Simulation of spray dryers using computational fluid dynamics

Chapter Introduction The first chapter provides a brief introduction to the background, the scope and outline of this thesis. 1.1 Background Spray drying is a unit operation that transforms a solution or suspension into particles or powders by evaporation of the volatile. [Masters, 1991; Filkova & Mujumdar, 1995; Masters, 2002] Most spray dryers can be found in the chemical, food, dairy, ceramic, dyestuff and pharmaceutical industries for processing of solutions, suspensions, emulsions and slurries [Huang et al., 2004; Masters, 2002]. Because spray drying usually is the end-point of a process and also influences the quality of the final product, more attention was paid to it over the last two decades. But the flow pattern inside is complicated and the understanding of the underlying processes has been poor: Thus with only empirical developments, it is unlikely to achieve satisfactory process intensification and further improvement in the performance of spray dryers. Therefore, Computational Fluid Dynamics (CFD) can be used as a design tool or as a design guide to compare the drying and hydrodynamic performance of chambers of different shapes, different arrangements of inlet drying gas (including single entry or multi-port entry), supplementary drying or cooling air inlets as well as effect of ambient air leakage due to poor sealing which is not uncommon in old spray chambers. It is too expensive to test the effect of all these parameters experimentally. Recent rapid developments in CFD and the ever-increasing computing power at decreasing cost makes it feasible to evaluate spray dryer designs without undertaking expensive experimental pilot or laboratory tests. Although simulation of the complex transport phenomena that occur in a spray dryer cannot yet be modeled with high accuracy, the results are nevertheless useful to guide design and operation of spray dryers when coupled with some empirical experience. Some commercial CFD codes [Dombrowski, 1993] are also available now, for example(s), PHOENIX, FLUENT, FLOW3D, FIDAP, CFX etc. to study the transport phenomena in spray dryers. However, lack of carefully obtained experimental data, primarily due to the often confidential nature of the process and difficulty of making the necessary detailed measurements, is currently hampering the development of CFD-based design and analysis of spray dryers. It is quite possible that perhaps the numerical predictions are almost as reliable as experimental data that can be obtained within the spray dryer chamber under operating conditions. However, there are still some limitations to the CFD approach since it does not typically include reliable and validated models for quality changes, attrition or agglomeration of particles that can occur within the chamber. 1.2 Scope and objectives of the thesis This dissertation addresses the operational aspects of spray drying performance with focus on the effect of various parameters on particle stick on the wall in drying chamber, heat/mass transfer coefficient in the drying chamber, heat consumption intensity per unit evaporative rate and volumetric effectiveness, and the impact of the geometry design on the airflow and particle motion in drying chamber. The goal is to contribute to a better fundamental understanding of the drying operation to improve the current spray drying technology. This thesis aims to develop a state-of-the-art CFD-based design and analysis methodology for spray drying plants. This design methodology enables the optimization of spray dryers in terms of more compact (intensified) plants, greater energy efficiency and higher product yield while maintaining product quality. The project results will assist the spray dryer designer to control the drying gas flow pattern, the droplet/particle trajectory and the heat and mass transfer process so as to prevent product degrading and deposits on the chamber walls. The first objective of this project is to develop and validate a CFD-based model to predict flow patterns and overall drying performance of a conventional cylinder-oncone spray dryer by comparing the results with published results as well as with new data supplied by collaborating researchers in