Measurement of the fractal order of wall void fraction during nucleate boiling

Sathyamurthi, Vijaykumar; Banerjee, Debjyoti; Sakamoto, Hitoshi; Kim, J.

doi:10.1016/j.ijheatfluidflow.2007.03.009

Cited by 9 publications

(5 citation statements)

References 23 publications

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“…D 2 values for our experimental series are comparable with those of Heish et al, Cammarata et al, Narayanan et al, Qu et al, and Sathyamurthi et al We note that the nuclear-coupled natural circulation loop has relatively less complex behavior than externally heated natural circulation loop. Interestingly, our D 2 (3.09) at Q = 4.0 kW and Δ T sub = 50 °C are very close to that (3.0) estimated by Sathyamurthi et al in their experiments on nucleate boiling. This is a very strong evidence that nucleate boiling occurs in our experiments at Q = 4.0 kW and Δ T sub = 50 °C.…”

Section: Nonlinear Analysis Of Experimental Time Seriessupporting

confidence: 90%

Nonlinear Analysis of Chaotic Time Series in a Natural Circulation Boiling Loop

Karmakar

Paruya

2012

Ind. Eng. Chem. Res.

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The present study reports chaotic flow oscillations observed in a natural circulation boiling loop. The periodic oscillations of wall temperature (thermal oscillations) initiate at a certain condition of heat flux and inlet subcooling in addition to geysering instability and pressure-drop oscillations. We observed that boiling regime changes from nucleate boiling to transition boiling as a result of decrease in inlet subcooling and increase in heat flux. The thermal oscillations are strongly coupled with pressure-drop oscillations. Nonlinear analysis of the time series of loop flow rate at various heater power and inlet subcooling have been carried out using statistical analysis, fast Fourier transform (FFT), time delay embedding for attractor reconstruction, autocorrelation, and correlation dimension. The analysis confirms that the oscillations are more chaotic at relatively low heater power and high inlet subcooling. The complexity of the oscillations strongly depends on boiling heat transfer regime. Our observations and analysis have been supported by other relevant experiments.

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Section: Nonlinear Analysis Of Experimental Time Seriessupporting

confidence: 90%

Nonlinear Analysis of Chaotic Time Series in a Natural Circulation Boiling Loop

Karmakar

Paruya

2012

Ind. Eng. Chem. Res.

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“…A priori it is expected that the periphery of round dry spots appearing well before the dryout has a fractal dimension close to unity and that it will increase for the ramified dry spots anticipating the film regime. For the computation of the fractal dimension, we use the box counting algorithm [33]. This method is illustrated in Figs.…”

Section: Boiling Crisis and Criticalitymentioning

confidence: 99%

“…In the past few years, different experimental approaches have suggested that the boiling crisis (BC) may be a scalefree phenomenon which implies criticality [22][23][24][25][26][27][28][29]. The appearance of 1/f noise [30,31] and the increase in magnitude of chaos quantifiers, like the fractal patterns of the wall temperature fluctuations [32] and of the outlines of the voids [33], are signatures of the absence of characteristic scales in the BC vicinity.…”

Section: Introductionmentioning

confidence: 99%

Criticality in the slowed-down boiling crisis at zero gravity

et al. 2015

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Boiling crisis is a transition between nucleate and film boiling. It occurs at a threshold value of the heat flux from the heater called CHF (critical heat flux). Usually, boiling crisis studies are hindered by the high CHF and short transition duration (below 1 ms). Here we report on experiments in hydrogen near its liquid-vapor critical point, in which the CHF is low and the dynamics slow enough to be resolved. As under such conditions the surface tension is very small, the experiments are carried out in the reduced gravity to preserve the conventional bubble geometry. Weightlessness is created artificially in two-phase hydrogen by compensating gravity with magnetic forces. We were able to reveal the fractal structure of the contour of the percolating cluster of the dry areas at the heater that precedes the boiling crisis. We provide a direct statistical analysis of dry spot areas that confirms the boiling crisis at zero gravity as a scale-free phenomenon. It was observed that, in agreement with theoretical predictions, saturated boiling CHF tends to zero (within the precision of our thermal control system) in zero gravity, which suggests that the boiling crisis may be observed at any heat flux provided the experiment lasts long enough.

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“…A brief description of the method for determination of box counting dimension has been included in this section. A detailed description can be found in [14][15][16]…”

Section: Determination Of Fractal Dimension Of Flame Structure From Imentioning

confidence: 99%

Dynamic Characterization of Candle Flame

Ghosh

Mondal

et al. 2010

International Journal of Spray and Combustion Dynamics

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The present work focuses on studying the flickering of a candle placed in a hollow cylindrical glass tube. Variations in flame area and intensity have been studied as the oscillating parameters of the flame with a camera and a Photomultiplier tube (PMT), and results have been found to be indicative of the presence of some well defined peaks in the amplitude spectrum of the flame intensity. Tests have been carried out with a range of candle diameters for the same glass tube giving similar results. Fluctuations in fractal dimension of the flame structure have also been studied in the course of the work. The time series data generated by processing camera images and also the PMT voltage output has been studied for existence of periodicity in the signal recorded. The correlation dimension has been determined for a number of experiments to characterize the dynamics of the signal.

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Measurement of the fractal order of wall void fraction during nucleate boiling

Cited by 9 publications

References 23 publications

Nonlinear Analysis of Chaotic Time Series in a Natural Circulation Boiling Loop

Nonlinear Analysis of Chaotic Time Series in a Natural Circulation Boiling Loop

Criticality in the slowed-down boiling crisis at zero gravity

Dynamic Characterization of Candle Flame

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