scholarly journals Measurements of the timescales for the mass transfer of water in glassy aerosol at low relative humidity and ambient temperature

2011 ◽  
Vol 11 (10) ◽  
pp. 4739-4754 ◽  
Author(s):  
H.-J. Tong ◽  
J. P. Reid ◽  
D. L. Bones ◽  
B. P. Luo ◽  
U. K. Krieger
Keyword(s):  
Mass Transfer ◽  
Glass Transition ◽  
Relative Humidity ◽  
Gas Phase ◽  
Mass Transfer Rate ◽  
Solution Viscosity ◽  
Bulk Solution ◽  
Size Change ◽  
Return To Equilibrium ◽  
Kinetics Of

Abstract. The influence of glassy states and highly viscous solution phases on the timescale of aerosol particle equilibration with water vapour is examined. In particular, the kinetics of mass transfer of water between the condensed and gas phases has been studied for sucrose solution droplets under conditions above and below the glass transition relative humidity (RH). Above the glass transition, sucrose droplets are shown to equilibrate on a timescale comparable to the change in RH. Below the glass transition, the timescale for mass transfer is shown to be extremely slow, with particles remaining in a state of disequilibrium even after timescales of more than 10 000 s. A phenomenological approach for quantifying the time response of particle size is used to illustrate the influence of the glassy aerosol state on the kinetics of mass transfer of water: the time is estimated for the droplet to reach the halfway point from an initial state towards a disequilibrium state at which the rate of size change decreases below 1 nm every 10 000 s. This half-time increases above 1000 s once the particle can be assumed to have formed a glass. The measurements are shown to be consistent with kinetic simulations of the slow diffusion of water within the particle bulk. When increasing the RH from below to above the glass transition, a particle can return to equilibrium with the gas phase on a timescale of 10's to 100's of seconds, once again forming a solution droplet. This is considerably shorter than the timescale for the size change of the particle when glassy and suggests that the dissolution of the glassy core can proceed rapidly, at least at room temperature. Similar behaviour in the slowing of the mass transfer rate below the glass transition RH is observed for binary aqueous raffinose solution droplets. Mixed component droplets of sucrose/sodium chloride/water also show slow equilibration at low RH, illustrating the importance of understanding the role of the bulk solution viscosity on the rate of mass transfer with the gas phase, even under conditions that may not lead to the formation of a glass.

scholarly journals Measurements of the timescales for the mass transfer of water in glassy aerosol at low relative humidity and ambient temperature

2011 ◽  
Vol 11 (2) ◽  
pp. 4843-4879 ◽  
Author(s):  
H.-J. Tong ◽  
J. P. Reid ◽  
D. L. Bones ◽  
B. P. Luo ◽  
U. K. Krieger
Keyword(s):  
Mass Transfer ◽  
Glass Transition ◽  
Relative Humidity ◽  
Sucrose Solution ◽  
Phenomenological Approach ◽  
Solution Viscosity ◽  
Bulk Solution ◽  
Initial State ◽  
Size Change ◽  
Kinetics Of

Abstract. The influence of glassy states and highly viscous solution phases on the timescale of aerosol particle equilibration with water vapour is examined. In particular, the kinetics of mass transfer of water between the condensed and gas phases has been studied for sucrose solution droplets under conditions above and below the glass transition relative humidity (RH). At RHs above the glass transition, sucrose droplets are shown to equilibrate on a timescale comparable to the change in environmental conditions. Below the glass transition, the timescale for mass transfer is shown to be extremely slow, with particles remaining in a state of disequilibrium even after timescales of more than 10000 s. A phenomenological approach for quantifying the time response of particle size is used to illustrate the influence of the glassy aerosol state on the kinetics of mass transfer of water: the time is estimated for the droplet to reach the halfway point from an initial state towards a disequilibrium state at which the rate of size change decreases below 1 nm every 10000 s. This half-time increases above 1000 s once the particle can be assumed to have formed a glass. The measurements are shown to be consistent with kinetic simulations of the slow diffusion of water within the particle bulk. Similar behaviour is observed for binary aqueous raffinose solution droplets consistent with the influence of a glass transition on mass transfer. Mixed component droplets of sucrose/sodium chloride/water also show slow equilibration at low RH, illustrating the importance of understanding the role of the bulk solution viscosity on the rate of mass transfer with the gas phase, even under conditions that may not lead to the formation of a glass.

