| In order to improve the efficiency and running cost of existing district cooling systems, it may be an ideal choice to use ice slurry as a substitute for traditional cold carrier fluid. When ice slurry is applied to district cooling systems, the pipe flow is an important component of ice slurry engineering application system. During ice slurry flow, the fluid presents special thermodynamic characteristics, such as heterogeneous flow patterns and latent heat release. And the special thermodynamic characteristics increase difficulty in characterizing ice slurry thermo-flow. Therefore, it is important to develop technologies that can describe ice slurry flow distribution, rheological behavior, flow resistance and heat transfer from the system design point of view.With the above objectives, this thesis uses solid-liquid flow theory and Computational Fluid Dynamics (CFD) as the main tool to study ice slurry thermodynamic characteristics in various pipes. Firstly, the present study treated ice particles interaction as the interaction of dense gas moleculars. And based on kinetic theory of granular flow, an Euler-Euler CFD model was applied to calculate ice slurry isothermal flow distribution. Then, the available flow characteristics were used to describe the rheological behavior piecewise. Meanwhile, the heterogeneous flow resistance was solved with Mixture model and piecewise rheological model. Further, by means of concentration diffusion equations and hypersurface equations, a ’quasi-two-dimensional’resistance model was derived from a three-dimensional Euler-Euler differential model. Finally, considering the heterogeneous ice slurry flow distribution characteristics and rheological properties, the ice slurry flow behaviour was experimentally investigated. And the experimental results were adopted to test the different flow resistance models. For ice slurry heat transfer behaviour, its phase change transfer characteristics and the effect on ice slurry flow distribution were discussed based on enthalpy-porosity model and Euler-Euler model.It is found that, based on kinetic theory of granular flow, the Euler-Euler CFD model was validated to be an effective tool for describing ice slurry flow in various pipes. In general, the ice slurry flow will become obviously heterogeneous with an increase of ice particle concentration and particle diameter but a decrease of flow velocity. In horizontal and vertical pipe flow, the phenomenon of ice particles repelling from the pipe wall appears in some conditions. In the horizontal90°elbow, it will gradually present a clear secondary flow image and the secondary flow action enhances the mixing between ice particles and carrier fluid. Considering the heterogeneous flow and the selected slurry composition, the ice slurry rheological behavior should be calculated piecewise for Newtonian and Non-Newtonian behaviour. When the flow velocity is high, Thomas equation can be appropriate for describing viscosity of ice slurry. With a decrease of flow velocity, the ice slurry can be treated as Bingham fluid. Based on the piecewise rheological model, the interaction between ice particles and pipe wall could be considered due to heterogeneous ice slurry flow. And the Mixture CFD model is able to calculate ice slurry flow resistance excellently. For further improving the solution efficiency of ice slurry flow resistance, a’quasi-two-dimensional’ resistance model was derived. The resistance model can not only realize the ice slurry flow resistance fast calculation, but also provide each flow phase resistance. For ice slurry heat transfer behaviour, the heat transfer process will be promoted with an increase of flow velocity and ice particle concentration. Meanwhile, melting of the ice particles makes the heterogeneous flow process be weakened, and the ice slurry flow resistance reduces along the pipe flow direction. |
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