Numerical Simulation Of Mass Transfer Research Articles

Numerical Simulation of Mass Transfer in Hollow Fiber Membrane Module for Membrane-Based Artificial Organs.

The mass transfer behavior in a hollow fiber membrane module of membrane-based artificial organs (such as artificial liver or artificial kidney) were studied by numerical simulation. A new computational fluid dynamics (CFD) method coupled with K-K equation and the tortuous capillary pore diffusion model (TCPDM) was proposed for the simulations. The urea clearance rate predicted by the use of the numerical model agrees well with the experimental data, which verifies the validity of our numerical model. The distributions of concentration, pressure, and velocity in the hollow fiber membrane module were obtained to analyze the mass transfer behaviors of bilirubin and bovine serum albumin (BSA), and the effects of tube-side flow rate, shell-side flow rate, and fiber tube length on the bilirubin or BSA clearance rate were studied. The results show that the solute transport mainly occurred in the near inlet regions in the hollow fiber membrane module. Increasing the tube-side flow rate and the fiber tube length can effectively enhance the solute clearance rate, while the shell-side flow rate has less influence on the BSA clearance. The clearance of macromolecule BSA is dominated by convective solute transport, while the clearance of small molecule bilirubin is significantly affected by both convective and diffusive solute transport.

Numerical simulations of mass transfer in turbulent pipe flow at high schmidt numbers

Numerical simulations of mass transfer in turbulent pipe flow at high schmidt numbers

Mathematical modeling of memristor resistive switching based on mass transfer full model of oxygen vacancies and ions

A relatively simple mathematical model of dynamic switching of a memristor has been created based on a fairly complete physical model of the processes of stationary mass transfer of oxygen vacancies and ions, considering their generation, recombination and diffusion in electric field in the “metal-oxide-metal” structure with the dominant transport mechanism of electron tunneling through oxygen vacancies. The results of numerical simulation of mass transfer of oxygen vacancies along thickness of the oxide layer of the memristor are presented. The distributions of vacancy concentration during their diffusion in an electric field are found, taking into account the processes of generation and recombination with ions, depending on the applied voltage to the electrodes and on the temperature of the memristor. A good coincidence of the volt-ampere characteristics part found as a result of numerical simulation and a series of experiments is obtained. It is shown that under conditions of more than 600 K memristor temperature, it is possible to neglect the process of ion-vacancy recombination and significantly simplify the procedure for mathematical modeling of memristor resistive switching by eliminating the oxygen mass transfer equation, as well as the recombination term in the stationary equation of oxygen vacancies mass transfer. The developed mathematical model of memristor dynamic switching, including a system of stationary ordinary differential equations, is designed to simulate the operation of large memristor arrays in neuromorphic computing devices and may be preferable in relation to known circuit models that include a certain set of fitting parameters to match the simulation results with the memristor experimental characteristics.

Numerical simulation of mass transfer dynamics in Taylor flows

Direct Numerical Simulations of mass transfer within Taylor flows are carried out using the periodic unit-cell approach by means of the Level-Set method, under the axisymmetric assumption. The considered cases are based on the experimental study of Butler et al. [1] (absorption of gaseous species) for bubbles of Reynolds numbers Reb>200 and capillary numbers Ca>10−3. Firstly, the hydrodynamics of five cases are calculated up to steady state, after which the bubble shape, lubrication film thickness and velocity profiles are compared to experimental and theoretical results. Using these converged hydrodynamics, the transient mass transfer between the gas and liquid phases is then simulated, assuming no change in bubble volume. The Péclet number Pe is varied between 10 and 900 by changing the diffusion coefficient, allowing for new insight into local phenomena of mass transfer. In this way, the maximal transfer fluxes at the interface are observed to be (i) close to the stagnation point at the film entrance, and (ii) at the rear cap where the tangential velocity is greatest. As once as the mass transfer coefficient becomes constant, the fluxes across the part of the interface in contact with the film and around the bubble caps are each characterised by a local Sherwood number. The latter evolves by Pefilm across the film and is found to be predictable by a simple model when Pefilm>1, where Pefilm is the film Péclet number. Concerning the caps, it evolves by Pe but only in a finite range of Pe, contrary to the common assumption of similarity of transfer around the caps with that around a rising unconfined spherical bubble. Such local analyses could be further used in multizone models of mass transfer for Taylor flows. Finally, a correlation is proposed to scale the global Sherwood number Sh∞ far from channel inlet, defined as a function of both a Péclet number PeR based on the relative velocity between the bubble and the two-phase flow, and the gas volume fraction in the unit cell. Its predictions are discussed against experimental results at much higher Péclet numbers, after showing that Sh∞ is independent on the initial concentration distribution in the liquid (the latter being sensitive to the injection conditions in experiments).

