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1.
Pore-Network Modeling of Isothermal Drying in Porous Media 总被引:1,自引:0,他引:1
A. G. Yiotis A. K. Stubos A. G. Boudouvis I. N. Tsimpanogiannis Y. C. Yortsos 《Transport in Porous Media》2005,58(1-2):63-86
In this paper we present numerical results obtained with a pore-network model for the drying of porous media that accounts for various processes at the pore scale. These include mass transfer by advection and diffusion in the gas phase, viscous flow in the liquid and gas phases and capillary effects at the liquid--gas interface. We extend our work by studying the effect of capillarity-induced flow in macroscopic liquid films that form at the pore walls as the liquid--gas interface recedes. A mathematical model that accounts for the effect of films on the drying rates and phase distribution patterns is presented. It is shown that film flow is a major transport mechanism in the drying of porous materials, its effect being dominant when capillarity controls the process, which is the case in typical applications. 相似文献
2.
In this article, a new model is developed to determine the solvent convective dispersion coefficient in a solvent vapor extraction
(VAPEX) heavy oil recovery process. It is assumed that solvent mass transfer by convective dispersion takes place along the
transition zone between the solvent chamber and untouched heavy oil, whereas solvent mass transfer by molecular diffusion
occurs in the direction normal to the transition zone. It is also assumed that the solvent-diluted heavy oil gravity drainage
through the transition zone has a linear or quadratic velocity profile in order to obtain analytical solutions of the solvent
convective dispersion coefficients for the solvent chamber spreading and falling phases. As a result, this analytical model
correlates the solvent convective dispersion coefficient to the maximum apparent oil gravity drainage velocity at the interface
between the solvent chamber and transition zone, solvent molecular diffusion coefficient, transition-zone thickness, and porosity
of the porous medium. To determine the solvent convective dispersion coefficient, the maximum apparent oil gravity drainage
velocity is calculated by using Darcy’s law and the transition-zone thickness is obtained either from a previous study or
by using a time similarity between the solvent molecular diffusion and oil gravity drainage. It is found that such a determined
solvent convective dispersion coefficient is two to five orders larger than the solvent molecular diffusion coefficient, depending
on the detailed experimental conditions of a specific VAPEX test. 相似文献
3.
This paper presents a general differential mathematical model to analyze the simultaneous heat and mass transfer processes
that occur in different components of an ammonia–water absorption system: absorber, desorber, rectifier, distillation column,
condenser and evaporator. Heat and mass transfer equations are considered, taking into account the heat and mass transfer
resistances in the liquid and vapour phases. The model considers the different regions: vapour phase, liquid phase and an
external heating or cooling medium. A finite difference numerical method has been considered to solve the resulting set of
nonlinear differential equations and an iterative algorithm is proposed for its solution. A map of possible solutions of the
mass transferred composition z is presented when varying the interface temperature, which enables to establish a robust implementation
code. The analysis is focused on the processes presented in ammonia–water absorption systems. The model is applied to analyze
the ammonia purification process in an adiabatic packed rectification column and the numerical results show good agreement
with experimental data. 相似文献
4.
V. I. Terekhov V. P. Lebedev N. E. Shishkin 《Journal of Applied Mechanics and Technical Physics》2000,41(4):692-698
Results of a thcoretical and experimental study of dynamics and mass transfer during desorption of a gas from a liquid film
in the presence of a cocurrent air flow are presented. The calculation model is based on solving integral momentum and diffusion
relations for the gaseous and liquid phascs. Both laminar and turbulent regimes of the film flow are analyzed. The experimental
study of mass transfer was conducted for carbon dioxide desorption from a water film. Criterial relations for mass transfer
in the gaseous and liquid phases are obtained. The experiments showed that the heat-transfer coefficients for the case under
study are one order of magnitude grcater than those for the flow of a smooth film. Possible mechanisms of such an appreciable
intensification of the liquid-film mass transfer in a cocurrent gas flow are discussed.
Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 4, pp. 131–138, July–August, 2000. 相似文献
5.
《International Journal of Multiphase Flow》2006,32(10-11):1191-1218
To clarify the impacts of the hydrodynamic boundary layer and the diffusion boundary layer in the near wall zone on gas–liquid two-phase flow induced corrosion in pipelines, the hydrodynamic characteristics of fully developed gas–liquid slug flow in an upward tube are investigated with limiting diffusion current probes, conductivity probes and digital high-speed video system. The Taylor bubble and the falling liquid film characteristics are studied, the effects of various factors are examined, and the experimental results are compared with the data and models available in literature. The length of Taylor bubble, the local void fraction of the slug unit and the liquid slug, the shear stress and mass transfer coefficient in the near wall zone, are all increased with the increase of superficial gas velocity and decreased with the increase of superficial liquid velocity, whereas the length of liquid slug and the liquid slug frequency are changed contrarily. The alternate wall shear stress due to upward gas–liquid slug flow is considered to be one of the major causes for the corrosion production film fatigue cracking. A normalized formula for mass transfer coefficient is obtained based on the experimental data. 相似文献
6.
