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Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators
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Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
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Original Research Paper
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Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators
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Feng Wu a,⇑, Lingyi Shang a, Zeyu Yu b, Xiaoxun Ma a,⇑, Wenjing Zhou c
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a
School of Chemical Engineering, Northwest University, Xi’an, China School of Urban Planning and Municipal Engineering, Xi’an Polytechnic University, Xi’an, China c School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, China b
a r t i c l e
i n f o
Article history: Received 18 March 2019 Received in revised form 25 May 2019 Accepted 27 June 2019 Available online xxxx Keywords: Spouted bed Particle diameter Particle density Row number of longitudinal vortex generators Experiment investigation
a b s t r a c t A spouted bed with longitudinal vortex generator (LVG) of sphere was built to enhance radial movement of particles. Particle Image Velocimetry (PIV) was applied to explore effects of longitudinal vortex flow and physical properties of particles on their radial velocity in a 152-mm-diametered spouted bed. The results show that, Compared with the conventional spouted bed, the existence of longitudinal vortex generator gives rise to a large amount of secondary fine vortex flow in the cross section of spouted bed. The enhancement factors of particles movement g with different particle densities are all greater than 1. The smaller the particle density, the more significant the effect of the longitudinal vortex on the radial velocity of the particles. The single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H0 = 165 mm). With the increase of the height of the static bed (H0), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle motion in the spouted bed with more particle handling capacity (H0 = 195 mm, 225 mm). Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
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1. Introduction
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Spouted beds are an alternative to fixed and fluidized beds and have been applied in industrial applications such as drying, coating, mixing, combustion, gasification and granulation [1,2]. In order to improve the effective use of cylindrical spouted beds in industrial applications, many experimental tests of spouted bed apparatuses have been performed to obtain detailed knowledge of gas and particle hydrodynamics [3–9]. Devahastin et al. [3,4] experimentally developed a Rotating Jet Annular Spouted Bed (RJASB) dryer for drying of particulates in the falling rate period. They also studied some hydrodynamic and mixing characteristics of a pulsed spouted bed dryer. Prachayawarakorn et al. [5] studied the heat transfer characteristics in a two-dimensional spouted bed with draft plates using three agricultural materials, paddy, corn and soybean. Zhong et al. [6–8] experimentally studied the particle mixing behavior in a large spout-fluid bed. Besides, they investigated the spout characteristics of a cylindrical spout-fluid bed with elevated pressure and the particle mixing in flat-bottom spout-
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⇑ Corresponding authors. E-mail addresses: [email protected] (F. Wu), [email protected] (X. Ma).
fluid bed. Sari et al. [9] measured the characterization of gassolid flow in conical spouted beds operating with heavy particles. Qin et al. [10] designed and set up a cold-state spouted bed for oil shale semi-coke and experimentally investigated the effect of static bed height and particle size on the spouting pressure drop. Sutkar et al. [11] analyzed the hydrodynamics of a pseudo-2D spout fluidized bed with draft plates by changing the background velocity from 0 to 1.75 m/s with interval of 0.25 m/s and the spout velocity from 10 to 50 m/s with interval of 5 m/s. Nagashima et al. [12] experimentally obtained the effects of operating parameters on hydrodynamic behavior of spout-fluid beds with and without a draft tube. Mostoufi et al. [13] experimentally studied flow structure characterization in conical spouted beds with the aid of pressure fluctuation signals. Wang et al. [14] developed a dual-column slot-rectangular spouted bed to improve solids exchange between two adjacent chambers. Recently, Parise et al. [15] experimentally investigated the hydrodynamics of a slot-rectangular spouted bed of biomass particles with simultaneous injection of spouting and pulsating air streams. Kiani et al. [16] experimentally studied the mixing and segregation of binary mixtures of particles with different sizes and densities in a pseudo-2D spouted bed. Breault et al. [17,18]
https://doi.org/10.1016/j.apt.2019.06.033 0921-8831/Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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Nomenclature dp Ds D H Ha H0 L R
89 90 91 92 93 94 95 96 97 98 99 100
S x, y, z
particle diameter [mm] diameter of the spouted gas inlet [mm] diameter of the bed [mm] vessel height [mm] height of cross section of data acquisition [mm] static bed depth [mm] distance between two centers of sphere [mm] radius of spheres [mm]
width of deflector [mm] Cartesian coordinates [m]
Greek symbols dimensionless enhancement factor of particle movement [—] q density [kg/m3] d thickness of deflector [mm]
g
experimentally studied the hydrodynamic characteristics of the gas-solid flow in a rectangular spouted bed (30.2 mm 101.6 mm) under three initial bed heights (0.0762 m, 0.102 m, and 0.127 m) for two different nozzle sizes (0.0096 m and 0.0127 m). They also investigated the spout characteristics and minimum spouting velocity of a flat-base spout-fluidized bed with different static heights and two materials (Al2O3 and high density polyethylene). Rao et al. [19] studied the pressure fluctuations emanating from three dimensional (3D) conical spouted bed using dense zirconia particles (6200 kg/m3) via high intensity microphone. Estiati et al. [20] conducted a study about the influence of geometry and configuration of both confiner and draft tube on article
Table 1 Operating conditions and properties of the particles used in the experiments. Particle density (q) Particle diameter (dp) Vessel height (H) Height of cross section of data acquisition (Ha) Static bed depth (H0) Spouting gas volume flow rate Diameter of the spout gas inlet (Ds) Diameter of the bed (Dt) Radius of spheres (R) Thickness of deflector (d) Distance between two centers of sphere (L) Width of deflector (S)
1897 kg/m3, 2200 kg/m3, 2603 kg/m3 0.72 mm, 1.13 mm, 1.42 mm 700 mm 230 mm 165 mm, 180 mm, 195 mm, 225 mm 400 L/min 19 mm 152 mm 10 mm 2 mm 35 mm 80 mm
Camera location
Ha
Cross section
z o
Fig. 1. Schematic diagram of the experiment setup: 1. Analysis, 2. Synchronizer, 3. Image shift electronics, 4. Laser, 5. Light sheet, 6. CCD camera, 7. Spouted-bed.
x y
Gas inlet
Fig. 3. Schematic diagram of cross section selected in spouted bed.
