Mass Transfer Velocity Research Articles

Non-similar solution of free convective flow of power law nanofluids in porous medium along a vertical cone and plate with thermal and mass convective boundary conditions

This paper investigates non-similar solution of free convective boundary layer flow of a viscous incompressible fluid along a vertical cone and plate embedded in a Darcian porous medium filled with power law non-Newtonian nanofluids. The effects of the thermal and mass convective boundary conditions are taken into account, which makes the present analysis practically applicable. The governing boundary layer equations are converted into a system of non-similar differential equations by using suitable transformations before being solved numerically. The effects of the controlling parameters on the dimensionless velocity, temperature, nanoparticle volume fraction, and the local Nusselt and Sherwood numbers are reported. It is found that the velocity, temperature, and concentration increase with mass transfer velocity for both the vertical plate and cone. Further, the velocity reduces whilst the temperature and concentration increase with increasing buoyancy ratio parameter for all three types of nanofluids in the case of both geometries. The local Nusselt and the local Sherwood numbers are found to be higher for dilatant nanofluids than pseudoplastic nanofluids and Newtonian fluids in each case. The numerical results for special cases are compared with the published data and an excellent agreement has been found.

Experimental study of liquid movement in free elementary convective cells

Elementary convection cells (ECC) are formed in horizontal layers of liquid heated from below, and they are experimentally investigated in this work. Results of experimental studies were adequately described by the theoretical model of ECC. It is shown that the addition of aluminum powder to oil transforms oil to a suspension, such that boundary conditions on the solid wall can be regarded as free because there is a slip through the tape of pure oil. Change in the character of boundary conditions is confirmed by the results of numerical processing of experimental results on formation of convective rings on the layer surface by other authors. Two independent methods for determining the velocity of mass transfer in cells with various diameters are described in the article. For cells with a large diameter (17 mm), the maximum velocity of mass transfer was measured at the upper boundary on a deflection angle of the probe. Measured in this way velocity was equal to V<sub>Oil</sub> ≈ 0.2 mm/sec. For cells with a smaller diameter (2 mm), the velocity of oil on the surface of a cell was measured using an optical method and constituted the value from 3.5 mm/s to 5.2 mm/s.

Numerical modelling on rate-limited dissolution mass transfer of entrapped petroleum hydrocarbons in a saturated sub-surface system

Petroleum hydrocarbons generally referred to as light non-aqueous phase liquid (LNAPL) entrapped within a saturated subsurface geological formation can result in longer duration of contamination due to mass transfer limitations associated with heterogeneity of the system. Considering a part of the total pore volume as immobile is significant in capturing the behaviour of extended tailing by solute breakthrough profiles. In this context, the present numerical model investigates dissolution characteristics of residual petroleum hydrocarbons (LNAPL) resulting from both mobile and immobile domains under varying conditions of rate-limited diffusive mass transfer, longitudinal dispersivity and mean mobile fluid velocity in a saturated groundwater system. The numerical results suggest that the influence of residual LNAPL saturation on dissolution mass transfer coefficient is critical in comparison with mobile flow velocity and dispersivity. In addition, the rate-limited effect becomes predominant with significant increase in advective velocity and reduction in residual LNAPL saturation for structured porous media. It is concluded from this study that the transport of dissolved contaminant is dominated by advection at the mobile pores, while the diffusive equilibrium at the immobile volume is significant in characterizing the extended tailing and subsequently determines the overall mass transfer resistance.

Estimation of the global air–sea CO2 gas flux considering wave breaking

We propose a new model with microbreaking and linear dependence on wind speed in the whitecap-free area and linear dependence on the fractional area of whitecaps, based on the whitecap model proposed by Monahan and Spillane (The role of oceanic whitecap in air–sea gas exchange. In: Brutsaert W, Jirka GH (eds) Gas transfer at water surfaces. Reidel, Dordrecht, 495–503, 1984). The relationship between whitecap coverage and wind–sea Reynolds number proposed by Zhao and Toba (J Oceanogr 57:603–616, 2001) provides the link among waves, wind, and whitecap coverage. This model yields a mass transfer velocity that is linear in wind speed at light winds and smoothly transitions with increasing wind to approximately cubic in wind speed and linear in wave age.

