THE HYDROGENATION OF BIOMASS IN A SHOCK TUBE

An oblique flat surface model is used lo simulate the rotating roll. The flow regions proposed by Landau and Levich is utilized in the analysis. The inertia force terms are included and a more realistic 2-dimensional boundary conditions for the free surface is used in this paper. Also, the solution is obtained by utilizing a refinement of integral method. The results are compared with available experimental data. It is shown that the prediction is sufficiently accurate over a wide range of capillary number, and better than the other existing results. The film thickness increase with respect to increasing capillary number up to a certain higher values, from then this tendency slows down and even decreases due to inertia effects     

Capillary Filling Flows inside Patterned‐Surface Microchannels

Capillary flows inside microchannels with patterned‐surfaces are investigated theoretically and numerically. The surface energy method is used to derive an equivalent contact angle (ECA) model for small capillary number flows. The SIMPLE algorithm using a volume of fluid (VOF) method is adopted to investigate the flows in those microchannels. The flow characteristics such as the liquid front shapes and the evolution of the liquid lengths are obtained. The numerical results reveal that capillary flows in a patterned‐surface microchannel still follow the traditional capillary theories. The ECA model is confirmed by the numerical results. It indicates that the capillary flows inside the patterned‐surface microchannels can be estimated by means of the homogeneous‐surface microchannels with the equivalent contact angle. The ECA model provides a good criterion for the total wettability of a patterned‐surface microchannel, as well.     

The Effects of Surface Waviness and Length on Electrokinetic Transport in Wavy Capillary

An electrokinetic model for a wavy capillary has been developed. Poisson‐Nernst‐Planck and Navier‐Stokes equations constitute the model that governs fluid and ionic fluxes and electric potential distribution inside the capillary. In the present paper, a finite wavy cylindrical capillary with a large reservoir at both capillary ends is analyzed using finite element method. The model is used primarily to examine the influence of capillary surface waviness on the electrokinetic transport behaviours. Different frequencies and amplitudes of the wavy surface are considered to investigate the influence of surface waviness on electrokinetic transport. Fluctuations in potential and ionic concentration distribution increase with the increase in either amplitude or frequency of the capillary surface waviness. However, for higher frequencies the fluctuation diminishes for all surface waviness amplitudes. It is observed that for any irregularity in the capillary surface results in higher salt rejection. Salt rejection is found to be dependent on capillary axial length as well as flow velocity. A critical Peclet number, beyond which salt rejection attains a constant steady value, dictates maximum salt rejection.     

Experimental study of the role of the Weber and capillary numbers on Mesler entrainment

Mesler entrainment is the formation of a very large number of very small bubbles by a relatively low velocity drop impacting a liquid surface. The role of the Weber number in Mesler entrainment has received significant attention. However, the effect of the capillary number, which quantifies the relative importance of viscous and surface tension forces, has not been explored. This is due primarily to the fact that virtually all Mesler entrainment research has used a single liquid, water, as the working fluid. This, combined with certain experimental restrictions, makes difficult an independent variation of the Weber and capillary numbers. To address this problem, Mesler entrainment was investigated using two silicone oils, having kinematic viscosities of 0.65 cSt and 10.0 cSt, respectively, revealing the effect of the capillary number on Mesler entrainment, a result which has not been obtained heretofore. The silicone oils give extremely repeatable results when compared to water. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

Investigation of droplet coalescence propelled by dielectrophoresis

We propose dielectrophoretic force driven coalescence of droplets having equal or nonequal sizes with an electrode base actuation system over a solid surface. Coupled electrohydrodynamic conservation equations are solved to simulate the phenomenon based on finite volume scheme. Volume of fluid technique is used to capture the interface. Electric potential and dissimilarity index are varied to comprehend the coalescence dynamics. The interplay between the capillary and electrostatic influences during the coalescence is analyzed by tracking the dimension of the liquid connection formed at the onset of fusion. Efforts have been made to characterize the liquid bridge formation as a function of inertia normalized time scale. The capillary force showed higher dominance in the initial period of agglomeration. The electrostatic influence can be perceived at the latter stages of the growth of liquid connection. Directional predilection in the flow field is observed during the coalescence of dissimilar droplets. © 2018 American Institute of Chemical Engineers AIChE J, 65: 829–839, 2019     