Brazil and Australia. The effects of operating parameters, different layouts on the drying performance and airflow patterns are studied as well. The second objective of the project is to evaluate novel spray dryer geometries that yield better volumetric effectiveness and higher heat/mass transfer performance than the conventional designs. The geometries being considered are conical, hour-glass shape and lantern shape chamber. The axi-symmetric CFD model is used to evaluate those designs. The third objective is to evaluate a spray dryer fitted with different atomizers, such as, rotating disc atomizer and ultrasonic nozzle. The performance is then compared with that of the normal spray dryer fitted with pressure nozzle. CFD model is first used in simulating the spray dryers fitted with rotating disc atomizer and ultrasonic nozzle. The fourth objective is to evaluate a new one-stage and two-stage, two dimensional horizontal spray dryer concept, proposed initially by Prof. Mujumdar, which is expected to allow longer drying times needed for heat-sensitive products and large droplet sizes. The fifth objective is to modify the drying model and add it into the commercial code by user-defined-functions. It definitely improves the prediction of the drying process in the spray drying chamber. Three different drying models are developed based on the characteristic drying curve. The final objective is to evaluate an industrial scale spray dryer. The necessary measurements are carried out. The comparisons between prediction and measurements are carried out, as well. Different pressure nozzle designs are evaluated. 1.3 Outline of the thesis In chapter 2, the literature pertaining to the key processes involved in a spray dryer, i.e., atomization, droplet and its drying, contact of droplet and drying medium, are reviewed. The models developed for simulation of spray dryers are reviewed as well. The CFD model used is described in chapter 3. A new drying model and newly defined parameters for describing the drying performance of spray dryer are also obtained. From chapter to chapter 9, selected predicted results and experimental data are presented. Chapter presents the validation of a CFD model using a published data by Kieviet [1997]. Then the parametric studies are carried out, e.g., effects of inlet temperature of drying medium, air leakage, heat loss from the chamber wall, operating pressure in the drying chamber, the environmental drying medium humidity etc. In chapter 5, an industrial spray drying of coffee is used as an example for modeling. It seems that this is the first time such a large-scale industrial spray dryer is modeled and tested using CFD. Different pressure nozzle designs are investigated. Some useful suggestions to improve the performance of this spray dryer are also provided. Chapter presents the predicted results of spray dryers using different atomizers except pressure nozzle, e.g., rotary disc atomizer and ultrasonic nozzle. These two types of spray dryers are also being modeled using CFD for the first time, as well. Chapter describes the development of a new spray dryer design using CFD, i.e., a horizontal spray dryer. An optimal horizontal spray dryer design is obtained using CFD simulations. Chapter evaluates alternative spray dryer designs without undertaking the expensive experimental pilot or laboratory tests. The four types of drying chamber, i.e., cylinder-on-cone, hour-glass, pure conical and lantern, are selected studied. Chapter investigates the new drying model that can be incorporated as part of the commercial CFD code to improve the performance of the CFD model already exists in the software. Finally, the conclusions of this study are given in chapter 10. The recommendations for future work in this field are discussed in chapter 11. Hence, this study is believed to present some novel approaches to modeling spray dryers and to the understanding of the performance of a spray dryer as well. Due to space limitations all the results obtained during the course of this study could not be accommodated in this thesis. Additional results are, however, available in a number of publications. Chapter Literature review 2.1 Fundamentals of spray drying Spray drying is a suspended particle processing (SPP) technique that utilizes liquid atomization to create droplets which are dried into to individual particles while moving in a hot gaseous drying medium, usually air [Masters, 1991]. Over 20,000 spray dryers are estimated to be presently in use commercially around the world to dry products from agro-chemical, biotechnology products, fine and heavy chemicals, dairy products, dyestuffs, mineral concentrates to pharmaceuticals in sizes ranging from a few kg per hour to 50 tons/h evaporation capacity [Mujumdar, 2000]. Liquid feedstocks, e.g., solutions, suspensions or emulsion, can be converted into powder, granular and agglomerate form in an one-step operation in the spray dryer. [Masters, 1991 & 2002; Filkova & Mujumdar, 1995; Huang and Mujumdar, 2003] Among the advantages of spray dryers, one may cite the following. It can: • Handle heat sensitive, non-heat sensitive as well as heat-resistant pumpable fluids as feedstocks from which a powder is produced. • Produce dry material of controllable particle size, shape, form, moisture content and other specific properties irrespective of dryer capacity and heat sensitivity • Provide continuous operation adaptable to both conventional and computer (PLC) control • Provide extensive flexibility in its design, such as, drying of organic solvent-based feedstocks without explosion and fire risk; drying of aqueous feedstocks (where the resulting powders exhibit potentially explosive properties as a powder cloud in air); drying of toxic materials; drying of feedstocks that require handling in aseptic/hygienic drying conditions; drying of feedstocks to granular, agglomerated and nonagglomerated products. • Handle a wide range of production rates, i.e., almost any individual capacity requirement can be designed by spray dryers However, they also suffer from some limitations, such as: • High installation costs; high electrical requirement • A lower thermal efficiency • Product deposits on the drying chamber walls may lead to degraded product or even fire hazard Examples of spray-dried products on industrial scale include the following: • Chemical industry, e.g., Phenol-formaldehyde resin; catalysts; PVC emulsion-type; Amino acid etc. [Kim et al., 2001] • Ceramic industry, e.g., Aluminium oxide; carbides, Iron oxide; Kaolin etc. [Yokota et al., 2001] • Dyestuffs and pigments, e.g., Chrome yellow; food colour; titanium dioxide; paint pigments etc. • Fertilizers, e.g., Nitrates; Ammonium salts; phosphates etc. • Detergent and surface-active agents, e.g., detergent enzymes; bleach powder; emulsifying agents etc. • Food industry, e.g., milk; whey; egg, soya protein etc. [Furuta et al., 1994] • Fruit and vegetables, e.g., banana; tomato; coconut milk etc. [Huang and Mujumdar, 2003a and 2003b] • Carbohydrates, e.g., glucose; total sugar; maltodextrine etc. [Watanabe et al., 2002] • Beverage, e.g., coffee, tea etc. • Pharmaceuticals, e.g., penicillin, blood products, enzymes, vaccines etc. [Newton et al., 1966; Broadhead et al., 1994] • Bio-chemical industry, e.g., algae; fodder antibiotic; yeast extracts; enzymes etc. [Huang et al, 2001] • Environmental pollution control, e.g., flue gas desulfurization; black liquor from paper-making; etc. [Hill et al., 2000; Huang et al, 2001] • Other new applications, e.g., nano-materials, spray freeze drying etc. [Li et al., 1999; Lo et al., 1996; Maa et al., 1999] A normal spray drying process usually consists of the following four stages: 1. Atomization of feed into droplets: The liquid feed which can be solutions, suspensions, emulsions or slurries is atomized to a spray that consists of fine droplets. Ordinarily there are two different atomization methods: Rotary disc or centrifugal atomizers and nozzle atomizers including pneumatic nozzle and pressure nozzle. 2. Heating of hot drying medium: The drying medium, such as air, is heated by steam, electricity, oil combustion or coal combustion etc. Then it will be sent into the drying chamber through the hot air dispenser. 3. Spray-air contact and drying of droplets: The liquid spray is mixed with the hot drying medium in the drying chamber. Then the volatile is evaporated into drying medium and dried into particles or powder. 