2
100
30
20
30 20
o
35 80 150
x
10
z
R10
y
(a) Conventional spouted bed
(b) Spouted bed with LVGs
Fig. 2. Geometry of multi-row spouted bed and the size of longitudinal vortex generator in spouted bed (unit: mm).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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entrainment, operating pressure drop, operating air flow rate and maximum cycle time. Longitudinal vortex technique is widely used in enhancing thermal efficiency of heat exchangers or micromixer of the microfluidic systems [21–27]. Ahmed et al. [21] reviewed heat transfer augmentation using vortex generators and nanofluids. Hsiao et al. [23] investigated the micromixers based on the T-shaped channel with longitudinal vortex generators mounted on the bottom of
Line 1 Line 2 Line 3
y o
Deflector x
Fig. 4. Location of particles velocity selected in cross section of spouted bed.
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the main channel. Datta et al. [24] numerically investigated fluid flow and heat transfer behavior in microchannel using inclined longitudinal vortex generator. Ebrahimi et al. [25,26] numerically simulated conjugated heat transfer and hydraulic performance for nanofluid flow in a rectangular microchannel heat sink with LVGs (longitudinal vortex generators). Wu et al. [28–30] numerically investigated the radial mixing behaviors of gas and particle phases in spouted beds with longitudinal vortex effects. They also numerically analyzed the influence of row number of LVGs on gassolid flow behaviors in a spouted bed. Despite the importance of numerical studies in spouted bed, the experimental study of gas-solid two-phase flow in spouted bed under the influence of longitudinal vortex is still lacking. The purpose of this work is to determine the enhancement ability and mechanism of longitudinal vortex to radial motion of particles in spouted bed. In the present work, a spouted bed with longitudinal vortex generators (LVGs) was investigated by experimental method. Particle Image Velocimetry (PIV) [31] was applied to explore effects of longitudinal vortex flow and physical properties of particles on radial velocity of particles in a spouted bed with LVGs, and the effects of LVGs, density of particles, static bed depth
(a) Conventional spouted bed
(b) Spouted bed with one row of LVG Fig. 5. Comparison of particles vector diagram in cross section of two kinds of spouted beds.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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and row numbers of LVGs on the movement of particles are investigated.
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2. Experimental
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2.1. Experimental apparatus
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The experimental apparatus used in this study is shown in Fig. 1. The experimental instruments mainly comprised a compressor of the type GX4FF-10 (AtlasCopco, The Kingdom of Sweden), a flowmeter of the type D07-60B, (Sevenstar, China), a spouted bed made of plexiglass and a PIV system. The PIV system mainly includes laser emitters, CCD cameras, synchronizers, image acquisition and processing software (Dantec Dynamics A/S, The Kingdom of Denmark). The geometry of multi-row spouted bed and the size of longitudinal vortex generator in spouted bed is shown in Fig. 2. As shown in Fig. 2, there are two kinds of spouted bed are used in the experimental investigation: the conventional spouted bed (Fig. 2(a)) and the spouted bed with one row of longitudinal vortex generator (Fig. 2(b)). Table 1 contains the main dimensions of the spouted bed contactor and properties of the particles used in the experiments.
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2.2. Experimental procedure
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During the experiment, the gas generated by the air compressor enters the spouted bed from the bottom of the bed. By adjusting the gas flow, the gas is driven to move the particles, and the spouting condition in the spouted bed is observed. The laser beam is illu-
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3. Results and discussion
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3.1. Effect of longitudinal vortex on particle motion
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The experimental device measures and analyzes the radial velocity of the particles in the spouted bed with LVGs, and focuses on the movement of the particle phase in the cross-section of the spouted bed under the effect of the longitudinal vortex. In order to investigate the effect of longitudinal vortex on gas-solid flow behavior in spouted bed, the static bed depth is kept constant at
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0.4
0.4
Particle radial velocity (m/s)
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0.2 0.0 -0.2 -0.4 0. 0
Line 1 Conventional spouted bed Spouted bed with one row of LVG
0. 2
0. 4
Line 2 Conventional spouted bed Spouted bed with one row of LVG
0.2
0.0
-0.2
-0.4
0. 6
0. 0
0.8
0. 2
0. 4
0. 6
0.8
x/D
x/D
(a) The location of line 1
(b) The location of line 2
0.3
Particle radial velocity (m/s)
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Particle radial velocity (m/s)
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minated in a cross section the spouted bed, then the camera is placed on the top of spouted bed to record the movement of particles. Finally, the acquired image is analyzed by Dynamic Studio Software, and the radial velocity vector and radial velocity distribution of the cross section are obtained. The schematic diagram of data acquisition process is shown in Fig. 3, In order to study the effect of longitudinal vortex on particle radial velocity in spouted bed with different static bed depth (H0), the height of cross section of data acquisition is kept constant Ha = 230 mm. With the addition of longitudinal vortex generator in the spouted bed, the radial movement of gas and particles occurs in spout and annulus regions, which destroys the distribution regularity of axial particles in the annulus of the bed. In order to obtain comprehensive information of particle velocity in the cross section of spouted bed, three parallel lines (Fig. 4) near the deflector and the annulus are selected as the data acquisition positions of the experiments in this paper, line 1 and 3 are located in annulus region, line 2 is located in spout region.
