KONA Powder and Particle Journal No. 41 (2024) 254–264/https://doi.org/10.14356/kona.2024007

Original Research Paper

The Mechanism behind Vibration Assisted Fluidization of
Cohesive Micro-Silica †Rens Kamphorst *, P. Christian van der Sande, Kaiqiao Wu *, Evert C. Wagner,
M. Kristen David, Gabrie M.H. Meesters and J. Ruud van Ommen
Department of Chemical Engineering, Delft University of Technology, The Netherlands

Vibro-assisted fluidization of cohesive micro-silica has been studied by means of X-ray
imaging, pressure drop measurements, and off-line determination of the agglomerate size.
Pressure drop and bed height development could be explained by observable phenomena taking
place in the bed; slugging, channeling, fluidization or densification. It was observed thatchanneling is the main cause of poor fluidization of the micro-silica, resulting in poor gas-solid
contact and little internal mixing. Improvement in fluidization upon starting the mechanicalvibration was achieved by disrupting the channels. Agglomerate sizes were found to notsignificantly change during experiments.
Keywords: fluidized bed, X-ray imaging, agglomeration, assistance methods, cohesive
powder

1. Introduction

Fluidization of cohesive powders has seen significant
interest in the last decades, fueled by the increase in applications of powders with small particle sizes. Cohesive
micro- and nanopowders find their use in medical applications (Prabhu and Poulose, 2012; Guo et al., 2013), catalysis (Li et al., 2003) and coatings (Mahato and Cho, 2016)
for example.
Due to their small particle size, the attractive van der
Waals forces between these particles are dominant, in theabsence of moisture, making them hard to fluidize(Kamphorst et al., 2023). Two main complications areseen: channeling and agglomeration. Channeling is thephenomenon where a gas bypass, or channel, is formed
through the bed in the vertical direction upon the introduction of gas. Gas mainly flowing through a channel has poorinteraction with the powder bed, meaning less drag is created and no fluidization takes place. Agglomeration is theformation of particle clusters as a result of dominant cohesive forces. Whereas agglomerates can sometimes be fluidized without assistance (Morooka et al., 1988), gas-solid
contact is reduced due to the surface area of particles being
inside the agglomerate and gas mostly passing outside of it,with diffusion into the agglomerates pores. A phenomenon
that is also sometimes observed, at startup, for cohesive
powder is slugging or plugging, here the entire bed is†*Received 4 November 2022; Accepted 24 February 2023
J-STAGE Advance published online 17 June 2023
Corresponding authors: Rens Kamphorst and Kaiqiao Wu;
Add: van der Maasweg 9, Delft, The Netherlands
E-mail: R.Kamphorst@tudelft.nl (R.K.); K.Wu-3@tudelft.nl (K.W.)
TEL: +31 (0)15 27 89806 (R.K.); +31 (0)15 27 89806 (K.W.)

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pushed up through the fluidization column. While one
could argue this to be a third complication of cohesive
powder fluidization, we consider this an extreme form of
agglomeration, where the entire bed acts as one large cluster. Slugging is typically not seen in industrial-scale beds.
In order to fluidize cohesive powders, assistance methods can be employed, which introduce an additional manipulation. For most assistance methods it was concluded,
by one or more studies, mostly done on nano-particles, thatthe mechanism by which fluidization was improved is bybreaking up agglomerates; mechanical vibration (Namet al., 2004; Barletta and Poletto, 2012), acoustic vibration(Guo et al., 2006), magnetic field (Zhou et al., 2013), stirring (Zhang et al., 2021), micro-jet (Quevedo and Pfeffer,
2010; Nasri Lari et al., 2017) and pulsed flow (Al-Ghurabi
et al., 2020; Ali et al., 2016; Ali and Asif, 2012). This conclusion is based on smaller agglomerate sizes being measured in beds that have been fluidized, using an assistancemethod, than one that could not be fluidized. However, themechanism of agglomerate breakage should be taken into
account. First of all, they can break as a result of collisions,either with other agglomerates or with the column wall.
However, in an unfluidized bed, agglomerates will be(mostly) static, meaning no collisions take place. Anotherway for agglomerates to decrease in size is due to shearwith the fluidizing gas, though simulations for nanoparticle
fluidization have shown this effect to be minor, even at highgas velocities (van Ommen et al., 2010). For this to happen
at a significant scale, there should be significant gas-solid
contact, which is also absent before fluidization is initiated.
Based on this, we hypothesize that agglomerates breakas a result of initiated fluidization, but this agglomerate

Copyright © 2024 The Authors. Published by Hosokawa Powder Technology Foundation. This is an open
access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/).

