Change search
ReferencesLink to record
Permanent link

Direct link
Study of Heat and Mass Transfer to Determine Multicomponent Liquid Diffusion Coefficients in Partially Saturated Capillaries
Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. (Drying)
2007 (English)In: Experimental heat transfer, ISSN 0891-6152, E-ISSN 1521-0480, Vol. 20, no 2, 147-157 p.Article in journal (Refereed) Published
Abstract [en]

A study of simultaneous heat and mass transfer in partially saturated capillaries has been performed in order to develop a method that determines the matrix of multicomponent diffusion coefficients in liquid phase. The literature provides a semi-empirical formula developed by Bandrowski and Kubaczka [4] to calculate the matrix of multicomponent diffusion coefficients. The method separates the kinetic and thermodynamic contributions to mass transfer, and it contains an empirical exponent to improve the calculations. The present work attempts an estimation of the empirical exponent by studying the redistribution of compositions in an unsaturated nonisothermal capillary, taking into consideration the nonideality described by the matrix of thermodynamic factors. Two different ternary mixtures were tested at different temperature gradients and saturation degrees. The results reveal that the method is effective since specific values of the empirical exponent that modifies the matrix of thermodynamic factors were obtained for each system. In addition, the exponent seems to be dependent on temperature.

Place, publisher, year, edition, pages
2007. Vol. 20, no 2, 147-157 p.
Keyword [en]
liquid mixture, Maxwell-Stefan diffusion, saturation, temperature gradient
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-28891DOI: 10.1080/08916150601091464ISI: 000245351000006ScopusID: 2-s2.0-33947374335OAI: diva2:390465

QC 20110124

Available from: 2011-01-21 Created: 2011-01-21 Last updated: 2016-05-04Bibliographically approved
In thesis
1. Transport Coefficients during Drying of Solids containing Multicomponent Mixtures
Open this publication in new window or tab >>Transport Coefficients during Drying of Solids containing Multicomponent Mixtures
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study investigated the transport coefficients involved in mass and heat transfer during the drying of a porous solid partially saturated with multicomponent mixtures.  It included the coefficients governing liquid transport through the solid, the matrix of multicomponent diffusion coefficients in the liquid phase, and the effective thermal conductivity.  As it is not possible to determine these coefficients by theoretical considerations alone and considerable experimental work is required to determine them in a broad range of process conditions, the principle of this study has been the use of mathematical models complemented with some empirical parameters.  These empirical parameters were determined by comparison between measurements in specially designed experiments and the results of mathematical models that describe the process.  In addition, the application of the multicomponent diffusion coefficients is described in two cases where liquid diffusion is important: convective evaporation of a multicomponent stationary liquid film and a falling film.

To study liquid transport through the solid, isothermal drying experiments were performed to determine the transient composition profiles and total liquid content of sand samples wetted with ternary liquid mixtures with different initial compositions and temperatures.  A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both the gas and liquid phases was developed.  To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids were weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained considering that axial dispersion was included in the model.

To study the matrix of multicomponent diffusion coefficients in the liquid phase, the redistribution of liquid composition in a partially filled tube exposed to a longitudinal temperature gradient was analysed.  Experimental work was carried out using two main ternary mixtures with different initial compositions and temperature gradients.  Experimental data were compared with the results of a theoretical model that describes the steady-state liquid composition distribution in a partially filled non-isothermal tube to find the empirical exponent that modifies the matrix of thermodynamic factors.  Correlations for the exponents as a function of temperature were determined for each particular multicomponent mixture.

The effective thermal conductivity of a porous solid containing multicomponent liquid mixtures was studied by measuring the liquid composition, liquid content and temperature distributions in a cylindrical sample dried by convection from the open upper side and heated by contact with a hot source at the bottom side.  Simulations performed at a quasi steady state were compared with experiments to estimate the adjusting geometric parameter of Krischer’s model for effective thermal conductivity, which includes the contribution of the evaporation-diffusion-condensation mechanism. The results revealed that a resistance corresponding to a parallel arrangement between the phases seems to dominate in this case.

In the study of the convective drying of a multicomponent stationary liquid film, the equations describing interactive mass transfer were decoupled by a similarity transformation and solved simultaneously with a conduction equation by the method of variable separation.  Variations of physical properties along the process trajectory were taken into account by a stepwise application of the solution in time intervals with averaged coefficients from previous time steps.  Despite simplifications, the analytical solution gives a good insight into the selectivity of the drying process and is computationally fast.  On the other hand, numerical simulations of the convective evaporation of the multicomponent falling liquid film into an inert gas with a co-current flow arrangement of the phases almost always revealed a transition from liquid-phase-controlled conditions to a process in which neither the gas nor the liquid completely controls the evaporation.

The results obtained in this work would be useful in implementing models to improve the design, process exploration and optimisation of dryers by incorporating the solid-side effects to describe the drying of liquid mixtures along the whole process.

Place, publisher, year, edition, pages
Stockholm: KTH, 2011. xii, 85 p.
Trita-CHE-Report, ISSN 1654-1081 ; 5
capillary, conduction, convection, diffusion, evaporation, heat transfer, hydraulic conductivity, liquid film, liquid transport, mass transfer, Maxwell-Stefan diffusion coefficients, molar fluxes, phase equilibrium, temperature gradient, ternary mixture, thermodynamic factors
National Category
Chemical Engineering
urn:nbn:se:kth:diva-28897 (URN)978-91-7415-850-2 (ISBN)
Public defence
2011-02-11, E3, entréplan, Lindstedtsvägen 3, Stockholm, 10:00 (English)
QC 20110124Available from: 2011-01-24 Created: 2011-01-21 Last updated: 2012-03-23Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Gamero, RafaelMartínez, Joaquín
By organisation
Transport Phenomena
In the same journal
Experimental heat transfer
Chemical Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 51 hits
ReferencesLink to record
Permanent link

Direct link