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In order to study the characters of particle fluctuation velocity at the minimum pressure drop (MPD) velocity in the acceleration and fully developed regimes of a horizontal pneumatic conveying, the particle fluctuation velocities measured by the high-speed particle image velocimetry (PIV) are first analyzed by time-averaged particle velocity, fluctuating energy, power spectrum and autocorrelation. Then the proper orthogonal decomposition (POD) and continuous wavelet transform are developed to reveal the particle fluctuation velocities in terms of the contributions to the particle fluctuation energy, time-frequency distribution, as well as probability density function from POD modes. The energy distributions of POD modes suggest that the first two POD modes are most energetic and dominate the particle motion, and the dominance increases from the acceleration regime to fully-developed regime. The time-frequency characteristics of POD modes reveal that small-scale particle fluctuations are suppressed in the fully-developed regime. It implies that the suppression of small-scale particle fluctuations may result in lower pressure drop at MPD velocity. The PDF distributions of POD modes exhibit that the particle fluctuation of first two POD modes follows the Gaussian distribution in the acceleration and fully developed regimes. However, the PDF distributions of POD modes gradually deviate from Gaussian distribution as increasing mode number. [ABSTRACT FROM AUTHOR]

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]

Abstract: Multi-scale characteristics of particle fluctuation velocity at the MPD (minimum pressure drop) air velocity in the acceleration and fully-developed regimes are experimentally investigated. The high-speed particle image velocimetry (PIV) is first used to measure the fluctuating particle velocities at the MPD air velocity in a horizontal pneumatic conveying. Then the fluctuating particle velocities in the acceleration and fully-developed regimes are analyzed by the continuous wavelet transform and orthogonal wavelet multi-resolution technique. It is found that the wavelet components of low frequency dominate the fluctuating energy of axial particle velocity in the bottom part of the pipe, and contribute about 70% and 84% to the acceleration and fully-developed regimes, respectively. The more contribution to the fluctuating energy of vertical particle velocity, however, comes from the wavelet components of high frequency, accounting for about 82%. The low frequency component of auto-correlation suggests a large-scale particle flow in both acceleration regime and fully-developed regime. The low frequency wavelet component also makes a large contribution to spatial correlation of axial particle velocity, which increases from the acceleration regime to fully-developed regime. The PDF of low frequency components are asymmetrical near the bottom of the pipe, but the PDF of the relatively high frequency exhibits symmetry and the spread of the PDF evidently shrinks for increasing frequencies, implying a reducing fluctuation of high frequency component. [Copyright &y& Elsevier]

This study is focused on reducing the pressure drop, conveying velocity, and power consumption in a horizontal gas–solid flow. Four types of lattice models, which are fixed in the particle inlet, are proposed to easily generate the oscillation of the wake flow to easily convey the gas–solid two-phase flow. A horizontal pipeline with an inner diameter of 80 mm and length of approximately 5 m was used. Polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were employed as conveying solid materials. The experimental ranges of the average gas velocity and solid mass flow rate were 10–16 m/s and 0.10–0.47 kg/s, respectively. Compared to the nonlattice gas–solid flow, reductions in the total pressure drop, conveying gas velocity, power consumption, and additional pressure loss were achieved in the range of lower gas velocity when using the lattice model. The highest reduction rates of the minimum conveying velocity and additional pressure drop were approximately 5.12% and 15.2%, respectively. In the acceleration region, the particle concentration in the flows with the lattice model was larger than that in the nonlattice flow near the upper part of the pipe and lower than those in the nonlattice flows in the lower part of the pipe. The time-mean axial particle velocity and particle fluctuating velocity in all lattice model flows were higher than those in the nonlattice flow, according to particle image velocimetry measurements, particularly in the upper part of the pipe. [Display omitted] • The lattice models were applied to gas-solid two-phase flow. • Pressure drop, minimum velocity, and particle velocity were measured. • The pressure drop and minimum velocity are reduced by using lattice model. • High particle velocity and fluctuating velocity were observed in the upper part of pipe. [ABSTRACT FROM AUTHOR]

