Mass Transfer Characteristics Research Articles

Influence of Dofour and Soret on Eyrig-Powell Nanofluid Flow from A Circular Cylinder with Viscous Dissipation

The impact of Viscous dissipation on the heat and mass transfer characteristics of an Eyring Powell nanofluid flow past a horizontal circular cylinder is intensively investigated in the presence of Dufour and Soret effects. The free laminar flow is subject to a uniform transverse magnetic field. The continuity, momentum, energy, and concentrations equations are transformed into a nonlinear system of partial differential equations using appropriate non-similarity variables. The transformed system was solved numerically using the fourth order Runge Kutta method. The effect of parameters including Prandtl number, Dufour effect, Soret effect and Schmidt number were studied and presented graphically. Nusselt and Sherwood numbers have also been derived and discussed numerically.

The role of ion‐membrane interactions in fast and selective mono/multivalent ion separation with hierarchical nanochannels

AbstractPrecise control over the nanofluid behavior of polyelectrolyte‐based membranes is a primary step toward understanding the structure‐morphology‐property relationships to ultimately determine the mass transfer characteristics. In this study, a high‐performance multistacked polyelectrolyte‐based cation exchange membrane (CEM) with a heterogeneous structure and versatile surface chemistry was developed to achieve selective ion conductance. The self‐assembled CEM can facilitate ion permeation with fluxes of 2.9 mol m−2 h−1 for K+ and 0.22 mol m−2 h−1 for Mg2+, reaching a mono/multivalent ionic selectivity of up to 13, outperforming mono/divalent fractionation when compared with state‐of‐the‐art membranes. Molecular dynamic (MD) simulations illustrated the ionic transport trajectory in hierarchical channels with angstrom‐scale cavities using multilayered CEMs. Both the experimental measurements and theoretical simulations indicated that ionic fractionation was associated with a large disparity in the energy barrier between mono/multivalent cations, which was the primary origin of the differences in the ion dehydration‐rehydration processes in the angstrom‐confinement membrane ion channels.

Performance evaluation and improvement of prototype rice husk fueled mixed flow rough rice dryer using CFD model

The majority of the rural areas in developing countries are not connected to the electric grid. Rice production produces a significant amount of rice husk as a byproduct/waste but this waste can be used as a source of energy for drying of the rough rice. The aim of this research was to evaluate the performance and improve the design and operation of a rice husk fueled mixed flow grain dryer for small scale rural farmers using a validated 3-D computational fluid dynamics (CFD) model. The model was applied to predict the airflow and heat and mass transfer characteristics of the designed prototype rough rice dryer. The model took into account the geometrical detail of the dryer assembly, the relevant boundary and initial conditions, and model input parameters. The results identified relatively stagnant regions at the top and the side walls of the dryer. The observed relatively high variation in drying air velocity distribution caused a relatively high variation in drying characteristics of the rice grain. The model was applied to modify the design and operation procedure of the dryer to improve the performance in terms of drying uniformity and drying time. After 2 h drying time, the difference between the maximum and minimum moisture content values for the original and modified design was 12.9% and 8.5%, respectively. There was an exponential relationship between drying time and drying air temperature and specific flowrate. Mixing and recirculation of the grain at 30 min interval significantly improved the uniformity of drying, and the difference between maximum and minimum moisture content after 2 h of drying was clearly reduced to 1.9%. The study indicated the capability of 3-D CFD model to improve the design and operation of mixed flow rice husk fueled dryer to attain the required performance.

Local and global gas–liquid mass transfer in a micro‐packed bed reactor utilizing a noninvasive colorimetric technique

AbstractMicro‐packed bed reactor (μPBR) presents great potential in the field of multiphase reactions due to the features of safety and high efficiency. However, the deeper cognition of mass transfer needs to be taken into consideration that is the foundation of reactor design. In this work, local and global gas–liquid mass transfer in the μPBR were studied utilizing a noninvasive colorimetric technique. In reactor level, the qualitative and quantitative comparisons were conducted; in particle level, liquid flow and mass transfer textures were assessed for the first time. The diversities of local mass transfer characteristics from temporal and spatial dimensions were obtained, and the heterogeneity of local and global mass transfer was revealed. The predicted correlations of in μPBR with churn flow and pseudo‐static flow were established with deviations generally within ±18%. This study contributes to improve the understanding of mass transfer and points out the process intensification direction of μPBR.