0.2 0.1 0.0 -0.1 -0.2 -0.3 0.0
Line 3 Conventional spouted bed Spouted bed with one row of LVG
0.2
0.4
0.6
0.8
x/D
(c) The location of line3 Fig. 6. Comparison of on particle radial velocity along radial direction in two kinds of spouted beds (one row of LVGs).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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H0 = 180 mm, the particle density is kept as 2603 kg/m3, the particle diameter is kept as 0.72 mm, and the row numbers of LVGs is kept constant at 1. Fig. 5 shows the comparison of particles vector diagram in cross section of two kinds of spouted beds. As shown in Fig. 5, when there is no-longitudinal vortex generator, the radial velocity of the particle phase exhibits an axisymmetric distribution
in the cross section of the bed. The addition of the longitudinal vortex generator causes vortex motion of the high-speed gas passing through the affected area, and drives particles to generate a large amount of secondary fine vortexes, especially in the annulus region, which strengthens the radial movement of the gas and the particles. Furthermore, the lateral mixing between particles
x/ mm
(a) =1897 kg/m3
x/ mm
x/ mm
x/ mm 3
(b) =2200 kg/m
x/ mm
(c) =2603 kg/m3
x/ mm
Fig. 7. Particles vector diagram in cross section of spouted bed for different particle density.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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and particles, gas and particles in the spout region and the annulus interval is enhanced, which effectively reduces the problem of layered flow of particles in the annulus of the spouted bed. Fig. 6 shows the radial profiles of particle velocities in opposite directions on the left and right sides of the axis. It can be seen that compared with the conventional spouted bed, the radial velocity of the particles is significantly enhanced by the longitudinal vortex. Meanwhile, the radial velocity of particles in the annulus is significantly higher than that in the spout region, which indicates that the longitudinal vortex can effectively enhance the radial motion of the particles, and its strengthening effect is consistent with the distribution of radial velocity vector of the particles obtained in Fig. 5.
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3.2. Effect of particle density on particle motion
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The particle density plays an important role in gas-solid twophase flow in spouted bed. In order to analyze the effect of particle density on particle motion enhanced by longitudinal vortex, Fig. 7 displays the distribution of radial velocity vector of particles in the cross section of the spouted bed with different particle densities (q = 1897 kg/m3, 2200 kg/m3, 2603 kg/m3) with the particle diameter is kept as 0.72 mm. It can be seen from the figure that, when the particle density is 1897 kg/m3, the vortex flow generated by the gas motion has the best effect on the movement of the particles. The smaller the particle density, the larger the radial velocity of the particles.
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g¼
-0.2 -0.4 0.0
jV L j
ð1Þ
jV N j
Line 1 3 =1897 kg/m 3 =2200 kg/m 3 =2603 kg/m
0.2
0.4
0.6
0.2 0.1 0.0 Line 2 3 =1897 kg/m 3 =2200 kg/m 3 =2603 kg/m
-0.1 -0.2 0.0
0.8
0.2
0.4
0.6
0.8
x/D (b) The location of line 2
0.4 0.2 0.0
Line3
0.0
3
=1897 kg/m 3 =2200 kg/m 3 =2603 kg/m 0.2
220 221 222 223 224 225
228
231
x/D
-0.4
219
longitudinal vortex. jV N j is the average value of absolute particle velocity distribution along the radial direction of spouted bed without the effect of longitudinal vortex. The larger the g value, the greater the enhancement effect of longitudinal vortex on the particle movement. Fig. 9 shows the variations of g with varying particle density. The calculated results exhibit that the enhancement factors g with different particle densities are all greater than 1, which indicates that the addition of the longitudinal vortex generator in spouted beds can effectively strengthen the radial velocity of the particles.
(a) The location of line 1
-0.2
218
229
0.3
0.0
217
where jV L j is the average value of absolute particle velocity distribution along the radial direction of spouted bed under the influence of
0.4 0.2
216
226
Particle radial velocity (m/s)
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Particle radial velocity (m/s)
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Particle radial velocity (m/s)
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Fig. 8 presents the effect of vortex generators on particle radial velocity for different particle densities. It can be seen that when the particle density equals 1897 kg/m3, the vortex flow generated by the gas motion has the best effect on the movement of the particles in annulus. The smaller the particle density, the larger the radial velocity of the particles, which means the effect of the longitudinal vortex on the radial velocity of the particles is more significant. In order to describe the enhancement effect of longitudinal vortex on particle velocity, a dimensionless enhancement factor of particle movement is defined, which is shown as follows:
0.4
0.6
0.8
x/D (c) The location of line3 Fig. 8. The effect of vortex generators on particle radial velocity for different particle density.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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2.8
Line 1 Line 2 Line 3
2.4
The smaller the particle density, the more significant enhancement effect of the longitudinal vortex on the radial velocity of the particles.
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3.3. Effect of row numbers of LVGs
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The effects of different static bed heights (H0 = 165 mm, 195 mm, 225 mm) and row number of LVGs on particle motion in spouted bed were analyzed (Table 2), the particle density is kept constant as q = 2200 kg/m3, and the particle diameter is kept as 0.72 mm. Fig. 10 shows the effect of row numbers of LVGs on particle radial velocity along radial direction when H0 = 165 mm (H0/Dt = 1.09). It can be observed that, the radial velocity enhancement factors (g) are all greater than 1, and the radial velocity enhancement factors of single row of sphere are significantly higher than those of double rows of spheres and three rows of spheres. According to the distribution of particle radial velocity, the effect of particle radial motion enhancement is the best when the sphere generator is in the form of single-row. The radial velocity of particles decreases with the increase of the number of rows of spheres, which indicates that the single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H0 = 165 mm). With the increase of the number of LVGs rows, the flow resistance effect of the LVGs increases, that is, the resistance effect of the LVGs is greater than enhancement effect of longitudinal vortex on particles, and the comprehensive result shows that the radial velocity of particles decreases.
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242 243
2.0 1.6 1.2 2000
2200
2400
2600 3
Particle density (kg/m ) Fig. 9. Variations of g with varying particle density.
