Two-phase flow instability in a parallel multichannel system

The two-phase flow instabilities observed in through parallel multichannel can be classified into three types, of which only one is intrinsic to parallel multichannel systems. The intrinsic instabilities observed in parallel multichannel system have been studied experimentally. The stable boundary of the flow in such a parallel-channel system are sought, and the nature of inlet flow oscillation in the unstable region has been examined experimentally under various conditions of inlet velocity, heat flux, liquid temperature, cross section of channel and entrance throttling. The results show that parallel multichannel system possess a characteristic oscillation that is quite independent of the magnitude and duration of the initial disturbance, and the stable boundary is influenced by the characteristic frequency of the system as well as by the exit quality when this is low, and upon raising the exit quality and reducing the characteristic frequency, the system increases its instability, and entrance throttling effectively contributes to stabilization of the system.     

Magnetohydrodynamic flows entering the region of a flow channel insert in a duct

In this study, three-dimensional developing liquid-metal (LM) magnetohydrodynamic (MHD) flows entering the region of the flow channel insert (FCI) under a uniform magnetic field are numerically analyzed. The features of the LM MHD flows in a square duct near the leading edge of the FCI are examined in terms of flow velocity, pressure, current, electric potential, and Lorentz force. Because near the leading edge of the FCI the current moves obliquely in the inner flow region, the pressure gradient along the main flow direction near the slit of FCI's leading edge is smaller, yielding a region of velocity recirculation with lower electric potential therein. The interdependency of current, fluid velocity, pressure, electric potential gradient, and Lorentz force is examined in order to describe the electromagnetic features of the current flows.     

Dynamics of multiple parallel boiling channel systems with forced flows

This work investigates the nonlinear dynamics of multiple parallel boiling channels with forced flows by using the Galerkin nodal approximation method. The stability maps for multiple-channel systems subject to a constant total mass flow rate are constructed on the basis of the average heat flux and mass flow rate on the parameter plane of the subcooling and phase change numbers. The limit cycle oscillations for 3-, 4- and 5-channel systems indicate that the most heated channel exhibits the largest magnitude of oscillation, and is out-of-phase with the other channels. Owing to that the boiling assembly contains only a small number of channels, the above system becomes unstable due to channel-to-channel interaction with an increase of the channel number. This work also elucidates the dynamics of a 3-channel system with a periodic total mass flow rate. In addition, complicated nonlinear oscillations are predicted for different operating points with high inlet subcooling numbers in the stable region. The system dynamics are highly sensitive to the frequency of the forcing function. Periodic, quasi-periodic and chaotic oscillations may appear in the forcing function system. Unstable oscillations appear when either the frequency of the forcing function is equal or extremely close to the system’s natural frequency or the two frequencies are frequency-locking.     

Study on intermittent flow behavior in a vertical channel under low-pressure condition

The intermittent flow behavior in a vertical annulus under a low-pressure condition was experimentally studied using a scaling experiment facility. The temperature and pressure variations in the channel had been obtained under the heat load ranging from 0 to 2.0 kW, initial subcooled water temperature ranging from 50 to 90 °C and length–diameter ratio ranging from 1.6 to 50. The effects of the heat load and length–diameter ratio of channel on the flow characteristics were investigated in detail. The experimental results showed that the steam bubbles erupted more frequently and regularly at a high heat load. The intermittent flow period decreased with increase of the heat load and aspect ratio. Based on the mechanism analysis, an empirical model considering the steam oscillation and the vapor–liquid interface rupture based on the experimental data was proposed. It was found that the accumulated steam basically increased linearly. The oscillation of the pressure and velocity decreased gradually with continuous steam accumulation. The Reynolds number of the liquid within the rising section was very small at the stagnation state since there was no forced circulation flow. Finally, a blockage was engendered in the pipeline with the steam accumulated.     

