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Arc modeling for welding analysis

Description: A one-dimensional model of the welding arc that considers heat generation by the Joule effect and heat losses by radiation and conduction has been used to study the effects of various gases and gas mixtures currently employed for welding applications. Minor additions of low ionization potential impurities to these gases are shown to significantly perturb the electrical properties of the parent gas causing gross changes in the radial temperature distribution of the arc discharge. Such changes are reflected in the current density distribution and ultimately in the input energy distribution to the weldment. The result is observed as a variation in weld penetration. Recently published experiments and analyses of welding arcs are also evaluated and shown to contain erroneous data and results. Contrary to previous beliefs, the inclusion of a radiation loss term in the basic energy balance equation is important and cannot be considered as negligible in an argon arc at temperatures as low as 10,000/sup 0/K. The one-dimensional analysis of the welding arc as well as the evaluation of these earlier published reports helps to explain the effects of various gases used for welding, improves our understanding of the physics of the welding arc, and provides a stepping stone for a more elaborate model which can be applied to help optimize welding parameters.
Date: April 1, 1978
Creator: Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Arc-weld pool interactions

Description: The mechanisms involved in arc-weld pool interactions are extremely complex and no complete theory is presently available to describe much of the phenomena observed during welding. For the past several years, experimental and analytical studies have been undertaken at the Bettis Atomic Power Laboratory to increase basic understanding of the gas tungsten arc welding process. These studies have included experimental spectral analysis of the arc in order to determine arc temperature and analytical modeling of the arc and weld puddle. The investigations have been directed toward determining the cause and effects of variations in the energy distribution incident upon the weldment. In addition, the effect of weld puddle distortion on weld penetration was investigated, and experimental and analytical studies of weld process variables have been undertaken to determine the effects of the variables upon weld penetration and configuration. A review of the results and analysis of these studies are presented.
Date: August 1, 1978
Creator: Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Temperature and distortion transients in gas tungsten-arc weldments

Description: An analysis and test program to develop a fundamental understanding of the gas tungsten-arc welding process has been undertaken at the Bettis Atomic Power Laboratory to develop techniques to determine and control the various welding parameters and weldment conditions so as to result in optimum weld response characteristics. These response characteristics include depth of penetration, weld bead configuration, weld bead sink and roll, distortion, and cracking sensitivity. The results are documented of that part of the program devoted to analytical and experimental investigations of temperatures, weld bead dimensions, and distortions for moving gas tungsten-arc welds applied to Alloy 600 plates.
Date: October 1, 1979
Creator: Glickstein, S.S. & Friedman, E.
Partner: UNT Libraries Government Documents Department

Dynamic and static error analyses of neutron radiography testing

Description: Neutron radiography systems are being used for real-time visualization of the dynamic behavior as well as time-averaged measurements of spatial vapor fraction distributions for two phase fluids. The data in the form of video images are typically recorded on videotape at 30 frames per second. Image analysis of he video pictures is used to extract time-dependent or time-averaged data. The determination of the average vapor fraction requires averaging of the logarithm of time-dependent intensity measurements of the neutron beam (gray scale distribution of the image) that passes through the fluid. This could be significantly different than averaging the intensity of the transmitted beam and then taking the logarithm of that term. This difference is termed the dynamic error (error in the time-averaged vapor fractions due to the inherent time-dependence of the measured data) and is separate from the static error (statistical sampling uncertainty). Detailed analyses of both sources of errors are discussed.
Date: March 1, 1999
Creator: Joo, H. & Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Development of a scattering probability method for accurate vapor fraction measurements by neutron radiography. Revision 1

Description: Recent test results indicated drawbacks associated with the simple exponential attenuation method (SEAM) as currently applied to neutron radiography measurements to determine vapor fractions in a hydrogenous two-phase flow in a metallic conduit. The scattering component of the neutron beam intensity exiting the flow system is not adequately accounted for by SEAM, and this leads to inaccurate results. To properly account for the scattering effect, a neutron scattering probability method (SPM) is developed. The method applies a neutron-hydrogen scattering kernel to scattered thermal neutrons that leave the incident beam in narrow conduits but eventually show up elsewhere in the measurements. The SPM has been tested with known vapor (void) distributions within an acrylic disk and a water/vapor channel. The vapor (void) fractions deduced by SPM are in good agreement with the known exact values. Details of the scattering correction method and the test results are discussed.
Date: November 1, 1998
Creator: Joo, H. & Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Detailed analyses of dynamic and static errors in neutron radiography testing

