flow to transfer heat economically.
Two-Phase Algorithm for Multi-warehouse and Multi-task Based Logistics Delivery
ZHANG Jun-wei; MA Fan-yuan
2005-01-01
To a scaled logistic company, assigning is an important part of logistic, and further development will make the optimized assigning of multi-warehouse and multi-task possible. This paper provided a two-phase multiwarehouse and multi-task based algorithm which has two phases. In the first phase, it combines sweep algorithm,saving algorithm and virtual task point to present a method. And in the second phase it provides an algorithm for the arrangement of goods loading which is based on the constraints of time-window and attributes of goods and vehicle. It uses the computing results of the first phase to form more detailed delivery scheme based on the constraints of time-window and attributes of vehicle and goods.
Ultrafast synthesis of LTA nanozeolite using a two-phase segmented fluidic microreactor.
Zhou, Jianhai; Jiang, Hao; Xu, Jian; Hu, Jun; Liu, Honglai; Hu, Ying
2013-08-01
Fast synthesis of nanosized zeolite is desirable for many industrial applications. An ultrafast synthesis of LTA nanozeolite by the organic-additive-free method in a two-phase segmented fluidic microreactor has been realized. The results reveal that the obtained LTA nanozeolites through microreactor are much smaller and higher crystallinity than those under similar conditions through conventional macroscale batch reactor. By investing various test conditions, such as the crystallization temperature, the flow rate, the microchannel length, and the aging time of gel solution, this two-phase segmented fluidic microreactor system enables us to develop an ultrafast method for nanozeolite production. Particularly, when using a microreactor with the microchannel length of 20 m, it only takes 10 min for the crystallization and no aging process to successfully produce the crystalline LTA nanozeolites at 95 degrees C.
Targeted Delivery by Smart Capsules for Controlling Two-phase Flow in Porous Media
Fan, J.; Weitz, D.
2015-12-01
Understanding and controlling two-phase flow in porous media are of particular importance to the relevant industry applications, such as enhanced oil recovery, CO2 sequestration, and groundwater remediation. We develop a variety of smart microcapsules that can deliver and release specific substances to the target location in the porous medium, and therefore change the fluid property or medium geometry at certain locations. In this talk, I will present two types of smart capsules for (a) delivering surfactant to the vicinity of oil-water interface and (b) delivering microgels to the high permeability region and therefore blocking the pore space there, respectively. We also show that flooding these two capsules into porous media effectively reduces the trapped oil and improves the homogeneity of the medium, respectively. Besides of its industrial applications, this technique also opens a new window to study the mechanism of two-phase flow in porous media.
Two-phase dusty fluid flow along a cone with variable properties
Siddiqa, Sadia; Begum, Naheed; Hossain, Md. Anwar; Mustafa, Naeem; Gorla, Rama Subba Reddy
2016-09-01
In this paper numerical solutions of a two-phase natural convection dusty fluid flow are presented. The two-phase particulate suspension is investigated along a vertical cone by keeping variable viscosity and thermal conductivity of the carrier phase. Comprehensive flow formations of the gas and particle phases are given with the aim to predict the behavior of heat transport across the heated cone. The influence of (1) air with particles, (2) water with particles and (3) oil with particles are shown on shear stress coefficient and heat transfer coefficient. It is recorded that sufficient increment in heat transport rate can be achieved by loading the dust particles in the air. Further, distribution of velocity and temperature of both the carrier phase and the particle phase are shown graphically for the pure fluid (air, water) as well as for the fluid with particles (air-metal and water-metal particle mixture).
Membrane-less micro fuel cell based on two-phase flow
Hashemi, S. M. H.; Neuenschwander, M.; Hadikhani, P.; Modestino, M. A.; Psaltis, D.
2017-04-01
Most microfluidic fuel cells use highly soluble fuels and oxidants in streams of liquid electrolytes to overcome the mass transport limitations that result from the low solubility of gaseous reactants such as hydrogen and oxygen. In this work, we address these limitations by implementing controlled two-phase flows of these gases in a set of microchannels electrolytically connected through a narrow gap. Annular flows of the gases reshape the concentration boundary layer over the surface of electrodes and increase the mass-transport limited current density in the system. Our results show that the power density of a two-phase system with hydrogen and oxygen streams is an order of magnitude higher than that of single phase system consisting of liquid electrolytes saturated with the same reactants. The reactor design described here can be employed to boost the performance of MFFCs and put them in a more competitive position compared to membrane based fuel cells.
Gas-driven subharmonic waves in a vibrated two-phase granular material.
Matas, J-P; Uehara, J; Behringer, R P
2008-04-01
Vibrated powders exhibit striking phenomena: subharmonic waves, oscillons, convection, heaping, and even bubbling. We demonstrate novel rectangular profile subharmonic waves for vibrated granular material, that occur uniquely in the two-phase case of grains, and a fluid, such as air. These waves differ substantially from those for the gas-free case, exhibit different dispersion relations, and occur for specific shaking parameters and air pressure, understandable with gas-particle flow models. These waves occur when the gas diffusively penetrates the granular layer in a time comparable to the shaker period. As the pressure is lowered towards P =0, the granular-gas system exhibits a Knudsen regime. This instability provides an opportunity to quantitatively test models of two-phase flow.
Computer code for gas-liquid two-phase vortex motions: GLVM
Yeh, T. T.
1986-01-01
A computer program aimed at the phase separation between gas and liquid at zero gravity, induced by vortex motion, is developed. It utilizes an explicit solution method for a set of equations describing rotating gas-liquid flows. The vortex motion is established by a tangential fluid injection. A Lax-Wendroff two-step (McCormack's) numerical scheme is used. The program can be used to study the fluid dynamical behavior of the rotational two-phase fluids in a cylindrical tank. It provides a quick/easy sensitivity test on various parameters and thus provides the guidance for the design and use of actual physical systems for handling two-phase fluids.
DESIGN OF TWO-PHASE SINUSOIDAL POWER CLOCK AND CLOCKED TRANSMISSION GATE ADIABATIC LOGIC CIRCUIT
Wang Pengjun; Yu Junjun
2007-01-01
First the research is conducted on the design of the two-phase sinusoidal power clock generator in this paper. Then the design of the new adiabatic logic circuit adopting the two-phase sinusoidal power clocks-Clocked Transmission Gate Adiabatic Logic (CTGAL) circuit is presented. This circuit makes use of the clocked transmission gates to sample the input signals, then the output loads are charged and discharged in a fully adiabatic manner by using bootstrapped N-Channel Metal Oxide Semiconductor (NMOS) and Complementary Metal Oxide Semiconductor (CMOS) latch structure.Finally, with the parameters of Taiwan Semiconductor Manufacturing Company (TSMC) 0.25 μm CMOS device, the transient energy consumption of CTGAL, Bootstrap Charge-Recovery Logic (BCRL)and Pass-transistor Adiabatic Logic (PAL) including their clock generators is simulated. The simulation result indicates that CTGAL circuit has the characteristic of remarkably low energy consumption.
MICROGRAVITY EXPERIMENTS OF TWO-PHASE FLOW PATTERNS ABOARD MIR SPACE STATION
赵建福; 解京昌; 林海; 胡文瑞; A.V. Ivanov; A.Yu. Belyaev
2001-01-01
A first experimental study on two-phase flow patterns at a long-term,steady microgravity condition was conducted on board the Russian Space Station "MIR" in August 1999. Carbogal and air are used as the liquid and the gas phase,respectively. Bubble, slug, slug-annular transitional, and annular flows are observed.A new region of annular flow with lower liquid superficial velocity is discovered,and the region of the slug-annular transitionalfiow is wider than that observed by experiments on board the parabolic aircraft. The main patterns are bubble, slug annular transitional and annular flows based on the experiments on board MIR space station. Some influences on the two-phase flow patterns in the present experiments are discussed.
Velocity measurements in the liquid metal flow driven by a two-phase inductor
Pedcenko, A; Priede, J; Gerbeth, G; Hermann, R
2013-01-01
We present the results of velocity measurements obtained by ultrasonic Doppler velocimetry and local potential probes in the flow of GaInSn eutectic melt driven by a two-phase inductor in a cylindrical container. This type of flow is expected in a recent modification to the floating zone technique for the growth of small-diameter single intermetallic compound crystals. We show that the flow structure can be changed from the typical two toroidal vortices to a single vortex by increasing the phase shift between the currents in the two coils from 0 to 90 degrees. The latter configuration is thought to be favourable for the growth of single crystals. The flow is also computed numerically and a reasonable agreement with the experimental results is found. The obtained results may be useful for the design of combined two-phase electromagnetic stirrers and induction heaters for metal or semiconductor melts.
Simon, Moritz
2013-01-01
Motivated by applications in subsurface CO2 sequestration, we investigate constrained optimal control problems with partially miscible two-phase flow in porous media. The objective is, e.g., to maximize the amount of trapped CO2 in an underground reservoir after a fixed period of CO2 injection, where the time-dependent injection rates in multiple wells are used as control parameters. We describe the governing two-phase two-component Darcy flow PDE system and formulate the optimal control problem. For the discretization we use a variant of the BOX method, a locally conservative control-volume FE method. The timestep-wise Lagrangian of the control problem is implemented as a functional in the PDE toolbox Sundance, which is part of the HPC software Trilinos. The resulting MPI parallelized Sundance state and adjoint solvers are linked to the interior point optimization package IPOPT. Finally, we present some numerical results in a heterogeneous model reservoir.
1991-07-01
The possible head degradation of the SRPR pumps may be attributable to two independent phenomena, one due to the inception of cavitation and the other due to the two-phase flow phenomena. The head degradation due to the appearance of cavitation on the pump blade is hardly likely in the conventional pressurized water reactor (PWR) since the coolant circulating line is highly pressurized so that the cavitation is difficult to occur even at LOCA (loss of coolant accident) conditions. On the other hand, the suction pressure of SRPR pump is order-of-magnitude smaller than that of PWR so that the cavitation phenomena, may prevail, should LOCA occur, depending on the extent of LOCA condition. In this study, therefore, both cavitation phenomena and two-phase flow phenomena were investigated for the SRPR pump by using various analytical tools and the numerical results are presented herein.
Bondar, A.; Buzulutskov, A.; Dolgov, A.; Nosov, V.; Shekhtman, L.; Shemyakina, E.; Sokolov, A.
2017-02-01
A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49±7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N2 content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 and 88 keV respectively. Such two-phase detectors, with enhanced sensitivity to the S2 (ionization-induced) signal, are relevant in the field of argon detectors for dark matter search and low energy neutrino detection.
A Batch Arrival Retrial Queue with Two Phases of Service and Bernoulli Vacation Schedule
Gautam Choudhury; Kandarpa Deka
2013-01-01
We consider an MX/G/1 queueing system with two phases of heterogeneous service and Bernoulli vacation schedule which operate under a linear retrial policy.In addition,each individual customer is subject to a control admission policy upon the arrival.This model generalizes both the classical M/G/1 retrial queue with arrivals in batches and a two phase batch arrival queue with a single vacation under Bernoulli vacation schedule.We will carry out an extensive stationary analysis of the system,including existence of the stationary regime,embedded Markov chain,steady state distribution of the server state and number of customer in the retrial group,stochastic decomposition and calculation of the first moment.
Two-Phase Reactions in Microdroplets without the Use of Phase-Transfer Catalysts.
Yan, Xin; Cheng, Heyong; Zare, Richard N
2017-02-22
Many important chemical transformations occur in two-phase reactions, which are widely used in chemical, pharmaceutical, and polymer manufacturing. We present an efficient method for performing two-phase reactions in microdroplets sheared by sheath gas without using a phase-transfer catalyst. This avoids disadvantages such as thermal instability, high cost, and, especially, the need to separate and recycle the catalysts. We show that various alcohols can be oxidized to the corresponding aldehydes and ketones within milliseconds in moderate to good yields (50-75 %). The scale-up of the present method was achieved at an isolated rate of 1.2 mg min(-1) for the synthesis of 4-nitrobenzylaldehyde from 4-nitrobenzyl alcohol in the presence of sodium hypochlorite. The biphasic nature of this process, which avoids use of a phase-transfer catalyst, greatly enhances synthetic effectiveness.
A two-phase tabu search approach to scheduling optimization in container terminals
ZENG Qing-cheng; YANG Zhong-zhen
2007-01-01
An optimization model for scheduling of quay cranes (QCs) and yard trailers was proposed to improve the overall efficiency of container terminals. To implement this model, a two-phase tabu search algorithra was designed. In the QCs scheduling phase of the algorithm, a search was performed to determine a good QC unloading operation order. For each QC unloading operation order generated during the QC's scheduling phase, another search was run to obtain a good yard trailer routing for the given QC's unloading order. Using this information, the time required for the operation was estimated,then the time of return to availability of the units was fed back to the QC scheduler. Numerical tests show that the two-phase Tabu Search algorithm searches the solution space efficiently, decreases the empty distance yard trailers must travel, decreases the number of trailers needed, and thereby reduces time and costs and improves the integration and reliability of container terminal operation systems.
Performance Prediction of Two-Phase Geothermal Reservoir using Lumped Parameter Model
Nurlaela, F.; Sutopo
2016-09-01
Many studies have been conducted to simulate performance of low-temperature geothermal reservoirs using lumped parameter method. Limited work had been done on applying non-isothermal lumped parameter models to higher temperature geothermal reservoirs. In this study, the lumped parameter method was applied to high-temperature two phase geothermal reservoirs. The model couples both energy and mass balance equations thus can predict temperature, pressure and fluid saturation changes in the reservoir as a result of production, reinjection of water, and/or natural recharge. This method was validated using reservoir simulation results of TOUGH2. As the results, the two phase lumped parameter model simulation without recharge shows good matching, however reservoir model with recharge condition show quite good conformity.