4. Product recovery and final air treatment: Separation of the dried particles from the exhaust drying air. The cleaned air will be drawn into the atmosphere or recycled. A typical spray drying process flowsheet is shown in Figure 2.1. Although the design, operation mode, handling of feedstock and product requirements are diverse, each stage must be carried out in all spray dryers. The formation of a spray and effective contact of the spray with air are the characteristic features of spray drying. This study mostly focuses on these two parts since the other two parts only satisfy the process requirements, e.g., air inlet temperature and mass flow rate through the drying medium heating system and the product recovery efficiency by the collecting system. Figure 2.1 Typical spray dryer layout 2.2 Atomization Since the choice of the atomizer is very crucial, it is important to note the key advantages and limitations of different atomizers (centrifugal, pressure and pneumatic atomizers). Other atomizers can also be used in spray dryers, such as, the ultrasonic nozzle [Bittern & Kissel, 1999], but they are expensive and have low capacity. Although different atomizers can be used to dry the same feedstock, the final product properties (bulk density, particle size, flowability etc.) could be quite different and hence proper selection is necessary. 2.2.1 Mean droplet diameter The mean droplet diameter is the first important parameter to characterize the distribution of a spray. There are several measures to define it, e.g., number median droplet diameter, d0.5, number mean diameter, d10, the surface mean diameter, d20, the volume mean diameter, d30, and the Sauter mean diameter, d32. The number median droplet diameter, d0.5, is defined as that diameter, in a sample of droplets, for which half of the droplets are smaller than d0.5 and the other half larger than d0.5. The general expression for the other four mean diameters is presented as follows: N d ab = ( ∑n d a i ∑n d b i i ) i N i ( a −b ) (2.1) i where di represents a drop of diameter di, ni the number of droplets with diameter di, and N is the sample number of droplets ( ∑ ni ), and a and b are integers designating i the specific type of mean. For example, the number mean diameter is given by N d10 = ∑n d i i (2.2) i N The surface mean diameter, d20, is expressed by N d 20 = ( ∑n d i i ) i N (2.3) The volume mean diameter, d30, is given by N d 30 = ( ∑n d i i N i ) (2.4) The Sauter mean diameter, d32, is probably the most widely used of the various mean diameter in spray drying. It takes the following form: 10 C.5 Conclusion In conclusion based on the above discussion, grid-independence results are obtained with the meshing used. Considering the comparison between the predicted results with measurements, the final mesh size, i.e., 0.03m, is selected as the testing mesh size. For three-dimensional cases, the similar method is used to mesh the geometry. Considering the computing time and predicting difficulty in modeling, the maximum difference among the predicted results is controlled within 10%. If less than this percentage is reached, the grid-independence results are considered to be obtained. 224 Appendix D: Typical predicted results The following predicted results are used and discussed in this thesis. The discussion is preferred to the corresponding chapters. These are presented as a sample of the output from the models developed. Figure D.1 Typical mesh for the 3D drying chamber simulated 225 Figure D.2 Test geometry with dimensions 226 Figure D.3 Axial and radial velocity distributions at different levels in the drying chamber (a) 0.3m (b) 0.3m (c) 2.0m (d) 2.0m 227 Figure D.4 Temperature profiles at different levels in the drying chamber (a) 0.3m (b) 2.0m 228 Figure D.5 Humidity profiles at different levels in the drying chamber (a) 0.3m (b) 2.0m Figure D.6 Temperature distributions along the chamber wall for all four cases 229 Figure D.7 Axial velocity profiles predicted using different turbulence models 230 Figure D.8 Tangential velocity profiles predicted using different turbulence models 231 Appendix E: Sample computation of the ‘Pseudo-pressure’ used in the new drying kinetics model E.1 Basic conditions E.1.1 Air conditions Ambient air temperature is 25oC – 34oC with relative humidity: 75-95%. In this case, the absolute