Spray Drying Technology.pdf - National University of Singapore

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Core model Air flow simulation Sub-models Particle tracking Droplet drying model Deposition model Particle interaction Particle quality Results Figure 1 Schematic layout of a CFD simulation of spray drying 2.1 Airflow simulation The core of a spray dryer CFD model from which other components are based on is the airflow simulation. Airflow pattern in the chamber mainly determines the movement of the particles which subsequently affects the residence time of the particles and whether the particles get deposited or escape from the chamber. In the computational sense, getting this right is the prerequisite for subsequent modelling effort. Most spray dryer CDF simulations reported are currently undertaken using commercial codes such as FLUENT, CFX, STAT3D e.g. as well as inhouse codes [3-6] . The basic CFD techniques are relatively established and will not be repeated here. It is expected that the reader is familiar in the technique and references can be found elsewhere [7] . However, we will only focus on some specific important general considerations when modelling the internal airflow within the chamber of a spray dryer: 1. Transient or steady simulation 2. Two-dimensional versus three-dimensional 3. Turbulence modelling approach Woo, Huang, Mujumdar, Daud – CFD modeling of spray dryers 3
Transient or steady simulation The steady state approach has been the work horse of many early reports on CFD simulation of spray dryers [8-12] . To be more specific, it implies that there are no long time scale changes in the flow, although there can still be turbulence fluctuations present. Under the assumption that the airflow within the chamber is steady, these simulations managed to capture engineering data of interest. In particular, the third report by Kieviet et al. [10] illustrated relatively good comparison between the simulated and the measured velocity profiles although some unsteady pattern can be observed in their experimental work. This work has further become a relatively ‘standard’ test case in some recent studies [13][14] . Relying on the ability of the steady state approach, a European Union (EU) project was funded, EDECAD, to implement the CFD technique to large industrial scale dryers [6] , further illustrates the application of the steady state approach. On the other hand, recent experimental work suggests that the internal airflow pattern can exhibit significant transient behaviour. Observations in a co-current pilot scale unit indicated that the central core flow tend to fluctuate sidewards with transient eddies being formed near the wall [15][16] . Not to be confused with rapid turbulence fluctuation, this transient behaviour refers to relatively long time scale self-sustained fluctuations. Figure 2 gives a simplified illustration of such transient behaviour in the airflow. There will be tendency for the central jet to deflect to the sides. The transient behaviour is also called self-sustained fluctuations as the transient behaviour is sustained due to pressure imbalances around the central jet. Additional experiments using a scaled down experimental unit provided more evidence of the transient behaviour particularly in the central core flow [17] . In order to obtain more insights into the transient behaviour, extensive simulations were further undertaken by making analogy to sudden pipe expansion flows. Depending on the inlet conditions, in general, it was found that a larger expansion ratio promotes more instability [18-20] . Some workers in the field have also recently switched to the transient approach [21][22] . However, based on a jet feed-back mechanism, it was recently numerically shown that the internal flow pattern in a spray dryer can exhibit steady-like behaviour, depending on the diameter of the chamber and the inlet velocity [23] . In a separate simulation for a unit with a rotating disk, Ullum (2006) also noted that their CFD predicted flow field resembles that of steady state; even when the simulation was switched to the transient solution framework. Harvie et al. [8] and Langrish et al. [5] further provide illustration of the contrasting effect of swirls in stabilizing or de-stabilizing the flow field. On more fundamental grounds analogous to the spray dryer, studies on sudden pipe expansion and cavity expansion systems showed that steady or transient behaviour in the flow is strongly dependent on the expansion ratio and operating conditions [19][24] . Coupled with the ability of the steady approach in the earlier work, these are strong evidence in the possible existence of a transient-steady stability map in spray dryers. However, this point is still expected to be under discussion in the near future and mapping out of the entire stability map might not be possible due to the myriad possible designs of spray dryers. The key objective in illustrating these different cases and in making the comparison is so that the readers are aware of the possible Woo, Huang, Mujumdar, Daud – CFD modeling of spray dryers 4
Page 1 and 2: Spray Drying Technology Volume One
Page 3 and 4: List of Authors Arun Sadashiv Mujum
Page 5 and 6: Content Preface Page i List of Auth
Page 7: 1.0 Introduction The CFD technique
Page 11 and 12: Initial conditions Steady state sol
Page 13 and 14: flow structures; limiting any possi
Page 15 and 16: ( ρ − ρ) du g P X P = FD ( u
Page 17 and 18: Group of particles with the same ma
Page 19 and 20: vortex in the region below the disk
Page 21 and 22: Another development is in the use o
Page 23 and 24: modulus, can be obtained to be used
Page 25 and 26: 3.1 Quantitative and qualitative ai
Page 27 and 28: 3.4 Residence time measurements The
Page 29 and 30: velocities at nozzle exit are fixed
Page 31 and 32: Figure 13 a b Spray dryer considere
Page 33 and 34: atomizer was operated at a higher c
Page 35 and 36: 6.0 Concluding remarks This chapter
Page 37 and 38: dryers. Chemical Product and Proces
Page 39 and 40: 56. Adhikari, B.; Howes, T.; Lecomt
Page 41 and 42: Woo, Huang, Mujumdar, Daud - CFD mo
Page 43 and 44: Since the current market requires f
Page 45 and 46: dryer operation conditions to those
Page 47 and 48: SPRAY DRYER DESIGN: • spray dryer
Page 49 and 50: spray-dried powders. This lognormal
Page 51 and 52: permeability, as the ESA (envelope
Page 53 and 54: Therefore, the ρ p determination d
Page 55 and 56: that can be universally accepted as
Page 57 and 58: inhalation. For that, product quali
