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Abstract: The particle fluctuation velocities of a horizontal self-excited gas–solid two-phase pipe flow with soft fins near MPD (minimum pressure drop) air velocity are first measured by high-speed PIV in the acceleration and fully-developed regimes. Then orthogonal wavelet multi-resolution analysis and power spectrum are used to reveal multi-scale characteristics of particle fluctuation velocity. It is observed that the pronounced peaks of the spectra of axial and vertical fluctuation velocities appear in the range of low frequency near the bottom of pipe. These peaks of spectra become larger and their frequencies decrease by using fins. In the range of low frequencies (3–25Hz), the wavelet components of the fluctuating energy of axial particle velocity make the main contribution accounting for 87% and 93% respectively for non-fin and using fins near the bottom of pipe. In the range of relatively high frequency (50–400Hz), however, the wavelet components of using fins, accounting for about 49%, become smaller than that of non-fin, accounting for about 72%, in the suspension flow regime near the top of pipe. The skewness factor of axial particle fluctuation velocity indicates that the wavelet components follow the Gaussian probability distribution as the central frequency decreases. [Copyright &y& Elsevier]

Abstract: In order to reveal the mechanism of the steady transport at the low conveying velocity by using soft fins, the high-speed particle image velocimetry (PIV) is used to measure and analyze particle fluctuation velocity near air conveying velocity of the minimum pressure drop (MPD) in a horizontal self-excited pneumatic conveying. The study focuses on the effect of the different fin's lengths on the horizontal pneumatic conveying in terms of the time-averaged particle concentration and velocity, power spectrum, auto-correlation coefficients, two-point correlation coefficients, fluctuation intensity of particle velocity, skewness factor and probability density function. It is found that the power spectra peaks of fins, especially the longer fins, are larger than that of non-fin even at lower air velocity, suggesting the accelerating efficiency of fins' vibration. Meanwhile, the profiles of particle fluctuation velocity intensity indicate that the fins' oscillation generates large particle fluctuating energy even at lower air velocity so that the particles are more easily accelerated and suspended. This is one of the important reasons why the fins' oscillation results in the low pressure drop and low MPD air velocity. From the distribution of the skewness factor and the probability density function, it is found that the particle fluctuation velocities of all cases follow the Gaussian distribution in the lower and middle parts of pipe, and departure from the Gaussian distribution in the upper part of the pipe. The particle fluctuation velocity of the most efficient Fin320 more obeys the Gaussian-type fluctuation. [Copyright &y& Elsevier]

Abstract: In order to reveal the reduction mechanism of conveying velocity and pressure drops in a horizontal self-excited pneumatic conveying by using soft fins, the distributions of particle velocity and concentration were measured by the high-speed particle image velocimetry (PIV) and image process at the minimum air velocity. The study focuses on the effect of the different fin’s lengths on the horizontal pneumatic conveying in terms of frequency features of fin’s oscillation, time-averaged particle concentration and velocity, fluctuation intensity of particle velocity and power spectrum of particle fluctuating velocity. It is found that the particle concentration of the fins is lower than that of non-fin near the bottom and is higher than that of non-fin near the top of pipe even at low air velocity. In the acceleration regime, the normalized particle velocity of the long fins is higher than that of non-fin, implying the efficiency of the long fin on reducing pressure drop and conveying velocity. For conveying particles having the relatively large terminal velocity, however, there is little effect of fins on particle velocity. The fluctuating energy of particle velocity of fins are larger than that of non-fin near the bottom of pipe, and the long fins exhibit the largest value in the top part of pipe in the fully developed regime. Based on analyzing the power spectrum of particle fluctuation velocity, it is indicated that the fins generate the large peaks of power spectrum in the low frequency range, which is related to the reduction of pressure drop. [Copyright &y& Elsevier]

High-speed PIV is first used to measure the fluctuating particle velocities of a horizontal self-excited pneumatic conveying at low air velocity of minimum pressure drop in the acceleration and fully-developed regimes. Then, an orthogonal wavelet multi-resolution analysis and power spectrum are employed to reveal multi-scale characteristics of particle fluctuation velocity. It is found that the pronounced peaks of the spectra of axial and vertical fluctuation velocities appear in the low frequency range near the bottom of the pipe, and the peaks of the spectra become larger by using fins. In the range of low frequencies (3–25 Hz), the wavelet components of the fluctuating energy of axial particle velocity are the main contributions, accounting for 35% and 91% for non-fin and using fins, respectively, near the bottom of the pipe. However, in the range of relatively high frequencies (50–400 Hz), the wavelet components of using fins, accounting for approximately 57%, become smaller than that of non-fin, accounting for approximately 66%, in the fully-developed regime near the top of the pipe. The auto-correlation with fins displays large quasi-periodical waves in the low frequency regime as τ increases. [ABSTRACT FROM AUTHOR]