Direct Numerical Simulation and Visualization of Subcooled Pool Boiling

A direct numerical simulation of the boiling phenomena is one of the promising approaches in order to clarify their heat transfer characteristics and discuss the mechanism. During these decades, many DNS procedures have been developed according to the recent high performance computers and computational technologies. In this paper, the state of the art of direct numerical simulation of the pool boiling phenomena during mostly two decades is briefly summarized at first, and then the nonempirical boiling and condensation model proposed by the authors is introduced into the MARS (MultiInterface Advection and Reconstruction Solver developed by the authors). On the other hand, in order to clarify the boiling bubble behaviors under the subcooled conditions, the subcooled pool boiling experiments are also performed by using a high speed and high spatial resolution camera with a highly magnified telescope. Resulting from the numerical simulations of the subcooled pool boiling phenomena, the numerical results obtained by the MARS are validated by being compared to the experimental ones and the existing analytical solutions. The numerical results regarding the time evolution of the boiling bubble departure process under the subcooled conditions show a very good agreement with the experimental results. In conclusion, it can be said that the proposed nonempirical boiling and condensation model combined with the MARS has been validated

A Large Scale Three-Dimensional Simulation on Thermal-Hydraulics of Supercritical Pressure Water in a Fuel Bundle for SCWR

Development of a numerical analysis method was performed to clarify thermal-hydraulic characteristics in supercritical water reactors. Because the thermo-physical property of fluids at the supercritical pressure condition is different from that at the subcritical condition and has a special feature, current numerical analysis codes cannot be applied. Then, Japan Atomic Energy Agency is developing a numerical analysis code which can calculate the thermo-fluid properties of the supercritical fluids correctly. This paper describes the predicted results of a newly developed analysis code and the comparison results with the experimental results

Large-Scale Numerical Simulations of Multiphase Flow

Introduction Although subchannel codes [1--3] are used for the thermal -hydraulic analysis of fuel bundles in nuclear reactors from the former, lots of composition equations and empirical correlations based on experimental results are needed to predict the water-vapor two-phase flow behavior. When there are no experimental data such as the reduced-moderation light water reactor (RMWR) [4, 5] which is currently developed by the Japan Atomic Energy Research Institute, therefore, it is very difficult to obtain highly precise predictions. The RMWR core has remarkably narrow gap spacing between fuel rods (i.e., around 1 mm) which are arranged at a triangular tight-lattice configuration in order to reduce the moderation of the neutron. In such a tight-lattice core, there is no sufficient information about the effects of the gap spacing and grid spacer configuration on the two-phase fluid flow characteristics. Then, the authors tried to analyze the Japan Atomic Energy Research Institute ha

NUMERICAL ANALYSIS ON HEAT TRANSFER-CHARACTERISTICS OF SUPERCRITICAL PRESSURE WATER IN A HEATED TUBE BASED ON THREE DIMENSIONAL TWO-FLUID MODEL

ABSTRACT In Japan Atomic Energy Agency (JAEA), the threedimensional two-fluid model analysis code considering the supercritical pressure water based on ACE-3D (Advanced Code for Evaluation of 3-Dimensional two-phase flow) has been developed to establish the thermal-hydraulics design by numerical analytical approach for the Super Critical Water Reactor (SCWR). In this paper, in order to evaluate the prediction accuracy of ACE-3D for the heat transfercharacteristics at the pseudo critical point, a numerical analysis of the supercritical water using ACE-3D based on the three dimensional two-fluid model has been conducted for simulating the experiments in a heated tube with both upward and downward flow. For the turbulence model in this analysis, both the standard k- model and the low-Reynolds number type k- model which uses the Launder-Sharma model were examined to investigate the influence of the turbulence model on the heat transfer-characteristics near the heated wall near the pseudo critical point. As a result, it was found that the numerical results of wall temperature using the low-Reynolds number k- model for upward flow in a heated tube were in good agreement with experimental data compared with that of using the standard k- model