Group Analysis of Free Convection Flow of a Magnetic Nanofluid with Chemical Reaction

A theoretical study of two-dimensional magnetohydrodynamics viscous incompressible free convective boundary layer flow of an electrically conducting, chemically reacting nanofluid from a convectively heated permeable vertical surface is presented. Scaling group of transformations is used in the governing equations and the boundary conditions to determine absolute invariants. A third-order ordinary differential equation which corresponds to momentum conservation and two second-order ordinary differential equations which correspond to energy and nanoparticle volume fraction (species) conservation are derived. Our (group) analysis indicates that, for the similarity solution, the convective heat transfer coefficient and mass transfer velocity are proportional tox-1/4whilst the reaction rate is proportional tox-1/2, wherexis the axial distance from the leading edge of the plate. The effects of the relevant controlling parameters on the dimensionless velocity, temperature, and nanoparticle volume fraction are examined. The accuracy of the technique we have used was tested by performing comparisons with the results of published work and the results were found to be in good agreement. The present computations indicate that the flow is accelerated and temperature enhanced whereas nanoparticle volume fractions are decreased with increasing order of chemical reaction. Furthermore the flow is strongly decelerated, whereas the nanoparticle volume fraction and temperature are enhanced with increasing magnetic field parameter. Increasing convection-conduction parameter increases velocity and temperatures but has a weak influence on nanoparticle volume fraction distribution. The present study demonstrates the thermal enhancement achieved with nanofluids and also magnetic fields and is of relevance to nanomaterials processing.

Prognosis and Diagnostics of Water-absorbing Capacity of Polydisperse Materials by pH-metry Data

The work focuses on the solution of the problem concerning the diagnostics and prognosis of water-absorbing capacity of polydisperse materials. The relation of water absorption and acid-base properties of the surface is considered. The advantages of the research of acid-base properties of the surface by the pH-metry method are illustrated. The algorithm of the processing and interpretation of pH metric results to diagnose water absorption of powdery substances is suggested. The diagnostics is based on the research of velocity variation of mass transfer in the reaction zone in time. The change of pH suspension per unit of time is considered for the first time as an analytic signal of «WрН» mass transfer velocity. It is demonstrated that the velocity variation of mass transfer in the system “solid body-water” reflects the stopping mechanism of ion exchange and can be used for prognosis of hydrophobic behavior of the solid body surface. The introduced material in the given article will be useful for implementation in research, industrial and school laboratories.

Kinetic characteristics of coal gas desorption based on the pulsating injection

In order to understand the kinetic characteristics of coal gas desorption based on the pulsating injection (PI), the research experimentally studied the kinetic process of methane desorption in terms of the PI and hydrostatic injection (HI). The results show that the kinetic curves of methane desorption based on PI and HI are consistent with each other, and the diffusion model can best describe the characteristics of methane desorption. Initial velocity, diffusion capacity and ultimate desorption amount of methane desorption after PI are greater than those after HI, and the ultimate desorption amount increases by 16.7–39.7%. Methane decay rate over the time is less than that of the HI. The PI influences the diffusion model parameters, and it makes the mass transfer Biot number Bi′ decrease and the mass transfer Fourier series F0′ increase. As a result, PI makes the methane diffusion resistance in the coal smaller, methane diffusion rate greater, mass transfer velocity faster and the disturbance range of methane concentration wider than HI. Therefore, the effect of methane desorption based on PI is better than that of HI.