Mass transfer characteristics at cathode/electrolyte interface during electrodeposition of nickel microcolumns with various aspect ratios

The filling behavior of electrodeposited microcolumns is strongly influenced by the mass transfer characteristics at the cathode/electrolyte interface. This study aims to elucidate the influence of the mass transfer characteristics (ion supplementation via diffusion and ion consumption via deposition) on the electrodeposition of microcolumns, thus providing feasible solutions for improving void defects with different feature sizes. The results indicate that ion consumption plays an important role in the mass transfer within large-width microcavities (100 μm). For large-width microcolumns, longer electroforming times lead to higher ion consumption, resulting in nonuniform ion concentration distribution, and consequently uneven deposition rates along the microcavity wall. In microcavities with high aspect ratio (5:1), ion supplementation plays a major role. The low ion supplementation rate does not support a uniform deposition, resulting in a large void defect and a low filling ratio in the deposited microcolumns. Therefore, reducing the ion consumption rate by decreasing the current density from 1 A dm−2 to 0.25 A dm−2 can effectively increase the filling ratio in large-width microcolumns with no significant effect on high aspect ratio microcolumns. On the contrary, the pulse reverse current (forward pulse current density 1 A dm−2, reverse pulse current density 2 A dm−2, frequency 1 Hz, forward pulse duty cycle 0.9) can increase the filling ratio in the high aspect ratio microcolumns by accelerating ion supplementation through dissolution of the deposited layer. By further increasing the reverse pulse current density from 2 A dm−2 to 6 A dm−2, void defects can be completely eliminated and even void-free deposition of high aspect ratio microcolumns (5:1) can be achieved.

Performance of high temperature steam injection in horizontal wells of heavy oil reservoirs

Steam huff and puff and steam flooding are important development methods for heavy oil reservoirs. At present, there are certain deficiencies in the research on the timing and methods of steam stimulation, steam flooding, and subsequent steam flooding. In addition, the research on the mass and heat transfer characteristics of high temperature steam injection in heavy oil reservoirs is still in the initiation stage. This article first studies the high temperature steam flow model in the horizontal wellbore of the SAGD process. On this basis, a horizontal well pattern model was established through numerical simulation software to analyze the heat and mass transfer characteristics of high temperature steam huff and puff and high temperature steam flooding. Results show that: (a) for heavy oil reservoirs with high temperature steam injection huff and puff, the first cycle of steam injection ends (day 22): the temperature near the well pattern of the horizontal well pattern is higher. In the area between the horizontal well patterns, the temperature rise is not obvious; (b) when the high temperature steam injection huff and puff phase of the heavy oil reservoir ends (900 days), most of the heat energy is recovered, and the formation residual heat is less; (c) After the huff and puff transfer, the thermal connectivity between the horizontal well patterns is better.

Investigation of surfactant effect on ozone bubble motion and mass transfer characteristics

The low solubility and low mass transfer efficiency of ozone (O3) in water are important reasons for limiting the application of ozone oxidation technology and advanced ozone oxidation technology. Low-dose surfactants were introduced to affect the behavior of ozone bubbles, influencing the ozone mass transfer efficiency. The motion of ozone bubbles in three different types of surfactant solutions (polyoxyethylene lauryl ether (Brij35), sodium dodecylsulfate (SDS), and cetyltrimethylammonium bromide (CTAB)) was observed. The decrease in surface tension led to a decrease in bubble size, a tendency to spherical shape, an increase in gas content and residence time, a decrease in lateral displacement of a single bubble, and a more stable trajectory. The effect of surfactants on ozone mass transfer was further investigated. The addition of surfactant was found to increase the gas-liquid interface area but decrease the liquid phase mass transfer coefficient, and the extent of the two opposite effects varied for different surfactants. The analysis combined with the removal of pollutant p-Nitrophenol (PNP) showed that the addition of the nonionic surfactant Brij35 and the anionic surfactant SDS inhibited ozone mass transfer, while low concentrations of the cationic surfactant CTAB enhanced ozone mass transfer. When the CTAB concentration was 3 mg L−1, the ozone volume mass transfer coefficient reached a maximum of 0.2902 min−1.

