Mean Mass Transfer Research Articles

The radius variations of accreting main-sequence stars and mass transfer instability

ABSTRACT Many previous works studied the dynamical time-scale mass transfer stability criteria based on the donor response with neglecting the stellar structure of the accretor. In this letter, we investigate the radial response of accretors with mass accumulation and its effect on the binary mass transfer stability. We perform a series of detailed stellar evolution simulations with different types of accretors and obtain the radial variations of stars accreting at different rates. Since the time within which the donor loses half of the original mass has a correlation with the donor mass, we approximately obtain the mean mass transfer rate as a function of mass ratio. Assuming that the common envelope (CE) phase occurs if the accretor radius exceeds the outer Roche lobe radius, we obtain the critical mass ratio of dynamically unstable mass transfer. We find the critical mass ratios for donors filling their Roche lobes at the Main Sequence (MS) and Hertzsprung Gap (HG) stages are smaller than that derived from the radial response of the donor in the traditional way. Our results may suggest that the binary is easier to enter into the CE phase for a donor star at the MS or HG stage than previously believed.

Salient features of wheel-vehicle aerodynamic interactions: Consequences for drag

Salient features of wheel–vehicle interactions and their consequences for drag are investigated experimentally based on a simplified square-back vehicle with different distances l between the rear wheels and the base of the vehicle. Two different mechanisms responsible for a base drag increase of up to 12% are distinguished. At the scale of the vehicle, whatever the distance l, wheels perturb the underflow and induce a global variation of the vertical balance of the vehicle wake. According to the state of the initial wake, significant base drag increase or decrease are observed. Considering the scale of the wheels, if the wheel-to-base distance l/w (w being the width of the wheels) is smaller than a threshold of order 3 in the present configuration, the base drag increases and is very sensitive to l/w. In this situation, a mean mass transfer from the vehicle wake to the wake of the rear wheels is observed. Based on these observations, a physical model is then proposed to explain this high-sensitivity regime.

Performance analysis and drying kinetics of beetroot slices dried in an innovative solar dryer without and with thermal storage unit

ABSTRACT An active indirect solar dryer (AISD) has been used to conduct drying experiments of beetroot slices without a thermal storage unit (TSU) (mode-I) and with TSU (mode-II) using paraffin wax as a phase change material. The performance analysis and drying curves of beetroot slices were assessed in both modes and compared. The average drying efficiency and drying rate were enhanced by 48.63% and 41.72% in mode-II compared to mode-I. Two-term exponential and modified Page models were the best models for beetroot slices in mode-I and mode-II, respectively. The specific energy consumption was estimated to be 1.706 and 0.96 kWh/kg, the average moisture diffusivity was 7.11 × 10−9 and 7.22 × 10−9 m2/s, and the mean mass transfer coefficients were 3.56 × 10−3 and 3.64 × 10−3 m/s, respectively. The specific moisture extraction rate was 0.586 and 1.041 kg/kWh and the mean heat transfer coefficient was 4.103 and 4.2 W/m2K, in mode-I and mode-II, respectively. The collector outlet temperature is increased by 2.5 to 10.7°C when the heat is discharged from TSU. In comparison to mode-I, the performance of AISD is superior in mode-II, exhibiting better drying performance due to TSU in the drying section in mode-II.

Further results on the mean mass transfer and fluid flow in a turbulent round jet

Further results on the mean mass transfer and fluid flow in a turbulent round jet

Determination of Crystal Growth Rates in Multi-Component Solutions

Many solid forming processes involve crystallization from multi-component solutions. In order to predict final phase assemblages, multi-component phase transfer kinetics must be known. It is not sufficient to have the kinetics of only one crystallizing component in the presence of other entities; the kinetics of concurrent crystallizing components are of interest as well. However, methods for their determination are currently lacking. We propose a new method comprising desupersaturation measurements of a 150 µm film of supersaturated solution in contact with a planar crystalline substrate. We show that concentration measurement at a single point in the film is sufficient to retrieve the phase transfer kinetics. For this, we use a confocal micro-Raman spectroscope, which is able to distinguish between different components and has a high spatial resolution. We chose crystallization of Na2SO4 and Na2CO3 decahydrate from aqueous solution as our model system because of its well-known phase equilibrium. In binary experiments, we demonstrate the mode of operation and its ability to reproduce known kinetics from the literature. In ternary experiments, we successfully distinguish two courses of crystallization, the first of which is a preferential crystallization of one component and the second a simultaneous crystallization of both crystallizing components. In both cases, the parameters for simple power law kinetics are determined. If sodium carbonate decahydrate crystallizes while sodium sulfate remains in solution, the mean mass transfer coefficient is revealed to be kg,CO3=6×10−7ms−1, which is about an order of magnitude lower compared to binary crystallization. If sodium carbonate decahydrate crystallizes concurrently with sodium sulfate decahydrate, the crystallization kinetics are similar to binary cases. The other component tends to be significantly slower compared to its binary crystallization.