Numerical Simulation of Mass Transfer in Pulsatile Flow of Blood Characterized by Carreau Model under Stenotic Condition

Numerical Simulation of Mass Transfer in Pulsatile Flow of Blood Characterized by Carreau Model under Stenotic Condition

Direct numerical simulation of mass transfer and mixing in complex two-phase systems using a coupled volume of fluid and immersed boundary method

In this paper, a hybrid computational technique for the Direct Numerical Simulation of hydrodynamics and (convective) mixing in complex two-phase systems is presented. The hybrid Immersed Boundary and Volume of Fluid method is based upon a single-fluid approach in combination with Henry’s law for the concentration jump. The convective species fluxes are evaluated using PLIC-based geometrical advection, which is consistent with the advection of the local fluid volume fractions. Complex geometries can be accounted for and are treated with the Immersed Boundary method. Following the verification for single phase and two-phase systems, the model was used to investigate the influence of the container geometry on the mixing of a tracer due to tilting of the container. For both cylindrical and rectangular containers, an increasing tilting angle enhances the convective motion and consequently the mixing efficiency. The cylindrical geometry was found to possess a better mixing efficiency than the rectangular geometry.

Direct numerical simulation of mass transfer in bidisperse arrays of spheres

AbstractIn this study, an efficient ghost cell‐based immersed boundary method is used to perform direct numerical simulations of mass‐transfer processes in bidisperse arrays. Stationary spherical particles, with a size ratio of 1.5, are homogeneously distributed in a periodic domain in the spanwise directions. Simulations are performed over a range of solids volume fractions, volume fraction ratios of small‐to‐large particles, and Reynolds numbers. Through our studies, we find that large particles have a negative influence on the overall mass‐transfer performance; however, the performance of individual particle species is independent on the relative volume fraction ratios. We propose two correlations: (a) a refitted Gunn correlation for a better description of the interfacial transfer performance based on individual particle species; (b) a fractional calculation for a simple estimation of the overall performance in bidisperse systems using characteristics of individual particle species. We also investigate how well the overall mass‐transfer coefficient can be predicted by defining an appropriate equivalent diameter.

Experiments and numerical simulations of mass transfer and flow evolution in transient rectangular free jet of air

The paper investigates the transient flow evolution, up to the steady state, of a rectangular free jet of air with aspect ratio AR = 6.3. The Reynolds number, Re, defined according to the hydraulic diameter, D, of the rectangular slot of height H, equal to about D = 2H, spans in the range from Re = 48,000 to Re = 3400. A centrifugal fan generates the jet flow with a velocity increasing, as a ramp, from zero up to a constant steady state value. In the transient state of the flow the jet is composed of a primary vortex (PV) and a quasi-stable stem. In the transient 2D experimental instant images the stem of the jet has a height equal to that of the slot and a length increasing with the time up to a maximum value, which is greater than the lengths observed in the steady state, i.e. Negligible Disturbance Flow (NDF) and Small Disturbance Flow (SDF). The experimental jet evolution, observed with measurements and image processing, show that the primary vortex pinch-off does not occur for all the Reynolds numbers investigated, while the leading vortex structure becomes progressively incoherent and breaks down into turbulence. Two-dimensional (2D) Large Eddy Simulations (LES) of mass transfer and fluid flow evolution confirm the experimental images. The transient LES simulations are in good agreement with the experimental results.

Numerical simulations of mass transfer in binaries with bipolytropic components

We present the first self-consistent, three dimensional study of hydrodynamic simulations of mass transfer in binary systems with bipolytropic (composite polytropic) components. In certain systems, such as contact binaries or during the common envelope phase, the core-envelope structure of the stars plays an important role in binary interactions. In this paper, we compare mass transfer simulations of bipolytropic binary systems in order to test the suitability of our numerical tools for investigating the dynamical behaviour of such systems. The initial, equilibrium binary models possess a core-envelope structure and are obtained using the bipolytropic self-consistent field technique. We conduct mass transfer simulations using two independent, fully three-dimensional, Eulerian codes - Flow-ER and Octo-tiger. These hydrodynamic codes are compared across binary systems undergoing unstable as well as stable mass transfer, and the former at two resolutions. The initial conditions for each simulation and for each code are chosen to match closely so that the simulations can be used as benchmarks. Although there are some key differences, the detailed comparison of the simulations suggests that there is remarkable agreement between the results obtained using the two codes. This study puts our numerical tools on a secure footing, and enables us to reliably simulate specific mass transfer scenarios of binary systems involving components with a core-envelope structure.