Ammonia decomposition over Ru-coated metal-structured catalysts for COx-free hydrogen production

We report the development of Ru/Mg–Al oxide coated metal-structured catalysts with excellent heat and mass transfer characteristics for efficient clean H2 production from ammonia decomposition. Ammonia is a promising carrier for the mass transport of hydrogen and facilitates the production of COx-free hydrogen by decomposing into nitrogen and hydrogen. Ru nanoparticles are uniformly dispersed on the Mg–Al oxide layer of the FeCralloy monoliths and foams via precipitation. The catalytic activities depend on the surface area and loading of the catalysts and the metal dispersion in the oxide layer. At temperatures <650 °C, and a gas hourly space velocity (GHSV) of 3,000 h−1, monolithic catalysts with a large surface area and evenly distributed active metals perform excellently. Foam catalysts with excellent heat transfer performance better at temperatures >650 °C and GHSV >6,000 h−1. Foam catalyst stability is verified for 100 h in a 20 Nm3/h high-purity hydrogen production system.

Synthesis and characterization of activated carbon monolith from African locust bean pods and polystyrene resin

ABSTRACT Activated carbon monoliths (ACMs) are single-piece, three-dimensional (3D) hierarchical porous structures with good permeability, high stability, and swift mass transfer features. Production of activated carbon monoliths from biomass has been identified as promising and sustainable for process development. In this study, ACM was synthesised from African locust bean pods and polystyrene resin. The pods were chemically activated using potassium hydroxide and then carbonised in a locally fabricated auto-thermal biomass-powered reactor for 100 minutes. The activated carbon was then hand-mixed with an organic binder, expanded polystyrene resin, and the product was thermally cured to form the ACM. The ACM was then characterised to determine its properties. Elemental determination revealed the ACM was mostly composed of carbon (63%), potassium (18%), oxygen (4%), and a host of other metals. SEM micrographs showed that the ACM’s surface is composed of irregular or heterogeneous-sized carbon materials firmly held by the resin with well-developed visible micropores. Some of the functional groups inherent in the ACM include hydroxyl, alkene, carbonyl, and alkyne. The ACM has a BET surface area of 237 m2/g, a pore diameter of 2.86 nm, and a Young modulus of 1.064 MPa. The synthesised ACM can be utilised as an adsorbent for pollution control, as a catalyst, and for electrochemical applications.

Raman spectroscopy of yeast cells cultured on a deuterated substrate

Raman spectroscopy of cells cultured in a deuterated substrate is a promising approach to the characterization of mass transfer and enzymatic reactions in living cells. Here, we studied the potential of this approach using the example of yeast cells cultured under aerobic and anaerobic conditions. In our experiments, unadapted to D2O Saccharomyces cerevisiae were cultured in a medium with different concentrations of deuterium oxide and deuterated glucose. It has been shown that the addition of even 10% heavy water leads to a general decrease in the amount of lipids in cells. In the Raman spectra of cells cultured at high concentrations of D2O, additional peaks are found, which are associated with the deuteration of entire chemical groups. We observed a similar effect in the ethanol synthesized by yeast fermentation, the deuteration of which also depends on the concentration of D2O. The results on the characterization of cell deuteration turned out to be in qualitative agreement with the known estimate that aerobic metabolism is 15 times more active than ethanol fermentation. The results of our work determine new limitations and prospects for further application and development of the Raman method of spectroscopy of deuterium tags.

Numerical study on the influence of the mixing chamber structure in a dilution refrigerator on the heat and mass transfer characteristics of 3He-4He at ultralow temperatures