To induce large oscillations of air flow and suspend particles easily near the particle supply point in a low air velocity region of horizontal air-solid two-phase flow, a short cylinder model with a streamlined front side (refer to streamlined model) is proposed and is fixed on the bottom or top of the pipe in front of the particle feed. The streamlined front side of the model is designed to reduce the flow resistance, and the rectangular rear section of the model generates wake vortical flow so as to induce large airflow oscillation. The test tube consists of a horizontal pipe having an inner diameter of 80 mm and a length of 5 m. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were used as the test solid particles. Average air velocities and particle mass flow rates ranged from 9 to 16 m/s and 0.11 to 0.51 kg/s, respectively. Compared with the non-model air-solid two-phase flow, the streamlined model has reduced the pressure drop, critical and minimum conveying air velocities, power consumption, and additional pressure drop. This model achieved the highest reduction rate with a minimum air velocity of approximately 6% and an additional pressure loss of approximately 37.5%. According to particle image velocimetry measurement of air-solid two-phase flow, the time-averaged particle velocity and fluctuating particle velocity generated by the streamlined model are larger than those in the non-model flow, so even low air velocities can easily convey particles. [Display omitted] • A short cylinder model with a streamlined front side to induce vortical flow is proposed. • Pressure drop and minimum air velocity of air-solid two-phase flow are reduced. • The highest reduction rate of an additional pressure loss is approximately 37.5%. • The time-averaged and fluctuating particle velocities increase. [ABSTRACT FROM AUTHOR]

The purpose of this study is to apply the oscillation flow induced by a combination of a circular cylinder and non-uniform soft fins to gas–solid two-phase flows to reduce the transport gas velocity and power consumption in a horizontal pipe. In order to evaluate the oscillation flow, several different sizes of square and circular cylinders are used to combine four pieces of soft fins with non-uniform lengths, which are mounted on the horizontal central plane in front of the particle supply. The test pipe comprises a horizontal acrylic pipe with a length of 5 m and an inside diameter of 80 mm. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were used as the test particles. The average gas velocity was 9–16 m/s, and the solid mass flow rate was 0.11–0.51 kg/s. It is found that the combination of a circular cylinder or square cylinder of L = 10 mm with non-uniform soft fins causes the lowest pressure drop and highest velocity fluctuation in the oscillation flow based on single-phase flow (gas only) measurement. Compared to conventional gas–solid two-phase flows, the reduction in the minimum transport velocity, pressure drop, power consumption, and additional pressure drop were obtained using a combination of a circular cylinder with non-uniform soft fins. This combination provides the highest reduction rates in the minimum conveying velocity and an additional pressure drop by approximately 10.0% and 34.1%, respectively. Based on particle image velocimetry measurements, the time-mean particle velocity and particle fluctuating velocity of a circular cylinder with non-uniform soft fins were higher than those of conventional flows near the bottom part of the pipe, thus easily accelerating and suspending particles near the pipe bottom, even at lower gas velocities. [Display omitted] • A combination of a circular cylinder and soft fins was used to induce the oscillation flow. • The oscillation flow was applied to gas-solid two-phase flow for energy-saving conveying. • The pressure drop, minimum velocity, and power consumption are reduced. • The particle velocity and fluctuating velocity were high near the bottom part of the pipe. [ABSTRACT FROM AUTHOR]

This study focuses on multi-scale particle dynamics of horizontal pneumatic conveying equipped with two types of soft fins at the air velocity of the minimum pressure drop. The particle velocity fields of non-fin and using soft fin's cases are measured by high-speed particle image velocimetry. Then the particle fluctuation velocities are decomposed into various scales based on one-dimensional orthogonal wavelet decomposition. It is found that the non-uniform case of Fin260 yields the highest axial- and vertical- particle velocities and fluctuation energies, giving rise to the lowest pressure drop and conveying air velocity. The overall relative energy distributions of wavelet components suggest that the particle fluctuation energies become more concentrated at wavelet levels 3 and 4 by using fins, especially for the case of non-uniform Fin260. The energy concentration on specific wavelet levels indicates a more organized particle motions under the effect of air turbulence induced by non-uniform soft fins. The correlation analysis suggests that the spatial correlation of wavelet component is associated with the contribution of wavelet component to the measured particle fluctuation energy. The oscillating soft fins modulate the air turbulence and promote the particle motions to be spatially correlated in a range of specific frequency. [Display omitted] • Multi-scale analysis of particle fluctuation velocity is performed • Particle fluctuation energies become concentrated at levels 3 and 4 by using fins • Multi-scale spatial correlation is associated with particle fluctuation energy • The oscillating soft fins promote the particle motions to be spatially correlated [ABSTRACT FROM AUTHOR]