Study of Flow Instabilities in a Natural Circulation Boiling System

2010 ◽  
Author(s):  
Arrdaneh Kazem ◽  
Ahmadi Asad allah ◽  
Mohsen Farahi ◽  
Zaferanlouei Salman
Keyword(s):  
Low Power ◽  
High Power ◽  
Parametric Study ◽  
Stability Region ◽  
Natural Circulation ◽  
Loss Coefficient ◽  
Circulation Loop ◽  
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. We obtain a stability map to explore the unstable 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.

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.

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.

Influence of bidirectional inclination on the stability of single-phase natural circulation loop

2019 ◽  
Author(s):  
Adarsh R. Nair ◽  
Rupesh Shanmughom ◽  
Raveesh Gopalakrishnan ◽  
Abhijith A. S. Nair
Keyword(s):  
Single Phase ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Natural Circulation Loop ◽  
The Stability

Steady State and Dynamic Analyses of Supercritical CO2 Natural Circulation Loop

2006 ◽  
Author(s):  
Prashant Jain ◽  
Rizwan Uddin
Keyword(s):  
Steady State ◽  
Natural Circulation ◽  
Stability Boundary ◽  
Operating Conditions ◽  
Circulation Loop ◽  
Steady State Flow ◽  
Natural Circulation Loop ◽  
Dynamic Analyses ◽  
The Stability ◽  
Flow Power

Numerical studies have been carried out to investigate supercritical flow instabilities in a CO2 natural circulation loop. For the steady state and dynamic analyses of the loop under supercritical conditions, a single-channel, one-dimensional model is developed. In this model, equations for the conservation of mass, momentum and energy are discretized using an implicit finite difference scheme. A computer code called FIASCO (Flow Instability Analysis under SuperCritical Operating conditions) is developed in FORTRAN90 to simulate the dynamics of natural circulation loops with supercritical fluid. Results obtained for the stability boundary substantially deviate from the results reported by previous investigators, and thus contradict some of the reported findings. The disagreement in results is most likely due to the undesirable dissipative and dispersive effects produced from the large time steps used in previous studies, thereby leading to a larger stable region than those found using smaller time step. Results presented here suggest that the stability boundary of a natural circulation loop with supercritical fluid, is not confined to the near-peak region of the (steady state) flow-power curve. Additional and more extensive experimental data are needed to resolve the differences between results obtained here and those reported earlier. However, results obtained for the range of parameter values used in this investigation always predict the stability threshold to be in the positive slope region of the (steady state) flow-power curve. Parametric studies for different operating conditions reveal the similarity of stability characteristics under supercritical conditions with those in two-phase flows.

The Qualitative Analysis of Vertical Seismic Acceleration Effect on a Single Nuclear-Coupled Boiling Channel Natural Circulation Loop

2018 ◽  
Author(s):  
Jin-Der Lee ◽  
Yuh-Ger Lin ◽  
Shao-Wen Chen ◽  
Chin Pan ◽  
Jinn-Jer Peir
Keyword(s):  
Natural Circulation ◽  
Loss Coefficient ◽  
System Stability ◽  
Circulation Loop ◽  
Stable Region ◽  
Type I ◽  
Resonance Oscillation ◽  
Seismic Acceleration ◽  
Natural Circulation Loop ◽  
Heated Channel

Based on the external force method, the present study integrates the nonlinear dynamic model developed previously by the authors with vertical seismic accelerations to investigate the seismic-induced effect on the single nuclear-coupled boiling channel natural circulation loop. The natural frequencies of the states in the stable region are widely explored through nonlinear analysis. The results indicate that the natural frequency of initial state tends to increase as the increase in the phase change number (operating power) or as the decrease in the subcooling number (inlet subcooling). As supposing that a real seismic acceleration is directly imposed on the system, some parametric effects on the seismic-induced oscillations are performed in the present natural circulation loop system. The seismic-induced oscillations are found to be consistent with the combined results of the inherent system stability characteristics and the impact of external seismic acceleration. The system with a larger outlet loss coefficient of the heated channel, or a longer heated channel, would destabilize the seismic-induced oscillations, while the inlet loss coefficient of the heated channel has a stable effect on the system. A much stronger resonance oscillation could be induced by the increase in the core inlet subcooling. Notably, the enlargement and contraction of the heated channel diameter would move the natural circulation system closer to type-I and type-II instability regions, respectively. These both generate unstable effects on the seismic-induced oscillations due to the inherent stability characteristics of the initial states.

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