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Understanding the flow dynamics of chemical species is important for characterizing, analyzing, and designing chemical reactors. Computational fluid dynamics (CFD) provides accurate flow patterns, but this approach can be computationally expensive for large or complex geometries. To overcome this limitation, a new Lagrangian‐based method is developed using smoothed particle hydrodynamics (SPH) to forecast the flow patterns and residence time distribution of two different fluids for various reactor geometries: (laminar, fractal, T‐mixer, Hartridge–Roughton (H‐R) mixer and packed bed with a gyroid internal packing) and compared the results with computational fluid dynamics (CFD) simulations. The SPH method is less accurate than the CFD analysis, but it obtained the approximate flow behavior much faster. Consequently, the SPH method has significant potential as a first screening technique to optimize reactor topologies and internal packing structures. [ABSTRACT FROM AUTHOR]

The use of fluidization assistance can greatly enhance the fluidization hydrodynamics of powders that exhibit poor fluidization behavior. Compared to other assistance techniques, pulsed flow assistance is a promising technique for improving conventional fluidization because of its energy efficiency and ease of process implementation. However, the inlet flow configuration of pulsed flow can significantly affect the bed hydrodynamics. In this study, the conventional single drainage (SD) flow strategy was modified to purge the primary flow during the non-flow period of the pulse to eliminate pressure buildup in the inlet flow line while providing a second drainage path to the residual gas. The bed dynamics for both cases, namely, single drainage (SD) and modified double drainage (MDD), were carefully monitored by recording the overall and local pressure drop transients in different bed regions at two widely different pulsation frequencies of 0.05 and 0.25 Hz. The MDD strategy led to substantially faster bed dynamics and greater frictional pressure drop in lower bed regions with significantly mitigated segregation behavior. The spectral analysis of the local and global pressure transient data in the frequency domain revealed a pronounced difference between the two flow strategies. The application of the MDD inlet flow strategy eliminated the disturbances from the pulsed fluidized bed irrespective of the pulsation frequency. [ABSTRACT FROM AUTHOR]

Assisted fluidization techniques can significantly improve the hydrodynamics of difficult- to-fluidize solids. Among these techniques, the pulsed flow strategy is highly promising owing to its cost-effectiveness and amenability to implementation for largescale processing. Using commercial-grade, highly porous nanosilica that shows strong agglomeration behavior, we implemented the pulsed flow with square-wave pulsation schemes of 0.05, 0.10, and 0.25 Hz frequencies, and compared their effectiveness in each case. Besides the conventional approach of assessing their efficacy using the pressure drop data, we have proposed a new approach in this work that consists of computing the power of the overall pressure drop transient signals. Using the theoretical value, i.e., the effective bed weight per unit area as a reference, the percentage increase in the power was 27 ± 4, 71 ± 5, and 128 ± 4, respectively, for 0.05, 0.10, and 0.25 Hz pulsation frequencies. In fact, the average pressure drop values were substantially higher when the partial bed collapse occurred between successive pulsations when compared with the case of low-frequency pulsations. The pulsation frequency also affected the evolution of local bed dynamics in various bed regions during the expansion and collapse of the bed. Moreover, the local and global pressure transients have shown interesting mutual correlations which were otherwise not evident from their individual transient profiles. [ABSTRACT FROM AUTHOR]

Bed collapse experiments provide vital information about fluidized bed hydrodynamics. In this study, the region-wise bed collapse dynamics of glass beads, titania (TiO2), and hydrophilic nanosilica (SiO2) particles with widely different voidages (ε) of 0.38, 0.80, and 0.98, respectively, were carefully investigated. These particles belonged to different Geldart groups and exhibited varied hysteresis phenomena and fluidization indices. The local collapse dynamics in the lower, lower-middle, upper-middle, and upper regions were carefully monitored in addition to the distributor pressure drop to obtain greater insight into the deaeration behavior of the bed. While the collapse dynamics of glass beads revealed high bed homogeneity, the upper middle region controlled the collapse process in the case of titania due to the size-based segregation along the bed height. The segregation behavior was very strong for nanosilica, with the slow settling fine agglomerates in the upper bed regions controlling its collapse dynamics. The collapse time of the upper region was 25 times slower than that of the lower region containing mainly large agglomerates. The spectral analysis confirmed the trend that was observed in the pressure transients. The clear presence of high frequency events at 20 and 40 Hz was observed in the nanosilica due to agglomerate movements. The residual air exiting the plenum was strongly affected by the bed voidage, being lowest for the nanosilica and highest for the glass beads. [ABSTRACT FROM AUTHOR]