Experimental study on friction and heat transfer characteristics of pulsating flow in rectangular channel under rolling motion

Friction and heat transfer characteristics of pulsating flow induced by rolling motion are experimentally studied. A series of single-phase forced circulation flow experiments are conducted in a vertical narrow channel. In the present study the flow rate is adjusted through control the impeller rotator speed of the pump. The results show that the flow rate pulsation simultaneously with the rolling motion and the relative amplitude of the flow rate pulsation decreases with the increasing flow rate. Accordingly, the relationships between the relative pulsation amplitude of friction factor, heat transfer coefficient and flow rate are classified. Therefore, the correlations have been developed to calculate the friction and heat transfer coefficient based on the relative pulsation amplitude of the flow rate.     

CFD analysis of flow and heat transfer of turbulent pulsating flow in a tube in rolling motion

The investigation of flow and heat transfer of turbulent pulsating flow is of vital importance to the nuclear reactor thermal hydraulic analysis in ocean environment. In this paper, the flow and heat transfer of turbulent pulsating flow is analyzed. The calculation results are firstly verified with experimental data. The agreement between them is satisfactory. The effect of spanwise and wall-normal additional forces is significant in small Reynolds number, and decreases with Reynolds number increasing. The rolling axis and rolling radius contribute slight to the flow and heat transfer. The effect of velocity oscillation period on the heat transfer is limited than that of Reynolds number and oscillating velocity Reynolds number. The traditional empirical correlations could not predict the flow and heat transfer of turbulent pulsating flow in rolling motion.     

裂变室镀层质量厚度的相对测量技术

基于在相同的中子辐照条件下,裂变数与裂变核素的数量成正比的原理,利用加速器14 MeV中子源研究了裂变室镀层重量的相对定量方法,介绍了实验布置及所获得的定量结果.将部分定量结果与其α定量结果进行比较,差异小于1%,证明该方法用于裂变室镀层重量的测定可行,定量结果的不确定度约为2%～4%.     

Experiment investigation on two-phase flow instability in a parallel twin-channel system

In this paper, the behavior of two-phase flow instability of a twin-channel system is studied experimentally. The two-phase flow instability between twin channels (FIBT) was observed in the experiments at three different system pressures, different inlet resistance coefficients and nonuniform heating condition. The instability boundaries of the twin-channel system are obtained in the phase plane of the subcooling and phase change number. The influences of inlet resistance, system pressure and nonuniform heating are obtained. In the end the numerical simulation results based on RELAP5/MOD3.4 code are also discussed.     

Numerical study of the MHD flow characteristics in a three-surface-multi-layered channel with different inlet conditions

A 3D MHD flow simulation was conducted to clarify the effects of the inlet flow conditions on the results of the validation experiment carried out previously and on the design window of the first wall using a three-surface-multi-layered channel. MHD pressure drop was largely influenced by the inlet condition. The numerical model with turbulent velocity profile showed qualitatively good agreement with the experimental result. The first wall temperature and pressure distributions obtained by the 3D simulation corresponded well to those obtained by the 2D simulation assuming fully developed flow. This suggested that complicated three-dimensional inlet flow condition generated in the L-shape elbow would not affects the existing design window.     

破口事故比例模拟中安全壳破口源项参数评估研究

采用基于破口总焓相似、强迫射流及浮力羽流流场相似及传热传质过程相似的多约束分析体系,归纳与质能源项相关的传热传质过程、耗散过程以及自然循环过程的时间尺度,确定模拟实验源项满足的各种模拟工况所必须遵循的设计约束条件。分析表明,自然循环过程时间常数是约束不同物理过程最重要的基础参数,也是模拟装置设计的基本约束参数。给出适用于确定安全壳破口源项试验参数的计算关系式,用于计算获得试验装置的几何参数和试验边界条件。     

极限干度现象区CHF评估

在圆形管内,对极限干度区的临界热流密度(CHF)进行了理论研究.通过对Whalley模型进行数值求解,并分析其在极限干度流动条件下的适应性,得到了适用于圆形管内环状流临界热流密度的本构方程.数值预测结果通过与几个主要的CHF预测模型相比较表明该本构方程对极限干度区CHF的预测精度较高.     