scholarly journals Kinetics of Iron (II) Removal from Aqueous Solution Using Activated Dolomite

2007 ◽  
Vol 1 (1) ◽  
pp. 23-29 ◽  
Author(s):  
G.M. Walker ◽  
G. Connor ◽  
S.J. Allen
Keyword(s):  
Mass Transfer ◽  
Removal Rate ◽  
Bulk Solution ◽  
Experimental Investigations ◽  
Particle Diffusion ◽  
External Mass Transfer ◽  
Experimental Conditions ◽  
Intra Particle Diffusion ◽  
Stage Process ◽  
Kinetics Of

Experimental investigations were undertaken in batch kinetic systems, for the removal of iron (II) from aqueous solutions using activated dolomite. The effect of the extent dolomite activation on the dissolution of magnesium and calcium from the dolomite lattice was determined. Under optimum experimental conditions there was a direct linear relationship between magnesium dissolution and iron (II) removal from bulk solution. The experimental data were mathematically described using empirical external mass transfer and pseudo-intra-particle diffusion models. The data show conformity with a three stage process, with the iron (II) removal rate showing good correlation with external mass transfer (t < 1 min) and two rates of pseudo-intra-particle diffusion (1 < t < 90mins, and t < 90mins).

scholarly journals How to avoid mass transfer limitations in ozonation kinetics of phenylphenol isomers?

2016 ◽  
Vol 37 (1) ◽  
pp. 5-13 ◽  
Author(s):  
Magdalena Olak-Kucharczyk ◽  
Stanisław Ledakowicz
Keyword(s):  
Mass Transfer ◽  
Rate Constants ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Liquid System ◽  
Chemical Absorption ◽  
Mass Transfer Limitation ◽  
Fast Reactions ◽  
Liquid Mass Transfer ◽  
Kinetics Of

Abstract Ozonation is a heterogeneous process of chemical absorption often controlled by a gas-liquid mass transfer rate. This paper presents the results of kinetics in a reaction between phenylphenol isomers and ozone. The degradation of phenylphenol isomers during ozonation proceeds quite fast. In order to avoid the influence of mass transfer limitation the kinetics experiments were conducted in a homogenous liquid-liquid system. The second-order rate constants were determined using classical and competition methods, which are especially recommended for fast reactions. The determined rate constants at pH 2 using the two different methods are almost the same. The increase of pH causes an increase of rate constants for the reaction of phenylphenol isomers with ozone.

scholarly journals The evaporation kinetics of pure water droplets at varying drying rates and the use of evaporation rates to infer the gas phase relative humidity

2018 ◽  
Vol 20 (36) ◽  
pp. 23453-23466 ◽  
Author(s):  
Yong-yang Su ◽  
Rachael E. H. Miles ◽  
Zhi-ming Li ◽  
Jonathan P. Reid ◽  
Jiang Xu
Keyword(s):  
Relative Humidity ◽  
Gas Phase ◽  
Aerosol Particles ◽  
Pure Water ◽  
Analytical Models ◽  
Volatile Components ◽  
Water Droplets ◽  
Drying Rates ◽  
Kinetics Of ◽  
Evaporation Kinetics

Numerous analytical models have been applied to describe the evaporation/condensation kinetics of volatile components from aerosol particles for use in many applications.

scholarly journals The effect of turbulence on mass transfer rates of small inertial particles with surface reactions

2017 ◽  
Vol 836 ◽  
pp. 932-951 ◽  
Author(s):  
Nils Erland L. Haugen ◽  
Jonas Krüger ◽  
Dhrubaditya Mitra ◽  
Terese Løvås
Keyword(s):  
Mass Transfer ◽  
Gas Phase ◽  
Transfer Rate ◽  
Relative Velocity ◽  
Surface Reactions ◽  
Mass Transfer Rate ◽  
Navier Stokes ◽  
Inertial Particles ◽  
Dense Particle ◽  
Simulation Tools

