ALPHA CHEM-1325 Liquid Diffusion Coefficients Apparatus

Which overcomes the traditional problem of slow diffusion rates in liquids requiring long observation times, but without sacrificing accuracy or introducing convective effects.  Essentially, the cell consists of a honeycomb of accurately dimensioned capillaries, positioned between two liquids of differing concentration of the solute whose diffusion coefficient is to be determined.

In practice, a small volume of concentrated solution is placed on one side of the honeycomb, whilst the other side consists initially of a large volume of pure solvent (water). As diffusion of the solute occurs, the concentration within the larger volume increases, and is monitored with a conductivity sensor and meter.

The mixture is continuously stirred with a magnetic stirrer to ensure uniform concentration within the bulk liquid. Whilst the conductivity sensor may be readily calibrated for any required aqueous system, for introductory studies, dilute solutions of sodium chloride are recommended, for which conductivity data is provided.

Diffuser vessel:    Capacity 1L

Conductivity meter:    3 ranges 199.9µS to19.99mS

Computer output:    RS232

Bench mounted apparatus for the determination of diffusion coefficients of components in the liquid phase. The method employs a diffusion cell of capillary tubes so constructed to permit equi-molar counter diffusion between liquids of differing concentration each side of the cell without convective effects being present

Concentration changes on one side of the cell with respect to time are measured with the conductivity cell and the meter provided, and a magnetic stirrer keeps the bulk solution well mixed

Possible to obtain reproducible and accurate values of diffusivity within a period of 1.5 hours of practical laboratory time

Experimental Capabilities

Accurate measurement of mass transfer rates in the absence of convective effects.

Use of gas laws to calculate concentration differences in terms of partial pressures.

Use of Fick’s Law to deduce diffusion coefficients

from measurement of mass transfer rate and

concentration difference.

Simple analysis of a first order unsteady state process

Effect of concentration on diffusion coefficients

Gaining familiarity with the use of laboratory instruments to achieve accurate measurements of data required for industrial process design

ALPHA CHEM-1325 Liquid Diffusion Coefficients Apparatus

Which overcomes the traditional problem of slow diffusion rates in liquids requiring long observation times, but without sacrificing accuracy or introducing convective effects.  Essentially, the cell consists of a honeycomb of accurately dimensioned capillaries, positioned between two liquids of differing concentration of the solute whose diffusion coefficient is to be determined.

In practice, a small volume of concentrated solution is placed on one side of the honeycomb, whilst the other side consists initially of a large volume of pure solvent (water). As diffusion of the solute occurs, the concentration within the larger volume increases, and is monitored with a conductivity sensor and meter.

The mixture is continuously stirred with a magnetic stirrer to ensure uniform concentration within the bulk liquid. Whilst the conductivity sensor may be readily calibrated for any required aqueous system, for introductory studies, dilute solutions of sodium chloride are recommended, for which conductivity data is provided.

Diffuser vessel:    Capacity 1L

Conductivity meter:    3 ranges 199.9µS to19.99mS

Computer output:    RS232

Bench mounted apparatus for the determination of diffusion coefficients of components in the liquid phase. The method employs a diffusion cell of capillary tubes so constructed to permit equi-molar counter diffusion between liquids of differing concentration each side of the cell without convective effects being present

Concentration changes on one side of the cell with respect to time are measured with the conductivity cell and the meter provided, and a magnetic stirrer keeps the bulk solution well mixed

Possible to obtain reproducible and accurate values of diffusivity within a period of 1.5 hours of practical laboratory time

Experimental Capabilities

Accurate measurement of mass transfer rates in the absence of convective effects.

Use of gas laws to calculate concentration differences in terms of partial pressures.

Use of Fick’s Law to deduce diffusion coefficients

from measurement of mass transfer rate and

concentration difference.

Simple analysis of a first order unsteady state process

Effect of concentration on diffusion coefficients

Gaining familiarity with the use of laboratory instruments to achieve accurate measurements of data required for industrial process design