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The purpose of this study is to reduce the conveying velocity and power consumption in gas–solid two-phase flows. Four pieces of soft fins with different (non-uniform) lengths, which are fixed on the horizontal central plane of the inlet, are employed to self-excite the gas–solid flow. A horizontal acrylic pipe, approximately 5 m long and with an inside diameter of 80 mm, is selected as the test pipeline. The test solid materials are spherical polyethylene particles with average diameter and density of 2.3 mm and 978 kg/m3, respectively. The solid mass flow rate and average gas velocity are 0.10–0.47 kg/s and 10–17 m/s, respectively. Compared with non-fin and previous uniform soft fin gas–solid flows, the minimum gas velocity, pressure drop, additional pressure drop, and power consumption are reduced when a lower gas velocity is achieved with the use of non-uniform soft fins. The highest reduction rates in power consumption and minimum velocity are approximately 5.87% and 10.04%, respectively. The particle concentration in flows with non-uniform soft fins is higher than that in the non-fin flow in the upper part of the pipe of the acceleration region and lower than those in non-fin and uniform fin flows near the pipe bottom. By employing particle image velocimetry measurement, the time-averaged axial particle velocity and fluctuating particle velocity in all non-uniform fin flows are found to be higher than those in non-fin and uniform fin flows, especially near the upper part of the pipe. Unlabelled Image • The fins of non-uniform length were used to excite the gas-solid two-phase flow • Pressure drop, minimum velocity and particle velocity were measured • The lowest pressure drop and gas velocity were realized by the non-uniform fins • Particle velocity and fluctuating velocity increased by using the non-uniform fins [ABSTRACT FROM AUTHOR]

Abstract The effect of self-excited soft fins on a pneumatic conveying with different vertical curved 90° bends was experimentally studied to reduce pressure drop, power consumption and conveying air velocity. The distributions of particle velocity and particle fluctuating velocity near and in the first bend were measured based on the high-speed PIV. The polyethylene particles with a diameter of 2.3 mm were used as conveying materials. The superficial air velocity was varied from 10 to 14 m/s, and the stable mass flow rate was fixed at 0.45 kg/s. Compared to the non-fin pneumatic conveying, the pressure drop, the minimum pressure drop (MPD) velocity, power consumption, and additional pressure drop can be reduced by using soft fins for two bends of different radii (R/D = 3.2 and 4.4) in lower air velocity range. The maximum reduction rates of the MPD velocity and power consumption by using soft fins is about 8.2% and 8%, respectively. At the upstream of the bend, the particle velocity of the soft fins is higher than that of the non-fin. The effect of soft fins on the particle velocity and its fluctuating energy remains in the bend. The particle velocity and fluctuating energy of particle velocity of the soft fins are higher than that of the non-fin in the first vertical bend. At the downstream of the bend, the fluctuating energy of particle velocity of the soft fins is higher than that of non-fin in the large radius bendon the top part of the pipe. Graphical abstract Unlabelled Image Highlights • A pneumatic conveying with vertical bends by using soft fins was studied. • The pressure drop, additional pressure drop and particle velocity were measured. • The pressure drop and conveying velocity were reduced by fins. • Particle velocity of fins was higher than that of non-fin near and in the bend. • Effect of fins on the particle velocity and fluctuating energy remains in the bend. [ABSTRACT FROM AUTHOR]

To further elucidate the mechanism of energy-conserving conveying in horizontal pneumatic conveying with the dune model, the high-speed particle image velocimetry is applied to measure particle fluctuation velocity near the minimum conveying velocity of the conventional pneumatic conveying. This study focuses on the effect of mounting dune models on the horizontal pneumatic conveying in terms of power spectrum, autocorrelation coefficients, two-point correlation coefficients, fluctuation intensity of particle velocity, skewness factor, and probability density function. It is found that the power spectrum peaks with the dune model are larger than those of the nondune system, suggesting the acceleration and suspending efficiency of the dune model, especially dune models mounted at the bottom of the pipe. Meanwhile, the profiles of particle fluctuation velocity intensity indicate that the large particle fluctuating energy is generated due to mounting the dune model so that the particles are more easily accelerated and suspended. This is one of the important reasons why the mounted dune model results in a low pressure drop and low minimum conveying velocity. Based on the distribution of skewness factor and 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 the pipe. The particle fluctuation velocities in the case of the dune models mounted at the bottom of the pipe obey the Gaussian-type fluctuation more. [ABSTRACT FROM AUTHOR]