Influence of different kinetic heating mechanisms on the dynamics of a trapped Brownian particle in a complex plasma

Combined effect of random forces of different origins and electrostatic confinement on the dynamics of a charged Brownian particle in a plasma is investigated. Analytical equations for the effective kinetic temperature, mean square displacement (MSD), mass transfer, and velocity autocorrelation functions (VAF) of a free and trapped microparticle under the action of two random forces governed by Gaussian and Ornstein–Uhlenbeck processes are derived. The results obtained are considered on examples of solitary passive microparticles with fluctuating charges due to the discrete charging process or inhomogeneity of the surrounding plasma, active light-absorbing particles with rotational fluctuations, and strongly coupled systems with nonreciprocal interparticle interactions. The applicability of the Langevin equations with a thermal noise temperature above the ambient gas temperature to model the dynamics of dust particles in a complex plasma is discussed. It is shown that, under certain conditions, the well-known Uhlenbeck–Ornstein–Wang equations for the MSD and VAF fail to describe the oscillations of both a solitary particle and a particle in a strongly coupled monolayer system suspended in a gas discharge.

Near wake interactions and drag increase regimes for a square-back bluff body

The three-dimensional near wake of a square-back bluff body in ground proximity is experimentally perturbed by placing a pair of D-shaped obstacles under the body. Five obstacle widths $d$ , from 12 % to 26 % of the height of the body, are used to perform a sensitivity study of the body's pressure drag by varying the relative distance $l$ between the obstacle pair and the base. Two successive drag-sensitive regimes are identified for obstacle-to-base distances $l/d < 2.5$ , where the pressure drag of the body is increased up to 22 %. In different regimes, the flow dynamics measured downstream of the obstacles are found to be very different. When the obstacles are the closest to the base, $l/d<1.5$ , the pressure drag changes of the main body are driven by mean merging between the wakes of the obstacles and of the main body, and scale with $d$ . Contrarily, when the obstacles are located farther from the base, $1.5< l/d<2.5$ , the wakes of the obstacles are isolated from the main body wake. Here the dynamics of the obstacle wake drive the pressure drag changes of the main body, which scale with $d^{2}$ . In both regimes, we measure a mean mass transfer from the wake of the main body to the wakes of the obstacles. This is the main mechanism responsible for the pressure drag changes. Using our results and reference studies describing the effects of base suction on the pressure drag of bluff bodies, a physical model is proposed to explain the contrasting scalings of the pressure drag increase in the different regimes observed in this study.

Numerical simulation and self-similarity of the mean mass transfer in turbulent round jets

The paper investigates the mean mass transfer/passive scalar spreading in turbulent submerged round jets. Two regions of flow are present in the jet evolution: the Near-Field Region (NFR) and the Fully Developed Region (FDR). This group of research investigates from some years the mean evolution of turbulent rectangular jets with the new physical finding that two sub-regions (not a single one) are present in the NFR. The first region of the two is the newly discovered Undisturbed Region of Flow (URF), while the second one is the known Potential Core Region (PCR). In a recent paper we showed that the flow evolution of turbulent round jets, as far as momentum spreading is concerned, is self-similar also in the NFR. Literature shows that mass transfer spreading is self-similar only in FDR. The present paper presents new mean mass transfer results of the numerical Large Eddy Simulation (LES) in turbulent round jets. Four Reynolds numbers, from 2492 to 19,988, and two laminar Schmidt numbers, 1 and 10, are investigated. The first novel result of this paper is that mass transfer is self-similar in the NFR. The second result is that two new analytical models describe the passive scalar spreading in the URF and PCR. The third result is that two new self-similar laws describe the passive scalar spreading in the FDR. The fourth result states that the well-known power-law relationship, between passive scalar and axial momentum in the FDR, holds regardless of the modeling of turbulent viscosity and turbulent Schmidt number.

Wall slip characteristics on the dynamics of radioactive Carreau fluid flow subjected to thermophysical properties of the rotating boundary layer

In this paper, we examine the theoretical and numerical study of the flow over a heated infinite rotating disk with temperature-dependent viscosity, conductivity and diffusivity. We utilized the Carreau model for shear thickening behavior and determine the steady flow profiles under the partial-slip and Darcy-Forhhemier effects near the rotating surface. Using heat and mass transfer phenomena, we determine this behavior with modified activation enthalpy, radiative heat flux and thermophoretic effect. These study has explored a great interest in applied engineering procedures due to increasing theoretical and mathematical elevation problem. For large Reynold's number, the basic flow may be determined numerically in terms of von-Kàrmàn similarity solution. Using von-Kàrmàn similarity solutions, the boundary layer equations are converted into a system of ordinary differential equations which have been solved by the shooting method. The effects of porosity, Darcy and slip parameters show a decrease behavior for the mean flow profiles. Variable diffusivity and thermal conductivity increases the concentration and temperature distributions. The mean flow concentration profile increases by increasing values of ε2 number, λc parameter and Du number. The numerical results obtained for different mechanisms are presented through graphs and tables. This study analyzes the interesting physical parameters on the mean flow, heat and mass transfer through graphs and tables.

Numerical study and correlations for heat and mass transfer coefficients in indirect evaporative coolers with condensation based on orthogonal test and CFD approach

Previous studies obtained the heat and mass transfer coefficients of Indirect evaporative coolers (IECs) with condensation based on the following assumptions: (1) empirical equations in the dry channel without water evaporation or condensation, or the boundary condition is assumed to be a constant surface heat flux or temperature so that constant values of Nusselt number can be employed for evaluating the heat transfer coefficient; and (2) Lewis number is assumed to be unity so that the mass transfer coefficients can be then calculated via the heat and mass transfer analogy. Thus far, the heat and mass transfer coefficients of IECs with condensation under naturally formed boundary condition are lacking. In this paper, an experimental-validated computational fluid dynamics (CFD) model has been established to investigate the heat and mass transfer processes of IECs incorporating the phenomenon of condensation. A single factor analysis and a multiple factor analysis are concurrently carried out to evaluate the effects of the nine parameters on the heat and mass transfer processes of IECs. Key findings revealed that both mean Nusselt and Sherwood numbers under the presented conditions are larger than those obtained under constant surface temperature and heat flux conditions; and the respective values of the primary and secondary Lewis numbers are observed to change from 0.37 to 0.75 and 0.70 to 0.85 which severely deviate from the conventional assumed value of unity. Finally, empirical correlations are developed for the mean heat and mass transfer coefficients based on an orthogonal test method. The simplified linear correlations can serve as new fundamental references to account for IEC that are consistently experiencing with condensation.

Double-diffusive natural convection in an inclined enclosure with heat generation and Soret effect

PurposeThe purpose of this paper is to study numerically thermosolutal natural convection within an inclined rectangular cavity in the presence of Soret effect and heat generation. The enclosure is heated and salted from its long sides with constant but different temperatures and concentrations. The study focuses on the effects of three main parameters which are, the Soret parameter (Sr = 0 and –0.5), the internal to external Rayleigh numbers ratio 0 ≤ R ≤ 80 and the cavity inclination γ, varied from 0° (vertical position) to 60°. The combined effects of these parameters on fluid flow and heat and mass transfer characteristics are examined for the external Rayleigh number RaE = 105, the Prandtl number Pr = 0.71, the buoyancy ratio N = 1, the Lewis number Le = 2 and the aspect ratio of the cavity A = 2.Design/methodology/approachA hybrid lattice Boltzmann-finite difference method (LBM-FD) was used to tackle the problem under consideration. The LBM with the simple relaxation time was used for the fluid flow in the presence of the gravity force, while the temperature and concentration equations were solved separately using an explicit finite-difference technique at the Boltzmann scale.FindingsThe monocellular nature of the flow, obtained for R = 0 is not destroyed by varying the cavity inclination and the Soret parameter but rather by the increase of the parameter R. The Soret parameter and the cavity inclination become perceptible at high values of R. The inclination γ = 60° leads to high mean temperatures compared to the other inclinations. The effect of R on mean concentration is amplified in the presence of Soret effect but limited in the absence of the latter. The negative Soret parameter combined with high internal heat generation and a relatively high inclination is important when the objective is to maintain the fluid at a high concentration of species. The presence of bicellular flow combined with the important elevation undergone by the fluid temperature, makes both the cold and hot walls playing a cooling role with the most important exchanges taking place at the upper part of these walls. The analysis of the mean mass transfer shows that the increase of the inclination may lead to an increase or a decrease of the mass transfer depending on the range of R, in the case of Sr = 0. However, for Sr = −0.5, it is observed that the increase of γ is generally accompanied by a reduction of the mass transfer.Originality/valueTo the best of the authors’ knowledge, the hybrid LBM-FD was not used before to study such a problem. Combined effect of R and inclination may be useful in charging the fluid with species when the objective is to maintain high concentrations in the medium.