Table 2 Average values of g for different static bed depth. Average values of g
Row numbers of LVGs
1 2 3
H0 = 165 mm
H0 = 195 mm
H0 = 225 mm
2.12 1.85 1.68
0.93 1.98 0.60
1.76 1.52 2.10
Particle radial velocity (m/s)
Particle radial velocity (m/s)
0.4 0.2 0.0
-0.2 -0.4 0.0
Line 1 One row of sphere ( =2.28) Two rows of spheres ( =2.19) Three rows of spheres ( =1.79) Conventional spouted bed
0.1
0.2
0.3 0.4 x/D
0.5
0.2
0.0 Line 2 One row of sphere ( =2.11) Two rows of spheres ( =1.67) Three rows of spheres ( =1.63) Conventional spouted bed
-0.2
0.6
0.7
-0.4 0.0
0.1
Particle radial velocity (m/s)
(a) The location of line 1
0.2
0.3 0.4 x/D
0.5
0.6
0.7
(b) The location of line 2
0.2
0.0 Line 3 One row of sphere ( =1.97) Two rows of spheres ( =1.68) Three rows of spheres ( =1.63) Conventional spouted bed
-0.2
-0.4 0.0
0.1
0.2
0.3 0.4 x/D
0.5
0.6
0.7
(c) The location of line3 Fig. 10. Effect of row numbers of LVGs on particle radial velocity along radial direction (H0 = 165 mm).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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is greater than 1, which indicates that the enhancement effect of longitudinal vortex on radial motion of particles in annulus is better than that in spout region when the amount of particles in spouted bed is large. The radial velocity of particles in three rows of LVGs in spout region is better than that in single row and double row, and the radial velocity of particles in single row of LVGs in annulus region is the largest. This is because the height of the static bed equal the height of the third row of spheres. The third row of spheres disturbs the particles rising in the spout region, which makes the radial velocity of particles increase locally by reducing cross-sectional area of flow passage. The resistance of the particles increases with the increase of the number of rows of spheres, which leads to the maximum particle velocity in the annular gap when the LVGs is single row. Figs. 10–12 show that with the increase of the height of the static bed (H0), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle movement in the spouted bed with more particle handling capacity (H0 = 195 mm, 225 mm).
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4. Conclusions
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(1) Compared with the conventional spouted bed, the addition of the longitudinal vortex generator generates a large amount of secondary fine vortex flow in the cross section of spouted bed, and the radial velocity of the particles is significantly enhanced by the longitudinal vortex.
0.4
Particle radial velocity (m/s)
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Fig. 11 shows the effect of row numbers of LVGs on particle radial velocity along radial direction when static bed heights increased to H0 = 195 mm. It can be seen in Fig. 11 that when H0/D = 1.28, the g of single-row and three-row LVGs are less than 1 in annulus region (line 1 and line 3), while those of double-row LVGs are greater than 1 in spout (line 2) and annulus. At different data locations, the radial velocity enhancement factors of particles are less than or greater than 1, which indicates that the spatial distribution of particle motion enhancement in spouted bed is inhomogeneous due to longitudinal vortex. According to the distribution of particle radial velocity, the longitudinal vortex strengthening effect on particle radial velocity near the spout is the best, and the overall strengthening effect of particle radial motion is the best when the LVGs have two-row setting. The overall strengthening effect of single row of LVGs in the spout region is better than that of three rows of LVGs, while the strengthening effect of single row of LVGs in the annulus of spouted bed is better than that of three rows of LVGs. On the whole, when the row number of LVGs equals 2, the radial velocity of particles is best enhanced. The results show that with the increase of particle handling capacity, the enhancement of radial motion of particles in multi-row LVGs is gradually presented. However, increasing the row number of LVGs will lead to a rapid increase in particle flow resistance, which will adversely affect the overall movement of particles. Fig. 12 shows the effect of row numbers of LVGs on particle radial velocity along the radial direction when the height of the static bed equals 225 mm. From Fig. 12, we see that when H0/D = 1.48, the enhancement factor of all rows of LVGs in annulus
0.2 0.0 -0.2
-0.6 0.0
0.1
0.2
0.3 0.4 x/D
0.5
0.6
0.4 0.2 0.0
-0.2
Line 1 One row of sphere ( =0.86) Two rows of spheres ( =1.11) Three rows of spheres ( =0.78) Conventional spouted bed
-0.4
Line 2 One row of sphere ( =1.12) Two rows of spheres ( =3.12) Three rows of spheres ( =0.53) Conventional spouted bed
-0.4
0.7
-0.6 0.0
0.1
(a) The location of line 1
Particle radial velocity (m/s)
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Particle radial velocity (m/s)
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0.2
0.3 0.4 0.5 0.6 x/D (b) The location of line 2
0.7
0.2
0.0 Line 3 One row of sphere ( =0.8) Two rows of spheres ( =1.7) Three rows of spheres ( =0.49) Conventional spouted bed
-0.2
-0.4 0.0
0.1
0.2
0.3 0.4 0.5 x/D (c) The location of line3
0.6
0.7
Fig. 11. Effect of row numbers of LVGs on particle radial velocity along radial direction (H0 = 195 mm).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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Particle radial velocity (m/s)
Particle radial velocity (m/s)
0.2 0.2
0.0
-0.2
Line 1 One row of sphere ( =2.47) Two rows of spheres ( =1.48) Three rows of spheres ( =2.16) Conventional spouted bed
-0.4 0.0
0.1
0.2
0.3 0.4 x/D
0.5
0.6
0.7
0.0
-0.2
Line 2 One row of sphere ( =1.31) Two rows of spheres ( =2.11) Three rows of spheres ( =2.63) Conventional spouted bed
-0.4 0.0
(a) The location of line 1
Particle radial velocity (m/s)
0.4
0.2
0.1
0.2
0.3 0.4 0.5 x/D (b) The location of line 2
0.6
0.7
Line 3 One row of sphere ( =1.5) Two rows of spheres ( =0.97) Three rows of spheres ( =1.52) Conventional spouted bed
0.0
-0.2 0.0
0.1
0.2
0.3 0.4 0.5 x/D (c) The location of line3
0.6
0.7
Fig. 12. Effect of row numbers of LVGs on particle radial velocity along radial direction (H0 = 225 mm). 323 324 325 326 327 328 329 330 331 332 333 334 335
(2) The enhancement factors g with different particle densities are all greater than 1. The smaller the particle density, the more significant the effect of the longitudinal vortex on the radial velocity of the particles. (3) The single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H0 = 165 mm). With the increase of the height of the static bed (H0), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle motion in the spouted bed with more particle handling capacity.