The effect of using the soft fins on a horizontal pneumatic conveying of granular particles in various curved 90° bends was studied in this paper, in order to reduce pressure drop and conveying air velocity. Experimental measurements were performed in terms of the pressure drop, conveying air velocity, power consumption and additional pressure drop. The distributions of particle velocity near and in the curved 90° bend were measured by high-speed PIV. The test pipeline consisted of a 4.5 m-long horizontal straight acrylic tube, a curved 90° acrylic bend and a 1.5 m-long horizontal straight acrylic tube, having an inside diameter of 80 mm. The polyethylene particles with diameter of 2.3 mm were used as conveying materials. The superficial air velocity was varied from 10 to 14 m/s, and the solid mass flow rate was fixed at 0.45 kg/s. Comparing with the dilute phase pneumatic conveying, the pressure drop, the minimum pressure drop (MPD) velocity, power consumption and additional pressure drop can be reduced by using soft fins for various bends in lower air velocity range. The reduction becomes more evident with increasing the radius ratio of bend. The maximum reduction rates of the MPD velocity and power consumption by using soft fins is about 8.2% and 11.7%, respectively. At the upstream of bend, the particle velocity of the soft fins is evidently higher than that of the dilute phase in the bottom part of pipe for all bends. The effect of soft fins on the particle velocity and its fluctuating energy still remains in the bend and the downstream of bend, and the fluctuating energy of particle velocity gradually decreases through the bend. At the downstream of bend, the fluctuating energy of particle velocity decreases with increasing the radius ratio of bend. [ABSTRACT FROM AUTHOR]

In order to reduce pressure drop and conveying air velocity, the paper studied the effect of the dune model and soft fins in horizontal pneumatic conveying involving a 90° bend. Experimental measurements were performed in terms of the pressure drop, conveying air velocity and additional pressure drop. The distributions of particle velocity near and in the curved 90° bend were measured by high-speed PIV. The test pipeline consisted of a 4.5m-long horizontal straight acrylic tube, a curved 90° acrylic bend (mean radius of curvature 250mm) and a 1.5m-long horizontal straight acrylic tube, having an inside diameter of 80mm. The polyethylene particles with diameter of 2.3mm were used as conveying materials. The superficial air velocity was varied from 10 to 14m/s, and the solid mass flow rate was fixed at 0.45kg/s. Comparing with the conventional pneumatic conveying, the pressure drop, the minimum pressure drop (MPD) velocity and additional pressure drop can be reduced by using soft fins in lower air velocity range. The reduction rates of the MPD velocity by using soft fins and dune model were about 4.1% and 8.3%, respectively. At the upstream of bend and in the bend, the particle velocity of using the dune model is evidently higher than that of the conventional pneumatic conveying and using soft fins. However, the effect of soft fins and dune model on the particle velocity is maintained downstream of the bend. [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 mechanism of the low pressure drop at low air velocity in a horizontal excited gas–solid two-phase pipe flow of using soft fins, the distributions of particle velocity and concentration are measured by the high-speed particle image velocimetry (PIV) and image process. The test pipeline consists of a horizontal smooth acrylic tube with an inside diameter of 80mm and a length of about 5m. The polyethylene particles of density 978kg/m3 and 952kg/m3 with diameters of 2.3 and 3.3mm are used as test materials. The distributions of the time-averaged particle velocity and concentration are measured at the minimum air velocity and the solid mass flow rates of 0.45kg/s and 0.40kg/s in the acceleration and fully developed regimes. It is found that the particle concentration of using fins exhibits almost same profile as that of non-fin although the air velocities of using fins are lower than that of non-fin. In the acceleration regime, there is little difference of the normalized axial particle velocity up /Ua between short fins and non-fin. up /Ua of the long fins having low air velocity, however, is slightly higher than that of non-fin. In the fully developed regime, even though up /Ua of using long fins is obviously lower than that of other fins and non-fin in the lower part of pipeline, the steady gas–solid two-phase flow can be observed. It suggests that the long fins easily accelerate the particles and result in low pressure drop and low air velocity. For the relatively large particles, the effect of fins on up /Ua is smaller than that for the small particles. Due to the effect of fins’ oscillation, the vertical particle velocity decreases in the low part of pipeline, resulting in the particle dispersion and the reduction of particles–wall collision. [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]