In this work, the wall shear stress and the mass transfer coefficient of the gas–liquid two-phase upward slug flow in a vertical pipe are investigated experimentally, using limiting diffusion current probes and digital high-speed video system. In experiments, the instantaneous and averaged characteristics of wall shear stress and mass transfer coefficient are concerned. The experimental results are compared with the numerical results in previous paper of the authors. Both experiment and numerical simulation show that the superficial gas and liquid velocities have an obvious influence on the instantaneous characteristics of the two profiles. The mass transfer coefficient has characteristics similar to the wall shear stress. The instantaneous wall shear stress and mass transfer coefficient profiles have the periodicity of slug flow. The averaged wall shear stress and mass transfer coefficient increase with increased superficial gas velocity. However, there is inconsistency in the variation trends of the averaged wall shear stress and mass transfer coefficient with superficial liquid velocity between experimental result and numerical simulation result, which can be attributed to the difference in flow condition. Moreover, the Taylor bubble length is also another impacting factor. The experimental and numerical results all shows that the product scale can not be damaged directly by the flow movement of slug flow. In fact, the alternative forces and fluctuations with high frequency acting on the pipe wall due to slug flow is the main cause for the slug flow enhanced CO2 corrosion process. 相似文献
7.
Dr.-Ing. M. Millies Dipl.-Ing. St. v. Bose Dipl.-Ing. A. Tokarz Univ.-Prof.Dr.-Ing. D. Mewes 《Heat and Mass Transfer》1994,30(1):17-25
The common methods for calculating the mass transfer across liquid-liquid interfaces in technical applications take into account the mass transfer resistances within the bulk phases. The transfer resistance of the interface and a possible coupling between the momentum and the mass transport is not taken into account. In the present paper a survey is given of theoretical approaches which can describe this coupling and the additional mass transfer resistance. A theory is proposed by Hampe which can be used to explain the coupling between momentum and mass transport employing thermodynamics of irreversible processes. On the basis of this work, the influence of the dilatation of a flat interface on the mass transfer is deduced. It is also concluded from this theory that the diffusion coefficients within the bulk phases are coupled near the thermodynamic equilibrium. 相似文献
8.
Rasoul Nazari Moghaddam Behzad Rostami Peyman Pourafshary Yaser Fallahzadeh 《Transport in Porous Media》2012,92(2):439-456
Dissolution of CO2 into brine causes the density of the mixture to increase. The density gradient induces natural convection in the liquid phase,
which is a favorable process of practical interest for CO2 storage. Correct estimation of the dissolution rate is important because the time scale for dissolution corresponds to the
time scale over which free phase CO2 has a chance to leak out. However, for this estimation, the challenging simulation on the basis of convection–diffusion equation
must be done. In this study, pseudo-diffusion coefficient is introduced which accounts for the rate of mass transferring by
both convection and diffusion mechanisms. Experimental tests in fluid continuum and porous media were performed to measure
the real rate of dissolution of CO2 into water during the time. The pseudo diffusion coefficient of CO2 into water was evaluated by the theory of pressure decay and this coefficient is used as a key parameter to quantify the
natural convection and its effect on mass transfer of CO2. For each experiment, fraction of ultimate dissolution is calculated from measured pressure data and the results are compared
with predicted values from analytical solution. Measured CO2 mass transfer rate from experiments are in reasonable agreement with values calculated from diffusion equation performed
on the basis of pseudo-diffusion coefficient. It is suggested that solving diffusion equation with pseudo diffusion coefficient
herein could be used as a simple and rapid tool to calculate the rate of mass transfer of CO2 in CCS projects. 相似文献
9.
Dong Eok Kim Ki Hoon YangKyung Won Hwang Young Ho HaMoo Hwan Kim 《International Journal of Multiphase Flow》2011
A new physical model for calculating the liquid film thickness and condensation heat transfer coefficient in a vertical condenser tube is proposed by considering the effects of gravity, liquid viscosity, and vapor flow in the core region of the flow. To estimate the velocity profile in the liquid film, the liquid film was assumed to be in Couette flow forced by the interfacial velocity at the liquid–vapor interface. For simplifying the calculation procedures, the interfacial velocity was estimated by introducing an empirical power-law velocity profile. The resulting film thickness and heat transfer coefficient from the model were compared with the experimental data and the results obtained from the other condensation models. The results demonstrated that the proposed model described the liquid film thinning effect by the vapor shear flow and predicted the condensation heat transfer coefficient from experiments reasonably well. 相似文献
10.