A state-of-the-art report on two-phase critical flow modelling
Jung, Jae Joon; Jang, Won Pyo; Kim, Dong Soo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1993-09-01
This report reviews and analyses two-phase, critical flow models. The purposes of the report are (1) to make a knowledge base for the full understanding and best-estimate of two-phase, critical flow, (2) to analyse the model development trend and to derive the direction of further studies. A wide range of critical flow models are reviewed. Each model, in general, predicts critical flow well only within specified conditions. The critical flow models of best-estimate codes are special process model included in the hydrodynamic model. The results of calculations depend on the nodalization, discharge coefficient, and other user`s options. The following topics are recommended for continuing studies: improvement of two-fluid model, development of multidimensional model, data base setup and model error evaluation, and generalization of discharge coefficients. 24 figs., 5 tabs., 80 refs. (Author).
Two-phase SPH modelling of waves caused by dam break over a movable bed
Seyedeh Leila RAZAVITOOSI; Seyed Ali AYYOUBZADEH; Alireza VALIZADEH
2014-01-01
This paper describes the application of the Smoothed Particle Hydrodynamics (SPH) method for modeling two dimensional waves caused by dam break over a movable bed in two dimensions. The two phase SPH method is developed to solve the Navier-Stokes equations. Both fluid and sediment phases are described by particles as weakly compressible fluids and the incompressibility is achieved by the equation of state. The sediment phase is modeled as a non-Newtonian fluid using three alternative approaches of artificial viscosity and Bingham Model. In this paper, the new formulations for two-phase flows are proposed. The numerical results obtained from the developed SPH model show acceptable accuracy with comparison to experimental data.
Cerroni, D.; Fancellu, L.; Manservisi, S.; Menghini, F.
2016-06-01
In this work we propose to study the behavior of a solid elastic object that interacts with a multiphase flow. Fluid structure interaction and multiphase problems are of great interest in engineering and science because of many potential applications. The study of this interaction by coupling a fluid structure interaction (FSI) solver with a multiphase problem could open a large range of possibilities in the investigation of realistic problems. We use a FSI solver based on a monolithic approach, while the two-phase interface advection and reconstruction is computed in the framework of a Volume of Fluid method which is one of the more popular algorithms for two-phase flow problems. The coupling between the FSI and VOF algorithm is efficiently handled with the use of MEDMEM libraries implemented in the computational platform Salome. The numerical results of a dam break problem over a deformable solid are reported in order to show the robustness and stability of this numerical approach.
Dynamic characteristics of two-phase thermal control system for spacecraft
Malozemov, Vladimir V.; Kudryavtseva, Natal'ya S.; Antonov, Viktor A.; Zagar, Oleg V.; Chernobaev, Nikolaj N.
1992-07-01
This paper deals with review of the issues associated with modelling the dynamic processes in the spacecraft two-phase thermal control systems. The work presents the results of modelling the nonstationary conditions of the evaporative and condensation heat exchangers functioning, investigates their response to the characteristic external influences. Disclosed are the results of the computer-aided modelling the two-phase thermal control system with a pump. The dynamic characteristics of the change in the inputs of pressures, temperatures and vapor content of a coolant in various branches of the system, as well as the lengths of the heat transfer zones in the evaporator and condenser under effect of the typical disturbing actions are obtained. The attained transients are analyzed.
Measurement of average density and relative volumes in a dispersed two-phase fluid
Sreepada, Sastry R.; Rippel, Robert R.
1992-01-01
An apparatus and a method are disclosed for measuring the average density and relative volumes in an essentially transparent, dispersed two-phase fluid. A laser beam with a diameter no greater than 1% of the diameter of the bubbles, droplets, or particles of the dispersed phase is directed onto a diffraction grating. A single-order component of the diffracted beam is directed through the two-phase fluid and its refraction is measured. Preferably, the refracted beam exiting the fluid is incident upon a optical filter with linearly varing optical density and the intensity of the filtered beam is measured. The invention can be combined with other laser-based measurement systems, e.g., laser doppler anemometry.
Numerical simulation of oil-water two-phase flow in horizontal pipes
Santos, Michelly Martuchele; Ramirez, Ramiro Gustavo [Federal University of Itajuba (UNIFEI), MG (Brazil)], E-mail: ramirez@unifei.edu.br
2010-07-01
The numerical simulation of two phase flow through the CFD techniques have become of great interest due to the complexity of this type of flow. The present work aims to simulate the oil-water two-phase flow in horizontal pipes for stratification analysis of the mixture. In numerical simulations, incompressible flow, isothermal, steady state and laminar flow were considered. Numerical analysis of flow stratification was carried out for horizontal straight and curved pipe. FLUENT was the commercial software employed in the simulation. Three-dimensional mesh generated by ICEM-CFD program was used for numerical simulation. The numerical analysis flow pattern was carried out employing the Eulerian model, considering the drag and lift interphase forces. The simulation results for the horizontal straight pipe were qualitatively validated with experimental data obtained in the Laboratory of Phase Separation of UNIFEI. (author)
Correlations for the partition behavior of proteins in aqueous two-phase systems
Schmidt, A.S.; Andrews, B.A.; Asenjo, J.A.
1996-01-01
was lower than that of subtilisin which was probably due to its higher hydrophobicity and, hence, a stronger salting-out effect. The protein concentration in each of the two phases was correlated with a ''saturation''-type equation. The partition coefficient could be satisfactorily predicted, as a function...... of the overall protein concentration, by the ratio between the ''saturation'' equations of the two individual phases. Better correlations were obtained when an empirical sigmoidal Boltzmann equation was fitted to the data, since in virtually all cases the partition coefficient is constant at low protein......The effect of protein concentration in partitioning in PEG/ salt aqueous two-phase systems has been investigated. PEG 4000/phosphate systems in the presence of 0% w/w and 8.8% w/w NaCl have been evaluated using amyloglucosidase, subtilisin, and trypsin inhibitor. Also, a PEG 4000/phosphate system...
Interfacial structures of confined air-water two-phase bubbly flow
Kim, S.; Ishii, M.; Wu, Q.; McCreary, D.; Beus, S.G.
2000-08-01
The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration along the axial direction of the flow is studied in view of the interfacial area transport and bubble interactions. The experimental data is compared with the drift flux model with C{sub 0} = 1.35.
Drop volumes and terminal velocities in aqueous two-phase systems
Bhavasar, P. M.; Jafarabad, K. R.; Pandit, A. B.; Sawant, S. B.; Joshi, J. B. [Bombay Univ. (India). Dept. of Chemical Technology
1996-12-01
Two phase aqueous extraction techniques employed in liquid-liquid extraction equipment such as spray columns and plate columns were studied, with particular attention to predicting drop sizes prior to jetting, and their terminal velocity. In the particular system studied, the values obtained by conventional models as found in the literature were considered inapplicable. A generalised model was constructed using video photographic measurements, and a correlation was developed for the terminal velocities of the drops in aqueous two-phase systems. This simplified model was found to be successful in expressing the terminal rise/fall velocities of droplets covering a specific range of Morton numbers (representing physical properties) from 0.00211 to 11050 and Eotvos numbers (representative of drop size) from 0.091 to 288. 22 refs., 6 figs.
Two-phase flow patterns in adiabatic and diabatic corrugated plate gaps
Polzin, A.-E.; Kabelac, S.; de Vries, B.
2016-09-01
Correlations for two-phase heat transfer and pressure drop can be improved considerably, when they are adapted to specific flow patterns. As plate heat exchangers find increasing application as evaporators and condensers, there is a need for flow pattern maps for corrugated plate gaps. This contribution presents experimental results on flow pattern investigations for such a plate heat exchanger background, using an adiabatic visualisation setup as well as a diabatic setup. Three characteristic flow patterns were observed in the considered range of two-phase flow: bubbly flow, film flow and slug flow. The occurrence of these flow patterns is a function of mass flux, void fraction, fluid properties and plate geometry. Two different plate geometries having a corrugation angle of 27° and 63°, respectively and two different fluids (water/air and R365mfc liquid/vapor) have been analysed. A flow pattern map using the momentum flux is presented.
Bondar, A; Dolgov, A; Nosov, V; Shekhtman, L; Shemyakina, E; Sokolov, A
2016-01-01
A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49$\\pm$7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N$_2$ content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 and 88 keV respectively. Such two-phase detectors, with enhanced sensitivity to the S2 (ionization-induced) signal, are relevant in the field of argon detectors for dark matter search and low energy neutrino detection.
Thermal test results of the two-phase thermal bus technology demonstration loop
Edelstein, Fred; Liandris, Maria; Rankin, J. Gary
1987-01-01
A two-phase heat transport system, the Thermal Bus Technology Demonstrator, has been built and tested for NASA Johnson Space Center for application on Space Station. The loop is a separated two-phase system that uses evaporator flow control valves and liquid condenser flooding to achieve temperature control. Both ambient and thermal vacuum tests have been completed in NASA's Chamber A, initially using Freon-11 and then ammonia as the working fluid. Overall, the tests were quite successful, with the bus achieving all major test objectives, including operation at 19.5 kW and set points at 35 F (1.7 C), 70 F (21.1 C) and 104 F (40.0 C), load sharing, asymmetrical heating and isothermality around the loop. Low plate to vapor temperature drops were obtained for the monogroove cold plate using ammonia and are indicative of the high evaporative film coefficients obtainable with this design.
Design of an ammonia two-phase Prototype Thermal Bus for Space Station
Brown, Richard F.; Gustafson, Eric; Parish, Richard
1987-07-01
The feasibility of two-phase heat transport systems for use on Space Station was demonstrated by testing the Thermal Bus Technology Demonstrator (TBTD) as part of the Integrated Two-Phase System Test in NASA-JSC's Thermal Test Bed. Under contract to NASA-JSC, Grumman is currently developing the successor to the TBTD, the Prototype Thermal Bus System (TBS). The TBS design, which uses ammonia as the working fluid, is intended to achieve a higher fidelity level than the TBTD by incorporating both improvements based on TBTD testing and realistic design margins, and by addressing Space Station issues such as redundancy and maintenance. The TBS is currently being fabricated, with testing scheduled for late 1987/early 1988. This paper describes the TBS design which features fully redundant plumbing loops, five evaporators designed to represent different heat acquisition interfaces, 14 condensers which mate with either space radiators or facility heat exchangers, and several modular components.
Modeling the behavior of a two-phase flow apparatus in microgravity
Baker, Eric W.; Tuttle, Ronald F.
1992-01-01
There are many unknown parameters in two-phase flow in microgravity environment. The database is incomplete and therefore correlations are unknown. This has prompted theoretical and experimental work in the area. A Phillips Laboratory program is currently exploring this area. The Phillips Laboratory experiment is a closed loop rankine cycle with a boiler, condenser/subcooler, accumulator and a pump. The work reported herein attempts to model the Phillips Laboratory Apparatus using a thermal-hydraulic software modeling system called Sim-Tool, developed by Mainstream Engineering. This work also explores the limitations of software modeling a microgravity environment. Results of this modeling effort indicate that Sim-Tool needs further development in order to correctly predict two-phase flow in a microgravity environment.
Effect of grain size reduction on high temperature oxidation ofbinary two-phase alloys
无
2001-01-01
The effect of grain size reduction on the high temperature oxidation of binary two-phase alloys was discussed based on the recent research progress. The results show that for those two-phase alloys with coarse grain prepared by the conventional methods, complex oxide scales are easily formed after oxidation under high oxygen pressure or under oxygen pressure below the stability limit of the less reactive component oxides. On the contrary, for the nano-sized alloys, an exclusive external oxidation of the most reactive component usually occurs during oxidation in air or pure oxygen even for much lower content of the most reactive component. So the gain size reduction is not always beneficial to improve the oxidation resistance of the materials, but exhibits different effects depending mainly on the protective feature of the scales. The transition mechanisms between the different oxidation modes are discussed with respect to the thermodynamic and dynamic aspects.
A splitting technique for analytical modelling of two-phase multicomponent flow in porous media
Pires, A.P.; Bedrikovetsky, P.G.; Shapiro, Alexander
2006-01-01
In this paper we discuss one-dimensional models for two-phase Enhanced Oil Recovery (EOR) floods (oil displacement by gases, polymers, carbonized water, hot water, etc.). The main result presented here is the splitting of the EOR mathematical model into thermodynamical and hydrodynamical parts....... The introduction of a potential associated with one of the conservation laws and its use as a new independent coordinate reduces the number of equations by one. The (n)x(n) conservation law model for two-phase n-component EOR flows in new coordinates is transformed into a reduced (n-1)x(n-1) auxiliary system...... containing just thermodynamical variables (equilibrium fractions of components, sorption isotherms) and one lifting equation containing just hydrodynamical parameters (phase relative permeabilities and viscosities). The algorithm to solve analytically the problem includes solution of the reduced auxiliary...
