Graduate Thesis Or Dissertation
 

High speed motion neutron radiography of two-phase flow

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/t148fn00k

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  • Current research in the area of two-phase flow utilizes a wide variety of sensing devices, but some limitations exist on the information which can be obtained. Neutron radiography is a feasible alternative to "see" the two-phase flow. A system to perform neutron radiographic analysis of dynamic events which occur on the order of several milliseconds has been developed at Oregon State University. Two different methods have been used to radiograph the simulated two-phase flow. These pulsed or "flash" radiography and high speed movie neutron radiography serve as a "snapshot" with an exposure time ranging from 10 to 20 milliseconds. In high speed movie radiography, a scintillator is used to convert neutrons into light which is enhanced by an optical intensifier and then photographed by a high speed camera. Both types of radiography utilize the pulsing capability of the OSU TRIGA reactor. In order to predict the visibility of the images in two-phase flow, two computer codes, an SN program and a Monte Carlo program, have been written. The visibility is expressed in the relative neutron density on the film. The principle difficulty with this type of neutron radiography is the fogging of the image due to the large amount of scattering in the water. This difficulty can be overcome by using thin regions for the two-phase flow, heavy water instead of light water, or an anti-scatter grid. The improvement using an anti-scatter grid has been modeled with the computer programs. The results obtained in this thesis demonstrate the feasibility of using neutron radiography to obtain data in two-phase flow situations. Both movies and flash radiographs have been obtained of air bubbles in water and boiling from a heater element. The neutron radiographs of the boiling element show both nucleate boiling and film boiling.
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