Analysis of Two-Phase Flow Instability for Steam Generator

2008 ◽  
Author(s):  
Su-Xia Hou ◽  
Yun Tai ◽  
Fu-Yu Zhao
Keyword(s):  
Steam Generator ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Computer Code ◽  
Frequency Domain Method ◽  
Phase Flow ◽  
Steam Generators ◽  
Two Phase ◽  
The Stability

Two-phase flow instability is an important problem that affects the running of steam generators in nuclear reactor systems. In this paper, two-phase flow instability in parallel channels of a steam generator are analyzed to disclose the mechanism of flow instability by using the frequency domain method. The mathematical expressions of heat transfer and flow for a steam generator are proposed, and the transfer function of the closed-loop system is deduced by using linearization and Laplace transfer. The steam generator’s stability is judged according to Nyquist stability criterion. Depending on this fundamental principal, the computer code is developed to analyze the stability of steam generators. The results displayed two conclusions; firstly, the increase of inlet orifices or mass flow rate enhances the stability of generator steam; secondly, the coupling interactions between channels and their external loop effects on the stability of generator steam are not ignored. The result show that the effects are non-monotonic on the stability of generator steam.

The Research of Flow Instability in Vertical Parallel Natural Circulation Channels Based on Relap5

2013 ◽  
Author(s):  
Jingjing Li ◽  
Tao Zhou ◽  
Mingqiang Song ◽  
Yanping Huang
Keyword(s):  
Two Phase Flow ◽  
Single Channel ◽  
Flow Instability ◽  
Natural Circulation ◽  
Computer Code ◽  
Phase Flow ◽  
Flow Oscillation ◽  
Two Phase ◽  
Best Estimate ◽  
Estimate System

The gas-liquid two phase flow oscillation in vertical parallel natural circulation channels was performed by the best estimate system computer code Relap5. The effects of symmetry and dissymmetry degree of heated power to flow oscillation and the effects of symmetry and dissymmetry throttling to flow oscillation were researched. The results says that when the twin channels under the same conditions of geometry and boundary, the parameters of the twin channel such as flow are the same. So under these conditions the twin channels can be researched as single channel. It is more possible of flow oscillation for the channels under condition of dissymmetry heating. The use of throttling will make the channels more stable, it is more stable when the throttling coefficient increases. With the implement of dissymmetry throttling, the system is possible for out of phase flow oscillation.

Power Rising and Descending Transient for the OTSG of a Small PWR

2020 ◽  
Author(s):  
Baihui Jiang ◽  
Zhiwei Zhou ◽  
Zhaoyang Xia ◽  
Qian Sun
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Stability ◽  
Phase Flow ◽  
Steam Generators ◽  
Two Phase ◽  
Water Reactors ◽  
Secondary Side

Abstract As key heat transfer system in small and medium size pressurized water reactors, once-through steam generators are important parts of energy exchange between primary and secondary circuits, and are very important for the design and operation of reactors. However, two-phase flow and heat transfer in once-through steam generators are very complicated. When a reactor experience power rising and descending transient, the heat removal of once-through steam generator, the flow rate, the inlet fluid temperature and outlet steam temperature will all change accordingly. Especially when a reactor is running at a low power, the flow rate of the secondary side of OTSG is extremely small and the single-phase region of the secondary side of OTSGs is also too small. The two-phase flow instability may occur, which has a serious impact on reactor operation and safety. So, a reasonable power-up and power-down transient scheme is required to ensure operational stability when starting up and shutting down a reactor. RELAP5/MOD4.0 is a commercial software developed by Innovative System Software, LCC for transient analysis of light water reactors (LWR). After years of development and improvement, RELAP5 has been a basic tool for analysis and calculation of various simulators of nuclear power plants. Scholars all over the world have carried out a large number of analysis of two-phase flow stability using RELAP5, and the results are reliable. This paper takes once through steam generators with given structural parameters as the research object, and uses RELAP5 as the calculation tool. The influencing factors of flow instability are discussed in this paper, and the operating parameters of the fluid on the primary and secondary sides are designed to satisfy the flow stability under different powers. And a set of power-up and power-down schemes for stable operation is proposed.

