Numerical Aspects on the Prediction of Stability Boundaries of Two-Phase Natural Circulation Circuits, Considering Flashing Evaluation

2005 ◽  
Vol 73 (6) ◽  
pp. 911-922
Author(s):  
P. Zanocco ◽  
D. Delmastro ◽  
M. Giménez
Keyword(s):  
Numerical Integration ◽  
Natural Circulation ◽  
Stability Limit ◽  
Linearization Method ◽  
Test Case ◽  
Implicit Methods ◽  
Two Phase ◽  
Circulation Circuit ◽  
Wide Range ◽  
The Stability

In this work, the stability of a two-phase, natural circulation circuit is analyzed, using a specially developed model. This thermohydraulic model results in a set of coupled, nonlinear, first-order partial differential equations, which are solved by means of the up-wind finite difference method, using combinations of explicit and implicit methods for the numerical integration of the different balance equations. An adaptive nodalization scheme is implemented, minimizing the error of the propagation of small perturbations through the discretized volumes and especially the ones having two-phase flow regime. A linearization method is implemented by means of numerical perturbations. Frequency domain calculations are carried out, allowing a rapid visualization of the stability of the linearized system. Two cases are analyzed: a test case, where the code is compared in a wide range of qualities with an analytical model, and an application case, where the model is used to analyze the stability of an integral reactor cooled by natural circulation. The CAREM prototype is taken as a reference. In both cases, the numerical diffusion and integration errors are analyzed in the stability limit prediction by means of a convergence analysis using different nodalization and numerical integration criteria.

Stability Analysis of a Supercritical Water Natural Circulation Loop

2012 ◽  
Author(s):  
ZhongChun Li ◽  
JiYang Yu ◽  
XiaoMing Song
Keyword(s):  
Supercritical Water ◽  
Natural Circulation ◽  
Basic Research ◽  
Circulation Loop ◽  
Two Phase ◽  
Water Reactor ◽  
Natural Circulation Loop ◽  
The Stability ◽  
Engineering Physics ◽  
Supercritical Water Reactor

As a part of “supercritical water reactor basic research”, the stability of the natural circulation research plays an important role on the feasibility of supercritical water reactor and experiment research. In this paper, the stability of a supercritical water natural circulation loop built by Department of Engineering Physics, Tsinghua University was studied by numerical method. It was confirmed that the static or Ledinegg instability doesn’t occur in HACA system, and there are no instabilities existing when the inlet enthalpy is larger than critical enthalpy. Instability was observed by numerical way, which is similar to DWOs and PDOs in two phase natural circulation loop. The system parameters’ influence on the instability of supercritical natural circulation loop was studied.

New phenomena in the Eckhaus instability of thermal Rossby waves

1990 ◽  
Vol 216 ◽  
pp. 613-628 ◽  
Author(s):  
A. C. Or
Keyword(s):  
Analytical Study ◽  
Rossby Waves ◽  
Solvability Condition ◽  
Stability Limit ◽  
Previous Method ◽  
New Findings ◽  
Wide Range ◽  
The Stability ◽  
New Phenomena ◽  
Eckhaus Instability

An analytical study on the Eckhaus instability of moderately nonlinear thermal Rossby waves is developed. A solvability condition of the lowest order is derived. The condition not only produces results that agree reasonably well with the earlier Galerkin formulation, but also leads to some new findings that are otherwise difficult to discover by the previous method. Over a wide range of parameters, this paper reports the existence of a branch of the stability limit that corresponds to a pair of disturbances with a finite, rather than an infinitesimal wavenumber modulation. As the Prandtl number tends to a small value, the asymmetry between the two branches of the stability limit becomes very pronounced, which is manifested as a severely distorted stability region.

Stability Behavior of a Natural Circulation Loop with End Heat Exchangers

2005 ◽  
Vol 127 (7) ◽  
pp. 749-759 ◽  
Author(s):  
N. M. Rao ◽  
B. Maiti ◽  
P. K. Das
Keyword(s):  
Heat Exchangers ◽  
Natural Circulation ◽  
Circulation Rate ◽  
Finite Element Program ◽  
Stability Behavior ◽  
Wide Range ◽  
Element Program ◽  
The Stability ◽  
The One ◽  
Two Parameters