Influence of the boundary conditions on heat and mass transfer in spacer-filled channels

The purpose of this study is to discuss some problems which arise in heat or mass transfer in complex channels, with special reference to the spacer-filled channels adopted in membrane processes. Among the issues addressed are the consistent definition of local and mean heat or mass transfer coefficients; the influence of the wall boundary conditions; the influence of one-side versus two-side heat/mass transfer. Most of the results discussed were obtained by finite volume CFD simulations concerning heat transfer in Membrane Distillation or mass transfer in Electrodialysis and Reverse Electrodialysis, but many of the conclusions apply also to different processes involving geometrically complex channels

Mass transfer correlations for dissolution of cylindrical additions in liquid metals with gas agitation

The results of an experimental study of the effect of gas agitation on mass transfer from cylindrical Si specimens to molten Al were used to deduce mean mass transfer coefficients in a two-phase flow. Then the three-dimensional gas-agitated liquid was simulated using the commercial software FLOW-3D, to obtain predictions of bubble distribution and estimates of the velocity field within the opaque liquid metal, to be used to predict mass transfer rates. An existing mass transfer correlation for a gas-agitated liquid without an external bulk flow was used to fit the experimental data within 5%. With a bulk velocity, a correlation for mass transfer from a vertical cylinder in cross flow was modified to incorporate the effect of gas injection, and it predicted the measured mass transfer coefficients within 11%.

Nonstationary Mass Transfer Near the Surface of a Cylindrical Body

The problem of nonstationary diffusion of the target component to a phase that is external relative to the surface of a cylindrical body has been formulated and solved analytically. From the found solution the dependences have been obtained for calculating the instantaneous mass transfer coefficient and the phase-contact-time mean mass transfer coefficient, on the basis of which the process of extraction of technological pollutants from fibrous materials has been analyzed.

Separation of In3+ and Fe3+ from sulfate solutions using D2EHPA in a laminar microreactor

A microfluidic solvent extraction method is put forward to solve the problems existing in the conventional solvent extraction of indium, such as large waste of extractant, fire hazards, etc. Experiments were performed in a series of microreactors to separate In3+ and Fe3+ from sulfate solutions using D2EHPA as the extractant. The effect of main parameters such as different contact times, microchannel sizes, interface to volume ratios and pH values on the indium extraction efficiency was investigated. The results show that the smaller the channel size, the more the beneficial diffusion and mass transfer. Specifically, in a microchannel, with a size of 100 μm × 50 μm × 120 mm, almost 100% extraction efficiency was reached with contact time about 0·5 s. The mean mass transfer rate can be as high as 0·291 g m− 2 s− 1, and the ratio of mean mass transfer rate of In3+ to that of Fe3+ can be as high as 29·76.

Comparative Studies of Silicon Dissolution in Molten Aluminum Under Different Flow Conditions, Part I: Single-Phase Flow

Following on a study of Si dissolution in molten Al, the effect of gas agitation is examined. The effects of gas flow rate, liquid bulk velocity, the position of a top injection lance, and bath temperature on the dissolution rate are quantified. A higher gas flow rate produced larger bubbles while bubble frequency remained relatively unchanged. This resulted in larger bubble-induced fluctuating velocities which in turn increased the dissolution rate. At lower bulk velocities, the effect of gas agitation is localized around the lance. By increasing the velocity, the effect of gas agitation is transported further into the bath. The dissolution rate enhancement varies with increasing bulk velocity, and explanations are provided. When combined with a bulk flow, gas agitation increases the dissolution rate regardless of lance position. Also, the enhancement of dissolution rate due to gas injection decreases at higher superheats, as the higher bath temperature increases the mass boundary thickness. In addition, the dissolution rate without gas agitation (single-phase flow) and with gas agitation (two-phase flow) is compared in terms of mean mass transfer coefficients. It was found that for the same liquid bulk velocities, the mean mass transfer coefficients are higher in two-phase flow than in single-phase flow. Finally, an increment to the single-phase flow bulk velocity that would be required to gain parity with the two-phase flow dissolution rate rise is demonstrated.