The acquisition and utilization of ultralow temperatures has become a popular research topic with great value. Dilution refrigerators (DRs) with 3He-4He mixtures as refrigerants are the main tool to obtain millikelvin temperatures and have been applied in space exploration, low-temperature physics experiments and other fields. As the mixing chamber at the cold end of DR, direct study on the influence of its structural parameters on heat and mass transfer at ultralow temperatures is still lacking. In this study, a coupled numerical model of the heat and mass transfer of 3He-4He mixture in the mixing chamber at ultralow temperature is established. The effects of various structural parameters are simulated using a finite element model, and the refrigeration performance of different mixing chambers is evaluated by refrigeration temperature and refrigeration power. First, the molar amount of the mixture in the mixing chamber affects the refrigeration temperature and refrigeration power. When the effective volume of the cylindrical mixing chamber increases twofold, the refrigeration power increases by 11.88%. When the volume of the cylindrical mixing chamber is expanded twofold, the cooling time required to reach 15 mK is increased by 57.29% compared to the standard cylindrical mixing chamber. We further found that appropriately reducing the proportion of the concentrated phase coolant is beneficial for refrigeration performance. In addition, cuboid mixing chambers achieve lower refrigeration temperatures than mixing chambers with other shapes. This study is of great significance to guide the design and optimization of mixing chambers.

The Condensation Characteristics of Propane in Binary and Ternary Mixtures on a Vertical Plate

Natural gas is one of the most common forms of energy in our daily life, and it is composed of multicomponent hydrocarbon gas mixtures (mainly of methane, ethane and propane). It is of great significant to reveal the condensation mechanism of multicomponent mixtures for the development and utilization of natural gas. A numerical model was adopted to analyze the heat and mass transfer characteristics of propane condensation in binary and ternary gas mixtures on a vertical cold plate. Multicomponent diffusion equations and the volume of fluid method (VOF) are used to describe the in-phase and inter-phase transportation. The conditions of different wall sub-cooled temperatures (temperature difference between the wall and saturated gas mixture) and the inlet molar fraction of methane/ethane are discussed. The numerical results show that ethane gas is more likely to accumulate near the wall compared with the lighter methane gas. The thermal resistance in the gas boundary layer is one hundred times higher than that of the liquid film, revealing the importance of diffusion resistance. The heat transfer coefficients increased about 11% (at ΔT = 10 K) and 7% (at ΔT = 40 K), as the molar fraction of ethane increased from 0 to 40%. Meanwhile, the condensation heat transfer coefficient decreased by 53~56% as the wall sub-cooled temperature increased from 10 K to 40 K.

Effects of carbon to nitrogen ratio on oxygen mass transfer characteristics in wastewater and biofilms

Systematic elucidation of the oxygen mass transfer (OMT) mechanism is the key to improving aeration and oxygenation efficiency. In this study, an aerobic fluidized bed biofilm reactor (AFBBR) was established to evaluate the OMT in the wastewater phase [macroscopic (reactor) scale] and diffusion kinetic parameters in the biofilm phase (microbiological scale) under different carbon-nitrogen(C:N) ratios. A model relating the oxygen concentration and the aerobic layer thickness of the biofilm was established based on oxygen mass balance theory and Fick's second law. The results showed that the average DO concentration decreased from 7.68 mg/L to 5.85 mg/L with increasing C:N ratio (from 4.79 to 13.94). The oxygen transfer rate (OTR) was consistent with the distribution of the total biomass (total suspended solids, TSS), which was the largest (9.74 ± 0.33 mg/(L·h) and 8178 ± 87 mg/L) under the highest C:N ratio (13.94). Additionally, the α-factor, as a key parameter for evaluating OMT efficiency, had an exponential correlation with chemical oxygen demand (CODcr). The oxygen concentration exhibited in a Gaussian distribution (0.9963 ≤R2 ≤0.9998) relative to the thickness of the aerobic layer. The mass transfer efficiency (ki) and diffusion coefficient (Di) of oxygen in the boundary layer both reached maxima [(8.1 ± 3.2)× 10−5 cm2/s and (2.0 ± 0.1)× 10−3 cm/s] under the condition of C:N = 9.49. However, under the lowest C:N ratio, the biofilm thickness (LF=2422 ± 411 µm) and oxygen diffusion coefficient (Db) both reached maxima. These results have important theoretical significance for improving OMT theory and reducing the energy consumption of the aeration process.

