R G Green

Velocity and mass flow rate profiles of dry powders in a gravity drop conveyor using an electrodynamic tomography system

This paper describes measurements made on a gravity drop conveyor using two arrays of axially spaced electrodynamic sensors to measure axial velocities close to the wall of the conveyor and velocity profiles both of flowing sand and of plastic beads. The level of correlation obtained using pixels is investigated. The velocity profile is combined with a tomographic concentration profile to estimate the mass flow profile, which is summed over the measurement cross section to estimate the mass flow rate. A calibration of the tomographically determined mass flow rate versus the actual mass flow rate is presented.

Optical sensor configurations for process tomography

This paper describes an investigation into the optimum design of optical fibre sensing arrays to be incorporated in an optical tomographic measurement system for on-line monitoring of particles and droplets. Two approaches are considered to cover opaque and transparent materials; optical path length and optical attenuation. Four flow models are investigated: single-pixel flow representing a single particle or droplet, two-pixel flow as a simple check on aliasing in the reconstructed image, half flow representing half the sensing cross section filled with material and full flow, where the whole sensing cross section is full of material. Six projection geometries of the fibre sensors are considered. For tomographic imaging, the forward problem, which assumes particles are placed in specific places in the measurement cross section and calculates voltage outputs for the individual sensors, is modelled. The solutions from the forward problem are used to solve the inverse problem, which uses actual sensor voltage readings to estimate the spatial distribution of the material in the measurement cross section. The solution of the inverse problem is used to derive the linear back projection (LBP) and filtered LBP algorithms. In order to improve image quality, a hybrid reconstruction algorithm is implemented. This algorithm first checks if any sensors read zero and sets (locks for this estimation) all pixels associated with them to zero (no material). The algorithm then proceeds as for the LBP.

Further development of a tomographic imaging system using optical fibres for pneumatic conveyors

This paper describes the further development of optical sensor hardware for a process tomography system in which emitters and detectors are used to exploit the optical characteristics of multiphase flow regimes. The optical arrangement is described and the importance of fibre beam position discussed. The proportion of the measurement volume interrogated by the beams is derived. The response of a single fibre is shown followed by a reconstructed concentration profile.

Concentration measurements of bubbles in a water column using an optical tomography system

Optical tomography provides a means for the determination of the spatial distribution of materials with different optical density in a volume by non-intrusive means. This paper presents results of concentration measurements of gas bubbles in a water column using an optical tomography system. A hydraulic flow rig is used to generate vertical air-water two-phase flows with controllable bubble flow rate. Two approaches are investigated. The first aims to obtain an average gas concentration at the measurement section, the second aims to obtain a gas distribution profile by using tomographic imaging. A hybrid back-projection algorithm is used to calculate concentration profiles from measured sensor values to provide a tomographic image of the measurement cross-section. The algorithm combines the characteristic of an optical sensor as a hard field sensor and the linear back projection algorithm.

Concentration profiles in a gravity chute conveyor by optical tomography measurement

This paper describes an investigation into the use of optical fibre sensors in a tomographic measurement system designed to measure the flow of dry solids in gravity drop and pneumatic conveyors. A simple model of the system is provided and used to predict the response of individual sensors and the full system. Results are provided which show the model is acceptable for use in a gravity conveyor. The system is used to provide tomographic images of solid concentration within a gravity chute.

Image analysis in dual modality tomography for material classification

A dual modality tomographic system is described for material classification in a simulated multi-component flow regime. It combines two tomographic modalities, electrical current and light, to image the interrogated area. Derived image parameters did not allow material classification. PCA analysis was performed on this data set producing a new parameter set, which allowed material classification. This procedure reduces the dimensionality of the data set and also offers a pre-processing technique prior to analysis by another classifier.

Optical fibre sensors for imaging concentration profile

The work presented here aims to investigate the use of optical fibre sensors arranged in multiple projections around a vertical transparent flow pipe for measurement of gas bubbles being conveyed by water. Light is injected through the measurement section and detected by fibre optic sensors, which transfer the light energy to photodiodes. These provide an electrical output, which is amplified, signal processed and fed to a PC for further analysis. The sensors measure the changes in absorption or attenuation of the conveyed material and information obtained in this way allows an image of the cross-section of the flow to be reconstructed by a computer.

On-line viscometer for measurement in the range 1 to 100 Pa s

The authors describe an on-line viscometer which has no moving mechanical parts. Measurements of the differential pressure developed along the measurement section and the temperature of the liquid are combined with the axial velocity of the test liquids to determine their mass/volume flow rates and viscosities. Results are presented for glucose syrup and melted chocolate.

Lensed optical fiber sensors for on-line measurement of flow.

This paper describes a system using lensed optical fiber sensors that are arranged in the form of two orthogonal projections. The sensors are placed around a process vessel for upstream and downstream measurements. The purpose of the system is for on-line monitoring of particles and droplets being conveyed by a fluid. The lenses were constructed using a custom heating fixture. The fixture enables the lenses to be constructed with similar radii resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. By collimating radiation from two halogen bulbs, radiation can be obtained by the sensors with radiation intensity related to the nature of the media. Each sensor interrogates a finite section of the measurement section. Each sensor provides a view. Parallel sensors provide a projection. Signal processing is carried out on the measured data in the time and frequency domains to investigate the latent information present in the flow signals.

Optical-fibre sensor for process tomography

Abstract This paper describes an investigation into the use of optical-fibre sensors in a tomographic measurement system, designed to measure the flow of dry solids in gravity-drop and pneumatic conveyors. A simple model of the system is provided and used to predict the response of both individual sensors and the full system. Results are provided which show that the model is acceptable. The system is used to provide tomographic images of solid concentration within a gravity conveyor.