The present investigation describes the stability behavior of NCL with end heat exchangers. The one-dimensional transient conservation equations of the loop fluid and the two fluid streams of cold end and hot end heat exchangers are solved simultaneously using the finite element program. For the stability analysis the loop response is found for an imposed finite perturbation to the loop circulation rate. Though the stability may depend on the number of parameters, variation of two nondimensional parameters, namely Ch* and GrL, is studied. Selecting the specific combinations of the above two parameters three different cases of stability, namely, stable, neutrally stable, and unstable, are demonstrated. The stability behavior is scanned over a wide range of Ch* and GrL values and the stability envelope is also constructed.

scholarly journals The development of a model for predicting the stability boundaries of natural circulation process

2020 ◽  
Author(s):  
Vyacheslav Andreev ◽  
Ekaterina Orekhova ◽  
Natalya Tarasova ◽  
Julia Perevezentseva
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Natural Circulation ◽  
Reactor Core ◽  
Passive Systems ◽  
Two Phase ◽  
Operating Personnel ◽  
Stability Boundaries ◽  
Operating Limits ◽  
The Stability

The concept of safety for facilities comprising nuclear power plants implies in large the use of passive systems. One of the main passive systems in a nuclear power plant is a system for cooling the reactor core with its action based on gravitational forces. In this regard, the importance of such a physical process as natural circulation is increasing with the development of nuclear power facilities. However, this system has not only advantages but some drawbacks as well. These are the emergence of instability in the two-phase coolant flow, pulsations of thermohydraulic parameters, possible circulation reversal and stagnation. This paper deals with the study of a generalized model of the natural circulation stability. The said model is designed to simplify the design engineering of power equipment. This model will also enable the operating personnel to predict the operating limits of the equipment and remain within the coolant stability bounds. This paper presents a model for predicting the stability boundaries of natural circulation process.

scholarly journals The Development of Models to Predict the Stability of Natural Circulation of Heatoolant

2018 ◽  
Vol 3 (3) ◽  
pp. 268
Author(s):  
Orekhova E.E. ◽  
Andreev V.V. ◽  
Tarasova N.P.
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Energy ◽  
Natural Circulation ◽  
Reactor Core ◽  
Passive Systems ◽  
Two Phase ◽  
Gravitational Forces ◽  
Temperature And Pressure ◽  
The Stability

Concept of safety of nuclear power plants involves in larger quantities the use of passive systems. One of the main passive systems in nuclear power plant – the system of cooling of the reactor core. This system is based on gravitational forces. In this regard, nuclear energy increases the significance of such physical process, as the natural circulation. In addition to the benefits of the system there are drawbacks. There is the instability of the two-phase coolant, pulsation temperature and pressure, rollover and stagnation of circulation. 

scholarly journals Design of a natural circulation circuit for 85 MW steam boiler

2017 ◽  
Vol 21 (3) ◽  
pp. 1503-1513 ◽  
Author(s):  
Konstantin Pleshanov ◽  
Ekaterina Khlyst ◽  
Mikhail Zaichenko ◽  
Kirill Sterkhov
Keyword(s):  
Natural Circulation ◽  
Steam Pressure ◽  
Point Of View ◽  
Steam Boiler ◽  
Heat Absorption ◽  
Simple Circuit ◽  
Two Phase ◽  
Circulation Circuit ◽  
Boiler Designer ◽  
Research And Design

The paper describes research and design of fluidized bed steam boiler natural circulation circuit. The capacity of the drum boiler is 85 MW, superheated steam pressure is 98 bar. There are two variants research results of the designed circulation circuit. The first circulation circuit variant was designed as a complex circuit with a common downcomers and risers for the boiler evaporating screen. In the second variant the flow is separately supplied to and discharged from the evaporator that is divided into independent sections. We have researched and described the influence of heat absorption inequality on the furnace evaporation pads using the Boiler Designer software. We also have calculated main characteristics of the two-phase flow in the evaporation pads and evaluated reliability of the natural circulation. The circulation circuit is optimized from point of view of reliability and metal expenses. Results demonstrate that the specific quantity of metal of complex and simple circuit variants is approximately the same with equal reliability.