humidity is assumed as 0.014kgH2O/kgdryAir. Drying air inlet temperature: 245oC, its corresponding density: 0.68kg/m3; viscosity: 27.35 × 10 −6 kg / m.s ; Prandtl Number: 0.68; Thermal conductivity: 41.57 × 10 −3 W / m.K ; Wet-bulb temperature: 50oC; Saturated pressure at wet-bulb temperature: 12336Pa; Air velocity at the pressure nozzle position: 1.3m/s E.1.2 Spray conditions Feed spray mass flow rate: 0.3667kg/s; feed temperature: 50oC; Feed density: 1198kg/m3; Feed spray volumetric flow rate: 3.06 × 10 −4 m / s Number of pressure nozzles: 2; Nozzle model: WC7-TC; operating pressure: 35bar; spray angle: 49o; Hole diameter of the nozzle: 2.39mm; minimum droplet diameter: 10 × 10 −6 m and maximum droplet diameter: 100 × 10 −6 m ; Mean droplet diameter: 43 × 10 −6 m ; Initial velocity: 33.8m/s E.2 Curve fitting based on characteristic drying curve In chapter 9, Model D is seen to be a good model among the three modified models. Here, it is selected as the base model for the improved model. 232 Figure E.1 Characteristic drying curve Curving fitting for Model D based on Figure E.1 gives the correlation between φ and κ as follows: φ = 1.3462κ − 3.387κ + 2.9895κ + 0.0346 (E.1) J X − X* where, φ = and κ = ; N and N c is the drying rate at any time and in the Jc Xc − X * constant drying rate period, respectively; and X , X * and X c are mole moisture content (dry basis) at any time, equilibrium moisture content and critical moisture content, respectively. E.3 Constant drying rate The Reynolds number for the droplet is computed as Re d = ρ g d p u p − ug µg (E.2) 233 = 0.68 × 43 × 10 −6 × 33.8 − 1.3 27.35 × 10 −6 = 34.75 The Nusselt number is obtained by equation (3.25) Nu = hg d p kg = 2.0 + 0.6 Re1d/ Pr / = 5.11 (E.3) Thus, the convective heat transfer coefficient is then given by: hg = 5.11 × kg = 5.11 × dp 41.57 × 10 −3 = 4940( J / m .K .s ) 43 × 10 −6 (E.4) Based on equation (3.35), the constant drying rate is estimated to be Jc = hg (Tg − Tw ) λM w = 4940 × (245 − 50) = 3.71(mol / m .s ) 540 × 4.18 × 18 (E.5) E.4 Derivation of the ‘pseudo-pressure’ based on the falling rate drying period Based on equation (B.15a), the diffusion coefficient of vapor in air is Dvapor = 3.0 × 10 −6 + 4.0 × 10 −8 T + 2.0 × 10 −10 T = 3.0 × 10 −6 + 4.0 × 10 −8 × (245 + 273) + 2.0 × 10 −10 × (245 + 273) = 7.7384 × 10 −5 (m / s ) (E.6) Schimit number is estimated by Sc = µg ρ g Dvapor = 27.35 × 10 −6 = 0.52 0.68 × 7.7384 × 10 −6 (E.7) Sherwood number is computed by Sh = kc d p Dvapor d = 2.0 + 0.6 Re Sc = 4.844 (E.8) Hence, the mass transfer coefficient is 234 7.7384 × 10 −5 = 8.7(m / s ) 43 × 10 −6 k c = 4.844 × (E.9) Here, the critical moisture content and equilibrium moisture content are assumed to be 20% and 0.5%, respectively. Thus, the corresponding mole fractions are obtained as Xc = 0.2 = 0.24 − 0.2 X* = 0.005 ≅ 0.005 − 0.005 Hence, equation (E.1) becomes J = J c (1.3462κ − 3.387κ + 2.9895κ + 0.0346) = J c [91.54( X − 0.005) − 56.4265( X − 0.005) + 12.202( X − 0.005) + 0.0346] = [2170.41( X − 0.005) − 1337.87( X − 0.005) − 289.31( X − 0.005) + 0.82] (E.10) If equation (3.36) is used to model the falling drying rate and based on mole unit, it becomes J = kc ( p G − X i op ) RT p RTg (E.11) Here, the vapor molar fraction in bulk drying air is calculated to be Xi = H ab M w, H 2O H ab 1.0 + M w, H 2O M w,air = 0.014 / 18 = 0.022 (0.014 / 18) + (1.0 / 29.0) (E.12) Vapor concentration in the bulk gas (kmol/m3) is computed as Cg = X i pop RTg = 0.022 × 1.01325 = 0.518 8.314 × ( 273 + 245) (E.13) Combining equations (E.9), (E.10), (E.11) and (E.13), finally the ‘pseudopressure’, i.e., G , is obtained as G = T p [2726.33( X − 0.005) − 1911.14( X − 0.005) + 413.2( X − 0.005) + 5.48] 235 It is noted that this ‘pseudo-pressure’ is a function of temperature and moisture content of the particles. This is not “true” vapor pressure of water within the particle. 