We analyze theoretically the drying of cylindrical filaments. For modelling the mass transfer on the gas side of the liquid-gas
interface of the shrinking circular cylindrical filament, we apply the model of Abramzon and Sirignano, which was originally
developed for spherical geometry. As a consequence of mass transfer at constant Sherwood number, we obtain a d2-law for the shrinkage of the cylinder as in the case of the spherical geometry, which expresses that the cross-sectional
area of the cylinder shrinks at a constant rate with time. For this situation, the diffusion equation for the liquid phase
mixture components becomes separable upon transformation into similarity coordinates and is solved analytically to obtain
the concentration profiles inside the filament as functions of time. The dependency of the profiles on the radial coordinate
is determined by a series of Kummer’s functions. Applying this result, we study the evolution of the concentration profiles
in the liquid phase with time as dependent on a parameter given as the ratio of rate of shrinkage of the cross-sectional area
of the cylinder to liquid-phase diffusion coefficient, which was identified as relevant for the shape of the concentration
profiles formed in the liquid during the drying process. As an example, we present computed results for the constant evaporation
rate regime in the dry-spinning process of a polyvinyl-alcohol (PVA)-water system. Comparison of our analytical results with
full numerical solutions of the diffusion equation from the literature, achieved with concentration-dependent diffusion coefficient,
reveals very good agreement. 相似文献
11.
《Particuology》2022
The gas–liquid–solid mini fluidized bed (GLSMFB) combines the advantages of fluidized bed and micro-reactor, and meets the requirements for safety and efficiency of green development of process industry. However, there are few studies on its flow performance and no studies on its mass and heat transfer performance. In this paper, the characteristics of gas–liquid mass transfer in a GLSMFB were studied in order to provide basic guidance for the study of GLSMFB reaction performance and application. Using CO2 absorption by NaOH as the model process, the gas–liquid mass transfer performance of GLSMFB was investigated. The results show that the liquid volumetric mass transfer coefficient and the gas–liquid interfacial area both increase with the increase of the superficial gas velocity within the experimental parameter range under the same given superficial liquid velocity. At the same ratio of superficial gas to liquid velocity, the liquid volumetric mass transfer coefficient increases with the increase of the superficial liquid velocity. Fluidized solid particles strengthen the liquid mass transfer process, and the liquid volumetric mass transfer coefficient is about 13% higher than that of gas–liquid mini bubble column. 相似文献
12.
Din-Yu Hsieh 《Acta Mechanica Sinica》2003,19(3):204-207
The damping coefficient of capillary waves due to the evaporation-condensation process at the interface of the two phases
of a fluid is evaluated. To highlight the mechanism of the effect of heat and mass transfer across the interface between regions
of liquid and vapor, potential flow of incompressible fluids are assumed. Thus other mechanisms of damping are neglected.
To fascilitate the analysis, the method of multiple-scale is employed in the analysis, even though the problem is linear. 相似文献
13.
In the present study the effects of surface tension on the growth and collapse stages of cavitation bubbles are studied individually for both spherical and nonspherical bubbles. The Gilmore equation is used to simulate the spherical bubble dynamics by considering mass diffusion and heat transfer. For the collapse stage near a rigid boundary, the Navier–Stokes and energy equations are used to simulate the flow domain, and the VOF method is adopted to track the interface between the gas and the liquid phases. Simulations are divided into two cases. In the first case, the collapse stage alone is considered in both spherical and nonspherical situations with different conditions of bubble radius and surface tension. According to the results, surface tension has no significant effects on the flow pattern and collapse rate. In the second case, both the growth and collapse stages of bubbles with different initial radii and surface tensions are considered. In this case surface tension affects the growth stage considerably and, as a result, the jet velocity and collapse time decrease with increasing surface tension coefficient. This effect is more significant for bubbles with smaller radii. 相似文献
14.
Theoretical and experimental study of the paper drying process are presented. A mathematical model developed for combined heat ad mass transfer analysis of paper drying is given for both impinging air jets and through air drying methods. In this model, it is simply assumed that during the drying period of the paper has porous media and on the drying surface the vapour pressure of the evaporating liquid remains at a quasi-saturated value corresponding to the temperature of the liquid. The calculated transient paper temperatures in both methods agree well with the experimental results. 相似文献
15.
Nonisothermal moisture transport in hygroscopic building materials: modeling for the determination of moisture transport coefficients 总被引:1,自引:0,他引:1
Menghao Qin Rafik Belarbi Abdelkarim Ait-Mokhtar Lars-Olof Nilsson 《Transport in Porous Media》2008,72(2):255-271
A mathematical model for calculating the nonisothermal moisture transfer in building materials is presented in the article.
