Water flow rate pulsations with a flicker power spectrum in a commercial sodium steam generator

Abstract

The spectral characteristics of the water flow rate pulsations in the evaporation module of a steam generator with sodium heating in the BN-600 power-generating unit at nominal power are investigated. The results show that the power spectrum of the flow rate pulsations vary inversely as the frequency (flicker pulsations). The appearance of the high-energy low-frequency pulsations of the water flow rate is attributed to a critical heat transfer regime (nonequilibrium phase transition) which is realized in the evaporation module.The presence of critical thermal loads in the components of power-generating equipment requires using not only average thermophysical process parameters but also fluctuation deviations from them as well as the dynamics of random pulsations. One of the most important characteristics of a random process is the power spectrum of the fluctuations -the frequency dependence of the spectral density of the pulsations S(ƒ). The spectral density is the ratio of the average squared amplitude of the noise signal near the frequency ƒ to the width ∆ƒ of the frequency band. A characteristic feature of systems with flicker noise is that the power spectrum corresponds to a 1/ƒ dependence at low frequencies. The inverse proportionality to the frequency shows that a substantial part of the energy fluctuations is due to very slow processes and, moreover, indicates the possibility of large excursions in the system.Flicker noise (1/ƒ noise) was discovered in 1925 by J. Johnson while studying the emission current of vacuum tubes [1]. Initially, flicker noise was studied in application to electronic devices. It was found that it is characteristic for all materials and components employed in electronics. Later it was found that flicker noise is a widely occurring phenomenon in nature [2][3][4]. A fluctuation power spectrum inversely proportional to frequency S~ 1/ƒ is encountered in physical, chemical, mechanical, and biological systems. The 1/ƒ dependence remains over several orders of magnitude of the power of the fluctuations. In astrophysics, 1/ƒ pulsations are observed in the intensity of quasar radiation and sun spots. In geophysics, a 1/ƒ power spectrum is used to describe earthquakes and floods. In biology, 1/ƒ spectra are observed in the fluctuations of insulin in the blood of diabetics and heart and brain rythyms in certain sicknesses. In economics, the money flows and stock-market fluctuations exhibit a 1/f spectral dependence. Flicker fluctuations are observed in fluctuations of the number of automobiles on roads and even in music and speech.Ordinarily, 1/ƒ noise is understood to be fluctuation processes with a power spectrum proportional to 1/ƒ α , where the exponent α varies over certain limits (0.8 < α < 2). A well-known property of 1/ƒ α fluctuations is scale invariance, which