Page 59 and 60:
4.1 Experimental design for empiric
Page 61 and 62:
X 1 X 3 X 2 Figure 8 Rotational Cen
Page 63 and 64:
6.0 References 1. Filková, I.; Muj
Page 65 and 66:
38. Birchal, V.S.; Passos, M. L.; W
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1.1 Effect on particle-wall deposit
Page 69 and 70:
These considerations regarding the
Page 71 and 72:
eported by Keey & Pham [19]. This a
Page 73 and 74:
⎛ ρ 1000 ⎞ pi − d p = d pi
Page 75 and 76:
2.5 Particulate drying kinetics Cor
Page 77 and 78:
may be the solid material that is s
Page 79 and 80:
10. Pokharkar, V.B.; Mandpe, L.P.;
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Langrish - Spray drying and crystal
Page 83 and 84:
1.0 Introduction Spray modeling has
Page 85 and 86:
As for the small-scale phenomena, c
Page 87 and 88:
Figure 5 Lagrangian approach for de
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2.1 Particle size distribution In c
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Figure 8 Property variations in par
Page 93 and 94:
More sophisticated treatments could
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⎛⎛ 1 1 ⎞ ln( P / P ) = −h
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3/2 3/2 3/4 k 2 k µ or T L = e C C
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ρ u − u C σ C µ dy m = m − m
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3 ⎛ 8K ρlr( t) 6K − 5 rp ( t +
Page 103 and 104:
Where 2χ 2bsin β −γ B = = d +
Page 105 and 106:
This Eq. (31) distinguishes the reg
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f γ = γ − 2.4γ + 2.7γ represe
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⎛ new 6m ⎞ t dl = ⎜ πρ ⎟
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in air. Park et al. [98] used the b
Page 113 and 114:
5. Batchelor ,G.K. Collected Works
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59. Ranz, W.E.; Marshall, W.R.; Eva
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112. Xu, L.; Zhang, W.W.; Nagel, S.
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1.0 Introduction Spray drying is a
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3.0 Relevant physical-chemical prop
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the rapid drying of the liquid feed
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degradation of the product during s
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Cyclodextrins are ‘bucketlike’
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were used as drying carriers. Their
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continuation Lime T in = 135 - 160
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herbal materials (leaves, roots, se
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taken in account simultaneously dur
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6.3 Microencapsulation of essential
Page 139 and 140:
in mixtures of gum arabic and malto
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and to examine their physicochemica
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Ersus and Yurdagel [135] investigat
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dried be cooled down to 30 °C or l
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Table 4 Miscellaneous food products
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8.0 Nomenclature Cs solid concentra
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24. Reineccius, G.A; Multiple-core
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57. Roustapour, O.R.; Hosseinalipou
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85. Cacace, J.E.; Mazza, G. Pressur
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110. Souza, C.R.F.; Schiavetto, I.A
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139. Shu, B.; Yu, W.; Zhao, Y.; Liu
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Oliveira, Souza, Kurozawa, Park - F
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1. Preparation and formulation step
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There are three fundamental stages
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2.0 Spray freeze drying Spray freez
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procaine hydrochloride, was success
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where ρ p is the particle density
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to be negligible [7,37,39] . The pa
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Figure 2 (a) Diagram of a material
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In Eq.(27), T interf , denotes the
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( z= Z t ) pw = f T at z = Z( t) ,
Page 181 and 182:
The current studies have shown that
Page 183 and 184:
22. Yin, W.; Yates, M.Z. Encapsulat
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k des rate constant in the desorpti
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Sadikoglu - Spray freeze drying 182
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However, there is no report on an e
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• Fine powder transport air tempe
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Nominal main process air flowrate (
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4.2 Mass balance Similar to the hea
Page 197 and 198:
obtained from established correlati
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droplet surface vapour concentratio
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5. Patel, K.C.; Chen, X. D.; Lin, S
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1.0 Introduction The demand of food
Page 205 and 206:
2.3 Particle shape All geometrical
Page 207 and 208:
factors such as the solvent tempera
Page 209 and 210:
A B Stereomicroscope (Nikon SMZ1500
Page 211 and 212:
4.4 Conventional and environmental
Page 213 and 214:
neutral networks that have as a com
Page 215 and 216:
Wen-Shiung et al. [44] . FDt was ca
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Morphological parameters of powder
Page 219 and 220:
Figure 7 Sample B of powder milk. a
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8.0 References 1. Hogekamp, S.; Sch
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35. Peighambardoust, S.H.; Dadpour,
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Diameter change correlation, 194 Di
Page 227 and 228:
Phenolic compounds, 114 Phytochemic
Page 230:
Spray drying is a ubiquitous indust
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