Numerical simulation of air-water two-phase flow over stepped spillways
CHENG; Xiangju; CHEN; Yongcan
2006-01-01
Stepped spillways for significant energy dissipation along the chute have gained interest and popularity among researchers and dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the finite volume computational fluid dynamics module of the FLUENT software was used to simulate the main characteristics of the flow. Adopting the RNG k-ε turbulence model, the mixture flow model for air-water two-phase flow was used to simulate the flow field over stepped spillway with the PISO arithmetic technique. The numerical result successfully reproduced the complex flow over a stepped spillway of an experiment case, including the interaction between entrained air bubbles and cavity recirculation in the skimming flow regime, velocity distribution and the pressure profiles on the step surface as well. The result is helpful for understanding the detailed information about energy dissipation over stepped spillways.
Monte Carlo simulation of a two-phase flow in an unsaturated porous media
Xu Peng
2012-01-01
Full Text Available Relative permeability is a significant transport property which describes the simultaneous flow of immiscible fluids in porous media. A pore-scale physical model is developed for the two-phase immiscible flow in an unsaturated porous media according to the statistically fractal scaling laws of natural porous media, and a predictive calculation of two-phase relative permeability is presented by Monte Carlo simulation. The tortuosity is introduced to characterize the highly irregular and convoluted property of capillary pathways for fluid flow through a porous medium. The computed relative permeabilities are compared with empirical formulas and experimental measurements to validate the current model. The effect of fractal dimensions and saturation on the relative permeabilities is also discussed
Jain, Ashu N; Khan, Tanya R; Daugulis, Andrew J
2010-11-01
The bioproduction of benzaldehyde from benzyl alcohol using Pichia pastoris was examined in a solid-liquid two-phase partitioning bioreactor (TPPB) to reduce substrate and product inhibition. Rational polymer selection identified Elvax 40W as an effective sequestering phase, possessing partition coefficients for benzyl alcohol and benzaldehyde of 3.5 and 35.4, respectively. The use of Elvax 40W increased the overall mass of benzaldehyde produced by approx. 300% in a 5 l bioreactor, relative to a single phase biotransformation. The two-phase system had a molar yield of 0.99, indicating that only minor losses occurred. These results provide a promising starting point for solid-liquid TPPBs to enhance benzaldehyde production, and suggest that multiple, targeted polymers may provide relief for transformations characterized by multiple inhibitory substrates/product/by-products.
Two phase continuous digestion of solid manure on-farm: design, mass and nutrient balance
Schäfer, Winfried; Evers, Lars; Lehto, Marja; Sorvala, Sanna; Teye, Frederick; Granstedt, Artur
2005-01-01
During the last decade some so called ‘dry fermentation’ prototype plants were developed for anaerobic digestion of organic material containing 15-50 % total solids. These plants show added advantages com-pared to slurry digestion plants: Less reactor volume, less process energy, less transport capacity, less odour emissions. However on-farm dry fermentation plants are not common and rarely commercially available. This paper reports about an innovative two phase prototype biogas plant designe...
Lattice Boltzmann Methods to Address Fundamental Boiling and Two-Phase Problems
Uddin, Rizwan
2012-01-01
This report presents the progress made during the fourth (no cost extension) year of this three-year grant aimed at the development of a consistent Lattice Boltzmann formulation for boiling and two-phase flows. During the first year, a consistent LBM formulation for the simulation of a two-phase water-steam system was developed. Results of initial model validation in a range of thermo-dynamic conditions typical for Boiling Water Reactors (BWRs) were shown. Progress was made on several fronts during the second year. Most important of these included the simulation of the coalescence of two bubbles including the surface tension effects. Work during the third year focused on the development of a new lattice Boltzmann model, called the artificial interface lattice Boltzmann model (AILB model) for the 3 simulation of two-phase dynamics. The model is based on the principle of free energy minimization and invokes the Gibbs-Duhem equation in the formulation of non-ideal forcing function. This was reported in detail in the last progress report. Part of the efforts during the last (no-cost extension) year were focused on developing a parallel capability for the 2D as well as for the 3D codes developed in this project. This will be reported in the final report. Here we report the work carried out on testing the AILB model for conditions including the thermal effects. A simplified thermal LB model, based on the thermal energy distribution approach, was developed. The simplifications are made after neglecting the viscous heat dissipation and the work done by pressure in the original thermal energy distribution model. Details of the model are presented here, followed by a discussion of the boundary conditions, and then results for some two-phase thermal problems.
A Variational Model for Two-Phase Immiscible Electroosmotic Flow at Solid Surfaces
Shao, Sihong
2012-01-01
We develop a continuum hydrodynamic model for two-phase immiscible flows that involve electroosmotic effect in an electrolyte and moving contact line at solid surfaces. The model is derived through a variational approach based on the Onsager principle of minimum energy dissipation. This approach was first presented in the derivation of a continuum hydrodynamic model for moving contact line in neutral two-phase immiscible flows (Qian, Wang, and Sheng, J. Fluid Mech. 564, 333-360 (2006)). Physically, the electroosmotic effect can be formulated by the Onsager principle as well in the linear response regime. Therefore, the same variational approach is applied here to the derivation of the continuum hydrodynamic model for charged two-phase immiscible flows where one fluid component is an electrolyte exhibiting electroosmotic effect on a charged surface. A phase field is employed to model the diffuse interface between two immiscible fluid components, one being the electrolyte and the other a nonconductive fluid, both allowed to slip at solid surfaces. Our model consists of the incompressible Navier-Stokes equation for momentum transport, the Nernst-Planck equation for ion transport, the Cahn-Hilliard phase-field equation for interface motion, and the Poisson equation for electric potential, along with all the necessary boundary conditions. In particular, all the dynamic boundary conditions at solid surfaces, including the generalized Navier boundary condition for slip, are derived together with the equations of motion in the bulk region. Numerical examples in two-dimensional space, which involve overlapped electric double layer fields, have been presented to demonstrate the validity and applicability of the model, and a few salient features of the two-phase immiscible electroosmotic flows at solid surface. The wall slip in the vicinity of moving contact line and the Smoluchowski slip in the electric double layer are both investigated. © 2012 Global-Science Press.
Konovalenko, Alexander; Basso, Simone; Kudinov, Pavel
2014-01-01
Melt fragmentation, quenching and long term coolability in a deep pool of water under reactor vessel are employed as a severe accident mitigation strategy in several designs of light water reactors. Success of the strategy is contingent upon effectiveness of natural circulation in removing the decay heat generated by the porous debris bed. Geometrical configuration of the bed is one of the factors which affect coolability of the bed. Boiling and two-phase turbulent flows in the pool serve as ...
Interfacial Tension Effect on Cell Partition in Aqueous Two-Phase Systems.
Atefi, Ehsan; Joshi, Ramila; Mann, Jay Adin; Tavana, Hossein
2015-09-30
Aqueous two-phase systems (ATPS) provide a mild environment for the partition and separation of cells. We report a combined experimental and theoretical study on the effect of interfacial tension of polymeric ATPS on the partitioning of cells between two phases and their interface. Two-phase systems are generated using polyethylene glycol and dextran of specific properties as phase-forming polymers and culture media as the solvent component. Ultralow interfacial tensions of the solutions are precisely measured using an axisymmetric drop shape analysis method. Partition experiments show that two-phase systems with an interfacial tension of 30 μJ/m(2) result in distribution of majority of cells to the bottom dextran phase. An increase in the interfacial tension results in a distribution of cells toward the interface. An independent cancer cell spheroid formation assay confirms these observations: a drop of the dextran phase containing cancer cells is dispensed into the immersion polyethylene glycol phase to form a cell-containing drop. Only at very small interfacial tensions do cells remain within the drop to aggregate into a spheroid. We perform a thermodynamic modeling of cell partition to determine variations of free energy associated with displacement of cells in ATPS with respect to the ultralow interfacial tensions. This modeling corroborates with the experimental results and demonstrates that at the smallest interfacial tension of 30 μJ/m(2), the free energy is a minimum with cells in the bottom phase. Increasing the interfacial tension shifts the minimum energy and partition of cells toward the interfacial region of the two aqueous phases. Examining differences in the partition behavior and minimum free energy modeling of A431.H9 cancer cells and mouse embryonic stem cells shows that the surface properties of cells further modulate partition in ATPS. This combined approach provides a fundamental understanding of interfacial tension role on cell partition in
Separation of Recombinant Î²-Glucuronidase from Transgenic Tobacco by Aqueous Two-Phase Extraction
2008-01-01
Separation of Recombinant Ã -Glucuronidase from Transgenic Tobacco by Aqueous Two-Phase Extraction Kristin Coby Ross Abstract Biopharmaceutical manufacturing is a rigorous and expensive process. Due to the medicinal nature of the product, a high purity level is required and several expensive purification steps must be utilized. Cost-effective production and purification is essential for any biopharmaceutical product to be successful and development of the fastest, most economical, ...
Stable response of axisymmetric two-phase water-saturated soil
蔡袁强; 孟楷; 徐长节
2004-01-01
Biot's dynamic consolidation equations and Hankel transform were used to derive the integral solutions of stress and displacement for axisymmetric harmonic excitations in the two-phase saturated soil with subjacent rock-stratum. The influence of the coefficient of permeability and loading frequency on the soil displacement at the ground surface were studied. The results showed that higher loading frequency led to more dynamic characteristics; and that the effect of the soil permeability was more obvious at higher frequencies.
Heat transfer performance of two-phase closed thermosyphon with oxidized CNT/water nanofluids
Zeinali Heris, Saeed; Fallahi, Marjan; Shanbedi, Mehdi; Amiri, Ahmad
2016-01-01
In this paper, the effects of different acids on the thermal performance of oxidized carbon nanotubes (CNT)/water nanofluids in a two-phase closed thermosyphon were studied. The structures morphology and functionalization degree were studied concurrently. The results indicated that strong oxidants increased dispersivity of CNT in the nanofluids. In other words, as the number of COOH groups increased in the nanofluids, an upward trend was also observed in the thermal efficiency of the thermosyphon.
Lattice-Boltzmann-based two-phase thermal model for simulating phase change
Kamali, M.R.; Gillissen, J.J.J.; Van den Akker, H.E.A.; Sundaresan, S.
2013-01-01
A lattice Boltzmann (LB) method is presented for solving the energy conservation equation in two phases when the phase change effects are included in the model. This approach employs multiple distribution functions, one for a pseudotemperature scalar variable and the rest for the various species. A nonideal equation of state (EOS) is introduced by using a pseudopotential LB model. The evolution equation for the pseudotemperature variable is constructed in such a manner that in the continuum l...
INFLUENCE OF SURFACTANT ON TWO-PHASE FLOW REGIME AND PRESSURE DROP IN UPWARD INCLINED PIPES
XIA Guo-dong; CHAI Lei
2012-01-01
The influence of a surfactant on the two-phase flow regime and the pressure drop in upward inclined pipes is investigated for various gas/liquid flow rates.The air/water and air/100 ppm sodium dodecyl sulphate aqueous solution are used as the working fluids.The influence of the surfactant on the two-phase flow regime in upward inclined pipes is investigated using the electrical tomographic technique.For 0°,2.5° and 5° pipe inclinations,the surfactant has obvious effect on the transition from the stratified wavy flow to the annular flow,and the range of the stratified smooth flow regime is also extended to higher gas velocities.For 10°pipe inclination,no stratified flow regime is observed in the air/water flow.In the air/surfactant solution system,however,the stratified flow regime can be found in the range of USG =10m/s-28m/s and USL =0.07 m/s-0.2 m/s.For all inclination angles,the changes of the pressure gradient characteristics are accompanied with the flow pattern transitions.Adding surfactant in a two-phase flow would reduce the pressure gradient significantly in the slug flow and annular flow regimes.In the annular flow regime,the pressure gradient gradually becomes free of the influence of the upward inclined angle,and is only dependent on the property of the two-phase flow.
Two-Phase Working Fluids for the Temperature Range 50 to 350 C
Saaski, E. W.; Owzarski, P. C.
1977-01-01
The decomposition and corrosion of two-phase heat transfer liquids and metal envelopes have been investigated on the basis of molecular bond strengths and chemical thermodynamics. Potentially stable heat transfer fluids for the temperature range 100 C to 350 C have been identified, and reflux heat pipes tests initiated with 10 fluids and carbon steel and aluminum envelopes to experimentally establish corrosion behavior and noncondensable gas generation rates.
PREPARATION OF MICROGEL-EPOXY RESIN TWO-PHASE POLYMERS BY IN SITU POLYMERIZATION
YU Yunzhao; WU Xianghong; SONG Aiteng
1991-01-01
Microgel-epoxy resin two-phase polymers were prepared by in situ copolymerization of ethylenic monomers with unsaturated polyesters. The choice of monomers and the effect of monomer concentration on microgel particle size were discussed. Agglomeration of particles played a significant role in the early stage of polymerization. The microgel dispersion in epoxy resin was stable after the finish of polymerization. Upon curing the particles remained well dispersed.