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breakage is not the cause of the improvement. Rather than
agglomeration, we propose channeling is the major hurdle
to overcome to achieve fluidization of cohesive powders.
By introducing additional manipulation, from an assistancemethod, the channels can be destabilized and will collapse.
Note that mechanical vibration, acoustic vibration, magnetic fields, pulsed flow, stirring, and a (micro-)jet all introduce additional motion of gas, column or internals into thebed, providing a mechanism by which the channeling canbe disrupted. In the absence of channels, all fluidizing gas
has to flow through the bed, creating drag. When sufficiently large drag is created, the particles or agglomerates
will be fluidized. This reasoning leaves one to conclude
that the best assistance methods are not the ones that are
best at breaking agglomerates, but those which most effectively destroy channels. For further development and optimization of assistance methods, it is essential to have acomplete understanding of the mechanism by which thefluidization is improved.
Characterization of the fluidization quality is often doneby measuring bed height expansion and pressure drop
(Nam et al., 2004; Barletta and Poletto, 2012; Mawatari
et al., 2003). These two measurements alone are insufficient when it comes to analyzing the cause of poor fluidization. Visualization of the temporal evolution ofhydrodynamics, going from poor fluidization with channeling to bubbling fluidization under the influence of an assistance method, could provide a better understanding of themechanism. Simple optical techniques that are typicallyused to visualize hydrodynamics in two-phase systems are,however, limited to acquiring information close to the wallregion, because the large solid fraction of the dispersion
phase makes the dense flow opaque to visible light. X-ray
imaging, on the other hand, has been demonstrated to be avaluable technique to study dynamics in opaque systems,
such as fluidized beds with nanoparticles (GómezHernández et al., 2017), irregular particles (Mema et al.,2020), sintering (Macrì et al., 2020) internals (Maurer etal., 2015; Helmi et al., 2017), and spouts (Barthel et al.,2015).
This study aims to characterize the hydrodynamics of agas-solid fluidized bed, consisting of cohesive micro-silica,
with and without vibration applied to it. This is done bymeans of X-ray imaging, pressure drop, and bed height
extension measurements. Channel formation and disruption are shown and agglomerate sizes are measured to elucidate the mechanism behind the employed assistancemethod.

Original Research Paper

drop was measured from the surface of the distributor plateto the breakout box, using OMEGA PX409-10WG5V pressure transducers. The static pressure of the powder was
2.3 mbar (2.3 × 102 Pa) for all experiments. The column
was mounted on a vibration table, a frequency of 30 Hz anda vertical amplitude of 1 mm was used for all experimentswith vibration. For this study, two gas velocities were used,
1.8 and 3.1 cm s–1. During the X-ray experiments, a remotely controlled camera was used to capture images of
the column from which the bed height was measured.
The used powder, KÖstropur 050818, consists of SiO2
particles with a volume-averaged primary particle size of
9.7 μm (as measured by laser diffraction); particle size
distribution is shown in Fig. 1. The powder was sieved beforehand (mesh size 1.25 mm). Note that this is orders ofmagnitude larger than the primary particle size, meaning it
did not affect the size distribution of the powder, but wasdone to establish an equal state of aeration at the start ofeach experiment, ensuring reproducibility. The bulk density after sieving was measured to be 134 kg m–3.
After each experiment, powder samples were taken fromthe plane center of the collapsed bed at heights 2.5, 6.5, and13.5 cm from the distributor plate. A Zeiss Colibri 7 Axio
Observer microscope, equipped with Orca Flash 4.0
Hamamatsu V2 camera was used for imaging. The images
were analyzed using ImageJ. The equivalent circle diameter of the agglomerates was calculated from the projectedarea of the agglomerates on the image. To avoid including
primary particles too, which will drastically shift the
number-based distribution, agglomerates with a diametersmaller than 35 μm were excluded. A minimum of 800 agglomerates was measured for each sample.
To be able to distinguish between the effect of 1) agglomerate breaking and 2) disrupting of channels on thefluidization quality, three sets of experiments were conducted. One where no vibration was used, one where vibration was used for 8 min, and finally one where vibration
was used for 5 s before the inlet gas and vibration were
switched off, all at the two aforementioned gas velocities.