The use of flow pulsation as an effective assisted fluidization technique has been suggested in a number of applications, such as drying of food and pharmaceutical products, dry beneficiation of coal, and deagglomeration of nanopowders, owing mainly to its cost‐effectiveness and ease of implementation. The efficacy of this technique is, however, greatly affected by the frequency of pulsation since it controls the collapse dynamics of the fluidized bed. In this study, using ultrafine hydrophilic nanosilica with strong agglomeration tendencies, the pulsation frequency was controlled to allow only partial collapse of the bed between two successive pulsations while the global and local dynamics in different bed regions were carefully monitored. Besides the usual advantages associated with assisted fluidization techniques, such as lower minimum fluidization velocity, higher bed expansion, and elimination of bed non‐homogeneities, the continuous and intense solid motion imparted by the partial bed collapse caused a more substantial increase in the overall pressure drop than the one obtained with the conventional unassisted fluidization. The results of the frequency domain analysis highlighted the fact that the effect of pulsation event was felt differently in different regions of the bed depending upon the amplitude of the pulsation. These results were further corroborated by the similarity analysis. [ABSTRACT FROM AUTHOR]

Nanosilica is widely used in various applications, with its market expected to grow over USD 5 billion by 2025. The fluidized bed technology, owing to its intimate contact and efficient mixing of phases, is ideally suited for the large scale processing of powders. However, the bulk processing and dispersion of ultrafine nanosilica using the fluidized bed technology are critically affected by the interparticle forces, such that the hydrophilic nanosilica shows agglomerate bubbling fluidization (ABF), while the hydrophobic nanosilica undergoes agglomerate particulate fluidization (APF). This study carried out a detailed investigation into the fluidization hydrodynamic of the hydrophobic nanosilica by monitoring the region-wise dynamics of the fluidized bed subjected to a regular step change of fixed duration in the gas velocity. The gas flow was controlled using a mass controller operated with an analog output signal from a data acquisition system. The analog input data were acquired at the sampling rate of 100 Hz and analyzed in both time and temporal frequency domains. The effect of velocity transients on the bed dynamics was quickly mitigated and appeared as lower frequency events, especially in regions away from the distributor. Despite the apparent particulate nature of the fluidization, strong hysteresis was observed in both pressure drop and bed expansion. Moreover, the fully fluidized bed's pressure drop was less than 75% of the theoretical value even though the bed appeared to free from non-homogeneities. Key fluidization parameters, e.g., minimum fluidization velocity (Umf) and the agglomerate size, were evaluated, which can be readily used in the large scale processing of nanosilica powders using fluidized bed technology. [ABSTRACT FROM AUTHOR]

Featured Application: As a first step towards developing a simple yet cost-effective technique based on the fluidized bed technology for the treatment of carbon dioxide present in post-combustion flue gases from power plants, we have rigorously investigated the improvement in the fluidized bed hydrodynamics of fine adsorbent particles by mixing with group B particles. Any improvement in the fluidization of fine particles will ultimately translate into higher capture efficiency of the carbon dioxide by the fluidized bed containing fine adsorbent powders. We have developed a new particle-mixing strategy for improving the fluidization hydrodynamics of Geldart group C powders by mixing with small proportions of group B particles. Two different group C particles with widely different physical properties, i.e., 1 μm calcium hydroxide powder and 27 μm porous activated carbon, were selected for investigation in the present work. A carefully sieved sample of inert sand was used as external group B particles for mixing. Fluidization experiments were carried out, and the quality of the fluidization was assessed using the fluidization index. For the monocomponent fluidization of fine calcium hydroxide powder, pressure drop was sometimes as much as 250% higher than the effective weight of the bed. The proposed strategy of particle mixing substantially improved its fluidization hydrodynamics. On the other hand, the development of channels and cracks during the monocomponent fluidization of the activated carbon led to gas bypassing, resulting in low pressure drop and poor contact of phases. Particle mixing was found to improve fluidization behavior, and the chi-squared test showed that the best results were obtained with 13 wt% particle mixing. [ABSTRACT FROM AUTHOR]

