dc.rights.license Restricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries. dc.contributor Podowski, M. dc.contributor Ji, Wei dc.contributor Sahni, Onkar dc.contributor Bolotnov, Igor dc.contributor Burdick, Gretchen dc.contributor.author Waite, Brian M. dc.date.accessioned 2021-11-03T09:00:57Z dc.date.available 2021-11-03T09:00:57Z dc.date.created 2018-07-27T15:11:21Z dc.date.issued 2018-05 dc.identifier.uri https://hdl.handle.net/20.500.13015/2215 dc.description May 2018 dc.description School of Engineering dc.description.abstract Overall, the study provides a greater understanding of multiphase flow in a nuclear reactor. The consistent physical approach that started with simpler problems and slowly expanded to a more involved analysis provided confidence and understanding of the models before proceeding to the next step. Rod bundle simulations with spacers have shown the importance of modeling the full geometry to capture more of the physical phenomena in the core. The modeling process must carefully consider the bubble size and shape as it has a large impact on the void distribution and development behavior downstream from the spacers. The numerical analyses examining the effects of spacer grids on boiling heat transfer is one of the first such studies. dc.description.abstract The most prevalent type of nuclear reactor in the world uses light water as the coolant and moderator. The vast wealth of knowledge already generated, due to years of research completed on light water reactors (LWRs), has greatly improved them from the original designs. The large amount of design and operation experience gained means that the use of light water reactors is likely going to continue for the foreseeable future. Improvements to the thermal hydraulics within these designs, using advanced models and tools, can allow current and future reactors to operate with higher fidelity. Nuclear reactor spacer grids have a large effect on the coolant distribution in the core. Historically, a majority of the effort in analyzing these complex designs focused on single-phase heat transfer rather than multiphase flow conditions. The focus of this work is to characterize and model the underlying physics governing multiphase flow and heat transfer around spacer grids in a rod bundle geometry. The complexity of the geometry introduces several new challenges. dc.description.abstract This work discusses the formulation of a two-phase dispersed field model and corresponding interfacial momentum closures, with an emphasis on the influence of bubble conditions within the channels. Reynolds-averaged Navier-Stokes level analyses are completed with the NPHASE-CMFD code which employs a multiphase formulation of the $k-\epsilon$ turbulence model. This study addresses many computational challenges that the complexity of the spacer grid geometry offers, such as grid formulation and boundary condition testing. dc.description.abstract An adiabatic two-field model was validated for flow around spacers in a 16-channel rod bundle (5x5) against experimental data. This methodology incorporates the uncertainties of the experimental methods and the bubble conditions within the flow. The large rod bundle simulations prove RANS methods are useful for these scenarios as a modest computational cost can achieve a high level of accuracy. The implications of non-fully-developed flow downstream of the spacer are thoroughly discussed. dc.description.abstract The adiabatic model consisting of the mass and momentum conservation equations is combined with the energy equation to show the effects of spacers on subcooled boiling heat transfer. A new model for wall temperature and bubble production in boiling channels is proposed. Results of the new model are compared against experimental data and show good agreement. Spacer grids have been shown to increase bubble condensation and reduce bubble production in the reactor channel due to the enhanced mixing caused by the flow blockages. dc.language.iso ENG dc.publisher Rensselaer Polytechnic Institute, Troy, NY dc.relation.ispartof Rensselaer Theses and Dissertations Online Collection dc.subject Nuclear engineering and science dc.title Mechanistic modeling of two-phase flow and heat transfer around light water reactor spacer grids dc.type Electronic thesis dc.type Thesis dc.digitool.pid 179052 dc.digitool.pid 179053 dc.digitool.pid 179054 dc.rights.holder This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author. dc.description.degree PhD dc.relation.department Dept. of Mechanical, Aerospace, and Nuclear Engineering
﻿