HEAT TRANSFER IN FLUIDS AT NEAR-CRITICAL PRESSURES: EXPERIMENTS AND MATHEMATICAL MODELING

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ABSTRACTNational Science FoundationProposal Number CTS-0553571Principal Investigator Warrier, GopinathAffiliation University of California-Los AngelesProposal Title Heat Transfer in Fluids at Near Critical Pressures: Experiments and Mathematical ModelingHigh pressure fluids are increasingly being promoted as heat transfer media in a number of thermal and chemical processes such as cryogenic cooling systems, thermosyphons, and large Supercritical Water-Cooled Reactors (SCWR). However, due to the rapid change in fluid properties close to the critical point, the experimental results have yielded both heat transfer enhancement and deterioration. The results for these contradictory results are not clearly understood. In this fundamental study, the heat transfer mechanisms involved during natural convection and boiling from microscale heater elements at near-critical pressures will be investigated. Both Schlieren photography and Particle Image Velocimetry will be employed. Models/correlations suitable for design purposes will be developed based on the experimental data. In addition to the experiments, numerical simulations using Direct Numerical Simulation (DNS) will also be performed. The temperature and velocity data obtained in the experiments will be used to validate the numerical simulations. Intellectual Merit: The proposed study will greatly advance the basic understanding of heat transfer in fluids at pressures near the critical pressure. The knowledge gained will provide researchers, in academia and industry, with a better understanding of the process. Potential innovative applications of this knowledge include miniature thermosyphons and heat pipes, cryogenic cooling systems, and in a broader sense SCWR thermal-hydraulics during shut down modes and reactor transients.Broader Impact: The project will support at least two undergraduate students from underrepresented groups to come and work in the laboratory during each summer. This will give the students a chance to gain valuable hands on experience and stimulate their interest in the field of thermal science and engineering. Two Ph.D. students will also be supported as part of this project. The research accomplished will be presented at conferences and published in archival journals for general dissemination by the technical community.