Neutron Imaging Techniques Research Articles

A flow channel design procedure for PEM fuel cells with effective water removal

Proper water management in polymer electrolyte membrane (PEM) fuel cells is critical to achieve the potential of PEM fuel cells. Membrane electrolyte requires full hydration in order to function as proton conductor, often achieved by fully humidifying the anode and cathode reactant gas streams. On the other hand, water is also produced in the cell due to electrochemical reaction. The combined effect is that liquid water forms in the cell structure and water flooding deteriorates the cell performance significantly. In the present study, a design procedure has been developed for flow channels on bipolar plates that can effectively remove water from the PEM fuel cells. The main design philosophy is based on the determination of an appropriate pressure drop along the flow channel so that all the liquid water in the cell is evaporated and removed from, or carried out of, the cell by the gas stream in the flow channel. At the same time, the gas stream in the flow channel is maintained fully saturated in order to prevent membrane electrolyte dehydration. Sample flow channels have been designed, manufactured and tested for five different cell sizes of 50, 100, 200, 300 and 441 cm 2. Similar cell performance has been measured for these five significantly different cell sizes, indicating that scaling of the PEM fuel cells is possible if liquid water flooding or membrane dehydration can be avoided during the cell operation. It is observed that no liquid water flows out of the cell at the anode and cathode channel exits for the present designed cells during the performance tests, and virtually no liquid water content in the cell structure has been measured by the neutron imaging technique. These measurements indicate that the present design procedure can provide flow channels that can effectively remove water in the PEM fuel cell structure.

Capillary Pressure Properties of Gas Diffusion Materials Used in PEM Fuel Cells

Capillary pressure curve is used to account for the mass transport limitation in the porous gas diffusion layer (GDL) in modeling two-phase phenomena in conventional distributors. Various assumptions and approximations on capillary pressure curve have been made to develop models. To date the capillary pressure curve in gas diffusion medium in PEM fuel cell does not seem to have been obtained. In this study, volume displacement technique and neutron imaging technique that can obtain capillary pressure curve in gas diffusion material is described. An experimental data of capillary pressure curve of porous material used in PEM fuel cell will help two-phase models of PEM fuel cell to be more accurate in their predictions of fuel cell behaviors.

Development of a non-destructive neutron radiography technique to measure the three-dimensional soot deposition profiles in diesel engine exhaust systems

A technique was developed to non-destructively measure the three-dimensional soot deposition thickness profiles in diesel engine exhaust components using a digital neutron imaging technique. In this technique, the test component positioned on a rotating platform is exposed to a thermal neutron beam from a nuclear reactor and the flux transmitted through the test object is measured using a digital neutron imaging system. The thickness of the diesel soot is then determined by analyzing the attenuation of this neutron flux. The technique was applied here to an aluminum pipe that was fouled for approximately 12 h by diesel exhaust from a diesel generator. The analysis of the neutron images indicated that the average soot thickness in the fouled pipe decreased nonlinearly along the pipe. It was also found that the measurements using this technique were within 16% of the direct destructive measurements of the thickness determined after sectioning the pipe.

In situ neutron imaging technique for evaluation of water management systems in operating PEM fuel cells

This paper explores the method of neutron imaging as an experimental tool to perform in situ non-destructive analysis on an operating polymer electrolyte membrane hydrogen fuel cell. Neutrons are ideal for the imaging of hydrogen fuel cells because of their sensitivity to hydrogen-containing compounds such as water. This research focused on using imaging techniques to develop methods for testing and evaluating the water management system of a fuel cell. A real-time radiography dataset consisting of 1000 images at 2-s intervals was used to create a movie which showed water production, transport, and removal throughout the cell. This dataset was also analyzed to quantify and calculate the amount of water present in the cell at any time and masking techniques were used to differentiate between water in the cell flow channels and in the gas diffusion layer. Additionally, a tomography dataset allowed for the creation of a digital 3-dimensional (3-D) reconstruction of the dry cell which can be analyzed for structural defects.

New features in cold neutron radiography and tomography Part II: applied energy-selective neutron radiography and tomography

Abstract The neutron attenuation coefficient drops for many solid materials quite drastically at a defined cold neutron energy known as a Bragg-cut-off in the cross-section diagrams. In many cases, the drop in attenuation for the corresponding elements is significant and this behavior can be exploited to change the material contrast in radiography and tomography images by modifying the spectrum of the applied neutron beam. The energy-dependent experiments were performed at the Prompt Gamma-ray Activation beam line where the irradiation position is at the end of a curved neutron guide, which delivers cold neutrons from the spallation source SINQ (PSI, Switzerland). This beam position gave the opportunity to perform radiography and tomography at low neutron energies. An effective monochromatization of the primary neutron beam was obtained by using a neutron velocity selector. The intensity of the modified beam was still reasonable for radiography images at different neutron energies and the experiments were performed in relatively short measuring times. A variety of samples were studied to illustrate possible applications of energy-selective radiography and tomography. This new neutron imaging technique provided encouraging results and projects of developing permanent facilities for such investigations at PSI and FRM II are under study.

Developments in radiation imaging techniques

For centuries, scientists and engineers dreamed of being able to peer into the interiors of microscopic and macroscopic objects. A variety of imaging techniques, both invasive and non-invasive, have been developed to accomplish this goal. The present article provides an overview of our work on non-invasive imaging techniques being used and developed for basic and applied sciences. The details of various developments in setting up X-ray and neutron imaging techniques for applications in the Indian nuclear programme, development of two- and three-dimensional tomography for industrial applications, digital medical imaging, X-ray diffraction imaging for exploring the condensed matter at normal and high pressure conditions, X-ray holography for atomic resolution imaging, phase-sensitive imaging and imaging of transient phenomenon are discussed in this paper.

Neutron Imaging Technique for In Situ Measurement of Water Transport Gradients within Nafion in Polymer Electrolyte Fuel Cells

Water transport is an important consideration in the optimization of polymer electrolyte fuel cell (PEFC) performance, affecting both internal resistance and cathode polarization losses. Novel experiments are described using neutron radiography to measure water gradient profiles within Nafion® in an operating PEFC. Preliminary neutron intensity gradients show qualitative agreement with the expected response of membrane water content to changes in feed gas humidification and fuel cell current. Previous experimental measurements of similar water gradients have generally relied on “integral” measurements such as ac impedance spectroscopy which cannot probe details of the gradient within the membrane. This is one of the first “differential” measurements of water gradients within Nafion. © 1999 The Electrochemical Society. All rights reserved.

Study on neutron imaging techniques and processings for developing quantitative neutron radiography

Four kinds of existing arrangements of neutron radiography techniques and a newly proposed arrangement were examined to evaluate the removing efficiency of the scattered neutron and gamma-ray contaminant. Techniques of dispersion, channel and umbra arrangement were evaluated to obtain quantitative neutron attenuation coefficient. A new combination technique of the neutron absorbing honeycomb collimator and the double X-ray films has verified that the relationship between the neutron transmittance and object thickness is fairly expressed by a single exponential curve in a transmission range from 1.0 to 0.01.

Exploratory studies on neutron radiography with a small neutron source using a nuclear scintillation imaging technique

Neutron radiography based on mobile neutron sources need optimum utilization of available neutron fluxes which are usually lower compared to those available from reactors. For optimum utilization of such low flux devices, a sensitive neutron imaging technique is required. Such a neutron imaging system based on a Li 6F-ZnS scintillator screen has been developed using a pair of image intensifier tubes and a charge coupled device. This detector system has been employed to study the feasibility of neutron radiography using low neutron fluences. The main feature of this imaging system is its ability to detect individual neutron scintillation events with a higher degree of spatial resolution. In order to test the efficiency of this imaging system, a small scale moderator-collimator assembly was designed using a Pu-Be neutron source of strength ≈2 × 10 7 n/s. Details of this imaging system and results of some exploratory experiments for low fluence neutron imaging are presented in this paper.