Nonlinear dynamics of a nuclear-coupled boiling channel with forced flows

The nonlinear dynamics of a nuclear-coupled boiling channel with forced flows was explored on the basis of the Galerkin nodal approximation method for the channel fluid flow and point kinetics for the neutron field dynamics. The marginal stability boundary (MSB) for a Freon boiling channel predicted by the model agreed well with experimental data from previous available literature, thereby verifying the model accuracy. A strip of limit cycle oscillation on the unstable side of the boundary was found to be system dependent. The marginal stability boundaries for boiling water channels with/without nuclear-coupled effects were also obtained. Moreover, the characteristics of limit cycle oscillations on the boundary were investigated. Routes from limit cycle oscillation to chaotic oscillation were identified under high inlet subcooling conditions. The strange attractor found in this study was characterized by a correlation dimension of 1.69±0.01.     

Influence of flow channel insert with pressure equalization opening on MHD flows in a rectangular duct

Direct simulation of 3D MHD flows in a duct with flow channel insert (FCI) relevant to R&D of fusion blanket has been conducted based on an electrical potential formula by using a consistent and conservative scheme. Comparison study of the pressure and velocity distributions of liquid metal in a poloidal duct with FCI, which has pressure equalization slot (PES) and pressure equalization holes (PEHs) with the same total area at the corresponding walls, is conducted. Both the PES and the PEHs have two kinds of locations, either in a Hartmann wall or in a side wall. 3D pressure and velocity distributions of the different cases have been given.     

Analytical calculation of the content of uranium isotopes in a cascade with two feed flows,two product flows,and one waste flow

The problem of estimating the ^232,234,236U content in the product flows of an optimal cascade is examined. Relations are found for studying the characteristics of the concentration variations along the cascade for various ratios of the feed flows. It is shown that an effective procedure is to obtain from the intermediate product of the cascade a diluent for high-enrichment uranium. __________ Translated from Atomnaya énergiya, Vol. 102, No. 4, pp. 241–244, April, 2007.     

Numerical evaluation of SmCo permanent magnet flowmeter measuring sodium flow in a low flow rate regime using FLUENT/MHD module

One of the several key subsystems in the test facility of Korean sodium-cooled fast reactor is a plugging meter system, which measures the impurities in the sodium using an indirect online technique. To measure the low flow rate, a permanent magnet flowmeter was developed owing to its inherent fast response time, non-invasive characteristic, relatively accurate flow rate measurements, and excellent linearity between the flow rate and flowmeter signal. However, several limitations have been reported in the experimental evaluation of the flowmeter under low flow rate conditions given the measurement capability of the current experimental facility. Thus, the performance of the flowmeter was evaluated numerically using a commercial computational fluid dynamics tool, a FLUENT/MHD module, based on the finite volume method with the help of electromagnetic analysis software, ANSYS MAXWELL. The FLUENT/MHD module was validated by comparing the simulation results with the experimental results. The relative error of the FLUENT simulation was estimated to be approximately 0.24% compared with the experimental results. After the validation process, MHD simulations were conducted to calculate the flowmeter voltage signals versus flow rates, especially in a low flow rate regime, where the linearity between the flow rate and flowmeter signal was carefully analyzed.     

The flow and heat transfer characteristics of turbulent flow in typical rod bundles in ocean environment

The flow and heat transfer characteristic of turbulent flow in typical 4 and 7 rod bundles in ocean environment is investigated theoretically. In ocean environment, the periodic variation of secondary flow in 7 rod bundles is not obvious. Because of the velocity oscillation, there is a periodic heat accumulation on the tube wall. And the restriction of the channel wall on the rolling motion is considerable. In 7 rod bundles, because of the restriction of the channel wall, the effect of the additional force perpendicular to flowing direction is limited, and the turbulent flowing and heat transfer is mainly determined by the axial turbulent intensity and inlet velocity. However, in the 4 rod bundles, the restriction of the channel wall is small. The effect of the additional force perpendicular to flowing direction on the flowing and heat transfer is significant. And the additional force perpendicular to flowing direction can also affect the Reynolds stress.     

