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Natural Circulation in Single and Multiple Channels
P. S. Adwani, Ph.D, 07
Supervisor(s): Kannan N. Iyer

Natural circulation in single and multiple channels P.S. Adwani, Ph. D., 2007, 190 pp, Energy Systems Engineering, IIT Bombay, Powai, Mumbai-400076. Supervisor(s): Kannan N Iyer Abstract This work is related to a single-phase natural circulation (NC) in single and multiple channels. The main concerns of this work include onset of bulk motion of fluid in NC loop from rest, multiple steady state solutions in multi-channel loops, and mapping of stability boundaries. The time delays in onset of bulk motion in NC loops determine the shift in mode of heat transfer and have significance. The parameters influencing the onset time were identified through governing equations for the transient situation. Using Buckingham-pi theorem, the number of non-dimensional parameters affecting the non-dimensional time of onset was found to be 11. The influences of individual parameters were determined for its selected range independently using numerical models. Ignoring the least effective and grouping the parameters of equal influence was carried out and a prediction correlation for the onset time was arrived at. This correlation could predict the experimental data of the present work and data from other works from literature fairly well. In multi-channel NC loop, the multiplicity of combinations of flow directions was predicted considering the total loop pressure drop to be zero. The algebraic equations so devised presuming the exponential temperature distribution in cooler predicted multiple flow ratios for the same heat input ratio. The predicted flow combinations in multi-channel NC loop was found to be experimentally realizable. This was demonstrated through the cases of unidirectional and bi-directional flows in a two-channel NC loop and a three-channel NC loop. In these cases, the predictions obtained through analysis for heat input ratios for given flow ratios were seen to have a fair match with experimentally observed values. A code developed for transient analysis of single phase NC was found to map almost identical stability boundaries with different node sizes. It was demonstrated that the code developed was able to capture transients with least numerical diffusion.