High sensitivity neutron imaging system for neutron radiography with a small neutron source

Although neutron radiography is a very useful NDT technique. its widespread use has been limited due to the lack of a mobile neutron radiography system. One of the major requirements in designing such a system is the development of a low fluence neutron imaging technique. In recent years several groups in France, Japan and the USA have been working on such an imaging system. We report in this paper the development of such a neutron imaging system based on a Li 6F-ZnS scintillator screen using a pair of image intensifier tubes and a charge coupled device. This detector system has been employed to study the feasibility of neutron radiography using low neutron fluences. The main feature of this imaging system is its ability to detect individual neutron scintillation events with a ligh degree of spatial resolution. Details of this imaging system and the preliminary results obtained using a Pu-Be neutron source of strength ≈ 2 × 10 7 n/s are reported in this paper.

Advanced imaging techniques: A new deal for neutron physics

Among non-destructive evaluations and methodologies—the important set of analyses which preserve the integrity of the tested object—neutron imaging techniques, and neutron computerized tomography in particular, represent powerful tools. Although they have been considered more an amusement for scientists rather than an effective tool for engineers until few years ago, it can be stated that they can now provide valuable quantitative results in many circumstances of interest, being the only available choice in some specific cases. This wider interest and the attempt to give neutron imaging a certain prominence reflect themselves in the birth of an international group of people involved in the field of neutron research; the so-called ENRWG (European Neutron Radiography Working Group). Connected to a general interest and a diffuse curiosity in the fascinating interactive world of INTERNET there is also the possibility, since last year, to get information about neutron radiography state of the art and current projects from a free-access WWW site. As a consequence of these fervent activities, a new deal in studies of advanced materials, sources, detectors and algorithms is now growing to promote and to develop the capabilities of neutron imaging techniques after a long period during which the interest in neutron physics and in their applications was limited to selected specialists involved in the nuclear-energy production. The results of this effort will not be limited to improved technological processes, but will include an improved knowledge in relevant fields of nuclear and material science.

Novel Diagnostics for Laser Fusion II. Secondary Nuclear Reaction, X-ray and Neutron Imagings.

Secondary nuclear reaction measurements, high speed x-ray framing camera for study of implosion dynamics and 14MeV neutron imaging technique are reviewed. Secondary nuclear reaction measurements can be used to evaluate a Fermi degenerate state in an imploded super dense plasma.

Neutron-imaging technique for monitoring high-temperature plasma dynamics

A preliminary design for the adaptation of a pinhole experiment (PINEX) technique to the monitoring of the dynamics of high-temperature plasmas is described. Specifically, this imaging technique uses a thick aperture, an efficient radiation converter, and highly intensified television cameras to provide real-time viewing of radiation sources, such as the neutron emissions from d-d and d-t fusion reactions in controlled thermonuclear research devices. The neutron emission strengths,R ∼ 51015 n/sec, recently achieved at the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) should be sufficient for 3 to 6-cm spatial resolution and 10 to 100-msec time resolution using such a system. Such information should be useful for on-line optimization of the plasma and for quantitative evaluation of its performance.

Characteristics of uranium-oxide cathode for neutron streak camera

Detection efficiency and secondary electron yield of the uranium-oxide cathode for a neutron streak camera were measured and found to be 2.3×10−7–1.6×10−6 events/neutron/μm and 60–150/fission, respectively. These measurements were performed for 14-MeV neutrons from a D-T neutron source (OKTAVIAN) by using neutron-imaging techniques. By defocusing an image due to a single fission event, each electron from the cathode was clearly distinguished, and the number of electrons could be counted. From the neutron images in the streak-mode operation, time dispersions due to the electron transit-time spread fell in the range of estimated values.