N. A. Mazheiko

1/f noise and self-organized criticality in crisis regimes of heat and mass transfer

Abstract Thermal fluctuations under the transition from nucleate to film boiling of water on a wire heater and fluctuations of jet form during an outflow of superheated liquid from a pressure vessel were experimentally investigated. It has been found that power spectrum of the fluctuations has got a low frequency component corresponding to a 1/f law (flicker noise). The effect given is connected with the occurrence of nonequilibrium phase transitions in the systems: a crisis of heat transfer under the transition from nucleate to film boiling and a crisis of a flow in boiling-up of superheated liquid jet.

Disintegration of flows of superheated liquid films and jets

This paper represents results on investigating the dynamics of boiling and disintegration of superheated liquid films and jets. The first part deals with experimental study of boiling liquid outflow through short cylindrical and slit channels. Evolution of disintegration of a hot water jet flow is observed both at low and moderate superheating and at high and limit superheating, and also for vaporization mechanisms corresponding to these superheatings. Peculiarities of disintegration of jets through slit and cylindrical channels are noticed. Results on measuring the reactive thrust of the jet through a slit channel under different geometrical conditions behind the channel outlet are represented. The 1/f fluctuations in transient regimes of superheated liquid boiling and in transient regimes of behavior of the jet shape are found. The second part of this article represents results on experimental investigation of nonsteady heat transfer and dynamics of the development of crisis phenomena at boiling of a falling subcooled liquid film in the conditions of stepwise heat release. The experimental data were obtained using synchronized high-speed infrared thermography and video. It is shown that with growth and condensation of vapor bubbles, on the liquid film interface appear large-amplitude waves that lead to considerably increasing local intensity of heat transfer. New data on the boiling incipience temperature in a subcooled liquid film, depending on the heat flux density, are obtained. It is found that the development of boiling crisis is a result of appearance of local dry patches and their subsequent growth by the mechanism of longitudinal thermal conductivity in the heat transfer wall as the equilibrium heat flux density is exceeded.

Nonequilibrium phase transitions in a jet of highly superheated water

Results are given of an experimental study into the dependence of integral and local characteristics of hot water flow on the value of superheating and on the kinetics of boiling in this water. Abrupt variations are revealed of parameters of a jet of boiling water such as the reactive force, the jet cone angle, and the rate of nucleation of vapor bubbles in the jet. Abrupt variations of modes of jet flow are treated as nonequilibrium phase transitions. This enables one to invoke model concepts of generation of 1/f fluctuations under conditions of nonequilibrium phase transitions in open systems. The inversely proportional dependence of power spectra of oscillation on frequency (1/f fluctuations) in a jet of highly superheated water is found experimentally both under laboratory conditions and in a commercial-scale steam generator. Characteristic scales are discussed for reducing the experimental results for reactive force to dimensionless form.

Jets of incipient liquids

Jets of incipient water escaping into the atmosphere through a short channel are photographed. In some experiments. complete disintegration of the jet is observed. The relationship of this phenomenon with intense volume incipience is considered. The role of the Coanda effect upon complete opening of the jet is revealed. Measurement results of the recoil force R of the jets of incipient liquids are presented. Cases of negative thrust caused by the Coanda effect are noted. Generalization of experimental data is proposed.

Pulsation dynamics during explosive boil-up of overheated water jets

We have studied dynamics of pulsation that develop during the explosion boil-up of overheated water jets emitted via a nozzle from a high-pressure vessel. At a temperature within 480–490 K, the water jet exhibits complete breakage accompanied by a sharp drop in the reactive force and the appearance of intense fluctuations. The power spectrum of these fluctuations has a divergent 1/f low-frequency component, which is indicative of the instability of flow and the possibility of large-scale low-frequency outbursts.

Reactive Recoil and Pressure Pulsations with 1/ f Power Spectrum under Conditions of Explosion Boiling of Jets of Superheated Liquid

The results are given of an experimental investigation of the reactive recoil of jets of boiling up liquids in a thermodynamically highly nonequilibrium mode of efflux. The experimental data are given in the dimensionless form using the thermodynamic similarity methods. The correlation is discussed between the abrupt decrease in the reactive power with a complete disintegration of the jet under conditions of explosion boiling. Local measurements are performed of pressure pulsations in a jet of superheated liquid with different mechanisms of vaporization. It is found that, under conditions of explosion boiling, the power spectrum of pulsations depends inversely proportionally on frequency (1/f or flicker noise). This form of power spectrum implies the possibility of strong low-frequency pulsations of reactive recoil of boiling up flows.

1/f Fluctuations in Critical Modes of Flow of Superheated Liquid

Experimental studies are performed into the variation of the shape of a jet of boiling liquid flowing out of a high-pressure vessel under conditions of high superheating. The mechanisms of bulk heterogeneous and homogeneous nucleation are identified, and the correlation between these mechanisms and critical modes of outflow is determined. The photometry of transmitted laser radiation is used to investigate the dynamics of photocurrent fluctuations. It is found that, in the case of intensive bulk boiling in a jet of superheated liquid, the fluctuation power spectrum has a low-frequency component (flicker noise) diverging as 1/f. This effect is associated with nonequilibrium phase transitions proceeding in the system.

The dynamic characteristics of flashing jets of superheated aqueous solutions

A diagram of discharge modes for ethanol-water solution is presented, which was constructed on the basis of results obtained from an experimental study of flashing jets of aqueous ethanol solutions discharging into the atmosphere through a short channel. A correlation between the flow modes of two-phase medium with certain mechanisms of vaporization is shown. The large-scale 1/f fluctuations revealed in a jet of flashing aqueous solutions of ethanol in transient flow modes point to the fact that catastrophic outbursts may occur in the flow.

Flicker noise and self-organized criticality in crisis boiling regimes

The paper describes an experimental study of thermal fluctuations during transition from bubble to film boiling of water on a wire heater and fluctuations of the shape of a superheated liquid jet discharged from a high‐pressure vessel. It is found that for a heat‐transfer crisis on the wire heater and for intense volume boiling of the superheated liquid jet, the fluctuation power spectrum has a low‐frequency component (flicker noise) that diverges under the law 1/f. This effect is due to nonequilibrium phase transitions in the system: the heat‐transfer crisis during transition from bubble to film boiling and a flow crisis during boiling of the superheated liquid jet.