A Heat Transfer Investigation of Liquid and Two-Phase Methane
VanNoord, Jonathan
2010-01-01
A heat transfer investigation was conducted for liquid and two-phase methane. The tests were conducted at the NASA Glenn Research Center Heated Tube Facility (HTF) using resistively heated tube sections to simulate conditions encountered in regeneratively cooled rocket engines. This testing is part of NASA s Propulsion and Cryogenics Advanced Development (PCAD) project. Nontoxic propellants, such as liquid oxygen/liquid methane (LO2/LCH4), offer potential benefits in both performance and safety over equivalently sized hypergolic propulsion systems in spacecraft applications. Regeneratively cooled thrust chambers are one solution for high performance, robust LO2/LCH4 engines, but cooling data on methane is limited. Several test runs were conducted using three different diameter Inconel 600 tubes, with nominal inner diameters of 0.0225-, 0.054-, and 0.075-in. The mass flow rate was varied from 0.005 to 0.07 lbm/sec. As the current focus of the PCAD project is on pressure fed engines for LO2/LCH4, the average test section outlet pressures were targeted to be 200 psia or 500 psia. The heat flux was incrementally increased for each test condition while the test section wall temperatures were monitored. A maximum average heat flux of 6.2 Btu/in.2 sec was achieved and, at times, the temperatures of the test sections reached in excess of 1800 R. The primary objective of the tests was to produce heat transfer correlations for methane in the liquid and two-phase regime. For two-phase flow testing, the critical heat flux values were determined where the fluid transitions from nucleate boiling to film boiling. A secondary goal of the testing was to measure system pressure drops in the two-phase regime.
On modeling shape memory polymers as elastic two-phase composite materials
Gilormini, Pierre; Diani, Julie
2012-01-01
International audience; A model has been proposed recently, which describes the experimentally observed mechanical behavior of some shape memory polymers. It considers a purely thermoelastic behavior, without strain rate effects, and assumes essentially that the polymer can be considered as a two-phase composite, with glassy and rubbery phases having volume fractions that depend on temperature only. Since a uniform stress hypothesis was used in the original formulation, with an inconsistency ...
One- and two-phase anaerobic digestion of ley crop silage with and without liquid recirculation
Nordberg, Aa.
1996-10-01
In this study the effects of liquid recirculation on hydrolysis and methanogenesis in one- and two-phase biogas processes were investigated in comparison with water-diluted processes. The operation of a water-diluted one-phase process resulted in process imbalances at a low loading rate. In a water-diluted two-phase process the fibre degrading capability was lost. The reason for the poor process performance was due to a deficiency in trace elements, since the supplementation of cobalt resulted in an increased conversion rate of acetate. The recirculation of process liquid resulted in an accumulation of different compounds which initially stabilized one-phase processes and stimulated the hydrolysis and the methane production in the liquefaction-acidogenesis stage of a two-phase process. However, upon continuous recirculation the concentration of free ammonia reached toxic levels, which resulted in a decrease in the methane yield both in the methanogenic reactor of the two-phase process and in the one-phase process. Due to the decreased methane production, acids started to accumulate which subsequently inhibited the hydrolysis in the one-phase process. The systematic variation in the processes were evaluated using principal component analysis and principal component regression. The interpretation of the dynamic behaviour of the processes was facilitated by the use of score plots and loading plots. The results indicate that ley crops do not meet the nutrient requirements of the bacteria in anaerobic digestion. Thus, the low content of trace elements and the high content of protein which subsequently will cause toxic levels of ammonia in digesting system with low water consumption, suggests co-digestion with supplementary feedstocks. 95 refs, 5 figs, 3 tabs
Heat pipes et two-phase loops for spacecraft applications. ESA programmes
Supper, W. [European Space Agency / ESTEC. Thermal control and life support division (France)
1996-12-31
This document is a series of transparencies presenting the current and future applications of heat pipes in spacecraft and the activities in the field of capillary pumped two-phase loops: thermal tests, high-efficiency low pressure drop condensers, theoretical understanding of evaporator function, optimization of liquid and vapor flows, trade-off between low and high conductivity wicks, development of high capillary capacity wicks etc.. (J.S.)
A two-phase free boundary problem for a nonlinear diffusion-convection equation
De Lillo, S; Lupo, G [Dipartimento di Matematica e Informatica, Universita degli Studi di Perugia, Via Vanvitelli 1, 06123 Perugia (Italy)], E-mail: silvana.delillo@pg.infn.it
2008-04-11
A two-phase free boundary problem associated with a diffusion-convection equation is considered. The problem is reduced to a system of nonlinear integral equations, which admits a unique solution for small times. The system admits an explicit two-component solution corresponding to a two-component shock wave of the Burgers equation. The stability of such a solution is also discussed.
Kharin, Stanislav N.; Sarsengeldin, Merey M.; Nouri, Hassan
2016-08-01
On the base of the Holm model, we represent two phase spherical Stefan problem and its analytical solution, which can serve as a mathematical model for diverse thermo-physical phenomena in electrical contacts. Suggested solution is obtained from integral error function and its properties which are represented in the form of series whose coefficients have to be determined. Convergence of solution series is proved.
Homogenization of. beta. -solid solution during fast heating of two-phase titanium alloys
Gridnev, V.N.; Zhuravlev, A.F.; Zhuravlev, B.F.; Ivasishin, O.M.; Markovskij, P.E. (AN Ukrainskoj SSR, Kiev. Inst. Metallofiziki)
1985-01-01
Using model alloy Ti-10%Mo as an example the homogenization of high-temperature ..beta..-phase during fast heating has been studied by calculational and experimental methods. The effect of heating rate and the initial structure disoersion on the homogenization is shown. A method is suggested for evaluation of the concentration state of ..beta..-solid solution depleted parts of commercial two-phase titanium alloys. The method has been used to study the homogenization process.
NUMERICAL SIMULATION ON 2-D WATER-AIR TWO-PHASE FLOW OVER TOP OUTLET
无
2002-01-01
Flood discharge over top outlet of dam is simu-lated by 2-dimension water-air two-phase mathematical model.Distribution of dynamic pressure, turbulent kinetic energy (k), turbulent dissipation rate (ε) , free water surface and veloci-ty field have been obtained. The simulated results were testedby physical model, which shows that the computed results areidentical with that of the physical model.
Modeling and simulation of nanoparticles transport in a two-phase flow in porous media
El-Amin, Mohamed
2012-01-01
In the current paper, a mathematical model to describe the nanoparticles transport carried by a two-phase flow in a porous medium is presented. Both capillary forces as well as Brownian diffusion are considered in the model. A numerical example of countercurrent water-oil imbibition is considered. We monitor the changing of the fluid and solid properties due to the addition of the nanoparticles using numerical experiments. Variation of water saturation, nanoparticles concentration and porosity ratio are investigated.
Shadow imaging in bubbly gas-liquid two-phase flow in porous structures
Altheimer, Marco; Häfeli, Richard; Wälchli, Carmen; Rudolf von Rohr, Philipp
2015-09-01
Shadow imaging is used for the investigation of bubbly gas-liquid two-phase flow in a porous structure. The porous structure is made of Somos WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of resulting in a hold-up of . The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas-liquid two-phase flows are determined to improve mass and heat transfer between the phases.
Two-phase PIV measurements of particle suspension in a forced impinging jet
Mulinti, Rahul; Kiger, Ken
2010-11-01
The condition of rotorcraft brownout is characterized by intense dust suspension that is uplifted during landing and takeoff operations in regions covered with loose sediment. To predict particle suspension and sedimentation within coupled particle-laden flows, detailed characterization of the micro-scale mechanics is needed within a prototypical flow that captures the essence of the rotorcraft/ground wake interactions. Two-phase PIV has been used to study the interaction of a sediment bed made of glass spheres with characteristic flow structures reminiscent from flow within a rotor wake. In order to make reliable simultaneous two-phase PIV measurements, a phase discrimination algorithm from a single two-phase image has been implemented. The validity of the separation is checked by processing images that consisted only of the very small tracer particles, or only the dispersed phase particles, and examining how much "cross-talk" was present between the phases. The mobilization and wall-normal flux of particulates by the vortex-wall interaction will be reported for several different operational conditions, and correlated to the local vortex conditions.
Simulation experiments for hot-leg U-bend two-phase flow phenomena
Ishii, M.; Hsu, J.T.; Tucholke, D.; Lambert, G.; Kataoka, I.
1986-01-01
In order to study the two-phase natural circulation and flow termination during a small break loss of coolant accident in LWR, simulation experiments have been performed. Based on the two-phase flow scaling criteria developed under this program, an adiabatic hot leg U-bend simulation loop using nitrogen gas and water and a Freon 113 boiling and condensation loop were built. The nitrogen-water system has been used to isolate key hydrodynamic phenomena from heat transfer problems, whereas the Freon loop has been used to study the effect of phase changes and fluid properties. Various tests were carried out to establish the basic mechanism of the flow termination and reestablishment as well as to obtain essential information on scale effects of parameters such as the loop frictional resistance, thermal center, U-bend curvature and inlet geometry. In addition to the above experimental study, a preliminary modeling study has been carried out for two-phase flow in a large vertical pipe at relatively low gas fluxes typical of natural circulation conditions.
Prediction of shear bands in sand based on granular flow model and two-phase equilibrium
张义同; 齐德瑄; 杜如虚; 任述光
2008-01-01
In contrast to the traditional interpretation of shear bands in sand as a bifurcation problem in continuum mechanics,shear bands in sand are considered as high-strain phase(plastic phase) of sand and the materials outside the bands are still in low-strain phase(elastic phase),namely,the two phases of sand can coexist under certain condition.As a one-dimensional example,the results show that,for materials with strain-softening behavior,the two-phase solution is a stable branch of solutions,but the method to find two-phase solutions is very different from the one for bifurcation analysis.The theory of multi-phase equilibrium and the slow plastic flow model are applied to predict the formation and patterns of shear bands in sand specimens,discontinuity of deformation gradient and stress across interfaces between shear bands and other regions is considered,the continuity of displacements and traction across interfaces is imposed,and the Maxwell relation is satisfied.The governing equations are deduced.The critical stress for the formation of a shear band,both the stresses and strains inside the band and outside the band,and the inclination angle of the band can all be predicted.The predicted results are consistent with experimental measurements.
The solidification of two-phase heterogeneous materials:Theory versus experiment
KIM; Tongbeum
2009-01-01
The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied.The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores.Experiments using distilled water simulating the aluminum melt to be solidified(frozen)were subsequently conducted to validate the analytical model for two selected porosities(ε),ε=0 and 0.5.Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification.The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores,as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.
Karimi, Amir
1991-01-01
NASA's effort for the thermal environmental control of the Space Station Freedom is directed towards the design, analysis, and development of an Active Thermal Control System (ATCS). A two phase, flow through condenser/radiator concept was baselined, as a part of the ATCS, for the radiation of space station thermal load into space. The proposed condenser rejects heat through direct condensation of ATCS working fluid (ammonia) in the small diameter radiator tubes. Analysis of the condensation process and design of condenser tubes are based on the available two phase flow models for the prediction of flow regimes, heat transfer, and pressure drops. The prediction formulas use the existing empirical relationships of friction factor at gas-liquid interface. An attempt is made to study the stability of interfacial waves in two phase annular flow. The formulation is presented of a stability problem in cylindrical coordinates. The contribution of fluid viscosity, surface tension, and transverse radius of curvature to the interfacial surface is included. A solution is obtained for Kelvin-Helmholtz instability problem which can be used to determine the critical and most dangerous wavelengths for interfacial waves.
Proportional electroluminescence in two-phase argon and its relevance to rare-event experiments
Bondar, A; Dolgov, A; Nosov, V; Shekhtman, L; Shemyakina, E; Sokolov, A
2015-01-01
Proportional electroluminescence (EL) in gaseous Ar has for the first time been systematically studied in the two-phase mode, at 87 K and 1.00 atm. Liquid Ar had a minor (56 ppm) admixture of N2, which allowed to understand, inter alia, the effect of N2 doping on the EL mechanism in rare-event experiments using two-phase Ar detectors. The measurements were performed in a two-phase Cryogenic Avalanche Detector (CRAD) with EL gap located directly above the liquid-gas interface. The EL gap was optically read out in the Vacuum Ultraviolet (VUV), near 128 nm (Ar excimer emission), and in the near Ultraviolet (UV), at 300-450 nm (N2 Second Positive System emission), via cryogenic PMTs and a Geiger-mode APD (GAPD). Proportional electroluminescence was measured to have an amplification parameter of 109+-10 photons per drifting electron per kV overall in the VUV and UV, of which 51+-6% were emitted in the UV. The measured EL threshold, at an electric field of 3.7+-0.2 kV/cm, was in accordance with that predicted by th...
An improved large eddy simulation of two-phase flows in a pump impeller
Xuelin Tang; Fujun Wang; Yulin Wu
2007-01-01
An improved large eddy simulation using a dynamic second-order sub-grid-scale (SGS) stress model has been developed to model the governing equations of dense turbulent particle-liquid two-phase flows in a rotating coordi-nate system, and continuity is conserved by a mass-weighted method to solve the filtered governing equations. In the cur-rent second-order SGS model, the SGS stress is a function of both the resolved strain-rate and rotation-rate tensors, and the model parameters are obtained from the dimensional consis-tency and the invariants of the strain-rate and the rotation-rate tensors. In the numerical calculation, the finite volume method is used to discretize the governing equations with a staggered grid system. The SIMPLEC algorithm is applied for the solution of the discretized governing equations. Body-fitted coordinates are used to simulate the two-phase flows in complex geometries. Finally the second-order dynamic SGS model is successfully applied to simulate the dense turbu-lent particle-liquid two-phase flows in a centrifugal impeller. The predicted pressure and velocity distributions are in good agreement with experimental results.