236 Publications arising from this thesis Chapter in Book Huang L. X. and Mujumdar, A.S., Spray Drying: Principle and Practice, in Guide to industrial drying, Ed by Mujumdar, A.S., 2nd Edition (in press) Papers in referred Journals (1) Huang, L. X., Kumar, K. And Mujumdar, A.S. (2003a), Use of Computational Fluid Dynamics to Evaluate Alternative Spray Chamber Configurations, Drying Technology, 21(3), p385-412 (2) Huang, L. X., Kumar, K. and Mujumdar, A.S., (2003b), A Parametric Study of the Gas Flow Patterns and Drying Performance of Co-current Spray Dryer: Results of a Computational Fluid Dynamics Study, Drying Technology, 21(6), p957-978 (3) Huang, L. X. and Mujumdar, A.S., (2003c), Classification & selection of spray dryers, Chemical Industry Digest (India), 7-8, p75-84 (4) Huang, L. X. and Mujumdar, A.S., (2003d), Design of spray dryers, Chemical Industry Digest (India), 11-12, p95-102 (5) Huang, L. X., Kumar, K. and Mujumdar, A.S., (2004a), Simulation of Spray Evaporation using Pressure and Ultrasonic Atomizer – a Comparative Analysis, Russia TSTU Trans (English Version), 10 (1A), pp83-100 (6) Huang, L. X., Kumar, K and Mujumdar, A.S., (2004b), Spray evaporation of different liquids in a drying chamber- Effect on flow, heat and mass transfer performance, China Journal of Chemical Engineering (English Version), (in press) 237 (7) Huang, L. X., Kumar, K. and Mujumdar, A.S., (2004c), Simulation of a spray dryer fitted with a rotary disk atomizer using a three dimensional computational fluid dynamic model, Drying Technology, 22(6), pp 1489-1515 (8) Huang, L. X. and Mujumdar, A.S., (2005a) Development of a new innovative conceptual design for horizontal spray dryer via mathematical modeling, Drying Technology (Accepted) Peer-reviewed papers for conferences (1) Huang, L. X., Kumar, K. And Mujumdar, A.S. (2003e), Numerical Experiments with evaporation of water droplets in a Mixed Flow Spray chamber, 2nd Nordic Drying Conference, 25-27/Jun/2003 (2) Huang, L. X., Kumar, K and Mujumdar, A.S., (2003f), Effects of Air Infiltration and Heat Losses on Spray Evaporation in a Cylinder-on-cone Spray Dryer Chamber, 3rd Asia-Pacific Drying Conference, 1-3/Sept./2003, pp97-112 (3) Huang, L. X., Passos, M.L., Kumar, K. and Mujumdar, A.S., (2004d), A threedimensional simulation of a spray dryer with a rotary atomizer,14th International Drying Symposium, August, 2004, Brazil, Vol. A, pp319-325 (4) Huang, L. X., Kumar, K. and Mujumdar, A.S., (2004e), Computational fluid dynamic simulation of droplet drying in a spray dryer, 14th International Drying Symposium, August, 2004, Brazil, Vol. A, pp326-331 (5) Huang, L. X., Passos, M. and Mujumdar, A.S., (2004f), Comparison of CFD model with experimental results for a spray dryer fitted with a rotary disk atomizer, IWSID2004, Dec. 20-23, 2004, Mumbai, India (6) Huang, L. X., (2004g) CFD Simulation of a Co-current Spray Dryer fitted with an Ultrasonic Atomizer, IWSID2004, Dec. 20-23, 2004, Mumbai, India 238 Papers submitted to Journals (1) Huang, L. X., Kumar, K. and Mujumdar, A.S., (2005b) A Comparative Study of A Spray Dryer with Rotary Disc Atomizer and Pressure Nozzle Using Computational Fluid Dynamic Simulations, Chemical Engineering Process, (2) Huang, L. X. and Mujumdar, A.S., (2005c) Simulation of an Industrial Spray Dryer and Prediction of Off-design Performance, Industrial & Engineering Chemistry Research (3) Huang, L. X., Passos, M.L., Kumar, K. and Mujumdar, A.S., (2005d), A simulation of spray dryer fitted with a rotary disk atomizer, Drying technology Other papers (1) Chan S. R. and Huang, L. X., (2004g), A parametric study of a novel two-stage horizontal spray dryer, IWSID2004, Dec. 20-23, 2004, Mumbai, India (2) Huang W. D. and Huang, L. X., (2004h) Computational Fluid Dynamic Simulation of an industrial spray dryer for coffee, IWSID2004, Dec. 20-23, 2004, Mumbai, India (3) Wang B. H., Zhang W.B., Zheng W., Mujumdar, A.S. and Huang, L. X., (2004i) Progress in drying technology for nanomaterials, Drying Technology (be in press) (4) Zhang W.B., Wang B. H., Fan F.R., Mujumdar, A.S. and Huang, L. X., (2004j) Effect of different drying methods on the morphology and particle size of Magnesium Oxide nanoparticle, IWSID2004, India 239 [...]