In this study, we investigate the effectiveness of particle mixing technique to improve the fluidization hydrodynamics of nanoparticles that show strong agglomeration behavior during their dry processing. We choose small proportions of particles belonging to Geldart group A classification as additive particles because of their superior hydrodynamic behavior. This strategy not only suppresses the hysteresis phenomenon, but also helps to substantially reduce the size of agglomerates. Moreover, mixing of external micron-sized Geldart group A particles with resident nanoparticles of fluidized bed causes a variation in the volume-change of mixing in the range of − 25% to − 60%, indicating a significant contraction of the bed. Conventional models reported in the literature were unable to describe such a high degree of volume contraction. Results obtained in this study clearly establish the efficacy of particle mixing as an effective assisted fluidization technique in eliminating bed non-homogeneities and promoting the deagglomeration of nanoparticles. [ABSTRACT FROM AUTHOR]

Deagglomeration of ultrafine powders poses an important challenge towards their efficient and effective utilization. In the present study, we investigate the effect of frequency on the hydrodynamics of pulsed fluidized beds of ultrafine powders that show strong agglomeration behavior. We have carefully selected square waves of three different frequencies: 0.05 Hz, 0.10 Hz, and 0.25 Hz. The lowest frequency used here allowed the fluidized bed to settle completely before another pulse was introduced whilst the highest frequency ensured that the bed remained in a state of continuous turbulence between occurrences of consecutive pulses. On the other hand, the intermediate frequency pulse was just sufficient to complete the process of bed collapse before the start of the next pulse. Both local and global bed dynamics in all the three cases were rigorously monitored using fast response pressure transducers. The pressure transient data during the bed collapse were processed using the bed collapse model reported in the literature to compute the effective hydrodynamic diameter of agglomerates. Though there was substantial decrease in the agglomerate size, the effect of the frequency appeared to be rather insignificant as the global pressure transients remained rather insensitive to the change of the fluidization velocity. [ABSTRACT FROM AUTHOR]

Abstract: The component additive rule for the prediction of the volume of fluidized mixtures of binary-solids does not hold owing to the phenomenon of the volume-change of mixing. A significant contraction in the volume of the mixed bed is often observed. This phenomenon has an important bearing on the hydrodynamics of the binary-solid fluidization. In the present, the volume-change of mixing is experimentally investigated for several liquid-fluidized binary-solid mixtures for a wide range of compositions at the incipient fluidization. Seven different binaries are composed from eight different solid species that differ in their sizes as well as densities, and therefore exhibit a wide range of stratification pattern. The use of packing models reported in the literature results in rather poor predictions of the observed volume-change of mixing. Incorporating the hydrodynamic aspects of the fluidization however helps to substantially improve predictions. A two-level integration of the hydrodynamic information is implemented here. The level one involves using the hydrodynamic drag diameter evaluated from the expansion of individual solid species instead of the commonly used volume-equivalent or the packing-equivalent diameter. The level two in addition involves accounting for the expansion of either of the solid species should it occur at the incipient fluidization of the mixture. [Copyright &y& Elsevier]