Direct numerical simulation of mass transfer in bubbly flows

Process design, especially in the chemical industry, often requires a detailed understanding and accurate quantification of interfacial mass transfer. Experimental investigations, however, are often infeasible as required measurement quantities and locations are inaccessible. Thus, Direct Numerical Simulations (DNS) have become a viable tool for the detailed study of mass transfer processes. This paper presents a numerical modelling framework for the simulation of dilute species transfer based on an algebraic Volume-of-Fluid method, aiming at the deduction of an improved closure model for interfacial species transfer from single rising bubbles. To this end, the Continuous Species Transfer (CST) model [18] and state-of-the-art high performance computing techniques are employed.

Numerical simulation of mass transfer and fluid flow evolution of a rectangular free jet of air

The paper presents Large Eddy Simulations (LES) of mass transfer and fluid flow evolutions of a submerged rectangular free jet of air in the range of Reynolds numbers from Re = 3400 to Re = 22,000, with the Reynolds number, Re, defined with the hydraulic diameter of the rectangular slot, of height H. The numerical simulations are 3D for Re = 3400 and 6800, while 2D for Re = 10,400 and 22,000 to reduce computational time costs. The average and instant LES numerical simulations are compared with the concentration visualizations, obtained with the Particle Image Velocimetry (PIV) technique, and the fluid dynamics variables, velocity and turbulence, measured with the PIV technique and the Hot Film Anemometry (HFA). In the numerical simulations, the Schmidt number is equal to 100 to compare the air concentration in the PIV experiments, while the turbulence on the exit of the slot is equal to the value measured experimentally, and ranging between 1% and 2%. The average 2-3D LES simulations are in agreement with the concentration and the fluid dynamics experimental results in the Undisturbed Region of Flow (URF) and in the Potential Core Region (PCR), while the vortex breakdown is captured only by the 3D LES approach. As far as the instant flow evolution is concerned, the 2-3D LES simulations reproduce the Negligible Disturbances Flow (NDF), where the jet height maintains constant, and the Small Disturbances Flow (SDF), where the jet height oscillates, with contractions and enlargements, but without the vortex formation. Average and instant velocity and turbulence numerical simulations on the centreline are in good agreement to the experimental PIV measurements.

Numerical simulation of mass transfer in centrifugal evaporator

Numerical simulation of mass transfer in centrifugal evaporator

Numerical simulation of mass transfer and convection near a hydrogen bubble during water electrolysis in a magnetic field

Numerical simulation of mass transfer and convection near a hydrogen bubble during water electrolysis in a magnetic field

Numerical Simulation of Mass Transfer and Three-Dimensional Fabrication of Tissue-Engineered Cartilages Based on Chitosan/Gelatin Hybrid Hydrogel Scaffold in a Rotating Bioreactor.

Cartilage tissue engineering is believed to provide effective cartilage repair post-injuries or diseases. Biomedical materials play a key role in achieving successful culture and fabrication of cartilage. The physical properties of a chitosan/gelatin hybrid hydrogel scaffold make it an ideal cartilage biomimetic material. In this study, a chitosan/gelatin hybrid hydrogel was chosen to fabricate a tissue-engineered cartilage in vitro by inoculating human adipose-derived stem cells (ADSCs) at both dynamic and traditional static culture conditions. A bioreactor that provides a dynamic culture condition has received greater applications in tissue engineering due to its optimal mass transfer efficiency and its ability to simulate an equivalent physical environment compared to human body. In this study, prior to cell-scaffold fabrication experiment, mathematical simulations were confirmed with a mass transfer of glucose and TGF-β2 both in rotating wall vessel bioreactor (RWVB) and static culture conditions in early stage of culture via computational fluid dynamic (CFD) method. To further investigate the feasibility of the mass transfer efficiency of the bioreactor, this RWVB was adopted to fabricate three-dimensional cell-hydrogel cartilage constructs in a dynamic environment. The results showed that the mass transfer efficiency of RWVB was faster in achieving a final equilibrium compared to culture in static culture conditions. ADSCs culturing in RWVB expanded three times more compared to that in static condition over 10days. Induced cell cultivation in a dynamic RWVB showed extensive expression of extracellular matrix, while the cell distribution was found much more uniformly distributing with full infiltration of extracellular matrix inside the porous scaffold. The increased mass transfer efficiency of glucose and TGF-β2 from RWVB promoted cellular proliferation and chondrogenic differentiation of ADSCs inside chitosan/gelatin hybrid hydrogel scaffolds. The improved mass transfer also accelerated a dynamic fabrication of cell-hydrogel constructs, providing an alternative method in tissue engineering cartilage.

