Mass Transport Rates Research Articles

Temperature effects on the electrodeposition of semiconductors from a weakly coordinating solvent

Temperature is an important variable in electrochemistry, increasing the operating temperature has the capacity to provide significant increases in mass transport and electron transfer rates. In the case of electrodeposition, it can also allow the deposition of crystalline material which would otherwise be amorphous when grown at lower temperatures. In this work we exploit a high boiling point, weakly coordinating solvent, o-dichlorobenzene, to electrodeposit the p-block semiconductors antimony and antimony telluride at temperatures up to 140 °C. The effect of the temperature on the morphology and crystallinity of the deposits is investigated using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and optical microscopy. An attempt is also made to rationalise the role of temperature in electrodeposition and its influence on the aforementioned properties.

Electrodialysis membrane desalination for water and wastewater processing: irregular attack angles of membrane spacers.

Electrodialysis desalination is constructed with a number of anion exchange membranes (AEM), cation exchange membranes (CEM), anode, cathode, adjacent silicon gasket integrated membrane spacers, and inlet/outlet holes per cell. At the boundary among an ionic solution and an ion exchange membrane, concentration polarization develops. Spacers placed in between channel's walls function as stream baffles to increase turbulence, improve heat and mass transfer, diminish the laminar boundary layer, and lessen fouling problems. The current study offers a systematic review of membrane spacers, spacer-bulk attack angles, and irregular attack angles. Spacer-bulk attack angle is accountable for variations in the pattern and direction of stream which impact heat-mass transfer and concentration polarization. Irregular attack angles (e.g., 0°, 15°, 30°, 37°, 45°, 55°, 60°, 62°, 70°, 74°, 80°, 90°, 110°, 120°) in the present study were found to provide unique stream patterns due to the spacer's filaments being less or more transverse in respect to the primary solution direction, which may significantly alter heat transfer, mass transport, pressure drop, and overall flow dynamics. Spacer applies shear stress resulting by continuous stream tangent to the membrane exterior, which lessens polarization. In the end, 45° is concluded as the preferred attack angle that offers balanced rates of heat transfer, mass transport, and pressure drop throughout the feed channel while greatly lowering the rate of concentration polarization.

Flow inspection of micropolar nanofluids with motile gyrotactic microorganisms across symmetric channel in porous medium by quasi-linearization technique

The current article investigates the influence of radiation as well as gyrotactic microbes in the flow of micropolar nanoliquids through a channel. Flow is assumed to be symmetric across a channel having permeable walls. The work also focuses on the change in mass transport rate and density distribution of motile microbes across flow regimes in a porous channel. The governing nonlinear partial differential equations of the present problem are transformed into ODEs through dimensionless variables. The coupled nonlinear ODEs are numerically addressed by utilizing the quasi-linearization technique. Impacts of the pertinent parameters on the fluid flow are analyzed and demonstrated through tables as well as figures by using the powerful tool MATLAB. The velocity profiles escalate near both walls with an enhancement in Reynolds number. Moreover, an enhancement in values of heat radiation parameter causes declination in the fluid temperature. An evaluation of the comparison with existing results reveals an excellent harmony. The nanofluids possess marvelous characteristics subject to heat transport as compared to other ordinary fluids. We intend to elaborate the interaction of micropolar nanofluids with the microbes in a symmetric channel flow.

Significance of Navier’s slip and Arrhenius energy function in MHD flow of Casson nanofluid over a Riga plate with thermal radiation and nonuniform heat source

Riga plate is known to create a crossing electric and magnetic field to generate a wall-parallel Lorentz force. The significance of Casson nanofluid flow past a Riga plate is observed in the sphere of engineering, such as polymer extrusion, food manufacturing, plastic films, oil reserves and geothermal manufacturing. Researchers are interested in this model because of its potential use in biological rheological models. As Casson nanofluid flows are of great interest, this study aims to investigate the three-dimensional magnetohydrodynamics (MHD) flow with heat and mass transport of Casson nanofluid over a flat Riga plate. As a novelty, this study also includes the effectiveness of wall velocity slip, activation energy, nonlinear radiation, and temperature and space-dependent heat source/sink. Suitable similarity transformations have been employed to generate the dimensionless ordinary differential equations (ODEs) from the partial differential equations (PDEs) regulating the fluid flow problem. The transformed nonlinear boundary value problem is then solved numerically using the in-built routine “bvp4c” in MATLAB. The visual demonstrations are provided for the effects of various significant physical factors on the flow, heat and mass distributions. On the other hand, wall shear stress and rates of heat and mass transport at the surface are measured and displayed numerically in tabular form. The findings indicate that the fluid velocity in both directions slows as the velocity slip parameter increases. However, the velocity profile is escalated with the boost of modified Hartmann number. An increase in heat source parameters leads to decrease the heat transmission rate at the wall. The higher values of the radiation parameter result in a better wall heat transmission rate. Further, the rate of mass transport drops when the activation energy parameter is hiked.