Comparative analysis of analytical and numerical approximations for the flow and heat transfer in mixed convection stagnation point flow of Casson fluid

A mathematical description of non-Newtonian mixed convective Casson fluid stagnation point flow and transfer of heat exists in terms of partial differential equations. We considered the same to study it further under the effects of unsteadiness and varied film thickness parameters. For inclusion of these parameters in the flow model study we modified the available similarity transformations. The governing equations with three independent variables are converted into ordinary differential equations by employing the modified invertible transformations. For the mass and heat transfer in the mixed convection stagnation point unsteady flow of Casson fluid over a stretching sheet, a detailed comparative analysis is carried out in this paper, of the analytical and numerical approximation techniques. The Homotopy Analysis Method is applied for the analytical solutions while the Runge-Kutta with a Shooting Method (RKF45) and Finite Difference Method are used for obtaining the numerical solutions. With these solution schemes we present an analysis of velocity and temperature profiles under the effects of embedded parameters such as the Casson fluid parameter, unsteadiness parameter, mixed convection parameter, Prandtl number, Eckert number, and stretching ratio. The results are presented in both graphical and tabulated forms and they illustrate the dependence of mass and heat transfer characteristics of Casson fluid upon the embedded parameters. Further, we have shown an agreement between the analytical and the approximate solutions for the considered flow and heat transfer which reflects a validation of the results presented here.

Heat and mass transfer in impulse grain drying

The technology of constant exposure to the grain with a drying agent is not optimal due to the fact that the grain overheats faster than moisture evaporates. It is necessary to lower the temperature of the drying agent to reduce the risk of deterioration in grain quality. Because of this, the performance of grain dryers with a constant heat supply is reduced. More promising is the drying technology with variable heat supply. The pulse mode is one of the varieties of the variable mode. This drying mode allows, while maintaining the passport performance of the dryers, to reduce the specific heat consumption. The purpose of the article is to calculate the pulse duration, pause and temperature of the drying agent. The duration of heating depends on the heat transfer coefficient, the physical and mechanical properties of the material and the logarithm of the temperature difference between the drying agent and the material. The duration of the deposit depends on the physical and mechanical properties of the material, the logarithm of the difference between the ratio of its moisture content and the diffusion coefficient. The article presents the characteristic features of heat and mass transfer and the main parameters of the process.&#x0D; Keywords: drying; corn; heat and mass transfer; pulse mode; drying agent.

Carbon coating optimization on porous silicon as high-performance anode material via fluidized bed chemical vapor deposition

The carbon layer coating is a promising solution to volume expansion and low electron conductivity in silicon-based anodes during lithiation. While numerous methods exist to generate these carbon coatings, Fluidized Bed Chemical Vapor Deposition (FBCVD) has proven superior due to its capacity for producing remarkably uniform and consistent carbon layers, primarily as a result of efficient mass and heat transfer characteristics. However, its application in the context of lithium-ion battery anodes has been sparsely explored and has been principally limited to silicon oxide as the base material. In this paper, porous silicon (PSi) obtained through acid etching of AlSi alloy with an average particle size of 300 mesh was taken as raw materials, and a fluidized bed reactor was employed to realize a uniform and tightly packed carbon layer. Relatively speaking, the PSi@C30 in this work offers a simpler process and promising electrochemical performance, opening a new door for the preparation of high-performance silicon-carbon anodes by FBCVD. Besides, PSi and high-quality carbon layers with structural advantages enabled the authors to obtain high-performance silicon-carbon anode materials. The resulting PSi@C30 composite demonstrated excellent initial coulomb efficiency (88.8 %) and cycling stability (with 83 % capacity retention after 100 cycles at 0.5 A g-1 and a reversible capacity of 1408 mAh g-1). Such a cost-effective and user-friendly technique facilitates the application of FBCVD in silicon-based anode materials for Li-ion batteries, thus accelerating the industrialization of silicon-carbon anodes for high-performance Li-ion batteries in the future.

Enhanced reverse osmosis filtration via chaotic advection induced by patterned membranes: A numerical study

This paper numerically explores the potential of patterned membranes inducing chaotic advection to enhance the efficiency of reverse osmosis (RO) filtration. We compared the filtration performance of four different membrane patterns: flat surface (FS), lateral pattern (LP), herringbone pattern (HP), and staggered herringbone pattern (SHP). The dimensionless pattern depth (dp∗) and the Reynolds number (Re) were chosen as key parameters with influence on the flow and mass transfer characteristics. The numerical scheme was validated by comparing concentration profiles and permeate flux to the experimental data. Poincaré sections were used to represent the dynamical systems in spatially periodic filtration modules. Numerical simulations were conducted for an RO process with an aqueous NaCl solution, varying dp∗ and Re within the ranges of dp∗≤0.3 and 100≤Re≤1000. The HP and SHP significantly enhanced filtration performance compared to the FS and LP, regardless of Re. Chaotic advection induced by the HP and SHP effectively suppressed concentration polarization by transporting solutes away from membrane surfaces and uniformly redistributing them back to the feed stream. Furthermore, this study demonstrates that the patterned membranes inducing chaotic advection can enhance the energy efficiency of RO filtration as well.