Analysis of Two-Phase Flow Instability in Multi-Channel System

2014 ◽  
Author(s):  
Genglei Xia ◽  
Minjun Peng ◽  
Du Xue
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Saturation Pressure ◽  
Computer Code ◽  
Phase Flow ◽  
Parallel Channel ◽  
Multichannel System ◽  
Two Phase ◽  
Forced Circulation ◽  
Channel System

Ledinegg instability is one of the most important static instabilities for two phase flow system, especially in microchannel systems. In this paper, the force circulation two phase flow instability in vertical multi-channel system is performed by the best estimate system computer code RELAP5. The process and inherent reason of flow instability between multichannel system (FIBM) and flow excursion in forced circulation parallel channel system are analyzed. The effects of main operating parameters related to static onset of flow instability are investigated. Inlet subcooling, inlet restrictor, and saturation pressure are sensitive to the stability of parallel channel system.

Analysis of Two-Phase Flow Instability in Multichannel System

2008 ◽  
Author(s):  
Fu-Yu Zhao ◽  
Su-Xia Hou ◽  
Yun Tai
Keyword(s):  
Characteristic Equation ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Transfer Functions ◽  
Flow Instability ◽  
Oscillation Mode ◽  
Phase Flow ◽  
Multichannel System ◽  
Two Phase ◽  
Oscillation Modes

Two-phase flow instability in parallel multichannels is an important problem that affects operation safety of all large-capacity power boilers and nuclear reactor systems. Occurrence of instabilities and their modes of oscillations can be evaluated by investigating into a characteristic equation, its roots and composing channels transfer functions. It is also shown that a governing matrix is reduced to a diagonal one by using its eigenvalues, the oscillation modes being divided into number of channels separate fundamental modes. Characteristics of each oscillation mode are given by examining corresponding characteristic equations, which are applied for the prediction of oscillation modes of systems composed of a few slightly different channels.

The Mechanism of Two Phase Flow Instability Enhanced the Interface Mass Transfer

2013 ◽  
Author(s):  
Yan Yang ◽  
Liang-ming Pan ◽  
Liu Hang
Keyword(s):  
Mass Transfer ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Mechanical Vibration ◽  
Phase Interface ◽  
Local Heat Transfer ◽  
Phase Flow ◽  
Regular Pattern ◽  
Two Phase

Two phase flow instability is a common phenomenon in many applications such as nuclear reactor, boiler, heat exchanger, chemical reactor, etc. Flow instability will cause mechanical vibration, which may bring about the local heat transfer deterioration. But for the gas-liquid reactor, the mechanical vibration caused by flow instability will strengthen the destabilization and increase the mass transfer at the gas-liquid interface. Therefore, the mass transfer will be enhanced. Such as in nuclear reactor, we need increase the mass transfer of boron. Currently, few studies did the researches on the mechanism of mass transfer enhancement and regular pattern of interface phenomenon caused by two phase flow instability. This paper deals with the problems in improving the mass transfer at two phase interface, studies the effects of flow pattern on the transfer characteristics and the influence of bubble’s growth and aggregation on the mass flow rate and outlet pressure. The mechanism and the regular pattern of interface destabilization are analyzed. The results reveal that the two phase instability has significant effects on the mass transfer through the interface.

scholarly journals The Effect of Slightly Upward and Downward Inclined Pipes on the Stability of Gas-Oil Two-Phase Flow

2014 ◽  
Vol 14 (1) ◽  
pp. 13
Author(s):  
Peyman Sabzi ◽  
Saheb Noroozi
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Fluid Model ◽  
Phase Flow ◽  
Momentum Exchange ◽  
Two Phase ◽  
Two Fluid Model ◽  
The Stability ◽  
Inclined Pipes ◽  
Two Fluid