Effects of Schmidt number on near-wall turbulent mass transfer in pipe flow

Large Eddy simulation (LES) of turbulent mass transfer in circular-pipe flow has been performed to investigate the characteristics of turbulent mass transfer in the near-wall region. We consider a fully-developed turbulent pipe flow with a constant wall concentration. The Reynolds number under consideration is Re τ = 500 based on the friction velocity and the pipe radius, and the selected Schmidt numbers (Sc) are 0.71, 5, 10, 20 and 100. Dynamic subgrid-scale (SGS) models for the turbulent SGS stresses and turbulent mass fluxes were employed to close the governing equations. The current paper reports a comprehensive characterization of turbulent mass transfer in circular-pipe flow, focusing on its near-wall characteristics and Sc dependency. We start with mean fields by presenting mean velocity and concentration profiles, mean Sherwood numbers and mean mass transfer coefficients for the selected values of the parameters. After that, we present the characteristics of fluctuations including root-mean-square (rms) profiles of velocity, concentration, and mass transfer coefficient fluctuations. Turbulent mass fluxes and correlations between velocity and concentration fluctuations are also discussed. The near-wall behaviour of turbulent diffusivity and turbulent Schmidt number is shown, and other authors’ correlations on their limiting behaviour towards the pipe wall are evaluated based on our LES results. The intermittent characteristics of turbulent mass transfer in pipe flow are depicted by probability density functions (pdf) of velocity and concentration fluctuations; joint pdfs between them are also presented. Instantaneous snapshots of velocity and concentration fluctuations are shown to supplement our discussion on the turbulence statistics. Finally, we report the results of octant analysis and budget calculation of concentration variance to clarify Sc-dependency of the correlation between near-wall turbulence structures and concentration fluctuation in the vicinity of the pipe wall.

Water droplet condensation and evaporation in turbulent channel flow

AbstractWe propose a point-particle model for two-way coupling of water droplets dispersed in the turbulent flow of a carrier gas consisting of air and water vapour. We adopt an Euler–Lagrangian formulation based on conservation laws for the mass, momentum and energy of the continuous phase and on empirical correlations describing momentum, heat and mass transfer between the droplet phase and the carrier gas phase. An incompressible flow formulation is applied for direct numerical simulation of differentially heated turbulent channel flow. The two-way coupling is investigated in terms of its effects on mass and heat transfer characteristics and the resulting droplet size distribution. Compared to simulations without droplets or those with solid particles with the same size and specific heat as the water droplets, a significant increase in Nusselt number is found, arising from the additional phase changes. The Nusselt number increases with increasing ambient temperature and is almost independent of the heat flux applied to the walls of the channel. The time-averaged droplet size distribution displays a characteristic dependence on position expressing the combined effect of turbophoresis and phase changes in turbulent wall-bounded flow. In the statistically steady state that is reached after a long time, the resulting flow exhibits a mean motion of water vapour from the warm wall to the cold wall, where it condenses on average, followed by a net mean mass transfer of droplets from the cold wall to the warm wall.

Intensity of convective mass/heat transfer in a rotary regenerator rotor with the transverse needle-fins

A forced convective mass transfer coefficient was electrochemically measured for a cylindrical bundle of transverse needle-fins ϕ1 × 10.9, applied as the rotor porous matrix of a rotary heat regenerator. The baffle inside the rotor was present. The technique based on the ferricyanide–ferrocyanide redox reaction controlled at the cathode, in the presence of a sodium hydroxide based electrolyte, was used in this experiment. A set of the six neighbouring fins, connected in parallel, was the cathode. The distribution of the mass transfer coefficient according to different static rotor angle position and the mean mass transfer Chilton–Colburn coefficient correlation j M = j M (Re) for rotation numbers, Ro: 0, 0.8, 1.6 and 2.0 were stated in the mean Reynolds number, Re, range 180–985. The comparison was made between the convective heat fluxes of the pin-fins and the sheet rotor, for Ro = 0.

Effect of Lewis Number on Double-diffusive Natural Convection in a Triangular Cavity

This paper concerned with the numerical study of thermal and mass diffusive natural convection flow inside a triangular shape solar collector using finite element method for the governing equations expressing the velocity pressure formulation along with the energy and concentration balance equations. In the solution procedure, the isothermal and isoconcentration boundary conditions are assumed at the absorber and covers of collector. Local and mean heat and mass transfer rates for the thermal Rayleigh number and Lewis number are presented. Streamlines, isotherms and isoconcentration are also presented for the aforesaid parameters. The result found in this study fully agreed with the previous published work. But this result will be profitable for the design of the collector.