Doctoral Dissertations (FESNS)
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Browsing Doctoral Dissertations (FESNS) by Author "Harvel, Glenn"
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Item CFD determination of fluid and geometry related localized heat transfer phenomena for supercritical water flow(2017-04-01) Farah, Amjad; Harvel, Glenn; Pioro, IgorThe proposed concept of Supercritical Water-cooled Reactor (SCWR) as part of the Generation IV International Forum aims to improve the thermal efficiency over current power plants by utilizing cooling water at pressures and temperature above the critical point. At supercritical conditions, however, the properties of the fluid can vary rapidly in response to changes in temperature and pressure, and without a phase change. One example is the specific heat, which exhibits a sharp peak at a point defined as the pseudocritical temperature. Computational Fluid Dynamics (CFD) is a numerical approach to model fluids in multidimensional space using the Navier-Stokes equations and databases of fluid properties to arrive at a full simulation of a fluid dynamics and heat transfer system. Turbulence models employed in CFD are a set of equations that determine the turbulence transport terms in the mean flow equations. They are based on hypotheses about the process of turbulence, and as such require empirical input in the form of constants or functions, in order to achieve closure. This work is conducted to further develop an understanding of supercritical water (SCW) flow by analyzing the flow- and geometry-dependent localized phenomena under supercritical conditions using CFD turbulence models. The numerical study employed the Realizable k-ε and the SST k-ω turbulence models. The created meshes are three dimensional to capture the multi-dimensional effects of SCW heat transfer phenomena. In the first part of the study, the turbulent Pr number effect on SCW heat transfer characteristics is determined by analyzing changes in fluid properties such as temperature profiles, turbulence intensity, and velocity in response to varying the turbulent Pr values in the CFD models. This investigation has shown the energy turbulent Pr to have the most effect on improving SCW heat transfer simulation results under the deteriorated heat transfer regime, by affecting the turbulence production in the fluid due to buoyancy forces. Buoyancy forces were also studied in downward flow under the same conditions and were shown to reduce the deterioration in heat transfer observed in upward flow. The second part involved an investigation of fluid property effects in complex geometries to determine important flow parameters that capture localized flow phenomena effects. Two geometries are considered: an annular channel with helical fins, and a tube with a sudden area change. The helicity of the first geometry did not appear to induce additional turbulence in the flow, compared to bare geometries. On the other hand, the sudden area change introduced large levels of turbulence, and while it dissipated quickly, it did show an enhancement in the heat transfer and lowered the outlet wall temperatures. These results can be used as a design input for SCWR fuel geometry design. As a result, this study contributes to the understanding of the SCW heat transfer fundamentals under normal and deteriorated regimes in bare and complex geometries, and identifies the areas of improvement in the related experimental work. Significant experimental work is needed to verify the findingsItem Characterization of eutectic In-Bi-Sn alloy (Field’s metal) for use in single and two-phase liquid metal flow in natural circulation systems(2015-04-01) Lipchitz, Adam; Harvel, GlennAn In-Bi-Sn eutectic alloy was characterized for the purpose of liquid metal natural circulation experiments. The alloy was chosen to reduce the power requirement and enhance the safety of these types of experiments. The initial characterization included the development of a method of fabrication, an investigation of the chemical compatibility with air, water, borosilicate glass, and stainless steel. An investigation to experimentally determine the thermo-physical properties (viscosity, density, specific heat capacity, and thermal conductivity) of the liquid metal was performed. A numerical model of the natural circulation loop was developed and compared to experimental results of a liquid metal natural circulation experiment.Item Specifics of forced-convective heat transfer to supercritical CO2 flowing upward in vertical bare tubes(2015-04-01) Saltanov, Eugene; Pioro, Igor; Harvel, GlennHeat transfer in the forced convection regime of fluids at supercritical conditions has been studied extensively for the past 60 years. The dominant approach to summarize the experimental results was by proposing empirical correlations for the data within the investigated range of parameters. It was soon realized by researchers worldwide that heat transfer coefficients become non-linear functions of wall and bulk-fluid temperatures at certain combinations of experimental parameters within the region of the peak of specific heat at supercritical pressures. Thus, it has become a standard approach to remove nonlinear experimental heat transfer coefficient values treating them as a sign of a deteriorated (as opposed to normal) heat transfer regime. There were recent attempts to address this shortcoming and extend the applicability of conventional empirical correlations to the deteriorated heat transfer regime. However, these attempts were not satisfactory. In this thesis, a new methodology has been developed that allows the use conventional empirical correlations without distinguishing entrance effects or deteriorated heat transfer regime. The methodology is based on binning experimental data according to the parameter X = (h_b - h_pc) / (q/G) and then combining correlations based on wall and bulk-fluid temperature on each bin to minimize RMS and maximal overprediction of heat transfer coefficients within each of the bins. Using this methodology, 95% of normal heat transfer data were predicted with a spread of ±19%, which is 1.74 times narrower compared to the prediction by the empirical correlations developed based on the conventional methodology and on the same data; while all the data (2786 points, including entrance effects and deteriorated heat transfer) were predicted with a spread of ±20% (based on 2σ-level). The data correlated based on the new methodology where obtained within the following range of experimental parameters: P = 7.58 – 8.91 MPa, Tb = 20 – 142 ˚C, Tw = 32 – 231 ˚C, G = 885 – 3048 kg/m2s, q = 26 – 616 kW/m2K, D = 8.1 mm. The experimental data were obtained based on a series of tests on supercritical CO2 flowing upwards in a bare tube at the MR-1 loop (located in Chalk River) of the former Atomic Energy of Canada Limited (AECL). Normal, deteriorated, and improved heat transfer regimes were covered in the experiments.