Mixing of two flows at varying temperatures in the secondary circuit of a liquid metal fast cooled reactor

This research work carried out a study on mixing of two flows in a T-junction pipe at varying temperatures in the secondary circuit of a French Phenix liquid metal cooled fast reactor. Mixing of flows is of vital significance in many engineering applications such as the nuclear reactor's operation and its design. Mixing of flows at different temperatures affects the performance and safety of fluid flow and heat transfer systems. The principal objective of this thesis is to investigate the fluid flow and heat transfer behavior of a T-junction pipe with mixing flows at different temperatures using the available industrial application. The computational fluid dynamics technique was applied by employing STAR CCM+ code. The STAR-CCM+ software was employed because it gives exact and productive multidisciplinary applications in a single integrated user interface. With the first specific objective being to determine the appropriate turbulence model, k-epsilon and k-omega turbulence models were employed for turbulence modelling and standard two-layer turbulence model which is a k-epsilon model emerged as the most appropriate turbulence model with the least mean deviation when compared with the experimental data. The temperature, pressure and mass flow rate distributions were also investigated in the T-junction pipe. The following findings were obtained. Non-uniform circumferential wall temperature distributions were obtained on the main pipe wall of the T-junction pipe. Axial temperature and pressure fluctuations (non-uniform axial temperature and pressure distributions) were obtained in the T-junction pipe. The cross-sectional temperature and pressure distributions were uniform at each axial location in the main pipe. Similar observations were made for mass flow rate distributions in the main pipe. The temperature and pressure fluctuation results obtained in the main pipe with T-junction confirmed other findings which adopted similar geometry. And these temperature and pressure fluctuations give indications thatpipes with T-junction for fluid flow and heat transfer might suffer from structural and mechanical degradation problems such as thermal fatigue, thermal stripping, thermal stratification, creep, corrosion and oxidation. This study which adopted liquid metal coolant as a mixing fluid and CFD tool to capture pressure and temperature fluctuations in a pipe with T-junction would guide the design of T-junction pipes for fluid flow and heat transfer and also add to the existing knowledge on fluid flow and heat transfer in pipes with T-junction. (author)