STABILITY OF VORTEX STREET IN GAS-LIQUID TWO-PHASE FLOW
Li Yong-guang; Lin Zong-hu
2003-01-01
The stability of the Karmen vortex street in gas-liquid two-phase flow was studied experimentally and theoretically. The values of the parameter h/l characterizing the vortex street structure (I.e., the ratio of the vortex street width to the distance between two vortexes) for a stable vortex street in gas-liquid two-phase flow were obtained for the first time. The parameter h/l was proved to be a variable, not a constant as in single-phase flow. H/l is related to the upstream fluid void fraction. In gas-liquid two-phase fluid flow to form a steady vortex street is more difficult than in a single-phase fluid flow. Because in the unsteady vortex shedding the vortex shedding band frequency is broader than the one in the single phase fluid flow, so it is easier to induce the cross-cylinder resonance than in the single phase fluid flow, and this case should give rise to the attention of engineers.
Gravitational instability in two-phase disks and the origin of the moon
Thompson, Christopher; Stevenson, David J.
1988-01-01
Two-phase disks may be gravitationally unstable at temperatures or surface densities at which a disk composed of either single phase would be highly stable. It is argued that two-phase disks can achieve a marginally unstable state (in addition to a highly unstable state that leads to fragmentation), limited by the ability of the photosphere to radiate the energy dissipated in the disk. A self-consistent prescription for the viscosity induced by the slow instabilities is provided. Two-phase disks are more centrally condensed than single-phase disks, and their secular cooling time may be comparable to their spreading time. A circumterrestrial disk of sufficient mass to form the moon provides a detailed example of all the preceding points. Its stability, structure, and dynamical evolution are investigated, and it is concluded that its spreading time is short (about 100 yr); the moon is formed molten, or partially molten; the moon's initial orbit lies in the earth's equatorial plane; and only a small fraction of the disk mass is lost in a wind, although this may represent a substantial fraction of volatiles. Most of these conclusions are independent of how the disk was formed, e.g., from a giant impact.
de Brito Cardoso, Gustavo; Souza, Isabela Nascimento; Pereira, Matheus M; Freire, Mara G; Soares, Cleide Mara Faria; Lima, Álvaro Silva
2014-11-05
In this work, it is shown that novel aqueous two-phase systems can be formed by the combination of acetonitrile and polysaccharides, namely dextran. Several ternary phase diagrams were determined at 25 °C for the systems composed of water + acetonitrile + dextran. The effect of the dextran molecular weight (6,000, 40,000 and 100,000 g.mol(-1)) was ascertained toward their ability to undergo liquid-liquid demixing. An increase in the dextran molecular weight favors the phase separation. Furthermore, the effect of temperature (25, 35 and 45 °C) was evaluated for the system constituted by the dextran of higher molecular weight. Lower temperatures are favorable for phase separation since lower amounts of dextran and acetonitrile are required for the creation of aqueous two-phase systems. In general, acetonitrile is enriched in the top phase while dextran is majorly concentrated in the bottom phase. The applicability of this new type of two-phase systems as liquid-liquid extraction approaches was also evaluated by the study of the partition behavior of a well-known antioxidant - vanillin - and used here as a model biomolecule. The optimized conditions led to an extraction efficiency of vanillin of 95% at the acetonitrile-rich phase.
Application of stereology for two-phase flow structure validation in fluidized bed reactors
Anweiler Stanisław
2016-01-01
Full Text Available Paper describes a novel method for two-phase gas-solid flow structure validation in fluidized bed reactors. Investigation is based on application of stereology techniques. This is an innovative approach in the field of fluidization phenomena research. Study is focused on the analysis of flow structure images, obtained with high-speed visualization of the fluidization process. Fluidization is conducted in transparent narrow channel, where plastic balls are fluidized by air. Applied stereological analysis is grounded on the linear method and on the method of random and directed secants. This enables 2-dimensional image measurement and 3-dimensional stereological extrapolation. The major result is that for each two-phase gas-solid flow structure a set of stereological parameters exists. This enables quantification of the process. It has been found that the observation of inter-relation of all stereological parameters, during the changing of the flow structure, can be used for system control. The basic conclusion is that knowledge about the character of the changes may be used for constant process adjustment for various two phase systems such as gas-solid or gas-liquid.
Numerical Simulation of Flow Field in the New Reactor with Two-Phase Fluid
Shu Xu
2013-03-01
Full Text Available On the basic of the PIV flows field measurement, mature commercial software to fit and test heat plate reactor momentum transfer mathematical model are used and the flow field in various operation conditions of heat plate reactor is simulated. The transfer process of two-phases flow is complicated, the ideal even bubbles model is used to simulate, analyze and calculate, the deviation values of temperature profile of two-phases flow and flow profile of H2O-Air are minor, but they are high than that of homogeneous phase flow. We use the mature business software (CFX of CFD not only to fit, prove the momentum and heat transfer model in reactor with the experiment data of flow profile and temperature profile, but also to simulate the whole flow profile and temperature profile of two-phase fluids, their deviation values between the calculated values and experiment value are lower than the values simulated by traditional empirical formula, these will provide analysis of the transfer process in reactor with reliable mechanism model and computing method.
Two-phase Flow Ejector as Water Refrigerant by Using Waste Heat
Yamanaka, H.; Nakagawa, M.
2013-04-01
Energy saving and the use of clean energy sources have recently become significant issues. It is expected that clean energy sources such as solar panels and fuel cells will be installed in many private dwellings. However, when electrical power is generated, exhaust heat is simultaneously produced. Especially for the summer season, the development of refrigeration systems that can use this waste heat is highly desirable. One approach is an ejector that can reduce the mechanical compression work required in a normal refrigeration cycle. We focus on the use of water as a refrigerant, since this can be safely implemented in private dwellings. Although the energy conversion efficiency is low, it is promising because it can use heat that would otherwise be discarded. However, a steam ejector refrigeration cycle requires a large amount of energy to change saturated water into vapour. Thus, we propose a more efficient two-phase flow ejector cycle. Experiments were carried out in which the quality of the two-phase flow from a tank was varied, and the efficiency of the ejector and nozzle was determined. The results show that a vacuum state can be achieved and suction exerted with a two-phase flow state at the ejector nozzle inlet.
Electrical Capacitance Probe Characterization in Vertical Annular Two-Phase Flow
Grazia Monni
2013-01-01
Full Text Available The paper presents the experimental analysis and the characterization of an electrical capacitance probe (ECP that has been developed at the SIET Italian Company, for the measurement of two-phase flow parameters during the experimental simulation of nuclear accidents, as LOCA. The ECP is used to investigate a vertical air/water flow, characterized by void fraction higher than 95%, with mass flow rates ranging from 0.094 to 0.15 kg/s for air and from 0.002 to 0.021 kg/s for water, corresponding to an annular flow pattern. From the ECP signals, the electrode shape functions (i.e., the signals as a function of electrode distances in single- and two-phase flows are obtained. The dependence of the signal on the void fraction is derived and the liquid film thickness and the phase’s velocity are evaluated by means of rather simple models. The experimental analysis allows one to characterize the ECP, showing the advantages and the drawbacks of this technique for the two-phase flow characterization at high void fraction.
Influences of physical properties of two-phase mixture on void fraction in an annular vessel
LI Xiao-Ming; BI Qin-Cheng; FENG Quan-Ke; CHEN Ting-Kuan; DU She-Jiao
2004-01-01
To keep the void fraction of two-phase hydrogen in the moderator cell of the cold neutron source (CNS)of China Advanced Research Reactor (CARR) to a specified range, an annular vessel with the same size as the actual moderator cell was used as test section. Deionized water and alcohol, sucrose, and sodium chloride solutions with different concentrations were used as working fluid to find out influences of physical properties, such as density, viscosity and surface tension, of the two-phase mixture on void fraction. The tests proved that the ratio of surface tension to density of liquid phase has great influence on void fraction: the larger the ratio, the smaller the void fraction.Since the ratio of surface tension to density of Freon 113 is lower than that of liquid hydrogen, Freon 113 can be used as a working fluid to study the void fraction in the two-phase hydrogen thermosiphon loop in the CNS of CARR and the results will be conservative.
NONUNIFORMITIES OF TWO-PHASE COOLANT DISTRIBUTION IN A HEAT GENERATING PARTICLES BED
V. V. Sorokin
2014-01-01
Full Text Available Sufficient atomic power generation safety increase may be done with microfuel adapting to reactor plants with water coolant. Microfuel particle is a millimeter size grain containing fission material core in a protecting coverage. The coverage protects fuel contact with coolant and provides isolation of fission products inside. Well thermophysical properties of microfuel bed in a direct contact with water coolant excludes fuel overheating when accidents. Microfuel use was suggested for a VVER, а direct flow reactor for superheat steam generation, a reactor with neutron spectra adjustment by the steam partial content varying in the coolant.Nonuniformities of two-phase coolant distribution in a heat generating particles bed are predicted by calculations in this text. The one is due to multiple-valuedness of pressure drop across the bed on the steam quality dependency. The nonuniformity decreases with flow rate and particle size growths absolute pressure diminishing while porosity effect is weak. The worse case is for pressure quality of order of one. Some pure steam filled pores appears parallel to steam water mixture filled pores, latter steam quality is less than the mean of the bed. Considering this regime for the direct flow reactor for superheat steam generation we predict some water drops at the exit flow. The two-phase coolant filtration with subcooled water feed is unstable to strong disturbance effects are found. Uniformity of two-phase coolant distribution is worse than for one-phase in the same radial type reactor.
Two-phase flow patterns characteristics analysis based on image and conductance sensors
Wang, Zhenya; Jin, Ningde; Wang, Chun; Wang, Jinxiang
2008-10-01
In order to study the temporal and spatial evolution characteristics of gas-liquid two-phase flow pattern, the two-phase flow monitoring system composed of high-speed dynamic camera and Vertical Multi-Electrode Array conductance sensor (VMEA) was utilized to shoot dynamic images and acquire the conductance fluctuating signals of 5 typical vertical gas-liquid two-phase flow patterns in a 125mm i.d. upward pipe. Gray level co-occurrence matrix (GLCM) was used to extract four time-varying characteristic parameter indices which represented different flow image texture structures and also Lempel-Ziv complexity of them were calculated. Then the transition of flow structure and flow property were comprehensively analyzed, combining the result derived from image information with recurrence plots (RPs) and Lempel-Ziv complexity of conductance fluctuating signals. The study showed that the line texture structure of RPs enabled to indicate flow pattern characteristics; the flow image texture structure characteristic parameters sequence described the variance of flow structure and dynamical complexity of different flow patterns.
Thick GEM versus thin GEM in two-phase argon avalanche detectors
Bondar, A; Grebenuk, A; Pavlyuchenko, D; Tikhonov, Y; Breskin, Amos
2008-01-01
The performance of thick GEMs (THGEMs) was compared to that of thin GEMs in two-phase Ar avalanche detectors, in view of their potential application in coherent neutrino-nucleus scattering, dark-matter search and in other rare-event experiments. The detectors comprised a 1 cm thick liquid-Ar layer followed by either a double-THGEM or a triple-GEM multiplier, operated in the saturated vapor above the liquid phase. Three types of THGEMs were studied: those made of G10 and Kevlar and that with resistive electrodes (RETHGEM). Only the G10-made THGEM showed a stable performance in two-phase Ar with gains reaching 3000. Successful operation of two-phase Ar avalanche detectors with either thin- or thick-GEM multipliers was demonstrated at low detection thresholds, of 4 and 20 primary electrons respectively. Compared to the triple-GEM the double-THGEM multiplier yielded slower anode signals; this allowed applying a pulse-shape analysis to effectively reject noise signals. Noise rates of both multipliers were evaluate...
2008-01-01
Single-phase and gas-liquid two-phase pressure drops caused by a sudden con-traction in microtubes were experimentally investigated at room temperature and atmospheric pressure,using nitrogen and water. The experimental results on pressure drop with a novel measurement method,the tiny gaps on the tubes,were used to characterize the sudden contraction pressure drop for tube diameters from 850 to 330 μm. The ranges of the gas and liquid superficial velocity were 2.55―322.08 and 0.98―9.78 m/s in the smaller tube respectively. In single-phase flow experiments,the contraction loss coefficients were larger than the experimental results from conventional tubes in the laminar flow. While in the turbulent flow,the contraction loss coefficients were slightly smaller than those from conventional tubes and predicted well by Kc=0.5×(1-σ2)0.75. In two-phase flow experiments,the slip flow model with a velocity slip ratio S=(ρL/ρG)1/3 showed a good prediction that reveals the occurrence of velocity slip. An empirical correlation for two-phase flow pressure drops caused by the sudden contraction was developed based on the proposed contraction loss coefficients correlation for single-phase flow and Mar-tinelli factor.
Nonlinear analysis of gas-water/oil-water two-phase flow in complex networks
Gao, Zhong-Ke; Wang, Wen-Xu
2014-01-01
Understanding the dynamics of multi-phase flows has been a challenge in the fields of nonlinear dynamics and fluid mechanics. This chapter reviews our work on two-phase flow dynamics in combination with complex network theory. We systematically carried out gas-water/oil-water two-phase flow experiments for measuring the time series of flow signals which is studied in terms of the mapping from time series to complex networks. Three network mapping methods were proposed for the analysis and identification of flow patterns, i.e. Flow Pattern Complex Network (FPCN), Fluid Dynamic Complex Network (FDCN) and Fluid Structure Complex Network (FSCN). Through detecting the community structure of FPCN based on K-means clustering, distinct flow patterns can be successfully distinguished and identified. A number of FDCN’s under different flow conditions were constructed in order to reveal the dynamical characteristics of two-phase flows. The FDCNs exhibit universal power-law degree distributions. The power-law exponent ...
Two-phase distribution in the vertical flow line of a domestic wet central heating system
Ge Y.T.