Abstract: The high-speed particle image velocimetry (PIV) is employed to measure the distribution of particle fluctuation velocity near the minimum conveying velocity in the acceleration and fully developed regimes in a horizontal pneumatic conveying. The fluctuation characteristics of particle velocity are examined in terms of time-averaged particle velocity and concentration, power spectrum, auto-correlation coefficients, two-point correlation coefficients, intensity of particle fluctuation velocity, skewness factor and probability density function. It is revealed that the profile of the time-averaged particle velocity depends on the conveying velocity and solids loading ratio in the bottom part of the pipe in the fully developed regime. A quasi-periodical particle flow pattern with the lower frequency appears in this region and dominates the pressure drop of the pneumatic conveying. The intensities of particle fluctuation velocity of the sliding strand flows in the bottom part of pipe are smaller that of the suspension flows in the top part of pipe, revealing that the low intensity of particle fluctuation velocity can result in the low conveying pressure drop. The particle fluctuation velocity of the low or minimum conveying velocity follows the Gaussian probability distribution in the fully developed regime. [Copyright &y& Elsevier]

Abstract: The purpose of this study focuses on analyzing the particle velocity and concentration characteristics in a horizontal pneumatic conveying with dune model, so as to reveal the mechanism of the low conveying velocity and saving-energy conveying. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80mm and a length of about 5m. The polyethylene particles of density 978kg/m3 and 952kg/m3 with diameters of 2.3 and 3.3mm are used as conveying materials. High-speed PIV was first applied to measure the time-averaged particle velocity and was proven to be an efficient measurement technique in the pneumatic conveying. Then the particle velocity and concentration distributions of three locations were measured at mean air velocities of 12m/s and 13m/s and the solid mass flow rates of 0.45kg/s and 0.43kg/s. A comparison of the particle velocity and concentration profiles between dune model and non-dune model was performed. It is found that the particle concentration of using dune model becomes higher in the upper part of pipeline and becomes lower near the bottom of pipeline in the acceleration region. The particle velocities of using dune model are clearly higher than that of the conventional pneumatic conveying along pipeline and display a uniform profile at the downstream. It is also clear that the particles can be effectively accelerated by increasing air velocity and impacting the surface of dune model. The effect of dune model on the velocity profile of relatively small particles is larger than that of the larger particles and maintains to the downstream. [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]

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]

The high-speed particle image velocimetry is applied to measure the particle velocities of a horizontal self-exited gas-solid two-phase pipe flow with soft fins at the air velocity of the minimum pressure drop. The detailed particle dynamics of using fins' cases are analyzed and compared with a conventional non-fin case. It is found that the particle accelerating process is delayed in the acceleration regime and the vertical particle velocity is decreased near the top part of fully-developed regime due to the effect of fins' oscillations. The continuous wavelet transform of axial particle fluctuation velocity suggests that the fins make the particle motions fall into a lower frequency range in the acceleration regime. In the fully-developed regime, the dominating frequencies of large-scale particle flows are decreased and the streaks appearing in the range of high frequency are weakened by using fins. The energy distributions of proper orthogonal decomposition (POD) modes indicate that the relative energy of POD mode1 is increased by using fins in both acceleration and fully-developed regimes, and the dominance is significantly enhanced by using fins in the fully-developed regime. The auto-correlation coefficients and central frequencies of POD modes exhibit that the dominating large-scale particle motion is enhanced by using fins, correspondingly, small-scale particle motion is suppressed. [Display omitted] • The particle velocity of a horizontal self-exited gas-solid two-phase pipe flow is measured at minimum air velocity by PIV. • POD and continuous wavelet transform is adopted to analyze the particle fluctuation velocities. • The dominating frequencies of large-scale particle flows are decreased. • The streaks appears in the range of high frequency are weakened by using fins. • The dominance of POD mode 1 is significantly enhanced by using fins in the fully-developed regime. [ABSTRACT FROM AUTHOR]