scholarly journals Volcanic tremor induced by gas-liquid two-phase flow: Implications of density wave oscillation

2011 ◽  
Vol 116 (B9) ◽  
Author(s):  
Eisuke Fujita ◽  
Kazuhiro Araki ◽  
Katsuhiro Nagano
Keyword(s):  
Two Phase Flow ◽  
Density Wave ◽  
Volcanic Tremor ◽  
Phase Flow ◽  
Two Phase ◽  
Wave Oscillation

Research on Two-Phase Flow Instability in Evaporator of Refrigeration System

2010 ◽  
Author(s):  
Nan Liang ◽  
Changqing Tian ◽  
Shuangquan Shao
Keyword(s):  
Pressure Drop ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Density Wave ◽  
Phase Flow ◽  
Constant Mass ◽  
Refrigeration System ◽  
Two Phase

As one kind of fluid machinery related to the two-phase flow, the refrigeration system encounters more problems of instability. It is essential to ensure the stability of the refrigeration systems for the operation and efficiency. This paper presents the experimental investigation on the static and dynamic instability in an evaporator of refrigeration system. The static instability experiments showed that the oscillatory period and swing of the mixture-vapor transition point by observation with a camera through the transparent quartz glass tube at the outlet of the evaporator. The pressure drop versus mass flow rate curves of refrigerant two phase flow in the evaporator were obtained with a negative slope region in addition to two positive slope regions, thus making the flow rate a multi-valued function of the pressure drop. For dynamic instabilities in the evaporation process, three types of oscillations (density wave type, pressure drop type and thermal type) were observed at different mass flow rates and heat fluxes, which can be represented in the pressure drop versus mass flow rate curves. For the dynamic instabilities, density wave oscillations happen when the heat flux is high with the constant mass flow rate. Thermal oscillations happen when the heat flux is correspondingly low with constant mass flow rate. Though the refrigeration system do not have special tank, the accumulator and receiver provide enough compressible volume to induce the pressure drop oscillations. The representation and characteristic of each oscillation type were also analyzed in the paper.

Experimental Study on Thermal-Hydraulics During Start-Up in the Natural Circulation Boiling Water Reactor Concept: Effects of System Pressure and Increasing Heat Flux on the Geysering and Density Wave Oscillation

2002 ◽  
Author(s):  
M. Hadid Subki ◽  
Masanori Aritomi ◽  
Noriyuki Watanabe ◽  
Chaiwat Muncharoen
Keyword(s):  
Heat Flux ◽  
Natural Circulation ◽  
Density Wave ◽  
Boiling Water ◽  
Phase Flow ◽  
Two Phase ◽  
Water Reactor ◽  
Wave Oscillation ◽  
System Pressure ◽  
Start Up

The feasibility study in thermal-hydraulics for the future light water reactor concept is carried out. One of the essential studies is the two-phase flow instability during start-up in the natural circulation boiling water reactor (BWR) concept. It is anticipated that the occurrence of the two-phase flow instabilities during start-up significantly affects the feasibility concept, since it would cause the complexity in raising and maneuvering the power output. The purpose of the current study is to experimentally investigate the driving mechanism of the geysering and density wave oscillation in the natural circulation loop, induced by a range of system operating pressure and increasing heat flux in vertical parallel channels. The pressure range of atmospheric up to about 4 bars, and the input heat flux range of 0 up to 577 kW/m2 are applied in these experiments. An experimental apparatus of twin boiling upflow channels to simulate natural circulation flow loop has been designed, constructed and operated. The natural circulation in the loop occurs due to the density difference between two-phase region in the channels and the single-phase liquid in the downcomer. The objective of the study is to propose a rational start-up procedure in which the geysering and density wave oscillation can be prevented during startup, according to its system pressure and heat flux. Previous studies have clarified that three (3) kinds of thermo-hydraulics instabilities may occur during start-up in the natural circulation BWR depending on its procedure and reactor configuration, which are (1) geysering induced by condensation, (2) natural circulation induced by hydrostatic head fluctuation in steam separator, and (3) density wave oscillation.

Fundamental and Higher-Mode Density-Wave Oscillations in Two-Phase Flow

1972 ◽  
Vol 94 (2) ◽  
pp. 189-195 ◽  
Author(s):  
G. Yadigaroglu ◽  
A. E. Bergles
Keyword(s):  
Heat Capacity ◽  
Atmospheric Pressure ◽  
Single Phase ◽  
Two Phase Flow ◽  
Density Wave ◽  
Phase Region ◽  
Flow Instabilities ◽  
Phase Flow ◽  
Two Phase ◽  
Density Wave Oscillations

This paper treats the oscillatory two-phase flow instabilities commonly referred to as density-wave oscillations. A dynamic analysis of the single-phase region of a boiling channel, accounting for wall heat capacity and the effect of pressure variations on the movements of the boiling boundary, is summarized. Experiments conducted with a Freon-113 channel at atmospheric pressure revealed the existence of “higher-mode” oscillations. These appeared at high subcoolings and low power levels and were characterized by unexpectedly short periods that were fractions of the transit time. The presence of the higher modes and other observations are explained in terms of the dynamic behavior of the boiling boundary.