Dynamics pattern of a radioactive rGO-magnetite-water flowed by a vibrated Riga plate sensor with ramped temperature and concentration

In recent times, the dynamics study of an electrically weak performing fluid stream regulated by Riga sensors has become an emerging research topic for scientists. Riga sensors’ utility for improving the effectiveness of heat and mass transport rates in industrial and engineering systems is diverse. This motivates us to inspect the stream pattern and heat-mass transmission mechanism of an electrically low-performing hybrid nanofluid (rGO-magnetite-water) near a vertically straightened Riga plate sensor embedding with absorbing materials under the guidance of thermal and concentration buoyancy and magnetization. The taken flow is being modelled by incorporating pertinent physical influences, namely radiation heat emission, chemical reaction, and ramped temperature and concentration at the boundary wall. The flow is presented mathematically in terms of unsteady partial differential equations. The compact-form expressions for model entities are founded by opting for the Laplace transform methodology. The Riga plate’s shear stress, heat and mass transfer rates are tabulated and graphed. The physical behaviours of substantial flow entities against model factors are conversed and judged graphically. The vital findings of this study demonstrate a swelling in the velocity distribution with an enhancement in modified Hartmann number and diminishing with an enlargement in the width of electrodes. The temperature and concentration are higher for constant plate temperature (CPT) and lower for ramped plate temperature (RPT). It is also motivating to note down that hybrid nanofluid containing reduced graphene nanomaterials will transmit extra heat in the flow regime. The heat flow across the Riga sensor elevates against the higher radiation parameter’s value. These novel findings will be extremely applicable in steam generators, chemical reactors, hybrid Riga plate electromagnetic devices, and phase transitions during material processing.

Effect of external magnetic field on mass transport of reactive species in the reaction between nano zero valent iron and selenate anions in a simulated flue gas desulfurization wastewater

The mechanism involved in the reaction of regulated ions with nano Zero-Valent Iron (ZVI) in the presence of an applied weak magnetic field (WMF) was investigated. The WMF effect on mass transport of reacting ions and morphology and composition of the oxide layer in nano ZVI was elucidated using Electron Energy Loss Spectroscopy (EELS). The magnetic gradient force produced by ferromagnetic ZVI particles had a greater influence on the rate of selenate diffusion in solution than the Lorentz force due to the externally applied weak magnetic field. Moreover, the magnetic gradient force was suggested to suppress ZVI corrosion reactions. Despite changes in the iron oxide layer under the WMF influence, the rate of selenate reduction has not been significantly affected over short term lasting several hours. Most crucially, WMF had a negligible effect on the rate of mass transport of selenate anions, as compared to the dominant effect of forced convection.

Approaches to Enhancing Cathodic Nickel Recovery from Ni-EDTA Containing Synthetic Wastewaters

Ethylenediaminetetraacetic acid (EDTA) is widely employed as a chelating agent in the electroless nickel plating industry to form stable metal–organic complexes (e.g., Ni-EDTA). These metal–organic complexes cannot be removed from plating wastewaters by traditional treatments in a cost-effective way. While electrochemical advanced oxidation processes (EAOPs) have been utilized for the efficient degradation of Ni-EDTA at the anode, challenges remain in the simultaneous and effective recovery of nickel at the cathode. In this study, we investigate the efficacy of five cathode materials [i.e., carbon felt (CF), titanium plate, graphite plate (GP), copper plate, and stainless-steel plate] with respect to Ni recovery. The highest Ni removal efficiency of 81.6 ± 0.1% was achieved with the carbon felt cathode which was 30% higher than that of the titanium cathode (52.1 ± 1.4%) with the improvement in performance attributed to the higher rate of mass transport of Ni ions (CF: 4.3 ± 0.4 × 10–4 s–1 vs Ti: 1.8 ± 0.2 × 10–4 s–1) toward the nanowire structure of carbon felt and to the large surface area of the carbon felt cathode compared with the other cathodes. While the chemical composition of the deposits was independent of the cathodic material or structure, the morphology of deposition varied with the cathode material. The accumulated Ni on the carbon felt surface was successfully recovered either as a nickel salt solution by acid leaching or as high purity NiO by calcinating the Ni-loaded carbon felt cathode at over 800 °C. The performance of the regenerated carbon felt after acid leaching was comparable to that of the fresh cathode even after 10 cycles of use and regeneration via acid leaching with this result confirming the stability and reusability of the carbon felt material.