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Acknowledgement
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This work is supported by National Natural Science Foundation of China (Grant No. 21878245, 21476181), Natural Science Foundation of Shaanxi Province (Grant No. 2019JM-039) and Cyrus Tang Foundation.
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References
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Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
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Original Research Paper
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Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators
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Feng Wu a,⇑, Lingyi Shang a, Zeyu Yu b, Xiaoxun Ma a,⇑, Wenjing Zhou c
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a
School of Chemical Engineering, Northwest University, Xi’an, China School of Urban Planning and Municipal Engineering, Xi’an Polytechnic University, Xi’an, China c School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, China b
a r t i c l e
i n f o
Article history: Received 18 March 2019 Received in revised form 25 May 2019 Accepted 27 June 2019 Available online xxxx Keywords: Spouted bed Particle diameter Particle density Row number of longitudinal vortex generators Experiment investigation
a b s t r a c t A spouted bed with longitudinal vortex generator (LVG) of sphere was built to enhance radial movement of particles. Particle Image Velocimetry (PIV) was applied to explore effects of longitudinal vortex flow and physical properties of particles on their radial velocity in a 152-mm-diametered spouted bed. The results show that, Compared with the conventional spouted bed, the existence of longitudinal vortex generator gives rise to a large amount of secondary fine vortex flow in the cross section of spouted bed. The enhancement factors of particles movement g with different particle densities are all greater than 1. The smaller the particle density, the more significant the effect of the longitudinal vortex on the radial velocity of the particles. The single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H0 = 165 mm). With the increase of the height of the static bed (H0), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle motion in the spouted bed with more particle handling capacity (H0 = 195 mm, 225 mm). Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
48 49
1. Introduction
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Spouted beds are an alternative to fixed and fluidized beds and have been applied in industrial applications such as drying, coating, mixing, combustion, gasification and granulation [1,2]. In order to improve the effective use of cylindrical spouted beds in industrial applications, many experimental tests of spouted bed apparatuses have been performed to obtain detailed knowledge of gas and particle hydrodynamics [3–9]. Devahastin et al. [3,4] experimentally developed a Rotating Jet Annular Spouted Bed (RJASB) dryer for drying of particulates in the falling rate period. They also studied some hydrodynamic and mixing characteristics of a pulsed spouted bed dryer. Prachayawarakorn et al. [5] studied the heat transfer characteristics in a two-dimensional spouted bed with draft plates using three agricultural materials, paddy, corn and soybean. Zhong et al. [6–8] experimentally studied the particle mixing behavior in a large spout-fluid bed. Besides, they investigated the spout characteristics of a cylindrical spout-fluid bed with elevated pressure and the particle mixing in flat-bottom spout-
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
⇑ Corresponding authors. E-mail addresses: [email protected] (F. Wu), [email protected] (X. Ma).
fluid bed. Sari et al. [9] measured the characterization of gassolid flow in conical spouted beds operating with heavy particles. Qin et al. [10] designed and set up a cold-state spouted bed for oil shale semi-coke and experimentally investigated the effect of static bed height and particle size on the spouting pressure drop. Sutkar et al. [11] analyzed the hydrodynamics of a pseudo-2D spout fluidized bed with draft plates by changing the background velocity from 0 to 1.75 m/s with interval of 0.25 m/s and the spout velocity from 10 to 50 m/s with interval of 5 m/s. Nagashima et al. [12] experimentally obtained the effects of operating parameters on hydrodynamic behavior of spout-fluid beds with and without a draft tube. Mostoufi et al. [13] experimentally studied flow structure characterization in conical spouted beds with the aid of pressure fluctuation signals. Wang et al. [14] developed a dual-column slot-rectangular spouted bed to improve solids exchange between two adjacent chambers. Recently, Parise et al. [15] experimentally investigated the hydrodynamics of a slot-rectangular spouted bed of biomass particles with simultaneous injection of spouting and pulsating air streams. Kiani et al. [16] experimentally studied the mixing and segregation of binary mixtures of particles with different sizes and densities in a pseudo-2D spouted bed. Breault et al. [17,18]
https://doi.org/10.1016/j.apt.2019.06.033 0921-8831/Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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Nomenclature dp Ds D H Ha H0 L R
89 90 91 92 93 94 95 96 97 98 99 100
S x, y, z
particle diameter [mm] diameter of the spouted gas inlet [mm] diameter of the bed [mm] vessel height [mm] height of cross section of data acquisition [mm] static bed depth [mm] distance between two centers of sphere [mm] radius of spheres [mm]
width of deflector [mm] Cartesian coordinates [m]
Greek symbols dimensionless enhancement factor of particle movement [—] q density [kg/m3] d thickness of deflector [mm]
g
experimentally studied the hydrodynamic characteristics of the gas-solid flow in a rectangular spouted bed (30.2 mm 101.6 mm) under three initial bed heights (0.0762 m, 0.102 m, and 0.127 m) for two different nozzle sizes (0.0096 m and 0.0127 m). They also investigated the spout characteristics and minimum spouting velocity of a flat-base spout-fluidized bed with different static heights and two materials (Al2O3 and high density polyethylene). Rao et al. [19] studied the pressure fluctuations emanating from three dimensional (3D) conical spouted bed using dense zirconia particles (6200 kg/m3) via high intensity microphone. Estiati et al. [20] conducted a study about the influence of geometry and configuration of both confiner and draft tube on article
Table 1 Operating conditions and properties of the particles used in the experiments. Particle density (q) Particle diameter (dp) Vessel height (H) Height of cross section of data acquisition (Ha) Static bed depth (H0) Spouting gas volume flow rate Diameter of the spout gas inlet (Ds) Diameter of the bed (Dt) Radius of spheres (R) Thickness of deflector (d) Distance between two centers of sphere (L) Width of deflector (S)
1897 kg/m3, 2200 kg/m3, 2603 kg/m3 0.72 mm, 1.13 mm, 1.42 mm 700 mm 230 mm 165 mm, 180 mm, 195 mm, 225 mm 400 L/min 19 mm 152 mm 10 mm 2 mm 35 mm 80 mm
Camera location
Ha
Cross section
z o
Fig. 1. Schematic diagram of the experiment setup: 1. Analysis, 2. Synchronizer, 3. Image shift electronics, 4. Laser, 5. Light sheet, 6. CCD camera, 7. Spouted-bed.
x y
Gas inlet
Fig. 3. Schematic diagram of cross section selected in spouted bed.