... droplets sprayed from an injection port into a hot drying medium was computed by Masters [1976] Janda [1973] developed a method to calculate the required diameter of a spray dryer with forced air circulation for drying particles of a given size The calculation of the diameter of the chamber is based on the required period of drying of a particle of given dimensions and of the radial course of its trajectory... morphology of each powder sample was examined using both optical and Scanning Electron 23 Microscopy Three distinct morphological types were identified, i.e., agglomerate, skin-forming and crystalline 2.5 Mathematical models of spray drying The objective of mathematical modeling of spray dryer is to predict the droplet/particle movement and the evaporation/drying of droplets in a spray dryer Two kinds of numerical... Two -fluid nozzle (Pneumatic nozzle) The mechanism of pneumatic nozzle atomization is one of high-velocity gas creating high frictional forces over liquid surfaces causing liquid disintegration into spray droplets [Masters, 2002] The schematic diagram of this type of nozzle is shown in Figure 2.3 The important design parameter for this nozzle type is the mass ratio of gas flow rate to the liquid spray. .. the amount of published data on sprayair contact is still limited and is mainly applicable to small-scale spray dryers Experimental measurements are difficult due to the complex and hostile environments in the drying chamber during the spray drying running 2.4 Drying of the droplets 2.4.1 Experiments and models for droplet drying Evaporation and drying of droplets occurs as soon as the spray emerging... investigated the drying curve for milk powder using a computational fluid dynamics model Adhikari et al [2001, 2003] and Tan [2004] carried out several experiments of single droplet drying in which he measured the droplet mass changes by suspending a droplet under a balance Different substances were tested 2.4.2 Morphology of spray dried products Most of the early important phenomenological studies... another method to calculate of the minimum required height of a drying tower using a pressure nozzle No comparison with experimental measurements was reported In order to calculate the drying time of the droplets, he assumed that drying of particles up to 300 microns in diameter occurred entirely within the constant drying rate period 25 Although many models for simulation of spray drying have been developed,... that numerical simulations using the k − ε turbulence model are useful for simulating the measured particle sizes and mean axial velocities in the industrial spray dryers Oakley and Bahu [1993] reported a three-dimensional simulation using the CFD code FLOW3D which is an implementation of the PSI-Cell model They proposed that additional research needs to be done to verify the performance of their model... model But in the open literature, most of the studies were carried out in small scale spray dryers For example, Oakley [1994] carried out an experiment in a 0.453m3 spray dryer and Langrish and Zbicinski [1994] in a 0.779m3 spray dryer Kieviet et al [1995, 1996 and 1997] carried out the measurement of air flow patterns and temperature profiles in a co-current pilot spray dryer (diameter 2.2m) A CFD package... CFD package (FLOW3D) was used to model such a spray dryer An industrial application of a CFD program to spray dryer design was reported by Masters [1994] Southwell and Langrish [2000], Harvie and Langrish et al [2001 and 2002] and Lebarbier et al [2001] also carried out the CFD simulation of typical spray dryers with co-current and counter-current flow using commercial code (CFX) Necessary comparison... atomizer gave a fountain spray shape Topp and Eisenklam [1972] listed the effects of different frequencies, but no information about the effects of liquid viscosity, density and flow rate was provided 18 Rajan and Pandit [2001] assessed the impact of various physico-chemical properties of liquid, its flow rate, the ampliture and frequency of ultrasonic and the area and geometry of the vibrating surface . performance of spray dryers. Therefore, Computational Fluid Dynamics (CFD) can be used as a design tool or as a design guide to compare the drying and hydrodynamic performance of chambers of different. two types of spray dryers are also being modeled using CFD for the first time, as well. Chapter 7 describes the development of a new spray dryer design using CFD, i.e., a horizontal spray dryer operation mode, handling of feedstock and product requirements are diverse, each stage must be carried out in all spray dryers. The formation of a spray and effective contact of the spray with air are