Description: Neutron radiography systems are being used for real-time visualization of the dynamic behavior as well as time-averaged measurements of spatial vapor fraction distributions for two phase fluids. The extraction of quantitative data on vapor-liquid flow fields is a significant advance in the methodology of fundamental two-phase flow experimentation. The data in the form of video images are typically recorded on videotape at 30 frames per second. Image analysis of the video pictures is used to extract time-dependent or time-averaged data. The determination of the average vapor fraction requires averaging of the logarithm of time-dependent intensity measurements of the neutron beam (gray scale distribution of the image) that passes through the fluid. This could be significantly different than averaging the intensity of the transmitted beam and then taking the logarithm of that term. This is termed the dynamic error (error in the time-averaged vapor fractions due t the inherent time-dependence of the measured data) and is separate from the static error (statistical sampling uncertainty). The results provide insight into the characteristics of these errors and help to quantify achievable bounds on the limits of these errors. The static error was determined by the uncertainties of measured beam intensities. It was found that the maximum static error increases as liquid thickness increases and can be reduced by increasing the neutron source strength. The dynamic error increased with large fluctuations in the local vapor fractions and with increasing liquid thickness. Detailed analyses of both sources of errors are discussed.
Date: January 1, 1999
Creator: Joo, H. & Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Vapor fraction measurements in a steam-water duct at atmospheric pressure using neutron radiography

Description: Real-time neutron radiography has been used to study the dynamic behavior of two-phase flow and measure vapor fractions in a steam-water duct at atmospheric pressure. This unique experimental technique offers one the opportunity to observe and record on videotape now Patterns and transient behavior of two-phase flow inside opaque containers without perturbing the environment. The neutron radiographic technique is non-intrusive and requires no special transparent window region. Data are recorded simultaneously over a large area of interest. Image processing of the video data can be employed to measure bubble velocities and time-averaged and Instantaneous vapor fractions.
Date: November 11, 1994
Creator: Glickstein, S.S.; Murphy, J.H. & Hammond, R.B.
Partner: UNT Libraries Government Documents Department

Simultaneous neutron radiography and infrared thermography measurement of boiling processes

Description: Boiling of water at 1 to 15 bar flowing upward within a narrow duct and a round test section was observed using both neutron radiography and infrared (IR) thermography. The IR readings of the test section outer wall temperatures show the effects of both fluid temperature and wall heat transfer coefficient variations, producing a difference between liquid and two phase regions. The IR images, in fact, appear very similar to the neutron images; both show clear indications of spatial and temporal variations in the internal fluid conditions during the boiling process.
Date: February 1, 1997
Creator: Murphy, J.H. & Glickstein, S.S.
Partner: UNT Libraries Government Documents Department

Void fraction measurements using neutron radiography

Description: Real-time neutron radiography is being evaluated for studying the dynamic behavior of two phase flow and for measuring void fraction in vertical and inclined water ducts. This technique provides a unique means of visualizing the behavior of fluid flow inside thick metal enclosures. To simulate vapor conditions encountered in a fluid flow duct, an air-water flow system was constructed. Air was injected into the bottom of the duct at flow rates up to 0.47 I/s (1 cfm). The water flow rate was varied between 0--3.78 I/m (0--1 gpm). The experiments were performed at the Pennsylvania State University nuclear reactor facility using a real-time neutron radiography camera. With a thermal neutron flux on the order of 10{sup 6}n/cm{sup 2}/s directed through the thin duct dimension, the dynamic behavior of the air bubbles was clearly visible through 5 cm (2 in.) thick aluminum support plates placed on both sides of the duct wall. Image analysis techniques were employed to extract void fractions from the data which was recorded on videotape. This consisted of time averaging 256 video frames and measuring the gray level distribution throughout the region. The distribution of the measured void fraction across the duct was determined for various air/water mixtures. Details of the results of experiments for a variety of air and water flow conditions are presented.
Date: December 31, 1992
Creator: Glickstein, S. S.; Vance, W. H. & Joo, H.
Partner: UNT Libraries Government Documents Department