2. Experimental and methodology
2.1 Fluidization procedure

A Perspex column with an inner diameter of 9 cm andsample ports at 2.5, 6.5, and 13.5 cm from the distributor
plate was used as the fluidized bed column. The pressure

Fig. 1 Volume based size distribution of micro silica powder acquiredwith the Coulter LS230 particle size analyzer.

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2.2 X-ray imaging setup

The gas-solids distribution inside the fluidized bed
column was measured using an in-house fast X-ray analysis setup. The complete setup consists of three standard
industrial-type X-ray sources (Yxlon International GmbH)with a maximum energy of 150 keV working in cone beammode. The sources are placed at 120° around a common
center, which forms the field of view. Three 2D detectors(Teledyne Dalsa Xineos) are placed opposite of the sources.
The sources and detectors are attached to a hexagonal support frame that enables translation of the detectors. Bychanging the distance between the source and detector, or
the relative position of the column, the magnification of theimage of the column can be adjusted. In this study the experiments were performed with one X-ray source-detector
pair to obtain a projected 2D output from the 3D column asshown in Fig. 2. The column was fixed to a vibration table
which was positioned in the center of the setup. The distance between the source and the detector was 128.8 cm.
The experimental procedure was controlled from aworkstation outside the setup room, guaranteeing a safe
working environment. The workstation was used to trigger
the X-ray source and read out the signals from the detector
plate. The theoretical spatial resolution of the X-ray detector was 0.15 mm per pixel. During all experiments the
X-ray images were recorded with a frequency of 50 Hz fora measurement time of 200 s for the channel-breaking experiments or 600 s for the full experiment, which corresponded to the acquisition of respectively 10,000 and
30,000 images per experiment. The measured data wasstored for further digital image analysis.

2.3 X-ray image processing

For each experiment, the attenuation of the X-ray beam
was measured at the detector plate to obtain the time-

Fig. 2

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Original Research Paper

resolved projected 2D intensity map of the reactor. The raw
images acquired were corrected for dead-pixels, originating from the construction of the detector plate, by means ofinterpolation to give pre-processed images.
In order to convert the measured X-ray attenuation to asolids concentration, a two points calibration protocol was
performed. First, a reference image was acquired of theempty column. Then, the column was completely filledwith the powder and vibrated for 10 minutes to approach
the maximum packing density. After packing, the full reference image was acquired. The X-ray measurement principle is based on the attenuation of X-rays that travel througha material in a straight line from an X-ray source to a scintillation detector. The law of Lambert-Beer describes thetransmission of a monochromatic beam of high energy
photons with initial intensity I0 through a material of constant density:
I(x) = I0 exp(–μx)(1)

where I(x) represents the intensity measured at the detector,
μ the attenuation coefficient, and x the thickness. In the caseof a varying attenuation, the measured intensity is the integral effect of the local attenuation with the local attenuation
coefficient. By applying the Lambert-Beer law the measurement gas-fraction map was obtained from the measurement intensity map by using the empty and full reference.
The normalized solids fraction α was calculated as follows:
α=1–log(Imeasured / Ifull)log(Iempty / Ifull)(2)

Note the range of normalized solid fraction used in thiswork is between 0 to 1, with 0 representing pure gas and 1
representing close packing of the solids. For the solid
fraction map, low attenuation of X-rays is represented bylight colors and indicates low solid concentrations. By

Experimental X-ray imaging setup showing the X-ray source and detector plate, fluidized bed column and the vibration table.

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contrast, high attenuation of X-rays is represented by thedark colors and indicates a high solids concentration. The
acquired images obtain time-resolved, or dynamic, information of the gas-solids distribution in the column.