Dispensing of rheologically complex fluids: The map of misery

Rheological effects may complicate the dispensing of complex fluids, when compared to their Newtonian counterparts. In this work, fluids with tailored rheological properties have been studied using high‐speed video‐microscopy. The level of viscosity, the degree of shear thinning, and the elasticity have been varied independently. At low‐flow rates, droplets are formed that pinch off. The drop volumes, breakup mechanisms, and times have been identified. At higher‐flow rates, a continuous jet is observed, with the transition depending on the rheology of the dispensed fluid. The relevant nondimensional groups are the Ohnesorge, Deborah, and elasto‐capillary number, for when viscosity, inertia, or elastic forces dominate flow. In each of these cases, the transition between dripping and jetting dispensing occurs, controlled by a critical Weber, capillary, and Weissenberg number, respectively. This set of six nondimensional groups can be used to construct an operating space and map out areas of potential problems. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3242–3255, 2012     

The coating of Newtonian liquids onto a roll rotating at low speeds

A theoretical treatment is presented for the prediction of the rate at which a liquid is entrained by a roll which is rotating partially submerged in a Newtonian liquid, and also for the prediction of the variation in the thickness of the film around the roll. The method involves the integration of the momentum equation after neglecting inertia forces in the dynamic meniscus region and the matching of the surface curvature with that derived for the static meniscus region near the liquid surface. The resulting equation allows the prediction of the relationship between a dimensionless film thickness parameter, T, and the capillary number, Ca, as a function of the radius of the roll, the withdrawal angle and the position of the roll periphery. The liquid flux on the roll can also be predicted.     

Numerical study of laminar condensation of downward flowing vapour on a single horizontal cylinder or a bank of tubes

The results of numerical calculations for the downward flow of pure vapour condensing on horizontal tubes are presented. An implicit finite difference method is used. The equality of shear stress at the liquid—vapour interface is used as the coupling condition between the two phases. The inertia and convection terms are retained in the analysis. The vapour phase velocity is obtained from potential flow. The method of source density distribution on the body surface is used for the determination of the vapour flow in tube banks. The effect of flooding produced by condensation on upper tubes is taken into account by assuming that the vapour velocity field is not affected by the condensate flow from one tube to another. The results presented show that the vapour boundary layer separation depends on the Froude number. The heat transfer in the intertube space is analyzed and compared with the theoretical and experimental results of other authors. Good agreement is shown.     

Kinetic model and effect of surface impurities on the crack healing of BK7 glass

When BK7 glass material is heated under appropriate conditions, surface cracks heal spontaneously under the action of viscous flow and capillary forces. In this paper, based on the theories of viscous fluid and capillary flow, a kinetic model for crack healing is established. A series of thermal healing experiments with different parameters are conducted on Vickers indentation radial cracks on BK7 glass, and the effects of surface impurities, heating temperature, crack size, and ambient humidity are studied. The results show that the surface impurities and humidity can promote crack healing. Upon combining the experimental results and relevant theories, the initial kinetic model is modified to accurately predict the healing process of the BK7 glass and describe the relationships among the crack healing length and these factors. In addition, the proposed model can be used for the healing of other materials with the mechanism of viscous capillary flow.     

THE KINETIC THEORY OP GASES AND MASS TRANSFER IN POEES IN THE PRESENCE OF HETEROGENEOUS PHASE AND CHEMICAL CONVERSIONS

The paper presents the investigation of gas transfer in cylindrical channels in the presence of heterogeneous physicochemical conversions (filler evaporation in a channel, evaporation on the internal surface of a channel, catalytic reaction of the first order). With the use of the model kinetic equations for the gas molecule velocity distribution function, the solutions of the above problems have been obtained, suitable for the arbitrary ratios of free molecule path length to capillary radius, i.e. the Knudsen number. The comparison between the theoretical and experimental results on filler surface recession in a capillary during evaporation in the presence of a foreign gas is carried out. The applicability limits for the well-known phenomenological relations, used in the theory of drying, are established.     

Capillary and van der Waals force between microparticles with different sizes in humid air