Soret and Dufour effects on the magnetohydrodynamic free convective flow of Maxwell nanofluid past an infinite stretching sheet

The authors are interested in understanding how a magnetic field and cross-diffusion influence non-Newtonian Maxwell nanoliquid boundary layer flow towards the non-linearly stretched sheet when there are also thermophoresis as well as Brownian movement effects present in the reference frame. Specifically, the purpose of this research is to learn more about the Maxwell nanofluid properties of a stretched sheet in a normal magnetic field, in addition to the effects of three distinct slip situations (velocity, thermal and solutal). The partially differential equations with non-linear coefficients are used to obtain the leading equations. These equations were distorted into advantageous non-linear ordinary differential equations by using the appropriate transformation variables and transformation coefficients. To investigate the computational resolutions of the reduced set of non-linear ordinary differential equations, it was developed and used the Keller box method, which was developed for numerical solutions. The simulation considers the nanofluid velocity, temperature, concentration, skin frictions coefficient, the rate of temperature transport, as well as the rate of mass transport, among other variables. The validity of this method is shown via the comparisons of the current results by the previous findings in the literature.

Mixing and Overturning Across the Brazil‐Malvinas Confluence

AbstractThe rates of isopycnal stirring and water mass transport by mesoscale eddies, and of diapycnal mixing by small‐scale turbulence, across the Brazil‐Malvinas Confluence (BMC) are assessed from a set of microstructure and hydrographic measurements in the Argentine Basin. This assessment is founded on a theoretical framework that applies a triple decomposition to the temperature variance equation and assumes eddies to transfer potential vorticity downgradient. The BMC is found to host widespread intense isopycnal stirring at rates of O(103–104 m2 s−1), and generally weak diapycnal mixing at rates of O(10−6–10−5 m2 s−1). Despite such disparity, both diapycnal mixing and isopycnal stirring play roles of comparable importance in determining regional water mass properties within surface and mode waters. In deeper layers, isopycnal stirring prevails. Eddies are further diagnosed to effect an important cross‐BMC transport, at rates of O(1 m2 s−1). When scaled by the along‐stream extent of the BMC, these rates integrate to volume transports that may be as large as O(10 Sverdrups). This suggests that cross‐BMC transfers of waters are substantially effected by eddy‐induced flows.

Directly Grow Ultrasmall Co2P QDs on MoS2 Nanosheets to Form Heterojunctions Greatly Boosting Electron Transfer toward Hydrogen Evolution

A green process to produce an efficient and inexpensive electrocatalyst toward hydrogen evolution reaction (HER) is of importance for hydrogen energy. Here, an efficient HER electrocatalyst is made by electrochemically depositing Co2P quantum dots (QDs) on MoS2-carbon cloth (Co2P QDs/MoS2-CC). Due to the MoS2 porous structure, ∼3 nm Co2P QDs uniformly deposit on MoS2. The produced unique 3D-structured Co2P QDs/MoS2-CC not only prevents an agglomeration of the active material and improves the diffusion rate of H2 but also renders large accessible surface area and hierarchical pores for high-density reaction sites and enhanced mass transport rate. Experimental results and theoretical analysis of this unique heterostructure indicate that the evolution process of hydrogen is dominated by proton adsorption, and the introduction of sufficient edge active sites can significantly promote the HER. As a consequence, the hierarchical Co2P QDs/MoS2-CC electrocatalyst affords an ultra-low overpotential (41 mV at a current density of 10 mA cm–2) that ranks the best among all reported MoS2 HER catalysts and exhibits excellent durability in 1 M KOH solutions, thus holding great promise for the practical application while shedding on fundamentals to nanoengineering an efficient electrocatalyst.