2.4 Pressure data processing

Pressure drop over the whole fluidized bed, or over partof it, is commonly used to evaluate fluidization. Whenmechanical vibration is applied, the periodic oscillation ofmass and gas induced is significantly greater than thatcaused by rising bubbles and suspension of solids. These
driven oscillations affect the measured time series of bed
pressure drop, greatly complicating the analysis of fluidization state. For example, Fig. 3(a) plots the time series of
bed pressure drop sampled over 600 s. The vibration was
introduced at around 120 s, after which the measured signal(black) fluctuates largely with an amplitude of up to triple
the theoretical bed pressure drop. To further determine thecomponents of such oscillations, one could analyze thesignal in the frequency domain (Wu et al., 2023). In
Fig. 3(b) the power spectrum for the signal sampled between 120–600 s is demonstrated. The dominant peaks occur at 30 Hz, corresponding to the vibration frequency
adopted in the experiment, as well as its sub-harmonic frequencies with reduced intensity. As a result, in the following sections, the 10 s time-averaged pressure drop is used
to assess fluidization quality during vibration, such as the
red lines in Fig. 3(a), while its standard deviation mainly
associated with the vibration is therefore neglected. For the

Fig. 3 (a) Pressure drop series and (b) power spectrum of the vibrated
bed at 1.8 cm s –1.

Original Research Paper

experiments where vibration was only used for 5 s, averages over 1 s were taken.

3. Results and discussion

3.1 Channel breakage by vibration
3.1.1 Pressure drop and X-ray images

In Fig. 4 the pressure drop and X-ray images of the experiments where vibration was used are shown. Experiment 1 and 2 (under the same conditions) were terminatedafter 5 s of vibration. The third one was vibrated for 8 minafter vibration started, in order to demonstrate the longterm fluidization behavior. The initial pressure drop fluctuations, seen in all pressure graphs, are caused by slugging
which is discussed in detail in Sections 3.2.1 and 3.2.3. For
each experiment, it can be seen that a semi-stable pressure
drop was achieved after roughly 75 s. The ΔP/ΔP0, the ratioof measured pressure drop over theoretical pressure drop(the static pressure of the powder; 2.3 mbar (2.3 × 102 Pa)
for all experiments) of full fluidization, after 90 s, shown in
Fig. 4(b)-1, Fig. 4(d)-1 and Fig. 4(f)-1, was found to below. The channeling, causing the low pressure drops, canclearly be seen. Comparing these images to Fig. 4(b)-2,
Fig. 4(d)-2 and Fig. 4(f)-2 it can also be seen that thesechannels were stable with time, as the images with sublabels 1 and 2 were taken 30 s apart. The relatively highand unstable pressure drop seen from 50 s to 120 s in
Fig. 4(e) is explained by the collapse and reforming of unstable channels, in Fig. 4(f)-2 the channel structure can beseen to have changed compared to Fig. 4(f)-1. We consider
this occurs simply as a matter of chance, since up to 120 s
there is no difference in operation between the three experiments. In the following images the effect of vibration,
within the first seconds of initiation, can be seen. For all
experiments, two types of channeling were observed: ratholes and vein-like channels. Where rat-holes run almost
vertically from bottom to top of the bed, creating a largegas bypass, vein-like channels branch out in several directions, resulting in a network of thinner interconnectedchannels. Not enough data was acquired to reliably assess
what causes either type of channeling to occur. It was consistently observed that the vein-like channels disappear bymerging together, due to the powder barriers, initially separating them, crumbling. The rat-holes, persist longer andare destroyed by powder falling into them, disrupting thegas flow and creating bubble-like gas pockets. In Fig. 4(a),Fig. 4(c) and Fig. 4(e) it can be seen that the ΔP/ΔP0
spiked to 0.89, 0.79 and 0.89 after 1 s, and kept increasing
to 0.91, 0.88 and 0.94 after 5 s, of vibration respectively.
Note that this increase over the first 5 s corresponds tomore and more channels breaking, as seen in the X-ray
images. The increase in the fluidized fraction of powder, as
measured by pressure drop, is in all experiments clearlycorrelated to the breaking of channels.

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Original Research Paper

Fig. 4 Images corresponding to channel breakage experiments at 1.8 cm s –1 gas velocity, in all images: ①= 90 s, ②= 120 s, ③= 120.5 s, ④= 121 s,⑤= 121.5 s, ⑥= 122 s, ⑦= 123 s and ⑧= 130 s into the experiment. (a) Pressure drop of experiment 1; (b) X-ray images of experiment 1; (c) Pressure
drop of experiment 2; (d) X-ray images of experiment 2; (e) Pressure drop of experiment 3; (f) X-ray images of experiment 3.