Degradation of 4-Clorophenol By Electro-Fenton Using Electrodes of Graphite

Electrochemical Advanced Oxidation Processes (EAOP) have been proposed like alternative processes for the treatment of industrial wastewater this is due to their high effectiveness in removing toxic organic compounds, low operating costs and minimum consumption of chemical reagents.In this work the main purpose is to find the better conditions to degradate an organic compound in this case 4-Clorophenol by Fenton´s reaction.Electrolytic System. Electrochemical cell is an undivided glass cell of 1 Liter. The electrodes (anode and cathode) are made of graphite. An oxygen flow of 50 mL*min-1 feeds with a diffuser to electro-generate hydrogen peroxide (H2O2) in situin the cathode.The diffuser, furthermore of provide oxygen also generates a bubble matrix which increase the velocity of mass transfer from the ions situated in the electrolyte to the electrodes surface.For applying constant current is necessary a power supply which maintaining a current at 0.2 A. In this case the support electrolyte is Na2SO4 0.05 mol*L-1, this solution was adjusted to pH=3.0 with sulfuric acid. With the above conditions, an experiment with a volume of 900 mL of electrolyte solution were conducted to electro-generate H2O2. The determination of the concentration of H2O2was followed by spectrophotometry UV-Vis at λ=408nm in an equipment HACH DR 500.Knowing that is possible to electro-generate H2O2 in situ in this electrochemical cell it was decided to carry out Fenton´s reaction. For this purpose the ions Fe2+were obtained from an iron piece which was placed within the cell and it was not connected to the circuit.To prove the catalytic activity of iron (Fe2+) and the oxidizing power of the radicals hydroxyls generated by Fenton´s Reaction, was added 4-Clorophenol to the electrolyte solution, maintaining the same reaction conditions of the electro-generation of H2O2. The degradation of 4-Clorophenol was followed by the determination of Total Organic Carbon (TOC) with an equipment Shimadzu TOC-L.Results show that the solution initial concentration is 59.39 mg*L-1 of TOC which decrease until 33.26 mg*L-as result of 3 hours of treatment by Electro-Fenton reaction, this is a 43.8% of remotion from initial concentration of 4-Clorophenol. This implies that this process must be improve to mineralize completly organic compounds and reduce treatment time.References.[1] Agladze G, Tsurtsumi G, Jung B, Kim J, Gorelishvili G. Journal of Applied Electrochemistry. 2007. 37 (385-393).[2] Brillas E, Sauleda R, Casado J. Journal of the Electrochemical Society. 1998. 145 (759-765).[3] Peralta E, Natividad R, Roa G, Marin R, Romero R, Pavon T. Sustainable Environment Research. 2013. 23 (259-266).[4] Song-Hu, Xiao-Hua L. Journal of Hazardous Materials. 2005. 118 (85-92).[5] Stasinakis A. Global Network for Environmental Science and Technology. 2008. 10 (376-385)

MHD Forced Convective Laminar Boundary Layer Flow from a Convectively Heated Moving Vertical Plate with Radiation and Transpiration Effect

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to whilst the magnetic field and mass transfer velocity are taken to be proportional to where is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory.

Mass transfer velocity across the breaking air–water interface at extremely high wind speeds

Mass transfer velocity k L across the wind-driven air–water interface was estimated at extremely high wind speeds (up to U 10=70 m s−1) in a high-speed wind-wave tank by measuring changes in CO2 concentration in the water. In addition, the volume flux of dispersing droplets lost from the tank and the wave height were measured. k L increases drastically with wind speed at extremely high wind speeds. The volume flux of dispersing droplets begins to increase drastically and the mean height of significant waves changes its rate of increase at almost the same wind speed as that at which the rate of increase of k L changed. These results suggest that intense wave breaking occurs at extremely high wind speeds and it has significant effects on mass transfer. k L is well correlated with the free-stream wind speed for both present laboratory and previous field measurements in the low and moderate wind speed regions. Present k L agrees well with the conventional correlation curves proposed by Wanninkhof (1992), Wanninkhof and McGillis (1999) and Wanninkhof et al. (2009) for low and moderate free-stream wind speeds. However, for extremely high free-stream wind speeds, the present data deviate upward from the correlation curves of Wanninkhof (1992) and Wanninkhof and McGillis (1999) and approach to that of Wanninkhof et al. (2009) as the wind speed increases. This indicates that the correlation curve of Wanninkhof et al. (2009) is more appropriate for the correlation between k L and free-stream wind speed than those of Wanninkhof (1992) and Wanninkhof and McGillis (1999) in extremely high wind speed region.

Monitoring and modelling carbon monoxide concentrations in a deep street canyon: application of a two-box model

Carbon monoxide concentrations were monitored at 3, 10 and 30 meters in a deep street canyon with an aspect ratio of (H/W)≈5.8 and were modelled using a two–box model developed in a previous CFD study. The monitoring campaign lasted 5 days, from 11th to 15th July, 2011. The turbulent kinetic energy at the rooftop level and traffic flow was also measured in the same period. Experimental data were used to evaluate parameters (mass transfer velocities and overall mass transfer velocity) of the box model. The daily pattern shows a significant increase of the overall mass transfer velocity from 9:00 to 11:00 and a decrease until 14:00. Turbulent kinetic energy measured at the rooftop level seems to play a major role with respect to wind velocity in determining the mass transfer between the canyon and the atmosphere above. The evaluation of the overall mass transfer velocity contributes to the use of operational street canyon dispersion models in the case of deep street canyons.

