Zunhong Yu

A new breakup regime of liquid drops identified in a continuous and uniform air jet flow

A new breakup regime of liquid drops, named the dual-bag breakup regime, in a continuous and uniform air jet flow is identified at We ranging from 28 to 41 at the present investigation. The dual-bag breakup regime is characterized by two successive bag breakup processes; the first one is suffered by the initial main drop, and the second one is suffered by the core drop produced in the first bag breakup process. Shadowgraph and high-speed cameras were used to record the temporal properties of liquid drops in the dual-bag breakup regime. Parameters including breakup time, drop deformation rate, and volume fraction of core drop, are measured and given as a function of Weber numbers in the dual-bag breakup regime.

Multifractality of drop breakup in the air-blast nozzle atomization process.

The multifractal nature of drop breakup in the air-blast nozzle atomization process has been studied. We apply the multiplier method to extract the negative and the positive parts of the f(alpha) curve with the data of drop-size distribution measured using dual particle dynamic analyzer. A random multifractal model with the multiplier triangularly distributed is proposed to characterize the breakup of drops. The agreement of the left part of the multifractal spectra between the experimental result and the model is remarkable. The cause of the distinction of the right part of the f(alpha) curve is argued. The fact that negative dimensions arise in the current system means that the spatial distribution of the drops yielded by the high-speed jet fluctuates from sample to sample. In other words, the spatial concentration distribution of the disperse phase in the spray zone fluctuates momentarily, showing intrinsic randomness.

Multifractal detrended fluctuation analysis of combustion flames in four-burner impinging entrained-flow gasifier

Abstract On a laboratory-scale testing platform of an impinging entrained-flow gasifier with four opposed burners, the flame images for diesel combustion and gasification process were recorded with a single charge coupled device (CCD) camera. The two-dimensional multifractal detrended fluctuation analysis was employed to investigate the multifractal nature of the flame images. Sound power-law scaling relations in the annealed average of detrended fluctuations were unveiled when the order q > 0 , and the multifractal feature of flame images was confirmed. Further analyses identified two multifractal parameters, the minimum and maximum singularities α min ⁡ and α max ⁡ , serving as characteristic parameters of the multifractal flames. These two characteristic multifractal parameters vary with respect to different experimental conditions.

On the properties of random multiplicative measures with the multipliers exponentially distributed

Under the formalism of annealed averaging of the partition function, a type of random multifractal measures with the multipliers exponentially distributed is investigated in detail. Branching emerges in the curve of generalized dimensions, and negative values of generalized dimensions arise. Three equivalent methods of classification of the random multifractal measures are proposed, which is based on: (i) the properties of the curves of generalized dimensions, (ii) the solution properties of equation τ(q)=0, and (iii) the relative position of the curve f(α) and the diagonal f(α)=α in the first quadrant. These classes of measures correspond to μ([0,1])=∞, μ([0,1])=1 and μ([0,1])=0, respectively. Phase diagram is introduced to illustrate the diverse performance of the random measures that is multiplicatively generated.

ANOMALOUS FEATURES ARISING FROM RANDOM MULTIFRACTALS

Under the formalism of annealed averaging of the partition function, two types of random multifractal measures with their probability of multipliers satisfying power law distribution and triangular distribution are investigated mathematically. In these two illustrations, branching emerges in the curve of generalized dimensions, and more abnormally, negative values of generalized dimensions arise. Therefore, we classify the random multifractal measures into three classes based on the properties of generalized dimensions. Other equivalent classifications are also presented by investigating the location of the zero-point of τ(q) or the relative position either between the f(α) curve and the diagonal f(α) = α or between the f(q) curve and the α(q) curve. We consequently propose phase diagrams to characterize the classification procedure and distinguish the scaling properties between different classes. The branching phenomenon emerging is due to the extreme value condition and the convergency of the generalized dimensions at point q = 1. We conjecture that the branching condition exists and that the classification is universal for any random multifractals. Moreover, the asymptotic behaviors of the scaling properties are studied. We apply the cascade processes studied in this paper to characterizing two stochastic processes, i.e. the energy dissipation field in fully developed turbulence and the droplet breakup in atomization. The agreement between the proposed model and experiments are remarkable.

Application of a Capacitance Solid Mass Flow Meter in a Dense Phase Pneumatic Conveying System of Pulverized Coal

Capacitance measurement is one of the available methods for measuring the solid mass flow rate in the field of gas‐solid flow. Performance of a capacitance solid mass flow meter was tested in a dense phase pneumatic conveying system of pulverized coal. Results have demonstrated that the deviations of mass flow rates in the experimental set‐up are almost within ±5% for stable flow patterns while unstable flow patterns and low conveying concentration pose great measurement deviations. On the other hand, the measurement accuracies in a vertical downward flow pipeline and a horizontal pipeline are almost identical and the both are slightly better man that in a vertical upward flow pipeline. Additionally, its performances in a pilot‐scale entrained‐flow gasification plant with dry feeding are also presented and satisfying results are achieved.

R/S method for unevenly sampled time series: Application to detecting long-term temporal dependence of droplets transiting through a fixed spatial point in gas–liquid two-phase turbulent jets

We perform rescaled range analysis upon the signals measure d by Dual Particle Dynamical Analyzer in gas-liquid two-phase turbulent jets. A novel re scaled range analysis is proposed to investigate these unevenly sampled signals. The Hurst ex ponents of velocity and other passive scalars in the bulk of spray are obtained to be 0.59 ±0.02 and the fractal dimension is hence 1.41 ± 0.02, which are in remarkable agreement with and much more pr ecise than previous results. These scaling exponents are found to be in dependent of the configuration and dimensions of the nozzle and the fluid flows. Therefore, su ch type of systems form a universality class with invariant scaling properties.

Inversion formula of multifractal energy dissipation in three-dimensional fully developed turbulence

The concept of inverse statistics in turbulence has attracted much attention in recent years. It is argued that the scaling exponents of the direct structure functions and the inverse structure functions satisfy an inversion formula. This proposition has already been verified by numerical data using the shell model. However, no direct evidence was reported for experimental three-dimensional turbulence. We propose to test the inversion formula using experimental data of three-dimensional fully developed turbulence by considering the energy dissipation rates instead of the usual efforts on the structure functions. The moments of the exit distances are shown to exhibit nice multifractality. The inversion formula between the direct and inverse exponents is then verified.