2013-04-01
Full Text Available The theoretical and experimental aspects of bubble distribution in bubbly two-phase flow are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. The latter systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air. This leads to micro bubble nucleation at the primary heat exchanger wall, followed by detachment along the flow. Consequently, a bubbly two-phase flow characterises the flow line of such systems. The two-phase distribution across the vertical and horizontal pipes was measured through a consideration of the volumetric void fraction, quantified through photographic techniques. The bubble distribution in the vertical pipe in down flow conditions was measured to be quasi homogenous across the pipe section with a negligible reduction in the void fraction at close proximity to the pipe wall. Such a reduction was more evident at lower bulk fluid velocities.
Two-phase distribution in the vertical flow line of a domestic wet central heating system
Fsadni, A.-M.; Ge, Y. T.
2013-04-01
The theoretical and experimental aspects of bubble distribution in bubbly two-phase flow are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. The latter systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air. This leads to micro bubble nucleation at the primary heat exchanger wall, followed by detachment along the flow. Consequently, a bubbly two-phase flow characterises the flow line of such systems. The two-phase distribution across the vertical and horizontal pipes was measured through a consideration of the volumetric void fraction, quantified through photographic techniques. The bubble distribution in the vertical pipe in down flow conditions was measured to be quasi homogenous across the pipe section with a negligible reduction in the void fraction at close proximity to the pipe wall. Such a reduction was more evident at lower bulk fluid velocities.
No, Hee Cheon; Kim, Sang Jae; Kim, Hyung Tae; Moon, Young Min [Korea Advanced Institute of Science and Technology, Taejon (Korea)
2000-04-01
An ultrasonic method is developed for the measurement of the two-phase mixture level in the reactor vessel or steam generator. The ultrasonic method is selected among the several non-nuclear two-phase mixture level measurement methods through two steps of selection procedure. A commercial ultrasonic level measurement method is modified for application into the high temperature, pressure, and other conditions. The calculation method of the ultrasonic velocity is modified to consider the medium as the homogeneous mixture of air and steam, and to be applied into the high temperature and pressure conditions. The cross-correlation technique is adopted as a detection method to reduced the effects of the attenuation and the diffused reflection caused by surface fluctuation. The waveguides are developed to reduce the loss of echo and to remove the effects of obstructs. The present experimental study shows that the developed ultrasonic method measures the two-phase mixture level more accurately than the conventional methods do. 21 refs., 60 figs., 13 tabs. (Author)
Wu, Hao; Tan, Chao; Dong, Feng
2016-07-01
Oil-water two-phase flow widely exists in industrial processes such as petroleum engineering and chemical engineering. Accurate and real-time measurement of water holdup is an important problem requiring urgent solutions. In this work, a conductance and capacitance combination sensor (CCCS) system with four conductance rings and two concave capacitance plates was validated for its measurement performance of in situ water holdup through dynamic experiments. An online adaptive weight Kalman estimation (OAWKE) fusion algorithm for the CCCS system is proposed to fuse the conductance measurement and capacitance measurement. The algorithm has fast and dynamic response for the water holdup measurement of oil-water two-phase flow and has improved measurement precision by the adaptive data fusion method. The OAWKE fusion algorithm also has the ability to deal with the abrupt change of water holdup during the measurement process. Therefore, in the low water conductivity condition (tap water), the CCCS system with the OAWKE fusion algorithm can dynamically estimate the real-time full range water holdup of oil-water two-phase flow, which has prospects in the petroleum industry.
Approximation of distributed delays
Lu, Hao; Eberard, Damien; Simon, Jean-Pierre
2010-01-01
We address in this paper the approximation problem of distributed delays. Such elements are convolution operators with kernel having bounded support, and appear in the control of time-delay systems. From the rich literature on this topic, we propose a general methodology to achieve such an approximation. For this, we enclose the approximation problem in the graph topology, and work with the norm defined over the convolution Banach algebra. The class of rational approximates is described, and a constructive approximation is proposed. Analysis in time and frequency domains is provided. This methodology is illustrated on the stabilization control problem, for which simulations results show the effectiveness of the proposed methodology.
Sparse approximation with bases
2015-01-01
This book systematically presents recent fundamental results on greedy approximation with respect to bases. Motivated by numerous applications, the last decade has seen great successes in studying nonlinear sparse approximation. Recent findings have established that greedy-type algorithms are suitable methods of nonlinear approximation in both sparse approximation with respect to bases and sparse approximation with respect to redundant systems. These insights, combined with some previous fundamental results, form the basis for constructing the theory of greedy approximation. Taking into account the theoretical and practical demand for this kind of theory, the book systematically elaborates a theoretical framework for greedy approximation and its applications. The book addresses the needs of researchers working in numerical mathematics, harmonic analysis, and functional analysis. It quickly takes the reader from classical results to the latest frontier, but is written at the level of a graduate course and do...
Using the New Two-Phase-Titan to Evaluate Potential Lahar Hazard at Villa la Angostura, Argentina
Sheridan, M. F.; Cordoba, G. A.; Viramonte, J. G.; Folch, A.; Villarosa, G.; Delgado, H.
2013-05-01
The 2011 eruption of Puyehue Volcano, located in the Cordon del Caulle volcanic complex, Chile, produced an ash plume that mainly affected downwind areas in Argentina. This plume forced air transport in the region to be closed for several weeks. Tephra fall deposits from this eruption affected many locations and pumice deposits on lakes killed most of the fish. As the ash emission occurred during the southern hemisphere winter (June), ash horizons were inter layered with layers of snow. This situation posed a potential threat for human settlements located downslope of the mountains. This was the case at Villa la Angostura, Neuquen province, Argentina, which sits on a series of fluvial deposits that originate in three major basins: Piedritas, Colorado, and Florencia. The Institute of Geological Survey of Argentina (SEGEMAR) estimated that the total accumulated deposit in each basin contains a ratio of approximately 30% ash and 70% snow. The CyTED-Ceniza Iberoamerican network worked together with Argentinean, Colombian and USA institutions in this hazard assessment. We used the program Two-Phase-Titan to model two scenarios in each of the basins. This computer code was developed at SUNY University at Buffalo supported by NSF Grant EAR 711497. Two-Phase-Titan is a new depth-averaged model for two phase flows that uses balance equations for multiphase mixtures. We evaluate the stresses using a Coulomb law for the solid phase and the typical hydraulic shallow water approach for the fluid phase. The linkage for compositions in the range between the pure end-member phases is accommodated by the inclusion of a phenomenological-based drag coefficient. The model is capable of simulating the whole range of particle volumetric fractions, from pure fluid flows to pure solid avalanches. The initial conditions, volume and solid concentration, required by Two-Phase-Titan were imposed using the SEGEMAR estimation of total deposited volume, assuming that the maximum volume that can
Park, Sun; Cho, Soon Gu; Kim, Mi Young; Woo, Je Hong; Shin, Seok Hwan; Lee, Kykung Hee; Suh, Chang Hae [Inha Univ. College of Medicine, Inchon (Korea, Republic of)
2001-04-01
To determine whether an analysis of two-phase CT features provides a sound basis for differential diagnosis between gallbladder carcinoma and cholecystitis. We reviewed a total of 89 cases of gallbladder carcinoma (n=35) or cholecystitis (n=54) in patients who had undergone two-phase spiral CT. For this, a GE Highspeed Advantage scanner (GE Medical Systems, Milwaukee, U . S . A .) was used. A total of 120ml of contrast material was injected at a rate of 2-3 ml/sec. Arterial and venous phase scans were obtained 35 and 65 seconds, respectively, after the initiation of contrast infusion. All cases of gallbladder carcinoma and 468 of cholecystitis (of a total of 482) were confirmed by histopathology. We reviewed the two phase spiral CT features, analyzing and assessing thickness of the lesion, the enhancement pattern seen during the arterial and the venous phase, invasion of liver, pericholecystic fat infiltration, dilatation of intrahepatic ducts, and other associated findings. Mean wall thickness was 12.6 mm in the gallbladder carcinoma group, and 7.2 mm in the cholecystitis group. The common enhancement patterns seen in gallbladder carcinoma were 1) a highly enhanced thick inner wall layer during the arterial phase which became iso attenuated with adjacent liver parenchyma during the venous phase (16/35; 45.7%) and 2) highly enhanced thick inner wall layer during both the arterial and venous phase (8/35; 22.9%). The most common enhancement pattern in cholecystitis cases was an iso attenuated thin inner wall layer during both the arterial and the venous phase (44/54; 81.5%). Findings of intrahepatic mass formation by direct invasion (9/35), lymph node enlargement (12/35), and metastasis to other organs (7/35) occurred only in cases of gallbladder carcinoma (18/35, 51.4%) than of cholecystitis (10/54, 18.5%). The incidence of pericholecystic fat infiltration and fluid collection was not significantly different between the gallbladder cancer and cholecystitis groups
P450cam biocatalysis in surfactant-stabilized two-phase emulsions.
Ryan, Jessica D; Clark, Douglas S
2008-04-15
Cytochrome P450 monooxygenases (P450s) are powerful biocatalysts that have the ability to oxidize a broad range of substrates, often at non-reactive carbon centers. However, incorporation of P450s into synthetic schemes has so far been limited to a few whole-cell transformations. P450 substrates are often hydrophobic and have low water solubility, limiting the amount of product that can be produced. To help overcome this limitation, we have examined P450cam activity in two-phase hexane/water emulsions with and without the anionic surfactant, bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT). Hydroxylation of camphor to hydroxycamphor by the three- component P450cam system was chosen as the model reaction, and regeneration of NADH was accomplished with yeast alcohol dehydrogenase (YADH). P450cam was activated in the surfactant-free emulsions, and addition of AOT improved the activity even further, at least over the range of camphor concentrations for which initial rates were readily measurable in all media. The largest observed rate enhancement was 4.5-fold. Nearly 50-times more product was formed in the surfactant-stabilized emulsions than was achieved in aqueous buffer, with total turnover numbers reaching 28,900 for P450cam and 11,800 for YADH. In the absence of surfactant, the two-phase reaction appeared to be mass-transfer limited, while inclusion of AOT alleviated transport limitations and/or afforded a larger interfacial area for P450 activation. The oxidation of hydroxycamphor to 2,5-diketocamphane was also observed, owing to the large concentration of hydroxycamphor relative to camphor in the aqueous phase of the two-phase emulsion. This competing reaction was accompanied by the uncoupled oxidation of NADH (i.e., NADH oxidation without formation of 2,5-diketocamphane), which reduced the availability of NADH for camphor oxidation and further limited the yield of hydroxycamphor in the two-phase emulsions. These results indicate that a surfactant
Experimental Assessment of the Two-Phase Flow in a Large Inclined Channel
Nguyen, Thanh Hung; Song, Ki Won; Revankar, Shripad T; Park, Hyun Sun [Pohang University of Science and Technology, Pohang (Korea, Republic of)
2014-10-15
In order to assess the cooling performance of the core catcher system, a model facility has been constructed in POSTECH using scaling analysis. This facility consists of horizontal, inclined and vertical section. To investigate the flow parameters in each section, the instrumentation is developed to measure two-phase characteristics such as local void fraction, bubble velocity and bubble size. To date, there has been a considerable amount of research conducted on the internal structure of two-phase flow in pipe. However, the number of attempts made on the experiment regarding large inclined channels has been still limited. One of the reasons for this lack of data is the difficulty in constructing experimental facility. In this paper, the parameters of the flow in the inclined section are presented. The inclined channel is 10 degree from the horizontal with the rectangular cross section of 300 cm{sup 2}. The distributions of local parameters are evaluated through the data of double sensor conductivity probes installed at different locations along the inclined section. The data sets of the structure of two-phase flow in an inclined large channel was acquired. The air was injected through the metal foam installed on the top surface wall of the inclined section. Water level was kept below the top of the inclined section so the amount of water was fixed during the experiment. 9 probes set up at the different locations to get the data of local two-phase parameters. The measurement at each location was conducted in 5 minutes to determine the mean value of each parameter. The result of local void fraction profiles at different locations indicates that the void distribution primarily changes along the height of the inclined section. The slug flow occurs in the channel which results in most bubbles attached to the top surface wall. This fact explains the high local void fraction near the top wall and its rapid decline towards the bottom wall of the inclined section. The
An experimental study of single-phase and two-phase flows in microchannels
Chung, Peter Mang-Yu
Recent literature on pressure drop and flow rate measurements in microchannels indicate that both the liquid and gas flow may deviate significantly from convention. Thus, an evaluation was made of the friction factor constant for laminar flow and critical Reynolds number for the laminar-to-turbulent flow transition. Experiments were performed to study the single-phase flow behaviour of water or nitrogen gas through a 100 mum circular microchannel. The liquid flow data were well predicted by the conventional friction factor equations for larger channels, and the critical Reynolds number was close to tradition. For single-phase gas flow, the measured friction factor agreed with theory if the effect of compressibility was considered. Rarefaction did not contribute to the experimental results. The effect of scaling on two-phase flow was investigated to identify micro-scale phenomena. Experiments were conducted with a mixture of nitrogen gas and water in circular channels of 530--50 mum diameter. The two-phase flow was characterized by the flow patterns, void fraction, and frictional pressure drop. In the 530 and 250 mum channels, the flow characteristics were typical of those obtained in minichannels. In the 100 and 50 mum channels, the flow behaviour was unconventional---the occurrence of slug flow dominated, the void fraction-volumetric quality relationship departed from tradition, and mass flux no longer influenced the two-phase frictional multiplier. Unique to these channels, the slug flow exhibited a ring-shaped liquid film or serpentine-like gas core. The sizing effect indicates that the critical diameter for a microchannel lies between 250 and 100 mum. A new model is proposed to expose physical insight into the observed flow patterns. To investigate the effect of channel geometry on two-phase microchannel flow, the same experiment was conducted in a 96 mum square microchannel and the data were compared with those obtained in the 100 mum circular microchannel
Two-Phase Flow Simulations In a Natural Rock Fracture using the VOF Method
Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H., Bromhal, Grant
2010-01-01
Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the
Features of two-phase flow patterns in horizontal rectangular microchannels of height 50 μm
Ron’shin Fedor
2016-01-01
Full Text Available The horizontal microchannel with the height of 50 micrometres and width of 40 mm of a rectangular cross-section has been used to study two-phase flow. The classical patterns of two-phase flow in the channel (bubble, stratified, churn, jet, and annular have been detected. Experimental information allows us to define the characteristics of the regimes and to determine precisely the boundaries between the patterns of the two-phase flows.
