André Bieberle

Data acquisition system for angle synchronized γ-ray tomography of rapidly rotating objects

We developed a fast read-out electronics for a gamma ray computed tomography radiation detector for measurements of two-phase flow distributions in rapidly rotating hydrodynamic machines. The electronics operates with a gamma ray detector comprising 320 single scintillation detector elements working in pulse counting mode. Digital pulses corresponding to gamma or x-ray absorption events in the scintillation crystals are counted with electronics implemented fully parallel in field programming gate array (FPGA) electronics. Data from these counters can be transferred to the measurement PC via a USB 2.0 interface. The design aim for the data acquisition electronics was to acquire data that then could be reconstructed as tomograms with 2 mm spatial resolution from objects rotating as fast as 1200 rpm. This requires approximately 800 tomographic projections during a single revolution in 50 ms. This aim has been achieved with an optimized read-out electronics that is able to transfer the data of all detector counters within 23 µs to the PC. As an example, in this paper we demonstrate the capability of the measurement system to reconstruct gas distributions in the turbine region of a stirred tank reactor at a stirrer speed of 1200 rpm.

Measurement of Fluid Distributions in a Rotating Fluid Coupling Using High Resolution Gamma Ray Tomography

Gamma ray tomography has been used to visualize fluid distributions in a rotating fluid coupling in different operation points at a pump speed of 780 rpm and lower turbine speeds. The gamma ray computed tomography system comprises a Cs-137 isotopic source and a high resolution gamma ray detector. An angle synchronized tomographic data acquisition technique was applied to produce sharp slice images from different positions along the coupling axis. The data have been used to assess the hydraulic behavior of the fluid coupling and to help improve our understanding of the flow structure development and its implications on torque transfer in such a device.

Compact high-resolution gamma-ray computed tomography system for multiphase flow studies

In this paper, a compact high-resolution gamma-ray Computed Tomography (CompaCT) measurement system for multiphase flow studies and tomographic imaging of technical objects is presented. Its compact and robust design makes it particularly suitable for studies on industrial facilities and outdoor applications. Special care has been given to thermal ruggedness, shock resistance, and radiation protection. Main components of the system are a collimated (137)Cs isotopic source, a thermally stabilised modular high-resolution gamma-ray detector arc with 112 scintillation detector elements, and a transportable rotary unit. The CompaCT allows full CT scans of objects with a diameter of up to 130 mm and can be operated with any tilting angle from 0° (horizontal) to 90° (vertical).

Temperature control design for a high-resolution gamma-ray tomography detector

In this paper, a thermal control design for a high-resolution gamma-ray computed tomography detector is presented. It accounts for the generation of heat produced by active electronic components as well as heat transfer from external heat sources. The development and implementation of this feature were motivated by stringent requirements for measurement accuracy at thermal hydraulic test facilities, where ambient thermal conditions are constantly changing. As a first step, the thermal behavior of the existing tomography detector was analyzed, critical components were identified, and different approaches for heat removal were tested. Eventually, an improved thermal detector design was elaborated and a controlled active cooling system was implemented. Performance tests proved its effectiveness and accuracy improvement.

Validation of high-resolution gamma-ray computed tomography for quantitative gas holdup measurements in centrifugal pumps

In this article, the capability of high-resolution gamma-ray computed tomography (HireCT) for quantitative gas–liquid phase distribution measurements in commercially available industrial pumps is experimentally investigated. The object of interest thereby operates under two-phase flow conditions. HireCT System comprises a collimated 137Cs isotopic source, a radiation detector arc with a multi-channel signal processing unit, and a rotary unit enabling CT scans of objects with diameters of up to 700 mm. The accuracy of gas holdup measurements was validated on a sophisticated modular test mockup replicating defined gas–liquid distributions, which are expected in impeller chambers of industrial centrifugal pumps under two-phase operation. Stationary as well as rotation-synchronized CT scanning techniques have been analyzed, which are both used to obtain sharply resolved gas phase distributions in rotating structures as well as non-rotating zones. A measuring accuracy of better than 1% absolute for variously distributed static gas holdups in the rotating frame has been verified with the modular test mockup using HireCT.