Diurnal and seasonal variability in size-dependent atmospheric deposition fluxes of polycyclic aromatic hydrocarbons in an urban center

Atmospheric gaseous and size-segregated particle samples were collected from urban Guangzhou at the heights of 100 and 150m above the ground in daytime and at night in August and December 2010, and were analyzed for polycyclic aromatic hydrocarbons (PAHs). Particulate PAHs were more abundant at night than in daytime, and significantly higher in winter than in summer. The observed vertical, diurnal, and seasonal variability in the occurrences of PAH were attributed to varying meteorological conditions and atmospheric boundary layers. More than 60% of the particulate PAHs were contained in particles in the accumulation mode with an aerodynamic diameter (Dp) in the range of 0.1–1.8μm. Different mass transfer velocities by volatilization and condensation are considered the main causes for the different particle size distributions among individual PAHs, while combustion at different temperatures and atmospheric transport were probable causes of the observed seasonal variation in the size distribution of PAHs. Based on the modeled size-dependent dry deposition velocities, daily mean dry deposition fluxes of particulate PAHs ranged from 604 to 1190ngm−2d−1, with PAHs in coarse particles (Dp>1.8μm) accounting for 55–95% of the total fluxes. In addition, gaseous PAHs were estimated to contribute 0.6–3.1% to the total dry deposition fluxes if a conservative dry deposition velocity for gaseous species (2×10−4ms−1) were used. Finally, disequilibrium phase partitioning, meteorological conditions and atmospheric transport were regarded as the main reasons for the variances in dry deposition velocities of individual PAHs.

Free Convection Boundary Layer Flow from a Heated Upward Facing Horizontal Flat Plate Embedded in a Porous Medium Filled by a Nanofluid with Convective Boundary Condition

The steady laminar incompressible free convective flow of a nanofluid over a permeable upward facing horizontal plate located in porous medium taking into account the thermal convective boundary condition is studied numerically. The nanofluid model used involves the effect of Brownian motion and the thermophoresis. Using similarity transformations the continuity, the momentum, the energy, and the nanoparticle volume fraction equations are transformed into a set of coupled similarity equations, before being solved numerically, by an implicit finite difference numerical method. Our analysis reveals that for a true similarity solution, the convective heat transfer coefficient related with the hot fluid and the mass transfer velocity must be proportional to x−2/3, where x is the horizontal distance along the plate from the origin. Effects of the various parameters on the dimensionless longitudinal velocity, the temperature, the nanoparticle volume fraction, as well as on the rate of heat transfer and the rate of nanoparticle volume fraction have been presented graphically and discussed. It is found that Lewis number, the Brownian motion, and the convective heat transfer parameters increase the heat transfer rate whilst the thermophoresis decreases the heat transfer rate. It is also found that Lewis number and the convective heat transfer parameter enhance the nanoparticle volume fraction rate whilst the thermophoresis parameter decreases nanoparticle volume fraction rate. A very good agreement is found between numerical results of the present article for special case and published results. This close agreement supports the validity of our analysis and the accuracy of the numerical computations.

Radiation and Mass Transfer Effects on a Free Convection Flow through A Porous Medium Bounded by a Vertical Surface

In this paper the effects of radiation on a free convection flow bounded by a vertical surface embedded in porous medium is studied. The problem is solved analytically and the expressions for velocity, temperature, concentration, skin friction and rate of heat and mass transfer are derived and the effects of various physical parameters like radiation parameter F, Grashof number Gr, modified Grashof number G , Prandtl number P , permeability of the porous medium k m r

Growth in the velocity of mass transfer through the CMX membrane during its aging by operation in intense current regimes

One of the causes for the aging of membranes during their operation in electrodialysis (ED) of solutions is irreversible chemical changes in the ion exchange or reinforcement polymer due to interaction of H+ and OH− ions (present in feed solutions or generated in the membrane system under intense current modes) with the matrix or fixed groups in the surface layer of the membranes. The reduction in current efficiency and an increase in energy consumption in the process of electrodialysis are usual consequences of these changes. It has been shown that the degradation of the ion-exchange polymer on the surface of the CMX membrane during its operation in intense current regimes results in the hydrophobization of the membrane surface, which, in turn, causes enhancement of electroconvection. As a result, the limiting current and the mass transfer coefficient of salt ions increase during membrane operation. In the case of desalination of dilute solutions, this growth can reach 50–70% in comparison with the fresh membrane.

Enhanced Arsenic Sorption by Hydrated Iron (III) Oxide‐Coated Materials—Mechanism and Performances

Mechanism and performances of arsenic(III) [As(III)] and arsenic(V) [As(V)] sorption onto hydrated iron(III) oxide (HFO)-coated materials were investigated at neutral pH where arsenic occurs in both molecular and ionic forms. Arsenic sorption by HFO-coated materials was proven to be a multistage process consisting of both macropore and intraparticle diffusion. Higher mass-transfer velocities were obtained for As(III), which is attributed to the beneficial features of HFO. Equilibrium studies revealed the spontaneous and favorable nature of the arsenic sorption process. The maximum sorption capacity and the Gibbs free energy values indicated that HFO-coated materials exhibit more affinity towards As(III). The Langmuir and Freundlich isotherm models revealed both the chemical and physical nature of the sorption process, while the Dubinin-Radushkevich model indicated that physical sorption is a more dominant process with HFO-coated materials.