The effect of turbulence on the mass transfer between a fluid and embedded small heavy inertial particles that experience surface reactions is studied. For simplicity, the surface reaction, which takes place when a gas phase reactant is converted to a gas phase product at the external surface of the particles, is unimolar and isothermal. Two effects are identified. The first effect is due to the relative velocity between the fluid and the particles, and a model for the relative velocity is presented. The second effect is due to the clustering of particles, where the mass transfer rate is inhibited due to the rapid depletion of the consumed species inside the dense particle clusters. This last effect is relevant for large Damköhler numbers, where the Damköhler number is defined as the ratio of the turbulent and chemical time scales, and it may totally control the mass transfer rate for Damköhler numbers larger than unity. A model that describes how this effect should be incorporated into existing simulation tools that utilize the Reynolds averaged Navier–Stokes approach is presented.

scholarly journals Modeling of kinetics of drying process of polycaproamide granules considering its sorption properties

2018 ◽  
Author(s):  
Marina Sergeevna Maklusova ◽  
Maria Konstantinovna Kosheleva ◽  
Olga Roaldovna Dornyak
Keyword(s):  
Mathematical Modeling ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Moisture Content ◽  
Gas Phase ◽  
Heat And Mass Transfer ◽  
Sorption Properties ◽  
Convective Drying ◽  
Drying Process ◽  
Kinetics Of

The object of research is a fiber-forming polymer - polycaproamide. The process of drying of polycaproamide granules, after aqueous extraction of low-molecular compounds from them, is an important stage of producing of polyamide fiber nylon and largely determines the quality of the target product. To obtain a high-quality fiber, the drying of the granules should provide a sufficiently high degree of its dehydration. The average final moisture content of the material should be no more than 0.1%. With a low moisture content, the drying process slows down, so the calculation of the kinetics of dewatering of granules can not be carried out using a constant effective mass-transfer coefficient (moisture diffusion). In this paper we present a calculation technique for determining two local parameters of mass transfer: the water diffusion coefficient in polycaproamide (as a liquid) and the so-called criterion for phase transitions, which depend on the moisture content of the material and are determined by its sorption properties. The report presents the results of numerical calculations illustrating the development of two-dimensional fields of moisture content, temperature, pressure and vapor concentration in the vapor-gas phase for cylindrical granules in convective drying. To describe the processes of heat and mass transfer during the drying of granules, a nonstationary nonlinear 2D model is used that includes transport equations averaged over the microvolume of the material: the liquid phase transfer equation; heat equation; equation for vapor-gas phase pressure; equation for the concentration of the vapor component. The nonstationary nonlinear conjugate mathematical model is studied numerically. A feature of the presented model is the possibility of an analytical calculation of the local mass transfer coefficients of a liquid, taking into account the sorption properties of the material, the permeability coefficient and the local values ​​of humidity and temperature. Determination of the local coefficients of moisture transfer is carried out on the basis of the formulas obtained in the analysis of a more general mathematical model of heat and mass transfer carried out based on the mechanics of multiphase systems developed in the works of R.I. Nigmatulin, and S. Whitaker. The structure of the samples was investigated by three independent methods in order to obtain the most complete idea of ​​it and to compare the obtained characteristics. The isotherms of the sorption of polycaproamide were obtained experimentally on a vacuum sorption plant with Mac-Ben-Bakr weights. Comparison of the results of mathematical modeling of heat and mass transfer in the granule and data of the laboratory experiment on the kinetics of polycaproamide granule drying showed good agreement between the calculated and experimental data. The constructed mathematical model allows to form energy-efficient resource-saving regimes for drying granules of polycaproamide.Keywords: convective drying, mathematical modeling, polycaproamide.

Modeling of aerated upflow fixed bed reactors for nitrification

1999 ◽  
Vol 39 (4) ◽  
pp. 85-92 ◽  
Author(s):  
J. Behrendt
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Liquid Phase ◽  
Gas Phase ◽  
Fixed Bed ◽  
Fixed Bed Reactor ◽  
Bulk Liquid ◽  
Initial Value ◽  
Fixed Bed Reactors ◽  
Number Of Cells

A mathematical model for nitrification in an aerated fixed bed reactor has been developed. This model is based on material balances in the bulk liquid, gas phase and in the biofilm area. The fixed bed is divided into a number of cells according to the reduced remixing behaviour. A fixed bed cell consists of 4 compartments: the support, the gas phase, the bulk liquid phase and the stagnant volume containing the biofilm. In the stagnant volume the biological transmutation of the ammonia is located. The transport phenomena are modelled with mass transfer formulations so that the balances could be formulated as an initial value problem. The results of the simulation and experiments are compared.

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