Showing papers on "Mass transfer published in 2005"

Membrane Distillation and Related Operations—A Review

Abstract: Membrane contactors represent an emerging technology in which the membrane is used as a tool for inter phase mass transfer operations: the membrane does not act as a selective barrier, but the separation is based on the phase equilibrium. In principle, all traditional stripping, scrubbing, absorption, evaporation, distillation, crystallization, emulsification, liquid‐liquid extraction, and mass transfer catalysis processes can be carried out according to this configuration. This review, specifically addressed to membrane distillation (MD), osmotic distillation (OD), and membrane crystallization (MCr), illustrates the fundamental concepts related to heat and mass transport phenomena through microporous membranes, appropriate membrane properties, and module design criteria. The most significant applications of these novel membrane operations, concerning pure/fresh water production, wastewater treatment, concentration of agro food solutions, and concentration/crystallization of organic and biologica...

Mass-Transfer Characterization of Metallic Foams as Supports for Structured Catalysts

Abstract: Open-celled metal foams have been characterized as supports for structured catalysts, considering their utilization in gas−solid catalytic processes with short contact times and high reaction rates, typically controlled by gas−solid diffusional mass transport Examples of such processes are found in the field of environmental catalysis, including, eg, catalytic combustion, selective catalytic reduction (SCR-DeNOx), and automotive exhaust gas after treatment In this work, foams with different cell sizes were coated with a thin layer of palladium−alumina and tested in a 9-mm inner diameter tubular reactor by performing the catalytic oxidation of CO at empty tube velocities in the range of 08−26 m/s The coated foams exhibited sufficient catalytic activity to achieve mass-transfer-limited operation in the temperature range of 300−450 °C Under such conditions, mass-transfer coefficients were determined according to a simple one-dimensional model of the test reactor Adopting the average diameter of the

Two‐scale continuum model for simulation of wormholes in carbonate acidization

Abstract: A two-scale continuum model is developed to describe transport and reaction mechanisms in reactive dissolution of a porous medium, and used to study wormhole formation during acid stimulation of carbonate cores. The model accounts for pore level physics by coupling local pore-scale phenomena to macroscopic variables (Darcy velocity, pressure and reactant cup-mixing concentration) through structure-property relationships (permeability-porosity, average pore size-porosity, and so on), and the dependence of mass transfer and dispersion coefficients on evolving pore scale variables (average pore size and local Reynolds and Schmidt numbers). The gradients in concentration at the pore level caused by flow, species diffusion and chemical reaction are described using two concentration variables and a local mass-transfer coefficient. Numerical simulations of the model on a two-dimensional (2-D) domain show that the model captures the different types of dissolution patterns observed in the experiments. A qualitative criterion for wormhole formation is developed and it is given by Λ ∼ O(1), where Λ = . Here, keff is the effective volumetric dissolution rate constant, DeT is the transverse dispersion coefficient, and uo is the injection velocity. The model is used to examine the influence of the level of dispersion, the heterogeneities present in the core, reaction kinetics and mass transfer on wormhole formation. The model predictions are favorably compared to laboratory data. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Constraining the mass transfer in massive binaries through progenitor evolution models of Wolf-Rayet+O binaries

Abstract: Since close WR+O binaries are the result of a strong interaction of both stars in massive close binary systems, they can be used to constrain the highly uncertain mass and angular momentum budget during the major mass transfer phase. We explore the progenitor evolution of the three best suited WR+O binaries HD 90657, HD 186943 and HD 211853, which are characterized by a WR/O mass ratio of ~0.5 and periods of 6...10 days. We are doing so at three different levels of approximation: predicting the massive binary evolution through simple mass loss and angular momentum loss estimates, through full binary evolution models with parametrized mass transfer efficiency, and through binary evolution models including rotation of both components and a physical model which allows to compute mass and angular momentum loss from the binary system as function of time during the mass transfer process. All three methods give consistently the same answers. Our results show that, if these systems formed through stable mass transfer, their initial periods were smaller than their current ones, which implies that mass transfer has started during the core hydrogen burning phase of the initially more massive star. Furthermore, the mass transfer in all three cases must have been highly non-conservative, with on average only ~10% of the transferred mass being retained by the mass receiving star. This result gives support to our system mass and angular momentum loss model, which predicts that, in the considered systems, about 90% of the overflowing matter is expelled by the rapid rotation of the mass receiver close to the Omega-limit, which is reached through the accretion of the remaining 10%.