Pipeline inclination has an important effect on the stability of two-phase flow and flow assurance in the pipeline. This inclination may be intentional; it may be inevitable in pipeline installation; or it may be due to an error in pipeline installation. In this situation, even the slight inclination of the pipe plays an important role in the growth or elimination of the instability of the two-phase flow. In this study using a code designed for the analysis of pipelines’ two-phase flow, the stability of the two-phase flow for Kerosene oil flow along with methane gas has been compared in downward inclined pipes, upward inclined pipes, and horizontal pipes. Using the mentioned computer code, it has been proved that the pipe’s upward inclination results in the increase of two-phase flow instability, while the pipe’s downward inclination is helpful in two-phase flow stability. In order to model two-phase flow in the pipe, two-fluid model has been used. This model considers each phase separately and the equations of mass conservation and momentum are written for each phase. The momentum exchange between the two phases and between each phase and the pipe wall has been considered. Conservation equations have been solved using SIMPLE algorithm in a numerical form with finite volume method.Keywords: Pipes, Two-Phase Flow, Inclined Stability, Two-Fluid Model

The influence of the Stokes and Archimedes forces on the stability of a two-phase flow

2003 ◽  
Vol 3 ◽  
pp. 266-270
Author(s):  
B.H. Khudjuyerov ◽  
I.A. Chuliev
Keyword(s):  
Spectral Method ◽  
Stability Region ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Solid Phase ◽  
Stability Characteristic ◽  
Phase Flow ◽  
Two Phase ◽  
The Stability

The problem of the stability of a two-phase flow is considered. The solution of the stability equations is performed by the spectral method using polynomials of Chebyshev. A decrease in the stability region gas flow with the addition of particles of the solid phase. The analysis influence on the stability characteristic of Stokes and Archimedes forces.

Time Domain Simulation of the Vibration of a Steam Generator Tube Subjected to Fluidelastic Forces Induced by Two-Phase Cross-Flow

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Téguewindé Sawadogo ◽  
Njuki Mureithi
Keyword(s):  
Steam Generator ◽  
Two Phase Flow ◽  
Work Rate ◽  
Fretting Wear ◽  
Phase Flow ◽  
Reference Case ◽  
Two Phase ◽  
Steam Generator Tube ◽  
Wide Range ◽  
Instability Regime

Having previously verified the quasi-steady model under two-phase flow laboratory conditions, the present work investigates the feasibility of practical application of the model to a prototypical steam generator (SG) tube subjected to a nonuniform two-phase flow. The SG tube vibration response and normal work-rate induced by tube-support interaction are computed for a range of flow conditions. Similar computations are performed using the Connors model as a reference case. In the quasi-steady model, the fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives. These forces have been measured in two-phase flow over a wide range of void fractions making it possible to model the effect of void fraction variation along the tube span. A full steam generator tube subjected to a nonuniform two-phase flow was considered in the simulations. The nonuniform flow distribution corresponds to that along a prototypical steam-generator tube based on thermal-hydraulic computations. Computation results show significant and important differences between the Connors model and the two-phase flow based quasi-steady model. While both models predict the occurrence of fluidelastic instability, the predicted pre-instability and post instability behavior is very different in the two models. The Connors model underestimates the flow-induced negative damping in the pre-instability regime and vastly overestimates it in the post instability velocity range. As a result the Connors model is found to underestimate the work-rate used in the fretting wear assessment at normal operating velocities, rendering the model potentially nonconservative under these practically important conditions. Above the critical velocity, this model largely overestimates the work-rate. The quasi-steady model on the other hand predicts a more moderately increasing work-rate with the flow velocity. The work-rates predicted by the model are found to be within the range of experimental results, giving further confidence to the predictive ability of the model. Finally, the two-phase flow based quasi-steady model shows that fluidelastic forces may reduce the effective tube damping in the pre-instability regime, leading to higher than expected work-rates at prototypical operating velocities.

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