Measuring and modeling the flux of fecal bacteria across the sediment‐water interface in a turbulent stream

Sediments are a pervasive source of fecal indicator bacteria (FIB) in rivers, lakes, estuaries, and oceans and may constitute a long‐term reservoir of human disease. Previous attempts to quantify the flux of FIB across the sediment‐water interface (SWI) are limited to extreme flow events, for which the primary mechanism of bacterial release is disruption and/or erosion of the sediment substrate. Here we report measurements of FIB flux across the SWI in a turbulent stream that is not undergoing significant erosion. The stream is formed by the steady discharge of bacteria‐free disinfected and highly treated wastewater effluent to an earthen channel harboring high concentrations of FIB in the sediment from in situ growth. The flux j″ of FIB across the SWI, estimated from mass balance on FIB measurements in the water column, scales linearly with the concentration of bacteria in sediment pore fluids Cpore over a 3 decade change in both variables: The magnitude of the observed mass transfer velocity ( m s−1) is significantly larger than values predicted for either the diffusion of bacteria across a concentration boundary layer ( m s−1) or sweep and eject fluid motions at the SWI ( m s−1) but is similar to the flux of water between the stream and its hyporheic zone estimated from dye injection experiments. These results support the hypothesis that hyporheic exchange controls the trafficking of bacteria, and perhaps other types of particulate organic matter, across the SWI in turbulent streams.

On mass transfer in three-dimensional flow of a viscoelastic fluid

This attempt theoratically examines the mass transfer analysis of the boundary layer flow caused by a stretching surface. Analytic solutions are derived with the Homptopy analysis method (HAM). Numerical values of skin friction coefficients and the surface mass transfer are reported. The effectiveness of this method is explicitly illustrated by discussing the convergence of the obtained series solutions. Velocity and gradient of mass transfer are shown graphically and discussed. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 27: 915–936, 2011

Mass Transfer Velocity and Momentum Vertical Exchange in Simulated Deep Street Canyons

A box model to simulate mass transfer inside deep street canyons and with atmospheric flow above is introduced and discussed. Two ideal deep street canyons with aspect ratios of 3 and 5 (the aspect ratio being the ratio between building height and street width H/W) are considered. This range of aspect ratios, found in many densely populated historical centres in Mediterranean cities as well as in other cities around the world, potentially creates high air pollutant concentration levels. Our model is based on a combination of analytical solutions and computation fluid dynamics (CFD) simulations using carbon monoxide (CO) as a tracer pollutant. The analytical part of the model is based on mass transfer velocity concepts while CFD simulations are used both for a preliminary validation of the physical hypothesis underlying the model (steady-state simulations) and to evaluate the concentration pattern with time (transient or wash-out simulations). Wash-out simulation curves were fitted by model curves, and mass transfer velocities were evaluated through a best-fitting procedure. Upon introducing into the model the contribution of traffic-produced turbulence, the modelled CO concentration levels became comparable with those obtained in real-world monitoring campaigns. The mass transfer rate between the canyon and the above atmosphere was then expressed in terms of an overall mass transfer velocity, which directly allows the evaluation of the mass transfer rate between the bottom volume of the canyon (pedestrian level) with the above atmosphere. Overall mass transfer velocities are reported as a function of the operating conditions studied (H/W = 3–5 and wind speeds = 2–8 ms−1). Finally, a simple expression is reported for determining pollutant concentrations at the pedestrian level based on the overall mass transfer velocity defined.

Effects of buoyancy assisting and opposing flows on mixed convection boundary layer flow over a permeable vertical surface

The present study deals with new similarity solution of steady mixed convection boundary layer flow over a permeable surface for convective boundary condition. It has been shown that a self similar solution is possible when the mass transfer velocity at the surface of the plate varies like x −1/2, where x is the distance from the leading edge of the solid surface. Two point boundary value problem governed by non-linear coupled ordinary differential equations have been solved numerically using implicit finite difference scheme in combination with the quasi-linearization technique. It is interesting to note that dual solutions exist for buoyancy assisting flow, besides that usually reported in literature for buoyancy opposing flow. Further, the buoyancy assisting force causes considerable overshoot in the velocity profile and the Prandtl number strongly affects the thermal boundary layer thickness including the surface heat transfer rate.