3.1.2 Agglomerate sizes

For the experiments displayed in Fig. 4, the agglomerate
sizes were measured after ending the experiment for the
top, middle and bottom of the bed (as described in Section
2.1). The resulting number-based cumulative percentiles,
d10, d50 and d90, are shown in Fig. 5. First comparing thetwo runs in which vibration only lasted for 5 s, labeled 1
and 2 in Fig. 5, no significant difference between them canbe seen, showing the data is reproducible. Also, comparing
the sizes in both of these experiments to the un-fluidized
powder, no significant change is observed. Looking at thesizes found after 8 min of vibro-fluidizing, labeled 3 inFig. 5, no big change in agglomerate sizes was found compared to the un-fluidized powder or compared to the otherexperiments.
It was hypothesized that channel disruption is the cause
of initiated fluidization upon the introduction of vibration.

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Fig. 5 Agglomerate sizes after vibration all with gas velocity of
1.8 cm s –1; 1) vibrated for 5 s; 2) vibrated for 5 s; 3) vibrated for 8 min;▶ = d10 ● = d50 ◀ = d90, number based.

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Original Research Paper

It was expected to find a decreased agglomerate size after
8 min of vibro-fluidization compared to 5 s, where virtually
no decrease was expected. While no significant change inagglomerate sizes was found for any of the experiments, it
can still be concluded that the break-up of agglomerates
does not play a role in initiating fluidization of the cohesive
powder.

3.2 Influence of vibration and gas velocity
3.2.1 No vibration, 1.8 cm s–1

In Fig. 6 the bed height, pressure drop and X-ray images
from the experiment without vibration and 1.8 cm s–1 gas
velocity are shown. It can be seen that the bed was initiallylifted as a plug, which corresponded to a large pressure
drop over the column. The plug eventually broke and fell
down in pieces, as seen in Fig. 6(c)-3, which lead to heavypressure swings in the system. Note that in this image mostof the powder bed is still out of frame, higher up in thecolumn. Right after, some fluidization took place, as seenby the pressure drop, significant bed height expansion anddilute X-ray image. Within 45 s after the plug fell down,
stable channels had formed (Fig. 6(c)-5), that did not significantly change over time anymore. The pressure drop
remained constant over this time with an average ΔP/ΔP0
of 0.57. Bed height was decreasing slowly due to the bed
compacting from its initial fluidized state. Still, an expansion ratio of 1.2 was maintained, caused by the added volume of the channels now present in the bed and the looser
packing state of the powder. This experiment shows all the
expected behavior of a cohesive powder upon the introduction of a gas flow.

3.2.2 Vibration, 1.8 cm s–1

The results shown in Fig. 7 are of the same experimentshown in Fig. 4(e) and Fig. 4(f), but extended to the fullexperimental time to assess the effect of vibration overtime. The bed initially rose as a plug again, the X-ray images corresponding to this were omitted since they are virtually identical to the experiment previously described in
Section 3.2.1 and the focus here is on the effect of vibration, which started at 120 s. In Fig. 7(c)-1 to Fig. 7(c)-5,
the initial stable channel collapsing and the initiation of
fluidization are shown. Over time, compaction and partial
de-fluidization took place. It can be seen that the bed heightdecreased, coupled with a decrease in ΔP/ΔP0 from 0.93 in
the first minute after vibration started to 0.87 in the lastminute of the run. From the X-ray images, it could also be
observed that the bed was densifying during this time, witha compacted region being present, dominantly at the bottom of the bed.

3.2.3 No vibration, 3.1 cm s–1

The obtained results for the 3.1 cm s–1 experiment without vibration are shown in Fig. 8. As in the other experi-

Fig. 6 Results of fluidization experiments, 1.8 cm s –1 without vibration, in all images: ①= 0 s, ②= 15 s, ③= 45 s, ④= 60 s, ⑤= 90 s,⑥= 120 s, ⑦= 300 s and ⑧= 540 s into the experiment. (a) Bed height;(b) Pressure drop; (c) X-ray images.

ments, the bed initially formed a plug. In Fig. 8(c)-3 thefragments of the broken plug can be seen falling down,corresponding with the pressure swing seen at 30 s in
Fig. 8(b). This was followed by some degree of fluidization, giving a bed height expansion ratio of 1.5 and a ΔP/
ΔP0 of 0.89 at the peak, 115 s. The dip in bed height andpressure drop that followed is explained by the formationof two rat-holes, seen in Fig. 8(c)-5, which collapsed later
leading to vein-like channel formation and some spouting259

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Original Research Paper

Fig. 7 Results of fluidization experiments, 1.8 cm s –1 with vibration,in all images: ①= 90 s, ②= 120 s, ③= 121 s, ④= 125 s, ⑤= 130 s,⑥= 180 s, ⑦= 300 s and ⑧= 540 s into the experiment. (a) Bed height;(b) Pressure drop; (c) X-ray images.