CFD study of CO2 separation in an HFMC: Under non-wetted and partially-wetted conditions

This paper applies computational fluid dynamics (CFD) to explore a numerical simulation of mass transfer in a hollow fiber membrane contactor (HFMC) for non-wetted and partially-wetted conditions. A comprehensive 2D mathematical model based on the finite element method (FEM) was developed for modeling a gas–solvent HFMC which was applied to CO2 removal from a CO2/N2 gas mixture. Aqueous mono-ethanol-amine (MEA) solution was used as the CO2 absorbent and flowed in the fiber bore and then the gas mixture was circulated counter-currently in the shell side of HFMC. The average outlet CO2 concentrations, the absorption flux, overall mass transfer coefficient and the CO2 removal efficiencies are parametrically simulated by using the operational parameters such as gas and solvent flow rates, operating temperature, the fiber porosity and other geometrical characteristics. As a novel work, the effect of opposite fluid direction, i.e. absorbent flow in the shell and gas mixture in the fibers, on the mass transfer coefficient and CO2 removal efficiency was also taken into account for further considerations. It was concluded that while gas flows in the fibers and solvent flows in the shell an HFMC with a smaller size can be used. Furthermore, the effect of aqueous solution types such as MEA, 2-amino-2-methyl-1-propanol (AMP) and NaOH on the overall mass transfer coefficient and on the percentage removal of CO2 was investigated numerically and interesting results were obtained. Generally, the results showed that a reasonable agreement exists between the experimental and CFD results.

1E16 透過性を考慮した膜による物質輸送の数値シミュレーション

1E16 透過性を考慮した膜による物質輸送の数値シミュレーション

M812 上昇気泡からの高シュミット数条件下における物質輸送の数値解析(GS5 流体工学(3),修士研究発表セッション)

M812 上昇気泡からの高シュミット数条件下における物質輸送の数値解析(GS5 流体工学(3),修士研究発表セッション)

Direct numerical simulation of gas transfer across the air–water interface driven by buoyant convection

A series of direct numerical simulations of mass transfer across the air–water interface driven by buoyancy-induced convection have been carried out to elucidate the physical mechanisms that play a role in the transfer of heat and atmospheric gases. The buoyant instability is caused by the presence of a thin layer of cold water situated on top of a body of warm water. In time, heat and atmospheric gases diffuse into the uppermost part of the thermal boundary layer and are subsequently transported down into the bulk by falling sheets and plumes of cold water. Using a specifically designed numerical code for the discretization of scalar convection and diffusion, it was possible to accurately resolve this buoyant-instability-induced transport of atmospheric gases into the bulk at a realistic Prandtl number ($\mathit{Pr}=6$) and Schmidt numbers ranging from$\mathit{Sc}=20$to$\mathit{Sc}=500$. The simulations presented here provided a detailed insight into instantaneous gas transfer processes. The falling plumes with highly gas-saturated fluid in their core were found to penetrate deep inside the bulk. With an initial temperature difference between the water surface and the bulk of slightly above$2$ K, peaks in the instantaneous heat flux in excess of$1600~\text{W}~\text{m}^{-2}$were observed, proving the potential effectiveness of buoyant-convective heat and gas transfer. Furthermore, the validity of the scaling law for the ratio of gas and heat transfer velocities$K_{L}/H_{L}\propto (\mathit{Pr}/\mathit{Sc})^{0.5}$for the entire range of Schmidt numbers considered was confirmed. A good time-accurate approximation of$K_{L}$was found using surface information such as velocity fluctuations and convection cell size or surface divergence. A reasonable time accuracy for the$K_{L}$estimation was obtained using the horizontal integral length scale and the root mean square of the horizontal velocity fluctuations in the upper part of the bulk.

D145 フロー型リチウム空気電池における物質移動・反応の数値シミュレーション(OS-05:燃料電池・二次電池関連研究の新展開(1))

D145 フロー型リチウム空気電池における物質移動・反応の数値シミュレーション(OS-05:燃料電池・二次電池関連研究の新展開(1))

Multiscale modeling of protein adsorption and transport in macroporous and polymer‐grafted ion exchangers

A multiscale model is presented to elucidate protein adsorption and transport behaviors in ion‐exchange chromatography (IEC) adsorbent particles that have either an open pore structure or charged dextran polymers grafted into the pores. Molecular dynamics simulation is used to determine protein diffusion and partitioning in different regions of the adsorbent pore, and these outputs are used in numerical simulations of mass transfer to determine the intraparticle protein concentration profile and the mass‐transfer rate. Modeling results indicate that, consistent with experimental observations, protein transport can be faster in the polymer‐grafted material compared to the open pore case. This occurs when favorable partitioning of protein into the polymer‐filled pore space is combined with relatively high protein mobility within this region. The modeling approach presented here should be applicable to proteins and adsorbents with different properties, and could help elucidate the factors that control adsorption and transport in various IEC systems. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3888–3901, 2014