TAKTAG Two-phase learning method for hybrid statistical/rule-based part-of-speech disambiguation
Lee, G; Shin, S; Lee, Geunbae; Lee, Jong-Hyeok; Shin, Sanghyun
1995-01-01
Both statistical and rule-based approaches to part-of-speech (POS) disambiguation have their own advantages and limitations. Especially for Korean, the narrow windows provided by hidden markov model (HMM) cannot cover the necessary lexical and long-distance dependencies for POS disambiguation. On the other hand, the rule-based approaches are not accurate and flexible to new tag-sets and languages. In this regard, the statistical/rule-based hybrid method that can take advantages of both approaches is called for the robust and flexible POS disambiguation. We present one of such method, that is, a two-phase learning architecture for the hybrid statistical/rule-based POS disambiguation, especially for Korean. In this method, the statistical learning of morphological tagging is error-corrected by the rule-based learning of Brill [1992] style tagger. We also design the hierarchical and flexible Korean tag-set to cope with the multiple tagging applications, each of which requires different tag-set. Our experiments s...
Taneja, Ankur; Higdon, Jonathan
2016-11-01
A spectral element method (SEM) is presented to simulate two-phase fluid flow (oil and water phase) in petroleum reservoirs. Petroleum reservoirs are porous media with heterogeneous geologic features, and the flow of two immiscible phases involves sharp, moving interfaces. The governing equations of motion are time-dependent, non-linear PDEs with strong hyperbolic nature. A fully-coupled numerical scheme using discontinuous Galerkin (DG) method with nodal spectral element basis functions for spatial discretization, and an implicit Runge-Kutta type time-stepping is developed to solve the PDEs in a robust, stable manner. Isoparameteric mapping is used to generate grids for reservoir and well geometry. We present the performance capabilities of the DG scheme with high-order basis functions to accurately resolve sharp fluid interfaces and a variety of heterogeneous geologic features. High-order convergence of SEM is demonstrated. Numerical results are presented for reservoir flows with various injection-production patterns. Typical reservoir heterogeneities like low-permeable regions, impermeable shale barriers, etc. are included in the numerical tests. Comparisons with commonly used finite volume methods and linear and quadratic finite element methods are presented. ExxonMobil Upstream Research Co.
Han, B.; Yang, B.W.; Zhang, H.; Mao, H.; Zha, Y. [Xi' an Jiaotong Univ., Shaanxi (China). Science and Technology Center for Advanced Nuclear Fuel Research
2016-07-15
As pressure drop is one of the most critical thermal hydraulic parameters for spacer grids the accurate estimation of it is the key to the design and development of spacer grids. Most of the available correlations for pressure drop do not contain any real geometrical parameters that characterize the grid effect. The main functions for spacer grid are structural support and flow mixing. Once the boundary sublayer near the rod bundle is disturbed, the liquid forms swirls or flow separation that affect pressure drop. However, under two phase flow conditions, due to the existence of steam bubble, the complexity for spacer grid are multiplied and pressure drop calculation becomes much more challenging. The influence of the dimple location, distance of mixing vane to the nearest strip, and the effect of inter-subchannel mixing among neighboring subchannels on pressure drop and downstream flow fields are analyzed in this paper. Based on this study, more detailed space grid geometry parameters are recommended for adding into the correlation when predicting pressure drop.
Frampton, John P.; White, Joshua B.; Simon, Arlyne B.; Tsuei, Michael; Paczesny, Sophie; Takayama, Shuichi
2014-05-01
Accurate disease diagnosis, patient stratification and biomarker validation require the analysis of multiple biomarkers. This paper describes cross-reactivity-free multiplexing of enzyme-linked immunosorbent assays (ELISAs) using aqueous two-phase systems (ATPSs) to confine detection antibodies at specific locations in fully aqueous environments. Antibody cross-reactions are eliminated because the detection antibody solutions are co-localized only to corresponding surface-immobilized capture antibody spots. This multiplexing technique is validated using plasma samples from allogeneic bone marrow recipients. Patients with acute graft versus host disease (GVHD), a common and serious condition associated with allogeneic bone marrow transplantation, display higher mean concentrations for four multiplexed biomarkers (HGF, elafin, ST2 and TNFR1) relative to healthy donors and transplant patients without GVHD. The antibody co-localization capability of this technology is particularly useful when using inherently cross-reactive reagents such as polyclonal antibodies, although monoclonal antibody cross-reactivity can also be reduced. Because ATPS-ELISA adapts readily available antibody reagents, plate materials and detection instruments, it should be easily transferable into other research and clinical settings.
Bacon, Stuart L; Peterson, Eric C; Daugulis, Andrew J; Parent, J Scott
2015-01-01
Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection.
Turbulence-resolving, two-phase flow simulations of wave-supported gravity flows: A conceptual study
Ozdemir, Celalettin Emre
2016-12-01
Discoveries over the last three decades have shown that wave-supported gravity flows (WSGFs) are among the participating physical processes that carry substantial amount of fine sediments across low-gradient shelves. Therefore, understanding the full range of mechanisms responsible for such gravity flows is likely to shed light on the dynamics of subaqueous delta and clinoform development. As wave-induced boundary layer turbulence is the major agent to suspend sediments in WSGFs, the scale of WSGFs in the water column is also bounded by the wave-induced boundary layer thickness which is on the order of decimeters. Therefore, in order to explore the details of participating physical mechanisms, especially that due to turbulence-sediment interaction, highly resolved and accurate numerical models or measurements in the laboratory and the field are required. In this study, the dynamics of WSGFs is investigated by using turbulence-resolving, two-phase flow simulations that utilize Direct Numerical Simulations (DNS). The effect of variable sediment loading, slope, and wave orbital velocity is investigated via 21 simulations.
Burkholder, Michael B.; Litster, Shawn
2016-05-01
In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurable regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.
Analysis and Comparison of Two-Phase Ejector Performance Metrics for R134a and CO2 Ejectors
Lawrence, Neal; Elbel, Stefan
2014-01-01
Two-phase ejectors have been gaining increased attention in recent years due to their ability to directly improve the COP of the cycle. Of common interest in two-phase ejector studies is how the ejector improves cycle COP. However, less emphasis is often given to the performance of the two-phase ejector itself. The amount of COP improvement offered by an ejector cycle is very strongly influenced by the performance of the two-phase ejector; thus, it is important to understand the operation and...
An Approximate Approach to Automatic Kernel Selection.
Ding, Lizhong; Liao, Shizhong
2016-02-02
Kernel selection is a fundamental problem of kernel-based learning algorithms. In this paper, we propose an approximate approach to automatic kernel selection for regression from the perspective of kernel matrix approximation. We first introduce multilevel circulant matrices into automatic kernel selection, and develop two approximate kernel selection algorithms by exploiting the computational virtues of multilevel circulant matrices. The complexity of the proposed algorithms is quasi-linear in the number of data points. Then, we prove an approximation error bound to measure the effect of the approximation in kernel matrices by multilevel circulant matrices on the hypothesis and further show that the approximate hypothesis produced with multilevel circulant matrices converges to the accurate hypothesis produced with kernel matrices. Experimental evaluations on benchmark datasets demonstrate the effectiveness of approximate kernel selection.
Speaking Fluently And Accurately
JosephDeVeto
2004-01-01
Even after many years of study,students make frequent mistakes in English. In addition, many students still need a long time to think of what they want to say. For some reason, in spite of all the studying, students are still not quite fluent.When I teach, I use one technique that helps students not only speak more accurately, but also more fluently. That technique is dictations.
Approximation techniques for engineers
Komzsik, Louis
2006-01-01
Presenting numerous examples, algorithms, and industrial applications, Approximation Techniques for Engineers is your complete guide to the major techniques used in modern engineering practice. Whether you need approximations for discrete data of continuous functions, or you''re looking for approximate solutions to engineering problems, everything you need is nestled between the covers of this book. Now you can benefit from Louis Komzsik''s years of industrial experience to gain a working knowledge of a vast array of approximation techniques through this complete and self-contained resource.
Achieser, N I
2004-01-01
A pioneer of many modern developments in approximation theory, N. I. Achieser designed this graduate-level text from the standpoint of functional analysis. The first two chapters address approximation problems in linear normalized spaces and the ideas of P. L. Tchebysheff. Chapter III examines the elements of harmonic analysis, and Chapter IV, integral transcendental functions of the exponential type. The final two chapters explore the best harmonic approximation of functions and Wiener's theorem on approximation. Professor Achieser concludes this exemplary text with an extensive section of pr
Rascle, P.; El Amine, K. [Electricite de France (EDF), Direction des Etudes et Recherches, 92 - Clamart (France)
1997-12-31
We are interested in the numerical approximation of two-fluid models of nonequilibrium two-phase flows described by six balance equations. We introduce an original splitting technique of the system of equations. This technique is derived in a way such that single phase Riemann solvers may be used: moreover, it allows a straightforward extension to various and detailed exchange source terms. The properties of the fluids are first approached by state equations of ideal gas type and then extended to real fluids. For the construction of numerical schemes , the hyperbolicity of the full system is not necessary. When based on suitable kinetic unwind schemes, the algorithm can compute flow regimes evolving from mixture to single phase flows and vice versa. The whole scheme preserves the physical features of all the variables which remain in the set of physical states. Several stiff numerical tests, such as phase separation and phase transition are displayed in order to highlight the efficiency of the proposed method. The document is a PhD thesis divided in 6 chapters and two annexes. They are entitled: 1. - Introduction (in French), 2. - Two-phase flow, modelling and hyperbolicity (in French), 3. - A numerical method using upwind schemes for the resolution of two-phase flows without exchange terms (in English), 4. - A numerical scheme for one-phase flow of real fluids (in English), 5. - An upwind numerical for non-equilibrium two-phase flows (in English), 6. - The treatment of boundary conditions (in English), A.1. The Perthame scheme (in English) and A.2. The Roe scheme (in English). 136 refs. This document represents a PhD thesis in the speciality Applied Mathematics presented par Khalid El Amine to the Universite Paris 6.
Role of Nucleation and Growth in Two-Phase Microstructure Formation
Shin, Jong Ho [Iowa State Univ., Ames, IA (United States)
2007-01-01
During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different
Adaptive, multi-domain techniques for two-phase flow computations
Uzgoren, Eray
Computations of immiscible two-phase flows deal with interfaces that may move and/or deform in response to the dynamics within the flow field. As interfaces move, one needs to compute the new shapes and the associated geometric information (such as curvatures, normals, and projected areas/volumes) as part of the solution. The present study employs the immersed boundary method (IBM), which uses marker points to track the interface location and continuous interface methods to model interfacial conditions. The large transport property jumps across the interface, and the considerations of the mechanism including convection, diffusion, pressure, body force and surface tension create multiple time/length scales. The resulting computational stiffness and moving boundaries make numerical simulations computationally expensive in three-dimensions, even when the computations are performed on adaptively refined 3D Cartesian grids that efficiently resolve the length scales. A domain decomposition method and a partitioning strategy for adaptively refined grids are developed to enable parallel computing capabilities. Specifically, the approach consists of multilevel additive Schwarz method for domain decomposition, and Hilbert space filling curve ordering for partitioning. The issues related to load balancing, communication and computation, convergence rate of the iterative solver in regard to grid size and the number of sub-domains and interface shape deformation, are studied. Moreover, interfacial representation using marker points is extended to model complex solid geometries for single and two-phase flows. Developed model is validated using a benchmark test case, flow over a cylinder. Furthermore, overall algorithm is employed to further investigate steady and unsteady behavior of the liquid plug problem. Finally, capability of handling two-phase flow simulations in complex solid geometries is demonstrated by studying the effect of bifurcation point on the liquid plug, which
Exact Jacobians in an implicit Newton method for two-phase flow in porous media
Büsing, H.; Clauser, C.