Evolution of debris flow activities in the epicentral area, 10 years after the 2008 Wenchuan earthquake

The occurrence of debris flows after the earthquake not only damaged infrastructure but also caused large numbers of casualties. Analyzing the evolution of debris flows after the Wenchuan earthquake is significant for understanding the long-term impacts of the earthquake on the subsequent debris flow activities. This study made a continuous track of mass movements of loose deposits in all debris flow gullies from 2008 to 2018 along Provincial Road 303 (PR303) after the Wenchuan earthquake according to remote sensing images interpretation and field investigations. Four aspects, i.e. vegetation recovery, source materials, runout characteristics, and human activities were analysed to describe the evolution laws based on the 10-year inventory of debris flows. The loose deposits on the hillslope were found to be gradually transported into channels. A declining trend of mass transport rate from 2010 (24.5%) to 2018 (6.5%) was found. The occurrence frequency, magnitude, and mobility of debris flows were found to decrease. Recovery of vegetation made the loose deposits stable, whereas human activities of excavation of debris flows deposits promoted the occurrence of landslides. Three stages were divided for debris flows activities: the active period (2010–2014), the unstable period (2014–2017), and the recession period (after 2017). The decreasing trend of debris flows in the future is predicted.

Entropy generation in chemically reactive and radiative Reiner-Rivlin fluid flow by stretching cylinder

Magnetohydrodynamic entropy optimized flow of Reiner-Rivlin liquid by stretched cylinder is addressed. Thermal relation comprises viscous dissipation, heat generation, Ohmic heating and radiation. Chemically reactive flow of binary reaction is accounted. Entropy generation is explored. Non-linear differential systems are numerically solved by Newton built in-shooting technique. Velocity, thermal field, concentration and entropy generation have been explored. Outcomes of coefficient of skin friction, gradient of temperature and mass transport rate are organized. It is noticed that fluid flow for magnetic field and curvature parameter intensifies. Drag force through magnetic field escalates while opposite trend holds for fluid variable. Thermal field against Prandtl number is decreased while opposite behavior holds for magnetic field and radiation. Temperature gradient versus radiation is decreased. Concentration decays versus Schmidt number. Decaying behavior of concentration holds for reaction variable. Solutal transport rate against reaction variable intensifies.

High-performance electrodeposited copper wicks for heat-spreading vapor chambers

A capillary wick structure is a key component for producing the capillary pressure that drives two-phase circulation in phase-change heat transfer devices such as heat pipes and vapor chambers. This study examines the capillary performance of a porous Cu wick structure fabricated using a new electrodeposition process. This Cu wick exhibits large channels generated by hydrogen bubbles and small pores in the dendritic Cu deposits resulting from high-current electrodeposition. The capillary wick performance can be effectively enhanced by adjusting the morphology of the dendritic Cu deposits. Dendritic Cu wicks with different porous features are prepared using different electrodeposition current densities and Cu sulfate concentrations in the electrolyte. A capillary rate-of-rise method is used to assess the liquid permeability (K), effective pore radius (Reff), and capillary performance (K/Reff) of dendritic Cu wicks with deionized wateras the working fluid. The Cu wick is then thermally treated at 700 °C in ambient N2 for 90 min to improve its structural integrity. Despite partial welding occurring between the fine Cu dendrites, the Cu wick shows a superior K/Reff of 1.5 ± 0.06 μm and excellent structural stability. The high capillary performance can enhance the mass transport rate and effective transport distance of the working liquid in vapor chambers for high-density and large-area heat dissipation applications. A vapor chamber integrated with an electrodeposited Cu wick demonstrates excellent heat-spreading characteristics, with a vapor thermal conductivity of up to 6500 W/m⋅K.

