Engineering

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  • (1973) Foster, Brian
    Thesis
    The suspension of solid spheres in fully developed vertical pipe flow has been investigated between particle Reynolds numbers of 2 and 10000 and between pipe Reynolds numbers of 25 and 37000 for sphere to conduit diameter ratios ranging from 0.046 to 0.274. It was found that the drag coefficient obtained in the present study was higher than that reported for spheres suspended or traveling in bounded or unbounded quiescent fluids. The drag coefficient was found to depend upon the particle Reynolds number and the sphere to conduit diameter ratio. The radial position adopted by the spheres was found to be near the conduit axis at particle Reynolds numbers below 80 but near the conduit wall at particle Reynolds numbers greater than 200. A secondary sphere to conduit diameter ratio effect upon radial position was observed when spheres were suspended near the conduit wall. The spheres underwent four distinct modes of motion; the particular mode adopted was primarily dependent upon the particle Reynolds number with a secondary dependency upon the sphere to conduit diameter ratio. Transitions between modes occurred at particle Reynolds numbers which were approximately the same as values reported for changes in the wake structure behind spheres.

  • (1970) Wilkinson, D L
    Thesis


  • (1978) Huang, Ruey Shing Star
    Thesis

  • (1972) Rothman, George Paul
    Thesis
    The formulation of an adequate description of neutron populations in the presence of boiling moderator or coolant is attempted. Starting from a framework of comprehensive stochastic descriptions we concentrate on the special requirements of the boiling system such as the use of transport theory and the retention of heterogeneity in our model. Working equations are derived which show how adequate corrections for boiling can be made to the approximate models currently used. The detailed distribution of bubbles in a boiling system should be accounted for in accurate evaluations of criticality, especially where the bubbles are large. Evaluations of leakage, resonance escape probability and thermal absorption are modified by the detailed bubble distribution. Explicit corrections are given for simple examples, while inclusion of the effects into a practical criticality code, such as WIMS, is discussed. The second moments of the neutron population in the presence of boiling media are also described. The power spectral density arising from the fission process is evaluated, showing how this spectrum is affected by the boiling. Usually more important sources of neutron noise in a boiling reactor are the fluctuations in cross-sections and collision probabilities arising directly from random local void ages. This 'bubble noise' is evaluated with particular emphasis on the detection of onset of boiling in a channel or change in boiling regime. The use of Monte Carlo techniques in calculating neutron transport in boiling media is discussed in some detail. The applicability of the analyses of neutron means and variances to fast reactor situations is considered. The bulk of the work treats critical reactors. However, a treatment of transients and feedback effects is also included. A new analysis is suggested whereby means and variances throughout the transient can be evaluated without extreme difficulty. The concepts of stochastic stability are discussed.