Fig. 8 Results of fluidization experiments, 3.1 cm s –1 without vibration, in all images: ①= 0 s, ②= 15 s, ③= 30 s, ④= 120 s, ⑤= 180 s,⑥= 240 s, ⑦= 300 s and ⑧= 540 s into the experiment. (a) Bed height;(b) Pressure drop; (c) X-ray images.

and bubbling in top of the bed, coupled with stable ΔP/ΔP0
of 0.77.

term structures could be observed anymore and the bed was
homogeneously fluidized. In the remaining time that theexperiment was running, densification was observed,
mainly at the bottom of the bed, as when 1.8 cm s–1 gas
velocity was used. The densifying resulted in a lower bed
height expansion ratio, eventually even lower than when no
vibration was used at 3.1 cm s–1, and a slight reduction in
ΔP/ΔP0 from 0.91 in the first minute after vibration started,
to 0.87 after 8 min.

3.2.4 Vibration, 3.1 cm s–1

Fig. 9 shows the data from the experiment at 3.1 cm s–1
with vibration. As for all experiments, slugging occurred
initially, followed by some degree of fluidization before
stable channels formed, which are seen in Fig. 9(c)-1 andFig. 9(c)-2. After 10 s of vibration (Fig. 9(c)-5), no long-260

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Original Research Paper

Fig. 10 Agglomerate sizes for experiments ran at 1.8 and 3.1 cm s –1,
with and without vibration for 8 min; ▶ = d10 ● = d50 ◀ = d90, number
based.

densification of the bottom bed—as observed after several
minutes of vibration—is not reflected by the agglomerate
size.

3.3 Channel formation

Channeling took place in all the experiments conducted,
either without vibration or before vibration was switchedon. From the X-ray images shown in the previous sections,the variety of the formed channels across different experiments is obvious. The diversity which is seen, even underidentical conditions, underlines the random nature of channel formation. It also shows no bias from the used experimental method, since no preferential place for the channels
to form is observed. The results also suggest that even theformation of rat-hole like or vein-like channeling is random
and not affected by gas velocity within the range used forthis study.

4. Conclusions

Fig. 9 Results of fluidization experiments, 3.1 cm s –1 with vibration, in
all images: ①= 90 s, ②= 120 s, ③= 121 s, ④= 125 s, ⑤= 130 s,⑥= 180 s, ⑦= 300 s and ⑧= 540 s into the experiment. (a) Bed height;(b) Pressure drop; (c) X-ray images.

3.2.5 Agglomerate sizes

For each 10 min experiment, the agglomerate sizes (d10,d50 and d90, number-based), at all sample heights, areshown in Fig. 10. Comparing the results, across gas velocities and with or without vibration to fresh powder, thedifferences are minor. The influence of vibration and gas
velocities, within the ranges used in this study, on agglomerate sizes is therefore concluded to be insignificant. The

In this work, the mechanism behind the initiation of fluidization of cohesive micro-sized powder, by vibrations,
was studied by means of X-ray imaging, pressure drop andbed height measurements. Agglomerate sizes were measured to decouple the phenomena of channel disruption andagglomerate breakage. When no vibration was used, thepowder could not be properly fluidized at either 1.8 or
3.1 cm s–1 and severe channeling was observed, which was
not always clearly reflected in the pressure drop or bed
height, showcasing the limitations of these techniques
when it comes to assessing the dynamics of complex systems. Gas velocity, vibration and vibration time were notfound to have any significant effect on agglomerate sizes,
within the parameter ranges applied in this work. From
this, it is concluded that vibrations initiate fluidization notby breaking agglomerates, but by disrupting channels.
Furthermore, it was found that narrow, vein-like channels
are disrupted significantly faster than the larger rat-holes.
Finally, when vibration was employed, bed compaction
was observed over time, as a dense phase formed on top of261

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the distributor plate, causing a decrease in bed height andpressure drop. The study was carried out using a single
micro-silica powder, meaning material- and size-specificinfluences, which might influence results, were not investigated. While variations are deemed likely when using otherpowders, based on the described mechanism by which assistance methods work and the absence of a mechanism bywhich agglomerates can be broken before fluidization is
initiated, it is expected that the disruption of channels is thecause of initiated fluidization for other cohesive powders
too. This study is a first step towards a better understandingof the mechanism behind vibro-assisted fluidization of cohesive powder and may contribute to the further development and optimization of assistance methods.