Nanofluid containing motile gyrotactic microorganisms squeezed between parallel disks

Advanced nano and microtechnologies for nano/micro-electronic devices have made substantial advances in the past few years. These technologies are rapidly incorporating advanced fluid media such as nanofluids and biological microorganisms. Inspired by bio-nanofluid applications in medicine, biological systems and biotechnology in the present study, mathematical model is evolved for unsteady bio convective conducting nanofluid along with gyrotactic micro-organisms squeezed between parallel disks. The lower disk and upper disks are solids. The temperature field is improved by the methods of haphazard motion of nanoparticles and thermophoresis parameters. The nano-bio transfer model is written as a series of non-linear partial differential equations that are reduced into a set of ordinary differential equations using suitable transforms. The dimensionless problem is then numerically solved by RK-4th order scheme utilizing MATLAB bvp4c solver’s package to investigate the impact of the squeezing parameter, Hartman number, Brownian motion and thermophoresis parameter on motile microorganism velocity, temperature, nanoparticle concentration, and density. The friction factor, Nusselt number, Sherwood number and microorganism number distributions on Hartman number, thermophoresis and Brownian motion factors are also computed. The Brownian motion and the thermophoresis factors of nanoparticles cause an increment in temperature profiles for both suction and injection. The concentration and motile microorganism are both amplified for the Brownian parameter in the case of injection, whereas they are declined for suction and the opposite trend is observed for the thermophoresis parameter. The motile microorganism is deflated for both suction and injection with thermophoresis parameter. Suction and injection adversely affect the transfer properties at the disks. The resistive magnetic body force prevails in the core zone, resulting in a decrease in velocity. The heat generation in squeeze films with motile microorganisms can be successfully removed with magnetic nanoparticles which require a longer serviceability of the lubrication system, bio-medical systems and need for less maintenance and a longer lifespan approach. The finding is pertinent to novel bio-microsystems that combine nanofluid and the bioconvection phenomenon. The percentage increase in heat, mass, and microorganism transport rates is calculated.

Falkner–Skan slip flow of non-Newtonian fluid over a moving and nonlinearly radiated wedge with variable heat source/sink and viscous dissipation

Analyzed in this paper is an investigation of the impacts of the varying source of heat or thermal sink and viscous dissipation on Casson fluid flow from a moving wedge by considering thermal and momentum slips in a mathematical model. Regarding the regulation of concentration fields, we incorporated the Soret and Dufour phenomena. The outcomes are analyzed numerically by using the shooting technique. The governing parametric effects of the flow characteristics are revealed graphically. We also presented the local Sherwood and Nusselt number values for non-Newtonian fluid (Casson fluid) and Newtonian. It is discovered that the thermal and concentration boundary layer is more extensive in Casson fluid while equated with the Newtonian fluid. The thermal and mass transmission in Newtonian fluid is significantly larger than in non-Newtonian fluid. The heat source/sink, Eckert number and Dufour number boost the rate of thermal transport and depreciate the rate of mass transport for both the Newtonian and non-Newtonian fluid cases.

Radiative flow of rheological material considering heat generation by stretchable cylinder

Background and objectiveMagnetohydrodynamic effect has various industrial applications in crystal growth, manufacturing, nuclear reactor cooling, mineral casting, polymer extrusion, cable coating, metallurgy, liquid--metal cooling etc. In view of these application here we addressed the magnetohydrodynamic radiative Reiner-Rivlin fluid flow by stretching cylinder. Consideration of heat generation and magnetic field scrutinizes the heat transport process. Modeling for binary chemical reaction is presented. MethodologyGoverning nonlinear ordinary systems through suitable transformation are obtained. The set of non-dimensional systems are computed for local similar solution by ND-solve method. ConclusionsTemperature, fluid flow and concentration have been analyzed. Computations for coefficient of skin friction, temperature gradient and solutal transport rate are organized. Magnetic field outcome for velocity and temperature is not similar. Enhancement in fluid flow versus curvature variable is found. Reduction occurs in fluid friction and velocity for Reiner-Rivlin liquid variable. Thermal field versus Prandtl number is decayed. Outcomes for magnetic field and radiation on temperature are alike. An augmentation of concentration is seen for curvature variable. Concentration versus reaction variable is decreased. Nusselt number for radiation and magnetic field is not similar. Large approximation of reaction variable boosts up mass transport rate.