MHD peristaltic flow of chemically reactive casson nanofluid in a nonuniform porous inclined flexible channel with cross-diffusion effects

This model is designed to provide clarity on how blood travels through tiny veins in physiological systems with heat and mass transfer characteristics. Further, the purpose of this paper is to examine the Ohmic heating and heat source/sink effects on peristaltic transport of radiative Casson nanofluid in a nonuniform porous inclined channel in the presence of a normal/inclined magnetic field. We also considered the sway of chemical reaction, Soret and Dufour effects. The momentum, temperature and mass equations for Casson fluid model are obtained with the utilization of the lubrication approach. The exact solutions have been acquired for stream function and axial velocity. Further, the temperature and concentration equations are solved numerically by using the R–K based shooting method. We also tabulated the Nusselt and Sherwood numbers for various relevant parameters. Finally, the impacts of all major factors on the physical properties of the flow for both normal and inclined magnetic fields are explored and discussed in depth using graphs. The Casson fluid velocity is more for an inclined magnetic field than a normal magnetic field. The nonuniform parameter of the channel boosts the trapped fluid bolus size. The heat source/sink parameter improves the temperature field but the opposite trend is observed in the field of concentration. Moreover, the findings are validated with the existing works for some special circumstances.

Air sparging remediation of VOCs contaminated low-permeability soil based on pressure gradient control

Air sparging (AS) is deemed unacceptable for remediating VOCs contaminated soil with low-permeability. To improve air flow and contaminant removal in sparging process, an original approach, termed as pressure gradient-enhanced air sparging (PGEAS) approach, is proposed by controlling pressure gradient in soil. Then the remediation efficiency, mass transfer characteristics, and remediation mechanism are investigated. Results showed that, the PGEAS approach accelerates gaseous contaminant exhaust, reduces residue contamination in soil, and promotes total contaminant removal, finally results in an improved remediation efficiency compared to the conventional approach. Controlled by sparging pressure and flow distance, the pressure gradient is created in soil, and a critical value needs to be exceeded to enhance the VOCs removal and mass transfer characteristics. The measured results of pore pressure and liquid saturation confirm a notable pressure gradient and drainage behavior in soil, which indicate the massive air subchannel formation during air sparging. At a two-dimensional scale, discrete distributions of contaminant concentrations in exhaust air and soil are presented, the removal extent and area are both enhanced using the PGEAS approach with a pressure gradient higher than the critical value. The reached conclusions are of great importance to contaminant removal in heterogeneous stratigraphy at sites.

Non-Newtonian Flow with Heat and Mass Transfer Over a Porous Stretching Sheet Under the Effects of Space Dependent and TGD Heat Sink, Non-Uniform Heat Source and Dissipation of Energy and CGD Mass Diffusion with Suction/Blowing

In the present paper, an analytical study of visco - elastic fluid flow with heat and mass transfer characteristics over a porous stretching sheet has been examined. Heat balance is maintained with space dependent and temperature gradient dependent heat sink/source, viscous dissipation, and non-uniform heat source on the non-Newtonian Walter’s liquid B' model. The mass balance is maintained with chemically reactive species of order I, variable mass diffusivity and concentration gradient dependent mass diffusion. Using similarity transformation technique on the highly non-linear differential equations, several closed form analytical solutions are obtained for non-dimensional temperature and concentration in both PST and PHF cases in the form of confluent hypergeometric (Kummar’s) functions. The effect of permeability parameter, viscoelastic parameter, suction parameter on velocity profiles and various physical fluid situations with different degrees of viscoelasticity, Prandtl number, Eckert number, heat source- sink strength, temperature field are discussed in detail and presented through graphs. Similarly in the mass transfer field the effects of Schmidt number, reaction rate parameters are discussed in detail and presented through graphs.