Characterization of flowing dispersions

Details Characterization of flowing dispersions Characterization of flowing dispersions

1998-06-09

2001-04-03

Tung, T. (Department: 1743)

Chemistry: analytical and immunological testing

Measurement of electrical or magnetic property or thermal...

Of a liquid

C073S861080, C324S600000, C324S686000, C324S688000, C324S691000, C422S098000, C436S151000

Reexamination Certificate

active

06210972

ABSTRACT:

This invention relates to an apparatus and methods for characterizing the properties of a multiphase dispersion flowing through a tube, for example, for measuring the size and concentration of solid particulates suspended in a liquid phase, and including the use of such information for monitoring and controlling dispersion manufacturing processes.
The dispersion would normally consist of one discontinuous phase (solid, gas or liquid) present in the form of particles, droplets or bubbles mixed in a second continuous phase (normally, a liquid). It is desirable to be able to measure-on-line and continuously, the characteristics of the mixture (size and size distribution of the discontinuous phase, the number concentration of discontinuous phase, the velocity of the discontinuous phase etc) since these determine the properties of the mixture.
Such mixtures are commonplace in many types of manufacturing processes in the form of emulsions, colloidal dispersions and suspensions, and are widely utilised in the cosmetics, food, pharmaceutical, medical, detergents, chemical, minerals, nuclear. biotechnical, ceramics, paper and environmental sectors. For instance, the production of liquid-liquid emulsions in which the discontinuous phase is often oil-based and the continuous phase is aqueous-based requires careful control. One specific example is the production of a food (mayonnaise) emulsion in which control of the droplet size is crucial to the shelf-life and taste of the product and the ease of use for the consumer. Changes in manufacturing conditions (addition of chemical reagents or different hydrodynamic conditions) can change the droplet size distribution or alter the kinetics of coagulation or cause breakage of the droplets during processing. The present invention provides a means of monitoring such properties routinely thus allowing the data so generated to be used to control the manufacturing process and also further allow correlation of the emulsion properties to the customers perception of the product.
Conventional measurement methods for monitoring the size of particulates of this type (in the size range 0.5-1000 microns) normally use ex-situ methods, requiring removal of a sample from the process stream. Common methods include light-scattering, x-ray absorption or particle counting using electrical zone sensors (T Allen, Particle Size Measurement. 4th edn., Chapman & Hall, London, 1990). The samples so removed often have to be further prepared for analysis by diluting the dispersion with additional continuous phase, which may alter the dispersion properties and which introduces further sampling error, and is time consuming.
The present invention facilitates the in-situ characteristic of the properties of a multiphase dispersion.
The present invention also permits in-situ derivation of the size distribution and the shape distribution of the dispersed phase.
Further, the present invention allows such measurements to be performed on dispersions moving within tubes or conduits of small diameter (less than ca. 10 mm).
Further still, the present invention provides two and three dimensional imaging of multiphase dispersions.
The present invention also permits the structure of flowing dispersions to be discerned for quality assessment and process control processes.
According to a first aspect of the invention there is provided a microelectrical resistance tomography sensor comprising a substrate of electrically insulating material and having an aperture bounding a fluid flow path and sensor electrodes on the substrate disposed around the aperture so as to contact fluid in the flow path and connected to a cable connector on the substrate.
The sensor electrodes may be disposed regularly around the aperture.
The sensor electrodes may extend into the aperture and alone the flow path.
The aperture may be circular.
The sensor electrodes may be printed on to the substrate.
The sensor may comprise guard electrodes which stand between sensor electrodes. The guard electrodes may terminate short of flow path fluid contact.
The guard electrodes may be electrically connected, and may be earthed.
The substrate may comprise a wafer of uniform thickness and may be adapted for clamping between pipe sections defining the fluid flow path. The sensor may have apertures displaced from the fluid flow path bounding aperture.
According to a second aspect of the invention there is provided a sensor arrangement for microelectrical resistance tomography comprising a plurality of sensors according to the first aspect of the invention disposed along said fluid flow path.
The sensors may have similar electrode configurations, which may be aligned.
According to a third aspect of the invention there is provided a microelectrical resistance tomography system comprising a sensor according to the first aspect of the invention or a sensor arrangement according to the second aspect of the invention, in a tube, flow means to flow a fluid under investigation past the sensor or arrangement and electrical control and measurement means adapted to apply selectively oscillating current to the sensor electrodes and measure electric potentials across the sensor electrodes.
The system may comprise fluid flow control means adapted to control fluid flow through the tube.
The system may comprise analysis means adapted to analyse the electric potentials measured by the control and measurement means. The analysis means may comprise tomographic “image” store means adapted to store a succession of tomographic images of a flowing fluid.
The analysis means may comprise computer means evaluating image data in accordance with predetermined algorithms.
The analysis means may comprise a neural net.
According to a fourth aspect of the invention there is provided a method for characterizing a non-homogeneous flowing material in which the material is passed through a tube having a plurality of electrodes disposed around the flow, oscillating current is injected into the flow via selected ones of the electrodes and the voltage response on other electrodes is measured.
A plurality of measurements may be made using different selected electrodes for current injection and/or measurement. All possible combinations of electrodes may be used for current injection and measurement to give a plurality of measurements.
The different measurements may be effected within a time interval which is small in comparison with the time taken for a particle in the flow to pass through the measurement region.
A tomographic image may be derived from the plurality of measurements. A plurality of such tomographic images may be derived at predetermined time intervals.
The plurality of measurements, or quantities related to or derived therefrom, may be analysed by a neural net.


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Microelectrical tomography of flowing colloidal dispersions and dynamic interfaces, R.A. Williams et al, The Chemical Engineering Journal, 56 (1995) Month Unavailable 143-148.
Pp. 771-773 ofElectronics Letters, M. Wang et al, “Electrical Resistance Tomography of Metal Walled Vessels and Pipelines”, May 12, 1994, vol. 30, No. 10.

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