Hydromagnetic flow of magnetite–water nanofluid utilizing adapted Buongiorno model

The hydromagnetic flow of magnetite–water nanofluid due to a rotating stretchable disk has been numerically assessed. The nanofluid flow has been modeled utilizing the adapted Buongiorno model that considers the volume fraction-dependent effective nanofluid properties and the major slip mechanisms. In addition, experimentally gleaned functions of effective dynamic viscosity and effective thermal conductivity are deployed. The modeled equations are transformed into a first-order ODEs scheme employing Von Kármán’s similarity conversions and then resolved via the Runge–Kutta algorithm through the shooting technique. The impact of pertinent terms over the physical quantities, nanoliquid temperature and nanoliquid concentration is explained with the support of graphs. Results show that rising volume fraction of magnetite nanoparticles (NPs) and magnetic field term enhance the drag force. Mass transport rate is demoted with augmenting values of magnetic field parameter whereas is promoted with increase in Schmidt number. Further, it is detected that the changes in stretching strength parameter are directly proportional to Nusselt number and inversely proportional to the thermal field. The findings of this numerical analysis have applications in spin coating, rotating disk reactors, storage devices for computers, food processing, and rotating heat exchangers.

Finite element analysis for sand and paraffin wax nanoparticles in propylene glycol–water mixture-based hybrid nanofluid flow over a swirling cylinder with Arrhenius kinetics

This study aims to investigate the impact of activation energy on the flow of a hybrid nanofluid over a rotating stretching cylinder with torsional motion and a heat source/sink. The paraffin wax-sand-propylene glycol–water-based hybrid nanofluid has been used in the study. By adopting appropriate similarity transformations, the modeled partial differential equations are transformed into a set of ordinary differential equations, which are then solved using the finite element method. The numerical integration’s validity and reliability, as well as the newly obtained discoveries, were thoroughly analyzed. Results reveal that the larger Reynolds number values enhance the system’s inertial force, which resists the liquid accelerating force and declines both velocities and heat transport. The heat source/sink parameter has a favorable impact on the thermal profile, but larger Schmidt number values restrict mass transfer. The improved values of the chemical reaction rate parameter augment the mass transport rate, but nondimensional activation energy parameter has negative impact on Sherwood number.

Dynamics of Soret and Dufour effects on oscillatory flow of couple stress fluid due to stretchable curved surface

In this theoretical study, we have discussed the impacts of Soret and Dufour on the flow of time-dependent couple stress fluid across a stretchable curved oscillatory surface with magnetic field. The to and fro motion of the surface causes the flow phenomenon. The boundary layer flow equations depicting the flow phenomena are expressed in mathematical form by means of a curvilinear coordinates system along with some suitable similarity variables. The developed flow equations in the form of partial differential equations are then solved analytically by utilizing a valuable method called the homotopy analysis method (HAM). A detailed examination is performed to evaluate the influence of various involved parameters namely, the non-dimensional radius of curvature, couple stress parameter, magnetic parameter, the relation of the parameter of the surface oscillating frequency to its stretching rate constant and Soret and Dufour numbers on velocity field, pressure distribution, concentration and temperature distribution, rate of heat transfer, coefficient of skin friction, and rate of mass transport via graphs and are explained in detail. It is confirmed that the amplitude of velocity and pressure distribution exhibits reducing behavior with higher values of the couple stress parameter. The concentration and temperature profiles also diminish with varying time instants.

Analysis of thermally radiative magnetized viscoelastic (second-grade) fluid by impermeable vertical cylinder

We made an attempt to disclose the phenomenon of dual stratification in magnetized viscoelastic second-grade fluid model generated by the movement of vertical cylinder. Mass and heat transportation is accounted under the aspects of Joule and Ohmic dissipations. The flow is coupled due to the consideration of nonlinear convected terms. Boundary-layer concept is implemented for the simplification of mathematical system. This system is made into the non-dimensional forms by reporting the similarity variables. The system of non-dimensional equations is executed with the use of homotopic criteria. The convergent region of solutions is reported and discussed. The convergent results are shown by graphical illustrations by considering distinct emerging constraint values. An increment in Darcy and inertia coefficient parameters corresponds to a decay in the flow. Temperature distribution is an increasing function of thermal Biot number and radiation parameter while it diminishes when thermal stratification parameter increases. Concentration is reduced for larger Schmidt number along with solutal stratification parameter. Besides the heat–mass transportation rates are increasing functions of thermo-solutal Biot numbers. The considered problem finds relevance in functional smart electro conductive enrobing coating processes in manufacturing. This is a principal application of the model studied where external axisymmetric boundary layers occur with combined magnetic, thermal and rheological effects.