Russell David Luggar

Development of a high speed X-ray tomography system for multiphase flow imaging

This paper describes a new system for quantitative measurement of multiphase flow. It is based on the use of high speed (50 frames per second) X-ray tomographic imaging. This requires a new X-ray tube concept to be implemented, together with an annular detector array and data acquisition system. A pressurised krypton microgap detector is being developed to give 90% quantum efficiency for detection of K/sub /spl alpha// radiation from the silver anode X-ray tube. Results from simulation work are presented to justify the overall design strategy selected.

X-Ray Tubes

THESE tubes when very highly exhausted become capricious; at times they will do good work, while at other times, and without any known cause, they refuse to illuminate.

Examining nanoparticle assemblies using high spatial resolution x-ray microtomography

An experimental system has been designed to examine the assembly of nanoparticles in a variety of process engineering applications. These applications include the harvesting from solutions of nanoparticles into green parts, and the subsequent sintering into finished components. The system is based on an x-ray microtomography with a spatial resolution down to 5μm. The theoretical limitations in x-ray imaging are considered to allow experimental optimization. A standard nondestructive evaluation type apparatus with a small focal-spot x-ray tube, high-resolution complementary metal oxide semiconductor flat-panel pixellated detector, and a mechanical rotational stage is used to image the static systems. Dynamic sintering processes are imaged using the same x-ray source and detector but a custom rotational stage which is contained in an environmental chamber where the temperature, atmospheric pressure, and compaction force can be controlled. Three-dimensional tomographic data sets are presented here for sample...

Energy dispersive X-ray scatter for measurement of oil/water ratios

Abstract A technique for measuring oil and water concentrations in a bulk liquid using energy-dispersive X-ray scatter will be discussed. It is a requirement of the oil industry to measure accurately on-line the oil/water ratio of fluids extracted from oil fields across a wide range of gas–liquid flow regimes. To this end, a low cost, robust system is being developed using the energy dependence of coherent scatter as a probe to measure oil/water ratios. The scatter profiles are inherently broad and thus the relaxed energy resolution requirements allow the use of CdZnTe detectors suitable for field deployment. Energy-dispersive diffraction spectra of a range of oil–water emulsions have been measured. The ratio of the scattering into two energy windows, where the diffraction spectrum from oil is maximised and minimised with respect to that of water, is shown to be dependent upon the oil/water mixture ratios. The measurement is made independent of gas volume flow rate by normalisation of the scattered data to the transmission data. A relative error of 0.6% in the oil/water ratio measurement at 80% water fraction, and independent of gas fraction, is obtained.

X-ray tomographic imaging in industrial process control

Abstract Optimisation is essential in modern industrial and chemical process industries to increase efficiency and decrease downtime and maintenance costs. X-ray tomography is being developed to address these issues both on the microscopic level to characterise and quantify unit cell parameters and the macroscopic level for real time measurement of multiphase flow. The behaviour of macroscopic flow can be predicted using finite element simulations. Three-dimensional X-ray micro-tomography with 100 micron resolution has been developed and could be used to determine, for example volume fractions, contact surface area and particle size distribution and used as basic data for modelling of macroscopic systems. Additionally, a high speed X-ray tomography instrument is being developed to measure on-line multiphase flow in fast moving systems. This system does not require moving parts and is expected to operate at up to 50 frames per second. In addition to a practical implementation of this system in an industrial environment it can also be used as a cross-validation of the macroscopic models. Details of each system will be described and the suitability of the applications discussed.

Optimisation of X-ray micro-tomography for the in situ study of the development of plant roots

X-ray micro-tomography is a well-established technique for non-invasive, three-dimensional imaging of heterogeneous materials. A new application for high resolution low-dose tomography is the study of the development of plant roots. A cone-beam tomography system has been designed specifically to image the early development of plant seeds after germination, with a cubic voxel linear dimension of 100 /spl mu/m, over a sample diameter of 25 mm. The X-ray source is a 50 kVp silver target X-ray tube which is quasi-monochromaticaly filtered about the 22 keV characteristic K/sub a/ silver peak. A 10 cm diameter X-ray image intensifier (XRII) is used to collect the two-dimensional projection images. The rotating sample table incorporates a linear translation mechanism to eliminate ring artefact that is commonly associated with 3/sup rd/ generation tomography systems. Developing wheat seeds (Triticum aestivum) have been imaged using the system and the root lengths and volumes measured. The X-ray dose to the plants was also assessed and found to have no effect on the development of plant root.

High speed imaging of dynamic processes with a switched source x-ray CT system

Conventional x-ray computed tomography (CT) scanners are limited in their scanning speed by the mechanical constraints of their rotating gantries, and as such do not provide the necessary temporal resolution for imaging of fast-moving dynamic processes, such as moving fluid flows. The Real Time Tomography (RTT) system is a family of fast cone beam CT scanners which instead use multiple fixed discrete sources, and complete rings of detectors in an offset geometry. We demonstrate the potential of this system for use in the imaging of such high speed dynamic processes, and give results using simulated and real experimental data. The unusual scanning geometry results in some challenges in image reconstruction, which are overcome using algebraic iterative reconstruction techniques and explicit regularisation. Through the use of a simple temporal regularisation term, and by optimising the source firing pattern, we show that temporal resolution of the system may be increased at the expense of spatial resolution, which may be advantageous in some situations. Results are given showing temporal resolution of approximately 500I¼s with simulated data, and 3ms with real experimental data.

Industrial potential of Rayleigh scattered x rays for identification of low-Z materials

An investigation is being carried out into the potential use of elastic (or Rayleigh) scattered photons for the rapid identification of low atomic number materials. This technique has applications in the food industry for on-line quality control as well as areas such as security screening, materials recycling, and possible medical diagnostics.

Gas microstrip detectors for X-ray tomographic flow imaging

Abstract A investigation into the suitability of gas microstrip detector technology for a high-speed industrial X-ray tomography system is reported. X-ray energies in the region 20– 30 keV are well suited to the application, which involves imaging two-dimensional slices through gas/liquid multiphase pipeline flows for quantitative component fraction measurement. Stable operation over a period representing several hundred individual tomographic scans at gas gains of 500 is demonstrated using a Penning gas mixture of krypton/propylene.

Electronically gated multiemitter x-ray source for high-speed tomography

High speed X-ray tomography is being developed for on-line measurement of multiphase flow for well management in the oil industry. To reduce motion artifacts to acceptable levels a source is required that can scan about a 100 mm diameter pipe in approximately 20 ms, thus rendering a rotating source an impractical solution. In order to achieve a spatial resolution of 2 mm in the reconstructed image a total of 105 individual projections over a 210 degree arc are required. The large number of point sources means individual X-ray tubes are not practicable. Our solution is to use multiple electron beams where the active focal spot can be rapidly scanned across the target in an arc about the pipe with the use of electronic grids. This paper describes a prototype of such a tube designed, in the first instance, to cover a 30 degree arc and consisting of 13 individual emitters. Having proved the principle of operation a full system is now in the design stage and shall be briefly discussed.