A numerical study for the evaluation of heat transfer correlations for sodium flows in a heat exchanger of a fast breeder nuclear reactor is performed. Three different types of flows such as parallel flow, cross flow, and two inclined flows are considered. Calculations are performed for these three typical flows in a heat exchanger changing turbulence models. The tested turbulence models are the shear stress transport (SST) model and the SSG-Reynolds stress turbulence model by Speziale, Sarkar, and Gaski (1991, “Modelling the Pressure-Strain Correlation of Turbulence: An Invariant Dynamical System Approach,” J. Fluid Mech., 227, pp. 245–272) . The computational model for parallel flow is a flow past tubes inside a circular cylinder and those for the cross flow and inclined flows are flows past the perpendicular and inclined tube banks enclosed by a rectangular duct. The computational results show that the SST model produces the most reliable results that can distinguish the best heat transfer correlation from other correlations for the three different flows. It was also shown that the SSG-RSTM high-Reynolds number turbulence model does not deal with the low-Prandtl number effect properly when the Peclet number is small. According to the present calculations for a parallel flow, all the old correlations do not match with the present numerical solutions and a new correlation is proposed. The correlations by Dwyer (1966, “Recent Developments in Liquid-Metal Heat Transfer,” At. Energy Rev., 4, pp. 3–92) for a cross flow and its modified correlation that takes into account of flow inclination for inclined flows work best and are accurate enough to be used for the design of the heat exchanger.

A computational study for an evaluation of the current turbulence models for the prediction of a thermal striping in a triple jet is performed. The tested turbulence models are the two-layer model, the shear stress transport model, and the elliptic relaxation model. These three turbulence models are applied to the prediction of a thermal striping in a triple jet in which detailed experimental data are available. The predicted time-averaged and root-mean-square values of the temperature are compared with the experimental data, and the capability of predicting the oscillatory behavior of the ensemble-averaged temperature is investigated. From these works, it is shown that only the elliptic relaxation model is capable of predicting the oscillatory behavior of the ensemble-averaged temperature. It is also shown that the elliptic relaxation model predicts best the time-averaged temperature and the root mean square of the temperature fluctuation. However, this model predicts a slower mixing at the far downstream of the jet.

A numerical study of the evaluation of turbulence models for predicting the thermal stratification phenomenon is presented. The tested models are the elliptic blending turbulence model (EBM), the two-layer model, the shear stress transport model (SST), and the elliptic relaxation model (V2-f). These four turbulence models are applied to the prediction of a thermal stratification in an upper plenum of a liquid metal reactor experimented at the Japan Nuclear Cooperation (JNC). The EBM and V2-f models predict properly the steep gradient of the temperature at the interface of the cold and hot regions that is observed in the experimental data, and the EBM and V2-f models have the capability of predicting the temporal oscillation of the temperature. The two-layer and SST models predict the diffusive temperature gradient at the interface of a thermal stratification and fail to predict a temporal oscillation of the temperature. In general, the EBM predicts best the thermal stratification phenomenon in the upper plenum of the liquid metal reactor.

An experimental study has been carried out to measure the pressure loss at the side orifice of a liquid metal reactor fuel assembly. The characteristics of the pressure loss at the side orifice are investigated using the experimental data measured from 17 different types of side orifices that have different geometric shapes, dimensions, and arrangements of nozzles, and a correlation that covers the whole flow range by one equation is developed. The error range of the correlation is within ± 10 % , and most of the errors occurred in a region where the Reynolds number is small. The range of Reynolds numbers based on the hydraulic diameter of the orifice is 2000–350,000. It is found that the geometric factor is the most important parameter for the pressure loss when the Reynolds number is > 30,000 . As the Reynolds number becomes smaller, its effect becomes larger, and when the Reynolds number is small, it is the most important parameter for the pressure loss at the side orifices. The measured data shows a trend that the pressure loss coefficient increases as the number of orifices increases, and the effect of the longitudinal arrangement is small.

This paper addresses three-dimensional numerical analyses of the unsteady conjugate heat transfer and thermal stress for a PWR pressurizer surge line pipe with a finite wall thickness, subjected to internally thermal stratification. A primary emphasis of the present study is placed on the investigation of the effects of surge flow direction on the determinations of the transient temperature and thermal stress distributions in the pipe wall. In the present numerical analysis, the thermally stratified flows (in-surge flow and out-surge flow) in the pipe line are simulated using the standard κ − ε turbulent model and a simple and convenient numerical method of treating the unsteady conjugate heat transfer on a non-orthogonal coordinate system is developed. The unsteady conjugate heat transfer analysis method is implemented in a finite volume thermal-hydraulic computer code based on a non-staggered grid arrangement, SIMPLEC algorithm and higher-order bounded convection scheme. The finite element method is employed for the thermal stress analysis to calculate non-dimensional stress distributions at the piping wall as a function of time. Some numerical calculations are performed for a PWR pressurizer surge line pipe model with shortened length, subjected to internally thermal stratification caused either by insurge or outsurge flow with a specified velocity, and the results are discussed in detail.

An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio P / D of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio H / D is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits best with the present experimental data among the four correlations considered.

This paper presents an effective numerical method for predicting the stratified flow in a horizontal circular pipe. The method employs a body-fitted, nonorthogonal grid system to accommodate the pipe wall of circular geometry and the interface of the two fluids at different temperatures, of which the level is variable. The transient behaviors of fluid flow and temperature distribution in the piping are simulated using the finite volume approach. The convection term is approximated by a higher-order bounded scheme named HLPA, which is known as a high-resolution and bounded discretization scheme. The cell-centered, nonstaggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of modified momentum interpolation scheme. The SIMPLE algorithm is employed for the pressure and velocity coupling. The new way of treating the unsteady conjugate heat transfer problem is presented. The present method has been applied to the stratified flow in the pressurizer surge line of the nuclear reactor, and the results have been discussed. In addition, this study has investigated the effects of level of the interface between the two stratified fluids on the transient evolution of temperature distributions in the piping wall.