Void fraction measurements of acrylic discs via neutron radiography

Description: Simulation experiments have been initiated to verify that neutron radiography methods can accurately measure void fractions under various operating conditions in a steam-water flow channel. Recent neutron radiography experiments measured void fractions in an air-water channel at atmospheric pressure and room temperature conditions. Because steam-water densities at atmospheric pressure and low temperature vary significantly from those at high pressure and high temperature, questions have been raised as to the ability of the neutron radiographic technique to deduce vapor fractions under various steam-water operating conditions. In response to this concern, the macroscopic neutron cross sections presented by two extreme steam-water conditions were simulated using acrylic discs containing various size holes. Acrylic, which contains hydrogen as a major constituent closely resembles the properties of water as seen by a thermal neutron beam. Through holes appear to the neutrons as steam voids at atmospheric pressure. The effect of increased vapor density, (and neutron macroscopic cross section), which would occur at high pressure, was simulated by not drilling the holes completely through the discs. The shallow hole plus the remaining material was made to simulate a through hole filled with a vapor density on the order of 14% of water. The measured void fractions deduced from digitally imaged neutron radiographs are in good agreement with the expected values for the two cases studied.
Date: May 1, 1994
Creator: Glickstein, S. S.; Joo, H.; Vance, W. H. & Murphy, J. H.
Partner: UNT Libraries Government Documents Department

Interpreting neutron radiographs via computer simulation

Description: Computer simulation of the neutron radiographic process has been performed using Monte Carlo techniques. The results were compared to extensive experimental studies aimed at interpreting neutron radiographs of a special gage that contained varying amounts of water. The gage is intended to be used as a calibration device for measuring the water content in an enclosure under varying experimental conditions. Edge effects between regions of changing water thicknesses complicated the calibration procedure. Computer simulation of the experimental gage provided considerable insight into understanding and interpreting the radiographs. The results of computer analysis of the neutron radiographic testing of the gage were in excellent agreement with densitometer scans for most of the cases that were evaluate. The computer simulation indicated that the importance of edge effects, beam divergence, position of the film, source neutron energy and effects of water temperature can be accurately and effectively studied using Monte Carlo computer simulation of the neutron radiographic experiment This type of analysis can significantly help in the interpretation of neutron radiographs as well as in the design of experimental systems that use neutron radiography as a measuring tool. Detailed results of the experimental tests and analyses are provided.
Date: May 1, 1992
Creator: Glickstein, S. S.; Joo, H. & Vance, W. H.
Partner: UNT Libraries Government Documents Department

Vapor fraction measurements in a steam-water tube at up to 15 bar using neutron radiography techniques

Description: Real time neutron radiography has been used to study the dynamic behavior of two phase flow and measure the time averaged vapor fraction in a heated metal tube containing boiling steam water operating at up to 15 bar pressure. The neutron radiographic technique is non-intrusive and requires no special transparent window region. This is the first time this technique has been used in an electrically heated pressurized flow loop. This unique experimental method offers the opportunity to observe and record on videotape, flow patterns and transient behavior of two phase flow inside opaque containers without disturbing the environment. In this study the test sections consisted of stainless steel tubes with a 1.27 cm outer diameter and wall thicknesses of 0.084 cm and 0.124 cm. The experiments were carried out at the Pennsylvania State University 1 megawatt TRIGA reactor facility utilizing a Precise Optics neutron radiography camera. The inlet water temperature to the test section was varied between 120 to 170 C and the flow rate set to 2.3 l/min. T{sub sat} 200 C at these conditions. The tube was resistivity heated by passing high currents ({approximately}1,000 A) through the stainless steel wall. Scattering due to water in the 1 cm tube is significant and Monte Carlo calculations simulating the experiment were made to correct for this effect on the vapor fraction measurement. Details of the experimental technique, methods for analyzing the data and the results of the experiments are discussed.
Date: February 1, 1998
Creator: Glickstein, S.S.; Murphy, J.H. & Joo, H.
Partner: UNT Libraries Government Documents Department