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Title: Critical heat flux in non-circular channels
Author: Manning, Jonathan Paul
ISNI:       0000 0004 7427 7598
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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In the design of nuclear reactors adequate cooling must be demonstrated for all operational states as well as during and after design basis accidents. A key aspect of this design activity is the prediction of the Critical Heat Flux (CHF). The focus of the work in this thesis was the prediction of CHF in non-circular channels. The Look Up Table was used to analyse several burnout studies for non-circular channels in the literature and was found to be a poor predictive tool for these geometries. A conventional phenomenological model developed for round tubes was also shown to give poor predictions, with a mean error of 25% and root mean square error of 31%. Phenomenological modelling requires correlations for the mass transfer processes in annular flow. Deposition rates for annular flow in rectangular channels have been determined by an analysis of upstream burnout data. This showed good agreement with the rates in round tubes and validated this aspect of the phenomenological approach. The conventional one-dimensional phenomenological model was extended to include a variation in film thickness around the periphery. This model was fitted to experimental data from the literature for burnout in asymmetrically heated tubes. The low mean and root mean square errors, 0.8% and 3.0% respectively, confirmed the principle of the model. A flow visualisation rig has been designed and successfully operated to produce a flow-regime map for a rectangular channel of 25 mm by 2.5 mm. This map showed that the gas momentum flux required to cause annular flow was higher than that in round tubes. A wide range of annular flow conditions were observed and shown to be generally consistent with the phenomenological modelling approach. However it was seen that there were novel flow features that will need to be accounted for when predicting CHF in these geometries.
Supervisor: Walker, Simon ; Bluck, Mike Sponsor: Engineering and Physical Sciences Research Council ; Royal Navy
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral