Natural Boiling Oscillation

The conclusion to be drawn from the above examples and many others is that softness in a boiling system, preceding the boiling channel inlet, may cause flow oscillations of low frequency. It is probably the pressure perturbations arising from the explosive nature of nucleate boiling that initiates the oscillation, and the reduced burn-out flux which follows probably corresponds to the trough of the flow oscillation, as a reduction in flow rate always drops the burn-out flux in forced-convection boiling. 

Pressure drop oscillations (Maulbetsch and Griffith, 1965) is the name given the instability mode in which Ledinegg-type stability and a compressible volume in the boiling system interact to produce a fairly low-frequency (0.1 Hz) oscillation. Although this instability is normally not a problem in modern BWRs, care frequently must be exercised to avoid its occurrence in natural-circulation loops or in downflow channels. 

The response of this detector is based on the fact that the frequency output from piezoelectric material is influenced by the weight of the coatings or layers on its surface. This effect has been used for many years to measure trace concentrations of water vapor in a gas and xylene vapor in air has been detected by this means at concentrations as low as lO g/ml. It was first introduced as a GC detecting system by King [22]. The detector consists of a quartz crystal (coated with a high boiling liquid) that is appropriately situated in an electronic circuit that causes it to oscillate at its natural frequency. The oscillation frequency is continuously monitored by a separate circuit. 

While the tg structure represents the most well-defined molecular geometry, it is not, unfortunately, one that exists in nature. Real molecules exist in the quantum states of the 3N-6 (or 5) vibrational states with quantum numbers (vj, V2.-..V3N-6 (or 5)). Vj = 0, 1, 2,. Even in the lowest (ground) (0,0...0) vibrational state, the N atoms of the molecule undergo their zero point vibrational motions, oscillating about the equilibrium positions defined by the B-O potential energy surface. It is necessary then to speak of some type of average or effective structures, and to account for the vibrational motions, which vary with vibrational state and isotopic composition. In spectroscopy, a molecule s structural information is carried most straightforwardly by its molecular moments of inertia (or their inverses, the rotational constants), which are determined hy analysis of the pure rotational spectrum or fire resolved rotational structure of vibration-rotation bonds. Thus, the spectroscopic determination of molecular structure boils down to how one uses the rotational constants of a molecule... 

Measurement of liquid level is usually noisy, because of splashing and turbulence of fluids entering the vessel. As we have seen, loops that resonate respond to random disturbances by oscillating at their natural period. As a result, level measurements are rarely quiet, often fluctuating 20 or 30 percent of scale. This is particularly true in vessels containing boiling liquids, where turbulence is high. 

Manavela Chiapero et al. (2012, 2013a,b) have reviewed pressure drop oscillations in boiling systems. The exhaustive nature of the research at the Norwegian University of Science and Technology cannot be overemphasized. Reviews of instabilities in the case of single and parallel channels include Ozawa et al. (1989), Tadrist (2007), and Kakac and Bon (2008). The latter is especially complete. March-Leuba and Rey (1993) presented a state-of-the-art review for the case of coupled thermo-hydraulic-neutronic instabilities in BWRs. 

Jain, K.C., 1965. Self-Sustained Hydrodynamic Oscillations in a Natural-circulation Two-Phase-Flow Boiling Loop. Argonne National Laboratory Report ANL-7073. 

Lakshmanan, S.P., Pandey, M., 2009. Analysis of startup oscillations in natural circulation boiling systems. Nuclear Engineering and Design 239, 2391—2398. 

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