It is well known that surface effect forces, such as van der Waals force and capillary force, are the major contributions to adhesion when microsized particles are in contact in humid environment. But it is very complex to calculate the adhesion force between two smooth unequal particles. In conventional approaches, the effective particle radius approximation and the constant half-filling angle assumptions are often used for computing the van der Waals forces between two microparticles. However, the approximation and the assumption are actually difficult to accurately model the forces between unequal particle sizes when the surfaces are with different properties. In this paper, we present a theoretical study of the van der Waals force and capillary force between two microparticles with different radii and the surface properties linked by a liquid bridge. The proposed model provides the adhesion force predictions in good agreement with the previous formula and existing experiment data. Considering the solid particles are partially wetted by the liquid bridge, the van der Waals force is calculated by divided the particle surface into a wetted part and a dry portion in our stimulation. Since the wetted surface portion of the particle is determined by the half-filling angle, the relationship between two half-filling angles of the unequal size particles is developed from the geometrical consideration, which is relate to the size ratio of the particles, the contact angle, and the separation distance. Then, the van der Waals force is determined using the surface element integration. Moreover, the influences of humidity, particles size, contact angle, and separation distance toward the adhesion forces are discussed using the proposed method. Simulations indicate that a higher relative humidity leads to bigger liquid bridges, suggesting a higher capillary force, but at the same time, the van der Waals force decreases due to the decrease in surfaces energy. As for the influence of contact angle, results show that a higher contact angle, that is, a more hydrophobic surface, reduces the capillary force but increases the van der Waals force (absolute value). The simulations also show that the both the capillary force and the van der Waals force (absolute value) increase as the particle size increases. When the particles are separated from each other, the capillary force and van der Waals force decreases gradually. These results are helpful to understand and utilize the adhesion interaction between particles with unequal sizes at the ambient condition.     

Meniscus behaviors and capillary pressures in capillary channels having various cross-sectional geometries

A numerical study has been conducted to simulate the liquid/gas interface (meniscus) behaviors and capillary pressures in various capillary channels using the volume of fluid (VOF) method. Calculations are performed for four channels whose cross-sectional shapes are circle, regular hexagon, square and equilateral triangle and for four solid/liquid contact angles of 30°, 60°, 120° and 150°. No calculation is needed for the contact angle of 90° because the liquid/gas interface in this case can be thought to be a plane surface. In the calculations, the liquid/gas interface in each channel is assumed to have a flat surface at the initial time, it changes towards its due shape thereafter, which is induced by the combined action of the surface tension and contact angle. After experiencing a period of damped oscillation, it stabilizes at a certain geometry. The interface dynamics and capillary pressures are compared among different channels under three categories including the equal inscribed circle radius, equal area, and equal circumscribed circle radius. The capillary pressure in the circular channel obtained from the simulation agrees well with that given by the Young–Laplace equation, supporting the reliability of the numerical model. The channels with equal inscribed circle radius yield the closest capillary pressures, while those with equal circumscribed circle radius give the most scattered capillary pressures, with those with equal area living in between. A correlation is developed to calculate the equivalent radius of a polygonal channel, which can be used to compute the capillary pressure in such a channel by combination with the Young–Laplace equation.     

Numerical simulation on wave behaviour and flow dynamics of laminar‐wavy falling films: Effect of surface tension and viscosity

Numerical simulation has been made on wave behaviour and flow dynamics of falling films of aqueous lithium bromide solution along a vertical wall in the present study. Volume of fluid model is used to track the free surfaces and continuum surface force model is used for dynamic boundary conditions considering the effect of surface tension. A small amplitude forcing perturbation is introduced at the inlet of the flow boundary. Effect of surface tension and viscosity on wave behaviour and flow dynamics has been investigated. The simulation results indicate that wave peak height decreases with increasing surface tension and the number of capillary waves in front of a large wave increases. With the decrease of viscosity wave shape changes from the sinusoidal shape to the solitary one. Furthermore, the flow dynamics underneath the typical waves are analysed, especially the pattern of backflow. © 2011 Canadian Society for Chemical Engineering     

The effects of viscosity, surface tension, and flow rate on gasoil-water flow pattern in microchannels

A microchannel was fabricated with glass tubes to investigate the effect of viscosity, surface tension, and flow rate on the liquid-liquid two-phase flow regime. Water and gasoil were selected as aqueous and organic working fluids, respectively. The two fluids were injected into the microchannel and created either slug or parallel profile depending on the applied conditions. The range of Reynolds and capillary numbers was chosen in such a way that neither inertia nor interfacial tension forces were negligible. Xanthan gum was used to increase viscosity and Triton X-100 (TX-100) and Sodium Dodecyl Sulfate (SDS) were used to reduce the interfacial tension. The results demonstrated that higher value of viscosity and flow rate increased interfacial area, but slug flow regime remained unchanged. The two surfactants showed different effects on the flow regime and interfacial area. Addition of TX-100 did not change the slug flow but decreased the interfacial area. In contrast, addition of SDS increased interfacial area by decreasing the slug’s length in the low concentrations and by switching from slug to parallel regime at high concentrations.     

Entrainment of air by a solid surface entering a liquid/air interface

The entrainment of air by a horizontal cylindrical roll rotating in a bath of liquid is considered. A simplified approach based on dimensionless analysis suggests that entrainment should occur at a critical value of the dimensionless capillary number, μU/σ. Experiments on a range of viscous glycerol/water solutions and hydrocarbon oils indicate that this is so. The value of the critical capillary number is about 1·2 for all the fluid systems and this value is not sensitive to the angle of incidence of the surface.This criterion could be of some value in a number of industrial coating processes.     

