Eckhard Schleicher

Capacitance wire-mesh sensor for fast measurement of phase fraction distributions

We introduce a new wire-mesh sensor based on capacitance (permittivity) measurements. The sensor can be used to measure transient phase fraction distributions in a flow cross-section, such as in a pipe or other vessel, and is able to discriminate fluids having different relative permittivity (dielectric constant) values in a multiphase flow. We designed and manufactured a prototype sensor which comprises two planes of 16 wires each. The wires are evenly distributed across the measuring cross-section, and measurement is performed at the wire crossings. Time resolution of the prototype sensor is 625 frames per second. Sensor and measuring electronics were evaluated showing good stability and accuracy in the capacitance measurement. The wire-mesh sensor was tested in a silicone oil/water two-phase bubbly flow.

An ultra fast electron beam x-ray tomography scanner

This paper introduces the design of an ultra fast x-ray tomography scanner based on electron beam technology. The scanner has been developed for two-phase flow studies where frame rates of 1 kHz and higher are required. Its functional principle is similar to that of the electron beam x-ray CT scanners used in cardiac imaging. Thus, the scanner comprises an electron beam generator with a fast beam deflection unit, a semicircular x-ray production target made of tungsten alloy and a circular x-ray detector consisting of 240 CZT elements with 1.5 mm × 1.5 mm × 1.5 mm size each. The design is optimized with respect to ultra fast imaging of smaller flow vessels, such as pipes or laboratory-scale chemical reactors. In that way, the scanner is capable of scanning flow cross-sections at a speed of a few thousand frames per second which is sufficient to capture flows of a few meters per second velocity.

High resolution gamma ray tomography scanner for flow measurement and non-destructive testing applications

We report on the development of a high resolution gamma ray tomography scanner that is operated with a Cs-137 isotopic source at 662 keV gamma photon energy and achieves a spatial image resolution of 0.2 line pairs/ mm at 10% modulation transfer function for noncollimated detectors. It is primarily intended for the scientific study of flow regimes and phase fraction distributions in fuel element assemblies, chemical reactors, pipelines, and hydrodynamic machines. Furthermore, it is applicable to nondestructive testing of larger radiologically dense objects. The radiation detector is based on advanced avalanche photodiode technology in conjunction with lutetium yttrium orthosilicate scintillation crystals. The detector arc comprises 320 single detector elements which are operated in pulse counting mode. For measurements at fixed vessels or plant components, we built a computed tomography scanner gantry that comprises rotational and translational stages, power supply via slip rings, and data communication to the measurement personal computer via wireless local area network.

Design of an optical tomograph for the investigation of single- and two-phase pipe flows

We describe a fast optical tomography sensor which has been designed for the investigation of single- and two-phase flows in smaller flow cross-sections, such as pipes and bubble columns. It enables image acquisition at frame rates of up to 4.5 kHz at roughly 2 mm image resolution. The sensor works similar to a conventional CT of the fourth generation with 256 light emitters and 32 light receivers arranged about the objects cross-section. The light emitters are sequentially flashed while the light receiver intensities are recorded synchronously. A primary area of application is single-phase flows with dye tracers. Another potential application is the investigation of bubbly two-phase flows at low gas fractions. Principle tests have been made for both problems.

A Novel Needle Probe Based on High-Speed Complex Permittivity Measurements for Investigation of Dynamic Fluid Flows

For the investigation of multiphase or multicomponent flows, which are of interest, for instance, in oil extraction and processing or in chemical engineering, there are only few suitable measuring techniques. For this reason, we have developed a high-speed complex permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical permittivity at a high data rate (up to 20 000 samples/s). The performance of the system, as well as its ability to differentiate organic substances, has been analyzed. A time-resolved experiment in an oil-water-gas flow, as well as a two-substance mixing experiment in a stirred tank, is presented.

Optical measurement of nasal swellings

We introduce a new optical method to noninvasively and continuously measure the swelling process of the nasal mucosa whereby we use light of different wavelengths in the red and near-infrared range which is transilluminated through the nasal tissue and whose extinction is recorded as a function of time. From the temporal and spectral extinction data, we are able to extract characteristic parameters that describe the swelling process quantitatively by means of a regression-type parameter estimation algorithm. The method has been applied to the nasal allergen provocation test and verified on a limited number of volunteers.

Planar Array Sensor for High-speed Component Distribution Imaging in Fluid Flow Applications

A novel planar array sensor based on electrical conductivity measurements is presented which may be applied to visualize surface fluid distributions. The sensor is manufactured using printed-circuit board fabrication technology and comprises of 64 × 64 interdigital sensing structures. An associated electronics measures the electrical conductivity of the fluid over each individual sensing structure in a multiplexed manner by applying a bipolar excitation voltage and by measuring the electrical current flowing from a driver electrode to a sensing electrode. After interrogating all sensing structures, a two-dimensional image of the conductivity distribution over a surface is obtained which in turn represents fluid distributions over sensors surface. The employed electronics can acquire up to 2500 frames per second thus being able to monitor fast transient phenomena. The system has been evaluated regarding measurement accuracy and depth sensitivity. Furthermore, the application of the sensor in the investigation of two different flow applications is presented.

Experimental Investigation of Horizontal Gas–Liquid Stratified and Annular Flow Using Wire-Mesh Sensor

Stratified and annular gas–liquid flow patterns are commonly encountered in many industrial applications, such as oil and gas transportation pipelines, heat exchangers, and process equipment. The measurement and visualization of two-phase flow characteristics are of great importance as two-phase flows persist in many fluids engineering applications. A wire-mesh sensor (WMS) technique based on conductance measurements has been applied to investigate two-phase horizontal pipe flow. The horizontal flow test section consisting of a 76.2mm ID pipe, 18m long was employed to generate stratified and annular flow conditions. Two 16 16 wire configuration sensors, installed 17 m from the inlet of the test section, are used to determine the void fraction within the cross section of the pipe and determine interface velocities between the gas and liquid. These physical flow parameters were extracted using signal processing and cross-correlation techniques. In this work, the principle of WMS and the methodology of flow parameter extraction are described. From the obtained raw data time series of void fraction, cross-sectional mean void fraction, time averaged void fraction profiles, interfacial structures, and velocities of the periodic structures are determined for different liquid and gas superficial velocities that ranged from 0.03m/s to 0.2m/s and from 9m/s to 34m/s, respectively. The effects of liquid viscosity on the measured parameters have also been investigated using three different viscosities. [DOI: 10.1115/1.4027799]

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.