High-resolution two-phase flow measurement techniques for the generation of experimental data for CFD code qualification

Abstract Computational fluid dynamics simulations for two-phase flows are important in different fields of engineering and science. Since two-phase flows are inherently complex, also CFD modeling development requires special attention. The validation of model implementation and the derivation of physics based models for momentum, heat, and mass transfer in two-phase flow require experiments with generation of high-resolution measurement data. This, however, is a great challenge, since most standard flow measurement tools used in single phase flow situations, are not suited for multiphase flows. In this article we report on advanced imaging and measuring methods for two-phase flow experiments, which have been extensively used in the recent past to conduct experiments for two-phase flows at the Helmholtz-Zentrum Dresden-Rossendorf. In particular the application of wire-mesh sensors, ultrafast X-ray tomography, gamma ray tomography and positron emission tomography will be introduced and discussed.

Process diagnostics and non-destructive testing using high-resolution gamma-ray tomography

In this paper, a high-resolution gamma-ray computed tomography (CT) measurement system is presented that was developed to determine phase fractions and other flow parameters in industrial devices operated under real industrial conditions. From CT scans non-superimposed cross-sectional images are reconstructed, which show the local gamma-ray attenuation coefficients within the scanned object slice. An advanced fast read-out electronics facilitates 2-D visualization of rapidly rotating multiphase distributions, such as in stirred chemical reactors or hydrodynamic machines. Furthermore, the CT measurement system can be applied to non-destructive testing of high-density devices to achieve information about the structure of material, i.e. when exposed to mechanical stress.

Advanced process-synchronized computed tomography for the investigation of periodic processes

Computed tomography (CT) is known for giving cross-sectional images of a body. As tomographic scans require mechanical movement of components, data acquisition is commonly too slow to capture dynamic processes, which are faster than the acquisition time for a single image. Time-averaged angle-resolved CT imaging is a more recent method, which has demonstrated a capability to sharply image fast rotating machinery components by synchronizing data acquisition with rotation. However, in this modality, all information on static parts disappears. In this paper, a novel data acquisition approach is introduced that combines both CT imaging methods. Eventually, the developed method is exemplarily applied to the study of gas-liquid flow in an industrial centrifugal pump using high-resolution gamma-ray tomography imaging.

Study of Flow Behavior of Granular Material Inside Cylindrical Silo Using Ultrafast X-Ray Imaging Technique

Abstract This paper presents an application of an ultrafast electron beam X-ray CT scanner for investigating the gravitational flow behavior of granulates through cylindrical silo model. The CT scanner allows obtaining crosssectional images of the granular material distribution with a spatial resolution of approximately 1 mm and a time resolution of 2 kHz. In order to conduct a deep analysis of the granular flow concentration changes, two image processing algorithm steps were applied. The first step deals with preprocessing and re-centering stacks of raw images. The second step divides the preprocessed image into several concentric rings and calculates the mean value to study radial concentration changes. Independent analysis of granular concentration in each ring provides useful knowledge to study the silo discharging during mass flow and funnel flow.

Guest Editorial Special Issue on Sensors for Process Imaging

Sustainable industrial production requires the use of advanced sensors and controls. In many industrial activities, the sensing and monitoring of processes provides valuable information for controlling and decision-making strategies as well as supporting the understanding and modeling of the phenomena involved. Since safety and efficiency requirements are continuously growing, the quality of information is becoming more and more important. A current trend to accomplish such requirements is the use of imaging sensors and systems generating and processing multidimensional data to extract key information from the processes. Further work is required to ensure that these imaging technologies are actually providing information that can be easily adapted and used in process control. This requires a holistic look at these sensing methods and data analysis.