Dynamic modeling of drainage through three-dimensional porous materials

The interplay of viscous, gravity and capillary forces determines the flow behavior of two or more phases through porous materials. In this study, a rule-based dynamic network model is developed to simulate two-phase flow in three-dimensional porous media. A cubic network analog of porous medium is used with cubic bodies and square cross-section throats. The rules for phase movement and redistribution are devised to honor the imbibition and drainage physics at pore scale. These rules are based on the pressure field within the porous medium that is solved for by applying mass conservation at each node. The pressure field governs the movement and flow rates of the fluids within the porous medium. Film flow has been incorporated in a novel way. A pseudo-percolation model is proposed for low but non-zero capillary number (ratio of viscous to capillary forces). The model is used to study primary drainage with constant inlet flow rate and constant inlet pressure boundary conditions. Non-wetting phase front dynamics, apparent wetting residuals (S_wr), and relative permeability are computed as a function of capillary number (N_ca), viscosity ratio (M), and pore-throat size distribution. The simulation results are compared with experimental results from the literature. Depending upon the flow rate and viscosity ratio, the displacement front shows three distinct flow patterns—stable, viscous fingering and capillary fingering. Capillary desaturation curves (S_wr vs. N_ca) depend on the viscosity ratio. It is shown that at high flow rates (or high N_ca), relative permeability assumes a linear dependence upon saturation. Pseudo-static capillary pressure curve is also estimated (by using an invasion percolation model) and is compared with the dynamic capillary pressure obtained from the model.     

矩形截面微通道内气-液两相流压力降的实验测定及关联(英文)

The pressure drop of gas-liquid two-phase flow in microchannel is of fundamental importance in heat and mass transfer processes. In this work,the pressure drop of gas-liquid two-phase flow in horizontal rectangular cross-section microchannels was measured by a pressure differential transducer system. Water,ethanol and n-propanol were used as liquid phase to study the effects of capillary number on pressure drop;air was used as the gas phase. Four microchannels with various dimensions of 100 μm× 200 μm,100 μm× 400 μm,100 μm× 800 μm and 100 μm× 2000 μm(depth × width) were used for determining the influence of configuration on the pressure drop. Experimental results showed that in micro-scale,the capillary number also affected the pressure drop remarkably,and in spite of only one-fold difference in aspect ratio,the variation of pressure drop reached up to near three times under the same experimental conditions. Taking the effects of aspect ratio and surface tension into account,a modi-fied correlation for Chisholm parameter C in the Chisholm model was proposed for predicting the frictional multi-plier,and the predicted values by the proposed correlation showed a satisfactory agreement with experimental data.     

Numerical simulation of a falling droplet surrounding by air under electric field using VOF method: A CFD study

This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD. The VOF method has been employed to model the two-phase flow of the present study. Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation. Also, the effects of electric potential on the heat transfer coefficient have been examined. The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by, with a subtle deformation to an oblate form. Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificant with time progressing; however, further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon. Ultimately, it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.     

Entwicklung einer präzisen Kapillar-GC-Methode zur schnellen Triglyceridanalytik von Milchfetten

Development of a Precise Capillary GC Method for Rapid Triglyceride Analysis of Milk Fats Quantitative analysis of triglycerides - partly in conjunction with triglyceride formulae - can be used for the gas chromatographic determination of various milk fat parameters. Since these examinations, for example the evaluation of the content of foreign fats in milk fat, require only the separation of triglycerides by carbon number and since the repeatability of analytical results, especially of the high-boiling triglycerides, has been worse with capillary columns in the past, packed columns have been used mostly. With respect to the increasing application of triglyceride formulae and the related demand for the use of capillary instead of packed columns extensive investigations have been carried out to that end now. For the development of this exacting high-temperature application a particularly temperature-stable metal capillary column was used. The effects of varying the temperature program, the carrier gas flow, the injection technique as well as the sample concentration on the resolution are demonstrated. Finally, the optimizing led to results that are comparable to those achieved by packed columns with regard to resolution and precision. Thus, the rapid gas chromatographic determination of milk fat parameters can now be carried out with a standardized capillary column as well.     

Numerical simulation of a falling droplet surrounding by air under electric field using VOF method: A CFD study

This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD. The VOF method has been employed to model the two-phase flow of the present study. Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation. Also, the effects of electric potential on the heat transfer coefficient have been examined. The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by, with a subtle deformation to an oblate form. Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificant with time progressing; however, further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon. Ultimately, it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.