The processing of fine and ultrafine particles using a fluidized bed is challenging in view of their unpredictable hydrodynamic behavior due to interparticle forces. The use of assisted fluidization techniques in such cases can be effective in improving the bed hydrodynamics. This work investigates the dynamics of pulsed fluidized bed of ultrafine nanosilica subjected to square-wave flow pulsations. The pulse duration used in this study is sufficient to allow the complete collapse of the pulsed fluidized bed between two consecutive flow pulsations. The proposed pulsation strategy is carefully implemented using electronic mass flow controllers with the help of analog output signals from data acquisition system. Given that the different regions of the fluidized bed exhibit varying dynamics, which together contribute to overall bed dynamics, the bed transients in the upper, central, and lower regions of the fluidized bed are monitored using several sensitive pressure transducers located along the height of the bed. The effect of the flow pulsation on the hydrodynamics of the fluidized bed is rigorously characterized. A significant reduction in the minimum fluidization velocity was obtained and an increase in the bed homogeneity was observed due to flow pulsations. The frequency domain analysis of the signals clearly delineated the frequency of the various events occurring during the fluidization. [ABSTRACT FROM AUTHOR]

Low-frequency flow pulsations were utilized to improve the hydrodynamics of the fluidized bed of hydrophilic ultrafine nanosilica powder with strong agglomeration behavior. A gradual fluidization of unassisted fluidized bed through stepwise velocity change was carried out over a wide range of velocities followed by a gradual defluidization process. Bed dynamics in different regions of the fluidized bed were carefully monitored using fast and sensitive pressure transducers. Next, 0.05-Hz square-wave flow pulsation was introduced, and the fluidization behavior of the pulsed fluidized bed was rigorously characterized to delineate its effect on the bed hydrodynamics by comparing it with one of the unassisted fluidized bed. Flow pulsations caused a substantial decrease in minimum fluidization velocity and effective agglomerate diameter. The frequencies and amplitudes of various events in different fluidized bed regions were determined by performing frequency domain analysis on real-time bed transient data. The pulsations and their effects promoted deagglomeration and improved homogeneity of the pulsed fluidized bed. [ABSTRACT FROM AUTHOR]

• Segregation of highly porous agglomerated ultrafine nanosilica was investigated. • Bed collapse studies were conducted using pressure transients. • Pronounced agglomerates' size-based segregation occurred due to initial flow spike. • Modified inlet flow strategy suppressed size-based segregation of agglomerates. Unlike conventional fluidization of micron-sized particles, the hydrodynamics of ultrafine nanopowders is controlled by their agglomerates, which show strong segregation pattern along the bed height. This aspect was carefully investigated in this study by carrying out collapse experiments in a low-frequency pulsed fluidized bed. Unlike previous studies, the inlet flow was modified with the help of four-way valve configuration to eliminate the inlet flow spike. The region-wise collapse dynamics was monitored by recording pressure transients along the height of the fluidized bed while double drainage deaeration strategy, termed modified dual drainage (MDD), was employed. The size of agglomerates in the different bed regions were evaluated and compared with the conventional single drainage (SD) and dual drainage (DD) deaeration configurations using two-way and three-way solenoid valves. The elimination of the flow spike with MDD helped to suppress the size-based segregation of agglomerates, thereby resulting in faster and smoother bed collapse. [ABSTRACT FROM AUTHOR]

• Effect of acoustic frequency on the fluidized bed hydrodynamics was investigated. • Transients in different sections were monitored using sensitive pressure transducers. • Response during both fluidization and defluidization were examined at several flows. • Defluidization behavior was markedly different from one of the fluidization. • Acoustic perturbations at non-resonant frequency failed to affect bed hydrodynamics. Sound-assisted fluidization has of late gained a significant research focus as a potential assisted fluidization technique for improving the hydrodynamics of solids that exhibit cohesive and non-homogeneous fluidization behavior. This study investigated the dynamics of a bed subjected to acoustic perturbations at different frequencies during the sound-assisted fluidization of a hydrophilic nanopowder with strong agglomeration behavior. The bed pressure transients were carefully monitored using sensitive pressure transducers in different sections of the bed over a wide range of velocities using ambient air as the fluidizing gas. Both fluidization and defluidization dynamics were investigated by varying the velocity in small steps using electronic mass flow controllers connected to a data acquisition system. In addition to the resonance frequency of 220 Hz, acoustic vibrations of 200 and 150 Hz frequency were also investigated to clearly delineate the effect of resonant frequency on the bed response. Our results clearly suggest that operation of sound-assisted fluidization at the resonant frequency greatly enhances its effectiveness. [ABSTRACT FROM AUTHOR]