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Two-Phase Flow Instabilities
Published in Maurizio Cumo, Antonio Naviglio, Thermal Hydraulics, 1988
Maurizio Cumo, Antonio Naviglio
The flow excursion instability (or Ledinegg instability)2 involves a sudden change of the flow to a considerably lower value. This happens when the slope of the characteristic curve — channel pressure losses vs. flow rate (channel internal characteristic) — becomes algebrically lower than the slope of the characteristic curve — motive-head vs. flow rate of the feeding component or system (channel external characteristic). The threshold criterion for this kind of instability is represented in Figure 1 and is expressed by the relationship: () (∂Δp/∂G)int<(∂Δp/∂G)ext
Heat Transfer, Thermal Hydraulic, and Safety Analysis
Published in Kenneth D. Kok, Nuclear Engineering Handbook, 2016
Ledinegg instability or flow excursive instability is characterized by a sudden change in the flow rate to a lower value or a flow reversal. This happens when the slope of the channel demand pressure drop versus flow rate curve (internal characteristics of the channel) becomes algebraically smaller than that of the loop supply pressure drop vs. flow rate curve (external characteristics of the channel). Physically, this behavior exists when the pressure drop decreases with increasing flow. The criterion or condition for Ledinegg instability to occur is expressed by the inequality (Boure et al., 1973)
Density Wave Instability Verification of 1-D Computational Two-Fluid Model
Published in Nuclear Science and Engineering, 2021
Krishna Chetty, Subash Sharma, John Buchanan, Martin Lopez-de-Bertodano
The DWI two-phase flow problem in a heated channel, Fig. 1, was first solved analytically by Ishii1 using the linearized equilibrium dynamic DFM. This and the flow excursion, i.e., the static Ledinegg instability,16 are old industrial problems that occur in boilers. In the case of DWI, the pressure losses at the inlet and outlet become out of phase because of the void wave transit time, leading to flow oscillations. These and other two-phase system instabilities may be analyzed within the DFM mathematical framework. Achard et al.2 obtained a full analytic solution of the DWI problem with the HEM, which allowed a nonlinear analysis. Achard et al.’s and Ishii’s solutions of the stability boundary in the linear limit were compared by Lopez-de-Bertodano et al.,17 and both solutions coincide. The linear theory is addressed in the present work. Although necessary for complete verification, the waveforms in the nonlinear regime are not compared in this work.