2
100
30
20
30 20
o
35 80 150
x
10
z
R10
y
(a) Conventional spouted bed
(b) Spouted bed with LVGs
Fig. 2. Geometry of multi-row spouted bed and the size of longitudinal vortex generator in spouted bed (unit: mm).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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entrainment, operating pressure drop, operating air flow rate and maximum cycle time. Longitudinal vortex technique is widely used in enhancing thermal efficiency of heat exchangers or micromixer of the microfluidic systems [21–27]. Ahmed et al. [21] reviewed heat transfer augmentation using vortex generators and nanofluids. Hsiao et al. [23] investigated the micromixers based on the T-shaped channel with longitudinal vortex generators mounted on the bottom of
Line 1 Line 2 Line 3
y o
Deflector x
Fig. 4. Location of particles velocity selected in cross section of spouted bed.
3
the main channel. Datta et al. [24] numerically investigated fluid flow and heat transfer behavior in microchannel using inclined longitudinal vortex generator. Ebrahimi et al. [25,26] numerically simulated conjugated heat transfer and hydraulic performance for nanofluid flow in a rectangular microchannel heat sink with LVGs (longitudinal vortex generators). Wu et al. [28–30] numerically investigated the radial mixing behaviors of gas and particle phases in spouted beds with longitudinal vortex effects. They also numerically analyzed the influence of row number of LVGs on gassolid flow behaviors in a spouted bed. Despite the importance of numerical studies in spouted bed, the experimental study of gas-solid two-phase flow in spouted bed under the influence of longitudinal vortex is still lacking. The purpose of this work is to determine the enhancement ability and mechanism of longitudinal vortex to radial motion of particles in spouted bed. In the present work, a spouted bed with longitudinal vortex generators (LVGs) was investigated by experimental method. Particle Image Velocimetry (PIV) [31] was applied to explore effects of longitudinal vortex flow and physical properties of particles on radial velocity of particles in a spouted bed with LVGs, and the effects of LVGs, density of particles, static bed depth
(a) Conventional spouted bed
(b) Spouted bed with one row of LVG Fig. 5. Comparison of particles vector diagram in cross section of two kinds of spouted beds.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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and row numbers of LVGs on the movement of particles are investigated.
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2. Experimental
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2.1. Experimental apparatus
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The experimental apparatus used in this study is shown in Fig. 1. The experimental instruments mainly comprised a compressor of the type GX4FF-10 (AtlasCopco, The Kingdom of Sweden), a flowmeter of the type D07-60B, (Sevenstar, China), a spouted bed made of plexiglass and a PIV system. The PIV system mainly includes laser emitters, CCD cameras, synchronizers, image acquisition and processing software (Dantec Dynamics A/S, The Kingdom of Denmark). The geometry of multi-row spouted bed and the size of longitudinal vortex generator in spouted bed is shown in Fig. 2. As shown in Fig. 2, there are two kinds of spouted bed are used in the experimental investigation: the conventional spouted bed (Fig. 2(a)) and the spouted bed with one row of longitudinal vortex generator (Fig. 2(b)). Table 1 contains the main dimensions of the spouted bed contactor and properties of the particles used in the experiments.
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2.2. Experimental procedure
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During the experiment, the gas generated by the air compressor enters the spouted bed from the bottom of the bed. By adjusting the gas flow, the gas is driven to move the particles, and the spouting condition in the spouted bed is observed. The laser beam is illu-
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151 152 153
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3. Results and discussion
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3.1. Effect of longitudinal vortex on particle motion
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The experimental device measures and analyzes the radial velocity of the particles in the spouted bed with LVGs, and focuses on the movement of the particle phase in the cross-section of the spouted bed under the effect of the longitudinal vortex. In order to investigate the effect of longitudinal vortex on gas-solid flow behavior in spouted bed, the static bed depth is kept constant at
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0.4
0.4
Particle radial velocity (m/s)
137
0.2 0.0 -0.2 -0.4 0. 0
Line 1 Conventional spouted bed Spouted bed with one row of LVG
0. 2
0. 4
Line 2 Conventional spouted bed Spouted bed with one row of LVG
0.2
0.0
-0.2
-0.4
0. 6
0. 0
0.8
0. 2
0. 4
0. 6
0.8
x/D
x/D
(a) The location of line 1
(b) The location of line 2
0.3
Particle radial velocity (m/s)
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Particle radial velocity (m/s)
135
minated in a cross section the spouted bed, then the camera is placed on the top of spouted bed to record the movement of particles. Finally, the acquired image is analyzed by Dynamic Studio Software, and the radial velocity vector and radial velocity distribution of the cross section are obtained. The schematic diagram of data acquisition process is shown in Fig. 3, In order to study the effect of longitudinal vortex on particle radial velocity in spouted bed with different static bed depth (H0), the height of cross section of data acquisition is kept constant Ha = 230 mm. With the addition of longitudinal vortex generator in the spouted bed, the radial movement of gas and particles occurs in spout and annulus regions, which destroys the distribution regularity of axial particles in the annulus of the bed. In order to obtain comprehensive information of particle velocity in the cross section of spouted bed, three parallel lines (Fig. 4) near the deflector and the annulus are selected as the data acquisition positions of the experiments in this paper, line 1 and 3 are located in annulus region, line 2 is located in spout region.
