| A comprehensive numerical model is developed to simulate the dynamic processes of bulk evaporation and condensation in an encapsulated container, associated with internal heat generation under different gravitational strengths. A complete set of equations governing the conservation of mass, momentum and energy is solved. The thermal performance of a multi-phase nuclear fuel element at zero gravity, micro-gravity, and normal gravity is investigated. In the simulation, the numerical solutions have revealed much useful information, including the evolution of the bulk liquid-vapor phase change process, the evolution of the liquid-vapor interface, the formation and development of the liquid film covering the side wall surface, the temperature distribution, the convection flow field, and the strong dependence of the thermal performance of such multi-phase fuel cells on the gravity conditions.; In regard to the development of computational techniques, the internal energy formulation for the constant volume phase change process is proposed. The heat transfer mechanism for this type of phase change problem, including the convection effect induced by the density change, is analyzed and discussed. The computational performance of the internal energy formulation is evaluated. The performance of two update methods for the vapor phase fraction, the E-based and T-based methods, is investigated. Simulation of a one-dimensional conduction-driven bulk evaporation and condensation problem is performed and the evolution of the phase change process is obtained.; Some natural convection problems with or without internal heating in the single-phase and two-phase systems are studied. The solutions agree quite well with benchmark solutions and experimental results. It is revealed that interactions between the convection cells in liquid and vapor phases can substantially complicate the flow fields and the computational modeling. |