Numerical investigation of liquid metal magnetohydrodynamic flow in multilayer flow channel inserts

In the high temperature liquid metal blanket of fusion-based hydrogen production reactor (named FDS-III), there is a remarkable feature that the multilayer flow channel inserts (MFCI) as function component are put into the breeding zone. The low thermal conductivity of MFCI can prevent the internal PbLi's heat conduct to the outside. So the outlet temperature can achieve high temperature around 1000 °C for high efficient production of hydrogen. However, the flow of liquid metal meandering through the MFCI will cause complex magnetohydrodynamic (MHD) effect under the strong fusion magnetic field. Liquid metal MHD effect is a key issue which should be concerned in high temperature breeder blanket (HTL). In this work, a numerical study was carried out to investigate the MHD effect of liquid metal PbLi in the MFCI. The MHD flows with typical modified geometry of the HTL MFCI were considered. The characteristics of flow and induced current fields were analyzed, and the pressure drop was evaluated. It also can be seen that the conductivity of the MFCI will have great impact on liquid metal flow's current and velocity distributions.     

Experimental study on combustion characteristics of sodium fire in a columnar flow

In the operation of the sodium-cooled fast reactor, the accident caused by the leakage and combustion of liquid sodium is common and frequent in sodium-related facilities. This paper is based on an experimental study of sodium fire in a columnar flow, which was carried out to focus on the burning characteristics by analyzing the temperature fields in the burner. The injection of 200 °C liquid sodium with the flux of 0.5 m³/h was poured into a 7.9 m³ volume stainless steel cylindrical burner to shape a sodium fire, and the data of temperature fields in the burner have been collected by dozens of thermocouples which are laid in the combustion space and sodium collection plate. These results show that the sodium fire in a columnar flow is composed of the foregoing centered columnar fire, the subsequent spray fire caused by atomization and the pool fire on the collection plate. The temperature close to the burning sodium flow maximally reaches up to 950 °C. The radial temperatures apart from the sodium flow are relatively low and generally about 200 °C, and maximally just 300 °C even when close to the sodium collection plate. The maximum temperature of the burning sodium dropping on the collection plate rises in the center of plate, about 528 °C. This study is helpful to evaluate the combustion characteristics, formation process and composing forms of the sodium fire in the sodium-related facilities.     

Computational thermal-fluid dynamics analysis of the laminar flow regime in the meander flow geometry characterizing the heat exchanger used in high temperature superconducting current leads

The Karlsruhe Institute of Technology and the Politecnico di Torino have developed and validated a computational thermal-fluid dynamics (CtFD) strategy for the systematic analysis of the thermal-hydraulics inside the meander flow heat exchanger used in high-temperature superconducting current leads for fusion applications. In the recent past, the application of this CtFD technique has shown that some operating conditions occurring in these devices may not reach the turbulent regime region. With that motivation, the CtFD analysis of the helium thermal-fluid dynamics inside different meander flow geometries is extended here to the laminar flow regime. Our first aim is to clarify under which operative conditions the flow regime can be considered laminar and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and for the heat transfer coefficient in the meander flow geometry have been derived, which are applicable with good accuracy to the design of meander flow heat exchangers over a broad range of geometrical parameters.     

Experimental study on characteristics of sodium fire in a columnar flow with discontinuous injections

In the operation of the sodium-cooled fast reactor, the accident caused by the leakage and combustion of liquid sodium is common and frequent in sodium-related facilities. In this paper, an experiment Harbin Engineering University-Sodium Columnar Fire 4 (HEU-SCF4) is carried out to focus on the combustion characteristics in a discontinuous columnar flow. Liquid sodium (250°C) with the flux of about 1.0 m³/h was injected into a 7.9 m³ stainless steel cylindrical test chamber twice to shape the sodium fire in a columnar flow with discontinuous injections. The temperature, pressure data, and heat release rate in the test chamber were acquired and analyzed. It is found that each injection would cause a peak of space temperature, and it takes much shorter time to reach temperature peak in the second injection than the first injection. The peaks of pressure and heat release rate caused by the second injection are much higher than those caused by the first injection. This study is promising to evaluate the combustion characteristics of sodium fire in a columnar flow with different injection forms in the sodium-related facilities.