Constraining the mass transfer in massive binaries through progenitor evolution models of Wolf-Rayet+O binaries

Abstract: Since close WR+O binaries are the result of a strong interaction of both stars in massive close binary systems, they can be used to constrain the highly uncertain mass and angular momentum budget during the major mass transfer phase. We explore the progenitor evolution of the three best suited WR+O binaries HD 90657, HD 186943 and HD 211853, which are characterized by a WR/O mass ratio of $\sim$0.5 and periods of 6..10 days. We are doing so at three different levels of approximation: predicting the massive binary evolution through simple mass loss and angular momentum loss estimates, through full binary evolution models with parametrized mass transfer efficiency, and through binary evolution models including rotation of both components and a physical model which allows to compute mass and angular momentum loss from the binary system as function of time during the mass transfer process. All three methods give consistently the same answers. Our results show that, if these systems formed through stable mass transfer, their initial periods were smaller than their current ones, which implies that mass transfer has started during the core hydrogen burning phase of the initially more massive star. Furthermore, the mass transfer in all three cases must have been highly non-conservative, with on average only $\sim$10% of the transferred mass being retained by the mass receiving star. This result gives support to our system mass and angular momentum loss model, which predicts that, in the considered systems, about 90% of the overflowing matter is expelled by the rapid rotation of the mass receiver close to the $\Omega$-limit, which is reached through the accretion of the remaining 10%.

Mass transfer modeling of apricot kernel oil extraction with supercritical carbon dioxide

Abstract: Effects of process parameters on extraction of apricot (Prunus armeniaca L.) kernel oil with supercritical carbon dioxide (SC-CO2) were investigated. The parameters included particle size (mean particle diameter < 0.425–1.5 mm), solvent flow rate (1–5 g/min), pressure (300–600 bar), temperature (40–70 °C) and co-solvent concentration (up to 3.0 wt.% ethanol). The model of broken and intact cells represented the apricot kernel oil extraction well. Grinding was necessary to release the oil from intact oil cells of kernel structure. About 99% apricot kernel oil recovery was possible if particle diameter decreased below 0.425 mm. Two extraction periods were distinguished. The released oil on the surface of particles was extracted in the fast extraction period while the unreleased oil in the intact cells was extracted in the slow extraction period. The amount oil recovered in the slow extraction period was negligible compared to the amount recovered in the fast extraction period. Extraction rate in the fast extraction period increased with increase in solvent flow rate, pressure, temperature, and ethanol addition. Mass transfer coefficients in the fluid phase and in the solid phase changed between 0.7 and 3.7 min−1, and between 0.00009 and 0.0005 min−1, respectively. Mass transfer coefficient in the fluid phase increased with decrease in particle size and pressure, and with increase in solvent flow rate, temperature and ethanol concentration.

Thermal model of nanosecond pulsed laser ablation: Analysis of energy and mass transfer

Abstract: A thermal model of nanosecond laser ablation considering kinetics of surface evaporation is proposed. Equations concerning heat transfer in the target and associated gas dynamics are coupled by mass and energy balances at the surface and Knudsen layer conditions. Rigorous analysis of gas-dynamics related to condensation at the target surface is introduced in this model. Laser energy absorbed by the target is partly spent for evaporation and partly dissipated in the target by thermal conduction. The sum of thermal and kinetic energies of the gas phase is, usually, less than the energy of evaporation. The fraction of energy lost for target heating increases with decrease in laser fluence and attains 100% at the ablation threshold. The dependence of ablated depth on fluence is, thus, determined by energy partition between the solid and gas phases. The gas-dynamic flow accompanying ablation consists of a layer of compressed high-temperature vapor adjacent to the target that expands and pushes the ambient gas ...