GB2147106A

GB2147106A - Method and apparatus for the measurement of the flow of particulate materials

Info

Publication number: GB2147106A
Application number: GB08423750A
Authority: GB
Inventors: Robert Garnett Green
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-09-19
Filing date: 1984-09-19
Publication date: 1985-05-01
Also published as: GB8423750D0; GB8325006D0; GB2147106B

Abstract

Apparatus for measuring the flow rate of particulate materials suspended in a hydrodynamic fluid has a pair of electrodes (4) forming a capacitive transducer (1) mounted on the carrier pipe (2). A first circuit (8) produces an output signal Cout dependent upon line static capacitance and a second circuit (9) produces an output DELTA Cout (a capacitive noise signal) dependent upon the concentration of particulate material in the fluid. The first and second output signals are combined in a microprocessor to obtain an indication of the flow rate and also the particle size. Two separate capacitor transducers may be employed each connected to a respective circuit. <IMAGE>

Description

SPECIFICATION Method and apparatus for the measurement of the flow of particulate materials This invention relates to methods and apparatus for the measurement of the flow of particulate materials. It finds especial application in the monitoring of slurries used for abrasive blasting.

In UK Patent 1 270 112 it has been proposed to measure the mass flow rate of particulate material conveyed hydrodynamically by a turbulently flowing fluid using a capacitive transducer through which the fluid flows. A noise signal was derived from the output of the transducer and an indication of the flow rate of the particulate material derived from the power of the noise signal.

It has now been found that the noise signal output from a capacitive transducer is also dependent on a particle size. Accordingly, the present invention provides apparatus for measuring the mass flow rate of particulate materials suspended in a hydrodynamic carrier fluid comprising a capacitive transducer having a conduit for the passage of a hydrodynamic carrier fluid, first measuring means coupled to the transducer to derive static capacitance measurement therefrom, second measuring means also coupled to the transducer to derive a capacitive noise signal dependent on the concentrations of particulate materials in said carrier fluid and combining means coupled to said first and said second transducer to give a first output signal dependent on the concentration of particulate materials in said carrier fluid and a second output signal indicative of the size of said particulate materials.

A specific application of this apparatus is in abrasive blasting. In this process a mixture of an abrasive (aluminium oxide or glass beads) and water are circulated in a machine by a centrifugal pump. The output from the machine (the blast nozzle) is directed at the target or workpiece.

The impact of the solids on the workpiece may produce several effects. It may machine by abrasion, polish by fine abrasion or increase the fatigue life of components intended to be highly stressed using a peening action.

In peening spherical particles are fired at a metal surface with sufficient energy to cause plastic deformation of the surface of the metal. This produces a high stress concentration in the surface which results in enhanced mechanical properties for the material. A typical example would be a turbine blade. Here the wet blast process is intended both to peen and impart a fine finish to the blade by means of the mechanical action of fine abrasive.

At the present time these machines are manually controlled and run with a predetermined cycle. It is desired to automate the process and this requires continuous monitoring of important factors in the process. One important factor is the concentration of the abrasive in the slurry; too low and the polishing process is too slow for the required production throughput, too high and either the blades are eroded or the machine blocks.

Another factor which is important in the process relates to the rate at which the grit breaks down during the blasting process.

The slurry, consisting of a mixture of water and abrasive, is never homogeneous. There is a continuously varying concentration of particles in the water passing through any specified pipe in the machine. The turbulant nature of the flow produces these concentration variations and the mixture may be considered as having a mean concentration and a superimposed variable concentration. This variable concentration is a natureal marker in the flow and may be termed "flow noise". It is a function of both velocity and solids concentration. Use is made of this latter fact in the capacitance noise transducer.

An embodiment of the invention will now be described by way of example applied to a particulate solid throughput system; Figure 2 shows the arrangement of the electrodes of a capacitive transducer for use in the apparatus of Fig. 1; Figure 3 is a block diagram of the electronic arrangement of the measuring system, and Figure 4 is a graph showing the results of measurements made using particulate materials of different consititution and size.

Referring now to the drawings the measuring system shown in Fig. 1 comprises a capacitive transducer 1 having a conduit 2 for the passage of particulate materials carried by a hydrodynamic carrier fluid 3. The arrangement of the transducer is depicted in Fig. 2.

Electrode plates 4 are formed around a rigid PVC pipe 5. The electrode plates are glued in position, surrounded by a metal screen 6, leads brought out for the transducer and the container forming the screen filled with a potting compound 7 for rigidity and to increase the mechanical strength of the pipe in the vicinity of the plates.

The output from the transducer comprises two components one dependent on the static value C of its electrode capacitance, the other dependent on the noise output signal C. A first transducer 8 (Fig. 3) produced an output signal dependent on the static electrode capacitance and a second transducer 9 produces an output signal dependent on the noise signal. (Conveniently the same transducer may be used and the two components derived by passirig the output signal respectively through a low-pass filter or a high-pass filter. The two signals are passed to a micro-processor 10 which will give an output signal from which can be derived a flow rate measurement correlated with particle size.

Fig. 4 illustrates measurements made using the electrical arrangement of Fig. 3. The abcissa shows the total solid present in a closed system and the ordinate represents the noise signal. The graphs show measurements for glass beads of 150-300 jum diameter A, alumina particles of 250 ,um diameter B, and alumina particles of 60-70 ,um diameter C.

It is to be understood that the term particulate materials also includes gases or nonmiscible liquids such as oil in water for which the measuring methods and apparatus are equally applicable.

Claims

1. Apparatus for measuring the flow rate of particulate material suspended in a hydrodynamic carrier fluid comprising a capacitive transducer having a conduit for the passage of a hydrodynamic carrier fluid, first measuring means coupled to the transducer to derive static capacitance measurement therefrom, second measuring means also coupled to the transducer to derive a capacitance noise signal dependent on the concentrations of particulate materials in said carrier fluid and combining means coupled to said first and said second transducer to give a first output signal dependent on the concentration of particulate materials in said carrier fluid and second output signal indicative of the size of said particulate materials.

2. Apparatus for measuring the flow rate of particulate material as claimed in Claim 1 wherein the transducer comprise a pipe having at least one pair of electrodes attached thereto.

3. Apparatus for measuring the flow rate of particulate material as claimed in either Claim 1 or Claim 2 having two pairs of electrodes attached to said pipe.

4. Appartus for measuring the flow rate of particulate material as claimed in Claim 1 and having a single pair of electrodes from which a first signal is derived directly and a second signal is derived by way of a high-pass filter.

5. Apparatus for measuring the flow rate of particulate material as claimed in any one of Claims 2 to 4 wherein said electrodes are coupled to a microprocessor to produce an output signal dependent on the flow rate correlated with particle size.

6. Apparatus for measuring the flow rate of particulate materials substantially as herein described with reference to and as shown in the accompanying drawings.