Nonlinear Analysis for a Two-Phase Natural Circulation Loop Under Low-Pressure

2010 ◽  
Author(s):  
Arrdaneh Kazem ◽  
Zaferanlouei Salman ◽  
Mohsen Farahi ◽  
Asad Allah Ahmadi
Keyword(s):  
Low Power ◽  
High Power ◽  
Parametric Study ◽  
Stability Region ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Two Phase ◽  
Natural Circulation Loop ◽  
The Stability ◽  
Power Region

The purpose of this paper is to develop a nonlinear model to investigate the instabilities of a two-phase natural circulation loop under low-pressure condition. Inlet velocity oscillations and the corresponding trajectories are respectively presented in the time evolution planes and phase planes. We obtain a stability map to explore the instability regions of this natural circulation loop. The results show that the considered loop has two unstable regions, instability type-I in the low power region and instability type-II in the high power region. Then the parametric study is carried out to understand the relation between the parameters of system and two types of instability. The parametric study reveals that lengthening the riser has an unstable effect on system stability. Thus, lengthening the riser causes a reduction in the stability region in the both low power and high power levels. Also it can be observed that by increasing the form loss coefficient at the inlet of heated section or in the downcomer section, the stability region expands, however by increasing the form loss coefficient at the outlet of heated section or in the upper horizontal section, the stability region decreases consequently.

scholarly journals Numerical validation of an analytical seal flutter model

2021 ◽  
Vol 5 ◽  
pp. 191-201
Author(s):  
Michele Greco ◽  
Roque Corral
Keyword(s):  
Analytical Model ◽  
Fluid Dynamic ◽  
Stability Limit ◽  
Labyrinth Seal ◽  
Analytical Models ◽  
Mode Shapes ◽  
Labyrinth Seals ◽  
Low Frequencies ◽  
Wide Range ◽  
The Stability

An analytical model to describe the flutter onset of straight-through labyrinth seals has been numerically validated using a frequency domain linearized Navier-Stokes solver. A comprehensive set of simulations has been conducted to assess the stability criterion of the analytical model originally derived by Corral and Vega (2018), “Conceptual Flutter Analysis of Labyrinth Seals Using Analytical Models - Part I: Theoretical Support,” ASME J. Turbomach., 140 (12), pp. 121006. The accuracy of the model has been assessed by using a simplified geometry consisting of a two-fin straight-through labyrinth seal with identical gaps. The effective gaps and the kinetic energy carried over are retained and their effects on stability are evaluated. It turns out that is important to inform the model with the correct values of both parameters to allow a proper comparison with the numerical simulations. Moreover, the non-isentropic perturbations included in the formulations are observed in the simulations at relatively low frequencies whose characteristic time is of the same order as the discharge time of the seal. This effect is responsible for the bending of the stability limit in the <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mn>0</mml:mn><mml:mi>t</mml:mi><mml:mi>h</mml:mi></mml:math></inline-formula> ND stability map obtained both in the model and the simulations. It turns out that the analytical model can predict accurately the stability of the seal in a wide range of pressure ratios, vibration mode-shapes, and frequencies provided that this is informed with the fluid dynamic gaps and the energy carried over to the downstream fin from a steady RANS simulation. The numerical calculations show for the first time that the model can be used to predict accurately not only the trends of the work-per-cycle of the seal but also quantitative results.

scholarly journals An Experimental and Numerical Analysis on the Dynamical Behavior of a Safety Valve in the Case of Two-Phase Non-Flashing Flow

2020 ◽  
Author(s):  
Mhd Ghaith Burhani ◽  
Csaba Hős
Keyword(s):  
Mass Fraction ◽  
Dynamical Behavior ◽  
Valve Lift ◽  
Test Facility ◽  
Maximum Pressure ◽  
Two Phase ◽  
Mixture Flow ◽  
System Pressure ◽  
Wide Range ◽  
The Stability

Pressure Relief Valves (PRVs) are key elements of any hydraulic system in the process industry, especially in chemical plants or hydraulic power transmission systems. Their task is to maintain the system pressure beneath a prescribed maximum pressure and vent the excessive fluid in an emergency scenario. This paper addresses the static and dynamic behavior of a Direct Spring-Operated PRV of conical shape in the presence of two-phase non-flashing flow, that is, water-air mixture. First, experimental results on the force and discharge characteristics of such a valve in a wide range of the air-to-water mass fraction are presented. Our test facility includes a custom-designed PRV with 42.5 mm inlet pipe diameter, an inlet pressure up to 6.6 bar(g) and a maximum lift of 10 mm. Additionally, the empirical results on the static characteristics, notably fluid force on the valve disc and discharge coefficients are reported as a function of the liquid mass fraction and valve lift. In the second part of the paper, we present the development of a Matlab-based simulation tool that is capable of predicting the dynamics and stability of such a valve in the case of two-phase, non-flashing, frozen-mixture flow. Moreover, the effect of system parameters, such as spring stiffness and reservoir capacity are recorded. Finally, we also present results on the stability of the opening and closing the multi-phase flow influence on the stability of the blowdown process.

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