SEMI-ANALYTICAL BIFURCATION ANALYSIS OF TWO-PHASE FLOW IN A HEATED CHANNEL

2005 ◽  
Vol 15 (08) ◽  
pp. 2395-2409 ◽  
Author(s):  
A. DOKHANE ◽  
D. HENNIG ◽  
R. CHAWLA ◽  
RIZWAN-UDDIN
Keyword(s):  
Hopf Bifurcation ◽  
Bifurcation Analysis ◽  
Two Phase Flow ◽  
Stability Boundary ◽  
Density Wave ◽  
Phase Flow ◽  
Two Phase ◽  
Drift Flux Model ◽  
Drift Flux ◽  
Heated Channel

Using a drift flux representation for the two-phase flow, a new reduced order model has been developed to simulate density-wave oscillations (DWOs) in a heated channel. This model is then used to perform stability and semi-analytical bifurcation analysis, using the bifurcation code BIFDD, in which the stability boundary (SB) and the nature of Hopf bifurcation are determined in a suitable two-dimensional parameter space. A comparative study is carried out to investigate the effects of the parameters in the drift flux model (DFM) — the radially void distribution parameter C0 and the drift velocity Vgj — on the SB as well as on the nature of Hopf bifurcation. It is the first time that a systematic analysis has been carried out to investigate the effects of DFM parameters on the nature of Hopf bifurcation in a heated-channel two-phase flow. The results obtained show that both sub- and super-critical Hopf bifurcations are encountered. In addition, it has been found that, while the SB is sensitive to both C0 and Vgj, the nature of Hopf bifurcation for lower values of N sub is more sensitive to Vgj than to C0. Numerical integration of the set of ODEs is carried out to confirm the predictions of the semi-analytical bifurcation analysis.

Stability and Bifurcation Analyses of Two-Phase Flow Using a Drift Flux Model and Bifurcation Code BIFDD

2002 ◽  
Author(s):  
A. Dokhane ◽  
D. Hennig ◽  
R. Chawla ◽  
Rizwan-Uddin
Keyword(s):  
Fluid Dynamics ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Nonlinear Differential Equations ◽  
Density Wave ◽  
Feedback Gain ◽  
Phase Flow ◽  
Two Phase ◽  
Reduced Order ◽  
Drift Flux Model

Nonlinear boiling water reactor (BWR) studies are generally pursued by employing large system codes, like RAMONA and RETRAN. However, detailed investigations using this approach in which parametric studies are to be carried out over large regions of parameter space are very expensive and time consuming. Therefore, it is necessary to use the so-called reduced order models containing a “manageable” number of system equations incorporating the essential features of the physical phenomena. Since the thermal-hydraulic model determines the main feedback gain and the associated time delay (void feedback reactivity), the modelling of the fluid dynamics is of paramount importance for the reduced order model analyses for BWRs. For a certain set of hydraulic parameter values, the system of nonlinear differential equations describing the fluid dynamics generates the so-called self-sustained density wave oscillations (DWO), which is a typical two-phase flow instability.

Experimental Study on Density Wave Instability of Sodium Boiling Two-Phase Flow in an Annulus

2002 ◽  
Author(s):  
Suizheng Qiu ◽  
Minoru Takahashi ◽  
Dounan Jia
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Density Wave ◽  
Inlet Temperature ◽  
Phase Flow ◽  
Wave Instability ◽  
Two Phase ◽  
System Pressure

Experiments of density wave instability in a liquid sodium boiling two-phase flow experiments in an annulus were carried out in the following parameters range: heat flux from 80kW/m2 to 976kW/m2, inlet subcooling from 25.6°C to 226.8°C, mass flow rate from 7.92kg/h to 68.9kg/h, system pressure from 2600Pa to 0.12Mpa. Not only the mechanism of the instability, critical conditions and oscillation period, but also the effects of pressure, mass flow rate and inlet subcooling on the density wave instability were explored experimentally and theoretically. From the experimental data, it was found that the lower the inlet temperature was, the higher the system pressure and the mass flow rate that could result in a more stable boiling two-phase flow were. A correlation for the density wave instability was obtained on from the dimensional analysis for the conservation equations of mass, momentum and energy.

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