The coupled heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as principal driving
potentials. The coupled equations were solved by an analytical method, which consists of applying the Laplace transform technique
and the Transfer Function Method. A new experimental methodology for determining the temperature gradient coefficient for
building materials was also proposed. Both the moisture diffusion coefficient and the temperature gradient coefficient for
building material were experimentally evaluated. Using the measured moisture transport coefficients, the temperature and vapor
content distribution inside building materials were predicted by the new model. The results were compared with experimental
data. A good agreement was obtained. 相似文献
16.
D. V. Sadin A. N. Dobrolyubov V. P. Zyuzlikov K. V. Mogilenko B. E. Sinil’shchikov 《Journal of Applied Mechanics and Technical Physics》2008,49(3):417-424
A mathematical model and a method for calculating a gas-droplet turbulent jet with allowance for velocity nonequilibrium and
virtual mass of the condensed phase during turbulent fluctuations and also heat and mass transfer within the three-temperature
scheme are developed. Methodical calculations are performed. The results of these calculations are in reasonable agreement
with available experimental data. The structure of the gas-droplet jet in a cocurrent high-velocity high-temperature gas flow
is studied by numerical methods. The ratio of intensities of heat and mass transfer between the phases and turbulent diffusion
transfers of substances is found to be different at the initial, transitional, and basic segments of the jet. This difference
is responsible for the nonmonotonic axial distribution of vapor density and the lines of the halved mass flow of the condensed
phase.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 85–94, May–June, 2008. 相似文献
17.
Film boiling of binary liquid mixtures may be significantly different from that of single-component liquids due to the mass diffusion effect. A theoretical analysis is performed to outline the effects of mass diffusion phenomena on film boiling heat transfer process from a horizontal cylinder heating surface to the binary liquid mixtures of ethylene oxide/water and ethanol/benzene over whole range of compositions. These two binary systems are chosen for illustrating the strong and weak mass diffusion effects, respectively, on film boiling. Furthermore, a simple correlation for predicting heat transfer coefficient is proposed to demonstrate the idea that the dimensionless F factor can satisfactorily account for the mass diffusion effect on film boiling heat transfer of binary mixtures. 相似文献
18.
Heat transfer and two-phase flow characteristics of refrigerants flowing under varied heat flux in a double-pipe evaporator 总被引:1,自引:0,他引:1
A mathematical model based on the annular flow pattern is developed to simulate the evaporation of refrigerants flowing under varied heat flux in a double tube evaporator. The finite difference form of governing equations of this present model is derived from the conservation of mass, energy and momentum. The experimental set-up is designed and constructed to provide the experimental data for verifying the simulation results. The test section is a 2.5 m long counterflow double tube heat exchanger with a refrigerant flowing in the inner tube and heating water flowing in the annulus. The inner tube is made from smooth horizontal copper tubing of 9.53 mm outer diameter and 7.1 mm inner diameter. The agreement of the model with the experimental data is satisfactory. The present model can be used to investigate the axial distributions of the temperature, heat transfer coefficient and pressure drop of various refrigerants. Moreover, the evaporation rate or the other relevant parameters that is difficult to measure in the experiment are predicted and presented here. The results from the present mathematical model show that the saturation pressure and temperature of refrigerant decrease along the tube due to the tube wall friction and the flow acceleration of refrigerant. The liquid heat transfer coefficient increases with the axial length due to reducing the thickness of the liquid refrigerant film. Due to increase of the liquid heat transfer coefficient, increasing wall heat flux is obtained.Finally, the evaporation rate of refrigerant increases with increasing wall heat flux. 相似文献
19.
M. Assar H. Abolghasemi M. Rajabi Hamane S. J. Hashemi H. Fatoorehchi 《Heat and Mass Transfer》2014,50(5):651-660
A boundary layer model is developed to analyze diffusion through a laminar falling film for incomplete penetration of the dissolved gas. Regarding the rather intractable nature of the problem, Kantorovich Integral Method is chosen. Accordingly, a mass transfer boundary layer is assumed to keep growing perpendicularly to the falling film until it hits the wall. Such an approach is superior to its preceding artworks based on Higbie’s penetration theory in terms of implementation of more realistic conditions/modeling assumptions. Furthermore, unlike penetration model, this approach gives a criterion whether the diffusion is complete. Comparing the two models, boundary layer model estimates up to 2.3 % larger mass transfer coefficients. Moreover, a sensitivity analysis of liquid velocity distribution upon Sherwood number is conducted. It is found that the local velocity at gas–liquid interface is of highest dominance. Experimental data of SO2 absorption in water reported in literature is exploited to validate the model. It is shown that boundary layer model better fits the experimental data. 相似文献
20.
Summary Two cases are considered for which mass transfer coefficients are calculated. The first case is a semi-infinite Couette flow bounded by a moving interface across which transfer takes place. In the second case the mass transfer coefficient is calculated for a liquid flow with a moving interface, along which a boundary layer develops. 相似文献