0.2 0.1 0.0 -0.1 -0.2 -0.3 0.0
Line 3 Conventional spouted bed Spouted bed with one row of LVG
0.2
0.4
0.6
0.8
x/D
(c) The location of line3 Fig. 6. Comparison of on particle radial velocity along radial direction in two kinds of spouted beds (one row of LVGs).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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H0 = 180 mm, the particle density is kept as 2603 kg/m3, the particle diameter is kept as 0.72 mm, and the row numbers of LVGs is kept constant at 1. Fig. 5 shows the comparison of particles vector diagram in cross section of two kinds of spouted beds. As shown in Fig. 5, when there is no-longitudinal vortex generator, the radial velocity of the particle phase exhibits an axisymmetric distribution
in the cross section of the bed. The addition of the longitudinal vortex generator causes vortex motion of the high-speed gas passing through the affected area, and drives particles to generate a large amount of secondary fine vortexes, especially in the annulus region, which strengthens the radial movement of the gas and the particles. Furthermore, the lateral mixing between particles
x/ mm
(a) =1897 kg/m3
x/ mm
x/ mm
x/ mm 3
(b) =2200 kg/m
x/ mm
(c) =2603 kg/m3
x/ mm
Fig. 7. Particles vector diagram in cross section of spouted bed for different particle density.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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and particles, gas and particles in the spout region and the annulus interval is enhanced, which effectively reduces the problem of layered flow of particles in the annulus of the spouted bed. Fig. 6 shows the radial profiles of particle velocities in opposite directions on the left and right sides of the axis. It can be seen that compared with the conventional spouted bed, the radial velocity of the particles is significantly enhanced by the longitudinal vortex. Meanwhile, the radial velocity of particles in the annulus is significantly higher than that in the spout region, which indicates that the longitudinal vortex can effectively enhance the radial motion of the particles, and its strengthening effect is consistent with the distribution of radial velocity vector of the particles obtained in Fig. 5.
204
3.2. Effect of particle density on particle motion
205
The particle density plays an important role in gas-solid twophase flow in spouted bed. In order to analyze the effect of particle density on particle motion enhanced by longitudinal vortex, Fig. 7 displays the distribution of radial velocity vector of particles in the cross section of the spouted bed with different particle densities (q = 1897 kg/m3, 2200 kg/m3, 2603 kg/m3) with the particle diameter is kept as 0.72 mm. It can be seen from the figure that, when the particle density is 1897 kg/m3, the vortex flow generated by the gas motion has the best effect on the movement of the particles. The smaller the particle density, the larger the radial velocity of the particles.
209 210 211 212 213 214 215
g¼
-0.2 -0.4 0.0
jV L j
ð1Þ
jV N j
Line 1 3 =1897 kg/m 3 =2200 kg/m 3 =2603 kg/m
0.2
0.4
0.6
0.2 0.1 0.0 Line 2 3 =1897 kg/m 3 =2200 kg/m 3 =2603 kg/m
-0.1 -0.2 0.0
0.8
0.2
0.4
0.6
0.8
x/D (b) The location of line 2
0.4 0.2 0.0
Line3
0.0
3
=1897 kg/m 3 =2200 kg/m 3 =2603 kg/m 0.2
220 221 222 223 224 225
228
231
x/D
-0.4
219
longitudinal vortex. jV N j is the average value of absolute particle velocity distribution along the radial direction of spouted bed without the effect of longitudinal vortex. The larger the g value, the greater the enhancement effect of longitudinal vortex on the particle movement. Fig. 9 shows the variations of g with varying particle density. The calculated results exhibit that the enhancement factors g with different particle densities are all greater than 1, which indicates that the addition of the longitudinal vortex generator in spouted beds can effectively strengthen the radial velocity of the particles.
(a) The location of line 1
-0.2
218
229
0.3
0.0
217
where jV L j is the average value of absolute particle velocity distribution along the radial direction of spouted bed under the influence of
0.4 0.2
216
226
Particle radial velocity (m/s)
208
Particle radial velocity (m/s)
207
Particle radial velocity (m/s)
206
Fig. 8 presents the effect of vortex generators on particle radial velocity for different particle densities. It can be seen that when the particle density equals 1897 kg/m3, the vortex flow generated by the gas motion has the best effect on the movement of the particles in annulus. The smaller the particle density, the larger the radial velocity of the particles, which means the effect of the longitudinal vortex on the radial velocity of the particles is more significant. In order to describe the enhancement effect of longitudinal vortex on particle velocity, a dimensionless enhancement factor of particle movement is defined, which is shown as follows:
0.4
0.6
0.8
x/D (c) The location of line3 Fig. 8. The effect of vortex generators on particle radial velocity for different particle density.
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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2.8
Line 1 Line 2 Line 3
2.4
The smaller the particle density, the more significant enhancement effect of the longitudinal vortex on the radial velocity of the particles.
241
3.3. Effect of row numbers of LVGs
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The effects of different static bed heights (H0 = 165 mm, 195 mm, 225 mm) and row number of LVGs on particle motion in spouted bed were analyzed (Table 2), the particle density is kept constant as q = 2200 kg/m3, and the particle diameter is kept as 0.72 mm. Fig. 10 shows the effect of row numbers of LVGs on particle radial velocity along radial direction when H0 = 165 mm (H0/Dt = 1.09). It can be observed that, the radial velocity enhancement factors (g) are all greater than 1, and the radial velocity enhancement factors of single row of sphere are significantly higher than those of double rows of spheres and three rows of spheres. According to the distribution of particle radial velocity, the effect of particle radial motion enhancement is the best when the sphere generator is in the form of single-row. The radial velocity of particles decreases with the increase of the number of rows of spheres, which indicates that the single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H0 = 165 mm). With the increase of the number of LVGs rows, the flow resistance effect of the LVGs increases, that is, the resistance effect of the LVGs is greater than enhancement effect of longitudinal vortex on particles, and the comprehensive result shows that the radial velocity of particles decreases.