2012-04-01
Geological storage of CO2 is one option for mitigating the effects of CO2 emissions on global warming. Since extensive on-site monitoring of the CO2 plume propagation is expensive, numerical simulations are an attractive alternative for gaining deeper insight in the dynamics of this system. We consider a model for two-phase flow in porous media for representing the injection stage of a CO2 sequestration scenario, when the plume propagation is dominated by advection. The porous medium filled by the two phases CO2 and brine is modelled as an initial-boundary-value problem consisting of two nonlinear, coupled partial differential equations, which are complemented by appropriate boundary and initial conditions. We present a new numerical approach to solve this fully coupled system using exact Jacobians. The method is based on the finite element, finite volume, box method [Huber & Helmig(2000)] for the space discretization and, since stability of the method is one of the main concerns, the fully implicit Euler method for the time discretization. A simple first order upwind method takes into account advective contributions. The resulting system of nonlinear algebraic equations is linearized by Newton's method. The required Jacobians can be obtained elegantly by automatic differentiation (AD) [Griewank & Walther(2008), Rall(1981)], a source code transformation giving exact derivatives of the discretized equations with respect to primary variables. The resulting system of linear equations is then solved by an iterative method (BiCGStab) with ILU0 preconditioning in every Newton step. We compare the forward AD differentiation mode to the standard finite difference method in terms of precision and performance. It turns out that AD performs favourable in both aspects. We also illustrate the advantages of exact Jacobians for two-phase flow in a sequestration scenario investigating the evolution of pressure and saturation.
Qian, Junfeng [Jiangsu Provincial Key Laboratory of Fine Petrochemical Engineering, Jiangsu Polytechnic University, Changzhou 213016 (China); College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009 (China); Yun, Zhi; Shi, Haixian [College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009 (China)
2010-12-15
In the present work, the preparation of biodiesel from cottonseed oil produced by two-phase solvent extraction (TSE) was studied. The experimental results of TSE process of cottonseed showed that the optimal extraction conditions were 30 g samples, 240 mL extraction solvent mixture and methanol/petroleum ether volume ratio 60:40, extraction temperature 30 C, extraction time 30 min. Under the extraction conditions, the extraction rate of cottonseed oil could achieve 98.3%, the free fatty acid (FFA) and water contents of cottonseed oil were reduced to 0.20% and 0.037%, respectively, which met the requirement of alkali-catalyzed transesterification. The free gossypol (FG) content in cottonseed meal produced from two-phase solvent extraction could reduce to 0.014% which was far below the FAO standard. And the nontoxic cottonseed meal could be used as animal protein feed resources. After the TSE process of cottonseed, the investigations were carried out on transesterification of methanol with oil-petroleum ether solution coming from TSE process in the presence of sodium hydroxide (CaO) as the solid base catalyst. The influences of weight ratio of petroleum ether to cottonseed oil, reaction temperature, molar ratio of methanol to oil, alkali catalyst amount and reaction time on cottonseed oil conversion were respectively investigated by mono-factor experiments. The conversion of cottonseed oil into fatty acid methyl ester (FAME) could achieve 98.6% with 3:1 petroleum ether/oil weight ratio, 65 C reaction temperature, 9:1 methanol/oil mole ratio, 4% (catalyst/oil weight ratio, w/w) solid base catalyst amount and 3 h reaction time. The properties of FAME product prepared from cottonseed oil produced by two-phase solvent extraction met the ASTM specifications for biodiesel. (author)
Qian Junfeng, E-mail: qianjunfeng80@126.co [Jiangsu Provincial Key Laboratory of Fine Petrochemical Engineering, Jiangsu Polytechnic University, Changzhou 213016 (China) and College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009 (China); Yun Zhi; Shi Haixian [College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009 (China)
2010-12-15
In the present work, the preparation of biodiesel from cottonseed oil produced by two-phase solvent extraction (TSE) was studied. The experimental results of TSE process of cottonseed showed that the optimal extraction conditions were 30 g samples, 240 mL extraction solvent mixture and methanol/petroleum ether volume ratio 60:40, extraction temperature 30 deg. C, extraction time 30 min. Under the extraction conditions, the extraction rate of cottonseed oil could achieve 98.3%, the free fatty acid (FFA) and water contents of cottonseed oil were reduced to 0.20% and 0.037%, respectively, which met the requirement of alkali-catalyzed transesterification. The free gossypol (FG) content in cottonseed meal produced from two-phase solvent extraction could reduce to 0.014% which was far below the FAO standard. And the nontoxic cottonseed meal could be used as animal protein feed resources. After the TSE process of cottonseed, the investigations were carried out on transesterification of methanol with oil-petroleum ether solution coming from TSE process in the presence of sodium hydroxide (CaO) as the solid base catalyst. The influences of weight ratio of petroleum ether to cottonseed oil, reaction temperature, molar ratio of methanol to oil, alkali catalyst amount and reaction time on cottonseed oil conversion were respectively investigated by mono-factor experiments. The conversion of cottonseed oil into fatty acid methyl ester (FAME) could achieve 98.6% with 3:1 petroleum ether/oil weight ratio, 65 deg. C reaction temperature, 9:1 methanol/oil mole ratio, 4% (catalyst/oil weight ratio, w/w) solid base catalyst amount and 3 h reaction time. The properties of FAME product prepared from cottonseed oil produced by two-phase solvent extraction met the ASTM specifications for biodiesel.
Interstellar Cloud Formation through Aggregation of Cold Blobs in a Two-Phase Gas Mixture
Kamaya, Hideyuki
1997-05-01
We propose a new formation scenario for interstellar clouds through the aggregation of dense cold blobs (phase II [PII]), which drift in a diffuse warm medium (phase I [PI]). We examine how important it is that there exist numerous PII blobs when the properties of such a two-phase flow are studied. First, we solve a one-dimensional shock-tube problem and find that the shock wave in the mixture is considerably damped because of the drag force between the two phases. This is because the PII blobs are left behind the shock front, since their inertia is larger than that of PI, thus suppressing large spatial variations of PI gas via the drag force. The PII blobs thus play the role of anchors. Therefore, mass aggregation by shocks may be ineffective in a two-phase medium. However, the PII blobs can still aggregate through a kind of fluid dynamical instability. We next suppose that the PI gas is accelerated upward by shocks against downward gravity, while the PII blobs are at rest because of balance between the drag force due to PI and gravity. If we put a positive perturbation in the number density of PII blobs, the upward PI flow above the perturbation is decelerated by the enhanced drag force, and the velocity difference between PI and PII is thereby reduced. Then the PII blobs above the perturbation are accelerated downward, since the gravity on PII now dominates the reduced drag force. As a result, the blobs will fall onto this perturbed region, and this region becomes denser and denser. This is the mechanism of the instability. Therefore, we expect efficient cloud formation by this instability in spiral arms, even when galactic shocks are extremely damped.
Li, Xuan; Kim, Tae Hyun; Nghiem, Nhuan P
2010-08-01
An integrated bioconversion process was developed to convert corn stover derived pentose and hexose to ethanol effectively. In this study, corn stover was pretreated by soaking in aqueous ammonia (SAA), which retained glucan ( approximately 100%) and xylan (>80%) in the solids. The pretreated carbohydrates-rich corn stover was converted to ethanol via two-phase simultaneous saccharification and fermentation (TPSSF). This single-reactor process employed sequential simultaneous saccharification and fermentation (SSF), i.e. pentose conversion using recombinant Escherichia coli KO11 in the first phase, followed by hexose conversion with Saccharomyces cerevisiae D5A in the second phase. In the first phase, 88% of xylan digestibility was achieved through the synergistic action of xylanase and endo-glucanase with minimal glucan hydrolysis (10.5%). Overall, the TPSSF using 12-h SAA-treated corn stover resulted in the highest ethanol concentration (22.3g/L), which was equivalent to 84% of the theoretical ethanol yield based on the total carbohydrates (glucan+xylan) in the untreated corn stover.
Ohtaki, Megu; Tonda, Tetsuji; Aihara, Kazuyuki
2015-10-01
We consider a two-phase Poisson process model where only early successive transitions are assumed to be sensitive to exposure. In the case where intensity transitions are low, we derive analytically an approximate formula for the distribution of time to event for the excess hazard ratio (EHR) due to a single point exposure. The formula for EHR is a polynomial in exposure dose. Since the formula for EHR contains no unknown parameters except for the number of total stages, number of exposure-sensitive stages, and a coefficient of exposure effect, it is applicable easily under a variety of situations where there exists a possible latency time from a single point exposure to occurrence of event. Based on the multistage hypothesis of cancer, we formulate a radiation carcinogenesis model in which only some early consecutive stages of the process are sensitive to exposure, whereas later stages are not affected. An illustrative analysis using the proposed model is given for cancer mortality among A-bomb survivors.
Ibragimov, Ranis N.
2010-09-01
We study the linearized stability of a planar dynamical model describing two-phase perfect fluid circulating around a circle with a sufficiently large radius within a central gravitational field. The model is associated with the spatial and temporal structure of the zonally averaged global-scale atmospheric longitudinal circulation around the Earth. Two cases are studied separately; in the first one, the simulations were carried out using the rigid lid approximation at the upper boundary of the outer atmospheric layer. In the second one, the free boundary nonlinear conditions (kinematic and dynamic) were assumed on the outer atmospheric layer. For the both cases, a certain family of steady, explicit solutions which have circular streamlines was considered. The governing equations were linearized at these solutions to find the typical wave numbers of the interfacial wave perturbation to the basic state at which the destabilizing effect of shear, which overcomes the stabilizing effect of stratification, occurs. It is shown that for the both cases, the model always have the same two potentially unstable wave modes while there always exist two wave modes which are stable for any wavelengths. The behavior of the stable and unstable modes were compared for the both cases to investigate the effects of the free boundary on the mixing process at the interface.
Lam Ghai Lim
2016-07-01
Full Text Available A 360° twisted helical capacitance sensor was developed for holdup measurement in horizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was optimized in such a way that a ‘sine-like’ function was displayed on top of the linear function. This concept of design had been implemented and verified in both software and hardware. A good agreement was achieved between the finite element model of proposed design and the approximation model (pure sinusoidal function, with a maximum difference of ±1.2%. In addition, the design parameters of the sensor were analysed and investigated. It was found that the error in symmetry of the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of air-water and oil-water stratified flows were carried out and validated the sinusoidal relationship with a maximum difference of ±1.2% and ±1.3% for the range of water holdup from 0.15 to 0.85. The proposed design concept therefore may pose a promising alternative for the optimization of capacitance sensor design.
Single and two-phase flows on chemical and biomedical engineering
Antonio, Martins; Rui, Lima
2012-01-01
""Single or two-phase flows are ubiquitous in most natural process and engineering systems. Examples of systems or process include, packed bed reactors, either single phase or multiphase, absorber and adsorber separation columns, filter beds, plate heat exchangers, flow of viscoelastic fluids in polymer systems, or the enhanced recovery of oil, among others. In each case the flow plays a central role in determining the system or process behaviour and performance. A better understanding of the underlying physical phenomena and the ability to describe the phenomena properly are both crucial to
Two phase flow and heat transfer in porous beds under variable body forces, part 2
Evers, J. L.; Henry, H. R.
1969-01-01
Analytical and experimental investigations of a pilot model of a channel for the study of two-phase flow under low or zero gravity are presented. The formulation of dimensionless parameters to indicate the relative magnitude of the effects of capillarity, gravity, pressure gradient, viscosity, and inertia is described. The investigation is based on the principal equations of fluid mechanics and thermodynamics. Techniques were investigated by using a laser velocimeter for measuring point velocities of the fluid within the porous material without disturbing the flow.
Two-Phase Cryogenic Heat Exchanger for the Thermodynamic Vent System
Christie, Robert J.
2011-01-01
A two-phase cryogenic heat exchanger for a thermodynamic vent system was designed and analyzed, and the predicted performance was compared with test results. A method for determining the required size of the Joule-Thomson device was also developed. Numerous sensitivity studies were performed to show that the design was robust and possessed a comfortable capacity margin. The comparison with the test results showed very similar heat extraction performance for similar inlet conditions. It was also shown that estimates for Joule- Thomson device flow rates and exit quality can vary significantly and these need to be accommodated for with a robust system design.
Measurements of viscosity and permeability of two phase miscible fluid flow in rock cores.
Williams, J L; Taylor, D G
1994-01-01
This paper describes the application of 1H magnetic resonance imaging (MRI) to the measurement of fluid viscosity and rock core plug permeability during two phase miscible displacements in certain rock types. The core plug permeability was determined by monitoring glycerol solutions displacing D2O. Simple physical principles were used to calculate the core permeability from the measured displacement angle for a set of Lochaline sandstone core plugs. In a further experiment the viscosity of polyacrylamide solution 1500 ppm was determined in the core plug. The permeability and viscosity results compared well to conventional core analysis methods.
NUMERICAL CALCULATION OF SOLID-LIQUID TWO PHASE FLOW BETWEEN STAY VANES IN HYDRAULIC TURBINE
无
2000-01-01
In this paper, an energy equation of silt-laden water flow is educed based on the energy equation of continuum fluid flow. The dissipation functions of liquid phase and solid phase are presented respectively. Then the extremity law of energy dissipation rate is introduced for the research of the silt-laden water flow and a new mathematical model is developed. The corresponding procedure based on the finite difference method (FDM) is developed to calculate the two phase flow in hydraulic turbine. The method is applied to analyze the silt-laden water flow between stay vanes, and the numerical results are in good agreement with the experimental ones.
On the upstream mobility scheme for two-phase flow in porous media
Mishra, Siddhartha
2009-01-01
When neglecting capillarity, two-phase incompressible flow in porous media is modelled as a scalar nonlinear hyperbolic conservation law. A change in the rock type results in a change of the flux function. Discretizing in one-dimensional with a finite volume method, we investigate two numerical fluxes, an extension of the Godunov flux and the upstream mobility flux, the latter being widely used in hydrogeology and petroleum engineering. Then, in the case of a changing rock type, one can give examples when the upstream mobility flux does not give the right answer.