Terrence C. Jensen

Using X-Rays for Multiphase Flow Visualization

Gas-liquid, gas-solid, liquid-solid, and gas-liquid-solid multiphase flows are difficult to visualize, characterize, and quantify because the systems are typically opaque. Invasive or noninvasive measurement methods are typically used for determining internal flow and transport characteristics of these complex flows. The difficulty with invasive methods is that they can alter the internal flow of a multiphase system causing interference with realistic process measurements. X-ray imaging provides one family of noninvasive measurement techniques used extensively for product testing and evaluation of static objects with complex structures. These techniques have been extended to visualize dynamic systems, such as those which characterize multiphase flows. This paper will describe a new X-ray flow visualization facility for large-scale multiphase flows. X-ray radiography and X-ray computed tomography of static and dynamic systems will be used to demonstrate system capabilities. Radiographic images will show bread dough rising, objects falling in a liquid, large bubbles rising in a 32 cm ID column of water, and operation of a 32 cm ID bubble column. X-ray computed tomography of a large static object will demonstrate visualization capabilities. X-ray computed tomography of a multiphase flow in a 32 cm bubble column will show local time-averaged gas holdup values for various operating conditions. Finally, challenges associated with X-ray stereographic imaging to capture time-resolved dynamic events will be outlined.Copyright

Human body radiography simulations : development of a virtual radiography environment

A simulation program for x-ray methods is discussed. Computational algorithms for definition of x-ray sources, interactions of x-rays with complex objects and formation of images are developed from first principles. Subject geometries can be accessed from CAD definitions or from CT sets. The principles underlying the image formation process are introduced and images in industrial and medical x-ray applications are displayed.

Visualizing Fluid Flows With X-Rays

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will be presented. When two X-ray sources and detectors simultaneously acquire images of the same process or object from different orientations, stereographic imaging can be completed; this type of imaging will be demonstrated by trickling water through packed columns and by absorbing water in a porous medium. Finally, local time-averaged phase distributions can be determined from X-ray computed tomography (CT) imaging, and this will be shown by comparing CT images from two different gas-liquid sparged columns.Copyright

RTSIM: A COMPUTER MODEL OF REAL-TIME RADIOGRAPHY

Real-time X-ray inspection is replacing film radiography in more and more applications. The rapid feedback provided by such systems greatly enhances throughput, especially in the case of complex objects requiring multiple views for complete inspection. When these systems are combined with powerful computing techniques, rapid image capture and enhancement and storage is possible. The productivity of these techniques would be increased with the ability to predict the sensitivity of a particular inspection without having to set up the equipment. Computer modeling of the inspection procedures can provide such information.

Using Energy Dispersive X-Ray Measurements for Quantitative Determination of Material Loss Due to Corrosion

Corrosion is a general term for the oxidation process of metal. In the case of aircraft, corrosion on aluminum airframe skin can often be recognized by dulling or pitting of an area, and sometimes by the white powdery deposit of aluminum corrosion product. Corrosion in these areas means loss of aluminum material from the airframe skin. Thus corrosion can seriously affect the structural integrity of an aircraft unless proper inspection and maintenance is systematically performed. During heavy structural aircraft maintenance, corrosions are still defined mostly in a qualitative rather than a quantitative sense. The qualitative evaluations are biased and unpredictable because corrosions are extremely hard to detect and to predict in their early stages of formation.

A Model of X-Ray Film Response

In the 100 years since Roentgen produced the first X-ray radiograph, many useful images have been produced for medical and industrial applications. To ensure high quality and reproducibility, standards have been developed to describe different types of film and methods of exposure and development[l]. It is desired to relate these film properties and other X-ray inspection parameters to a probability of detection for a certain type of flaw in a given object.

Cavitation From a Butterfly Valve: Comparing 3D Simulations to 3D X-Ray Computed Tomography Flow Visualization

Flow control valves may experience localized cavitation when the local static pressure drops to the liquid vapor pressure. Localized damage to the valve and surrounding area can occur when the vapor cavity collapses. Valve designs that reduce cavitation are based on empirical evidence and accumulated experience, but there are still considerable cavitation problems in industry. Valve designers may use computational fluid dynamics (CFD) to simulate cavitation in flow control valves, but model validation is challenging because there are limited data of local cavitation from the valve surface. Typically, the intensity of cavitation in a control valve is inferred from measurements of observable side effects of cavitation such as valve noise, vibration, or damage to the valve assembly. Such an indirect approach to characterizing cavitation yields little information about the location, degree, and extent of the cavitation flow field that can be used in CFD validation studies. This study uses 3D X-ray computed tomography (CT) imaging to visualize cavitation from a 5.1 cm diameter butterfly valve and compares the resulting vapor cloud to that predicted by CFD simulations. Qualitative comparisons reveal that the resulting cavitation structures are captured by the simulations when a small amount of non-condensable gas is introduced into the fluid and the simulations are completed in a transient mode.Copyright

Porosity detection in ceramic armor tiles via ultrasonic time-of-flight

Some multilayer armor panels contain ceramic tiles as one constituent, and porosity in the tiles can affect armor performance. It is well known that porosity in ceramic materials leads to a decrease in ultrasonic velocity. We report on a feasibility study exploring the use of ultrasonic time‐of‐flight (TOF) to locate and characterize porous regions in armor tiles. The tiles in question typically have well‐controlled thickness, thus simplifying the translation of TOF data into velocity data. By combining UT velocity measurements and X‐ray absorption measurements on selected specimens, one can construct a calibration curve relating velocity to porosity. That relationship can then be used to translate typical ultrasonic C‐scans of TOF‐versus‐position into C‐scans of porosity‐versus‐position. This procedure is demonstrated for pulse/echo, focused‐transducer inspections of silicon carbide (SiC) ceramic tiles.

Material Thickness Measurements Using Compton Backscatter

As the age of airplanes in the commercial fleet has increased, inspection and maintenance costs have steadily increased. The fact that aircraft have a fairly complicated structure and operate under a wide range of environmental conditions means that detection of the onset of structural deterioration is often difficult. In particular, corrosion of aluminum structures may begin on interior layers and be visually evident only at fairly advanced stages. Present maintenance requirements dictate that airplane skin (typical thickness 1mm) must be repaired if more than 10% thickness of the material has corroded[l]. A number of nondestructive inspection techniques are being applied to assist in early detection of corrosion in aircraft structures[2]. However, it is often difficult to determine whether these small thickness variations are due to corrosive material loss or to inherent variations introduced in the manufacturing process. X-ray scattering is sensitive to variations in material type and density, and hence offers the possibility of distinguishing between corroded material and intrinsic thickness variations.

Imaging a Gas-Sparged Stirred-Tank Reactor With X-Ray CT

X-ray computed tomography (CT) is used to explore the differences in gas dispersion in a gas-sparged stirred-tank reactor (STR) for different operating conditions. X-ray CT imaging is completed for various impeller speeds and gas flow rates in a 0.21 m ID STR made out of acrylic and equipped with a nylon Rushton-type impeller. From the CT slices, major differences in local time-averaged gas holdup can be seen, depending on the operating condition. Completely dispersed conditions have a relatively uniform holdup profile while flooded conditions have an increase in gas holdup towards the center of the tank. The high resolution of the X-ray system allows for visualizing time-averaged gas flow details such as low gas holdup regions directly above the impeller region under certain operating conditions and recirculation regions behind the baffles.Copyright