245
242 243
2.0 1.6 1.2 2000
2200
2400
2600 3
Particle density (kg/m ) Fig. 9. Variations of g with varying particle density.
Table 2 Average values of g for different static bed depth. Average values of g
Row numbers of LVGs
1 2 3
H0 = 165 mm
H0 = 195 mm
H0 = 225 mm
2.12 1.85 1.68
0.93 1.98 0.60
1.76 1.52 2.10
Particle radial velocity (m/s)
Particle radial velocity (m/s)
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Line 1 One row of sphere ( =2.28) Two rows of spheres ( =2.19) Three rows of spheres ( =1.79) Conventional spouted bed
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0.0 Line 2 One row of sphere ( =2.11) Two rows of spheres ( =1.67) Three rows of spheres ( =1.63) Conventional spouted bed
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Particle radial velocity (m/s)
(a) The location of line 1
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(b) The location of line 2
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0.0 Line 3 One row of sphere ( =1.97) Two rows of spheres ( =1.68) Three rows of spheres ( =1.63) Conventional spouted bed
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(c) The location of line3 Fig. 10. Effect of row numbers of LVGs on particle radial velocity along radial direction (H0 = 165 mm).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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is greater than 1, which indicates that the enhancement effect of longitudinal vortex on radial motion of particles in annulus is better than that in spout region when the amount of particles in spouted bed is large. The radial velocity of particles in three rows of LVGs in spout region is better than that in single row and double row, and the radial velocity of particles in single row of LVGs in annulus region is the largest. This is because the height of the static bed equal the height of the third row of spheres. The third row of spheres disturbs the particles rising in the spout region, which makes the radial velocity of particles increase locally by reducing cross-sectional area of flow passage. The resistance of the particles increases with the increase of the number of rows of spheres, which leads to the maximum particle velocity in the annular gap when the LVGs is single row. Figs. 10–12 show that with the increase of the height of the static bed (H0), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle movement in the spouted bed with more particle handling capacity (H0 = 195 mm, 225 mm).
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4. Conclusions
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(1) Compared with the conventional spouted bed, the addition of the longitudinal vortex generator generates a large amount of secondary fine vortex flow in the cross section of spouted bed, and the radial velocity of the particles is significantly enhanced by the longitudinal vortex.
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Particle radial velocity (m/s)
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Fig. 11 shows the effect of row numbers of LVGs on particle radial velocity along radial direction when static bed heights increased to H0 = 195 mm. It can be seen in Fig. 11 that when H0/D = 1.28, the g of single-row and three-row LVGs are less than 1 in annulus region (line 1 and line 3), while those of double-row LVGs are greater than 1 in spout (line 2) and annulus. At different data locations, the radial velocity enhancement factors of particles are less than or greater than 1, which indicates that the spatial distribution of particle motion enhancement in spouted bed is inhomogeneous due to longitudinal vortex. According to the distribution of particle radial velocity, the longitudinal vortex strengthening effect on particle radial velocity near the spout is the best, and the overall strengthening effect of particle radial motion is the best when the LVGs have two-row setting. The overall strengthening effect of single row of LVGs in the spout region is better than that of three rows of LVGs, while the strengthening effect of single row of LVGs in the annulus of spouted bed is better than that of three rows of LVGs. On the whole, when the row number of LVGs equals 2, the radial velocity of particles is best enhanced. The results show that with the increase of particle handling capacity, the enhancement of radial motion of particles in multi-row LVGs is gradually presented. However, increasing the row number of LVGs will lead to a rapid increase in particle flow resistance, which will adversely affect the overall movement of particles. Fig. 12 shows the effect of row numbers of LVGs on particle radial velocity along the radial direction when the height of the static bed equals 225 mm. From Fig. 12, we see that when H0/D = 1.48, the enhancement factor of all rows of LVGs in annulus
0.2 0.0 -0.2
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Line 1 One row of sphere ( =0.86) Two rows of spheres ( =1.11) Three rows of spheres ( =0.78) Conventional spouted bed
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Line 2 One row of sphere ( =1.12) Two rows of spheres ( =3.12) Three rows of spheres ( =0.53) Conventional spouted bed
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Particle radial velocity (m/s)
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0.3 0.4 0.5 0.6 x/D (b) The location of line 2
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0.0 Line 3 One row of sphere ( =0.8) Two rows of spheres ( =1.7) Three rows of spheres ( =0.49) Conventional spouted bed
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0.3 0.4 0.5 x/D (c) The location of line3
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Fig. 11. Effect of row numbers of LVGs on particle radial velocity along radial direction (H0 = 195 mm).
Please cite this article as: F. Wu, L. Shang, Z. Yu et al., Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.06.033
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Particle radial velocity (m/s)
Particle radial velocity (m/s)
0.2 0.2
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Line 1 One row of sphere ( =2.47) Two rows of spheres ( =1.48) Three rows of spheres ( =2.16) Conventional spouted bed
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Line 2 One row of sphere ( =1.31) Two rows of spheres ( =2.11) Three rows of spheres ( =2.63) Conventional spouted bed
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(a) The location of line 1
Particle radial velocity (m/s)
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Line 3 One row of sphere ( =1.5) Two rows of spheres ( =0.97) Three rows of spheres ( =1.52) Conventional spouted bed
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0.3 0.4 0.5 x/D (c) The location of line3
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Fig. 12. Effect of row numbers of LVGs on particle radial velocity along radial direction (H0 = 225 mm). 323 324 325 326 327 328 329 330 331 332 333 334 335
(2) The enhancement factors g with different particle densities are all greater than 1. The smaller the particle density, the more significant the effect of the longitudinal vortex on the radial velocity of the particles. (3) The single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H0 = 165 mm). With the increase of the height of the static bed (H0), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle motion in the spouted bed with more particle handling capacity.
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Acknowledgement
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This work is supported by National Natural Science Foundation of China (Grant No. 21878245, 21476181), Natural Science Foundation of Shaanxi Province (Grant No. 2019JM-039) and Cyrus Tang Foundation.
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