Supplementary information

The online version contains supplementary material
available at https://doi.org/10.14356/kona.2024007.

Acknowledgments

We want to thank Stefan ten Hagen for his contribution
to designing and manufacturing the column used in thisstudy.
This work is part of the Advanced Research Center for
Chemical Building Blocks, ARC CBBC, which is cofounded and co-financed by the Dutch Research Council(NWO) and the Netherlands Ministry of Economic Affairs
and Climate Policy. The work has also received funding
from the NWO under the grant number ENPPS.
LIFT.019.027.

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Authors’ Short Biographies
Rens Kamphorst
MSc Rens Kamphorst is a PhD researcher in the department of Chemical Engineering at Delft
University of Technology (The Netherlands). In 2020 he completed his MSc in Chemical Engineering, also at this university. His research is focused on atomic layer deposition in a fluidized bed
consisting of cohesive powders.

P. Christian van der Sande
MSc Christian van der Sande is a PhD researcher in the department of Chemical Engineering at
Delft University of Technology (The Netherlands). He completed his MSc in Chemical Engineeringwith a specialization in process engineering at the same university. His research activities involvehydrodynamic studies with radiation-based imaging methods to study gas hold up, flow patterns andflow velocities inside multi-phase reactors. He has supervised over 10 BSc and MSc students for their
thesis work.

Kaiqiao Wu
Dr. Kaiqiao Wu obtained his PhD from University College London in 2020. He has publishedseveral works of gas-solid fluidization in international journals, and has presented at conferences. He
has won prizes for best talk in sessions, and placed second in the IChemE Young Researcher Awards
at UK-China International PTF VII, 2019, and also received the Springer Theses Award for recognizing outstanding PhD research in 2021. He is currently a postdoctoral researcher at TU Delft.

Evert C. Wagner
Ing. Evert Wagner is a research assistant at Delft University of Technology, The Netherlands. He
obtained a BSc degree in Applied Physics at the Technische Hogeschool, Rijswijk. Starting at TU
Delft in 2006, he has been involved in most of the development of the X-ray setup used in this paper.
He’s a co-author of over 30 papers using this experimental technique.

Kristen David
Ing. Kristen David is a lab manager at Delft University of Technology (The Netherlands). She
obtained her BSc degree in Chemical Engineering at De Haagse Hogeschool in Den Haag in 2019.
She started at TU Delft on the same year and has been involved in managing the ML-1 labs of the
Product and Process Engineering group of the Chemical Engineering department.

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Original Research Paper

Authors’ Short Biographies
Gabrie M.H. Meesters
Dr. Gabrie Meesters has 27 years of industrial formulations experience at Gistbrocades, Genencor
International and DSM. He has 23 years of experience as a Part-Time Professor at TU Delft in particle technology and product design. From January 2019, he became a fulltime Assistant Professor at
the TU Delft, Faculty of Applied Sciences, Product and Process Engineering. He is a contributor toseveral books on formulation. He is the editor of three books on product design and solids processing.
He published over 70 refereed papers, has more than 20 patents and supervised more than 100 BSc,
MSc and PhDs. He is a regular speaker at conferences and workshops. He was the organizer of the2010 Partec and the 2010 World Congress on Particle Technology in Nuremberg, Germany.

J. Ruud van Ommen
Professor of Chemical Engineering at Delft University of Technology (The Netherlands). He obtained his PhD degree at Delft in 2001. He has been Visiting Professor at Chalmers University ofTechnology (Gothenburg, Sweden) and the University of Colorado (Boulder, USA). In recent years,
he expanded his research from chemical reactor engineering to the scalable production of advanced,
nanostructured materials. In 2011, he started an ambitious program (funded by an ERC Starting
Grant) to investigate the interplay between agglomeration and coating of nanoparticles in the gas
phase. He has published about 200 journal papers, of which a considerable part on powder technology.

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