INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...

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2 1. Introduction Fig. 1.1: A schematic diagram of the spray drying process [3]. Spray drying is a complex process and it is very difficult to predict the quality, properties and characteristics of the product such as particle size, density, porosity, flowability, shape, compressibility, etc. for the given drying conditions. The industrial practice to design is always based on the field experience and know-how followed by experimentation in pilot plant trials, which can be very expensive in case of rare materials [1, 4]. Problems associated with scale-up and hydrodynamics of the driers have resulted in limited success. The progress in computational techniques and computing prowess has given the advantage to develop a robust model of heat and mass transfer based on the equations of fluid flow within the spray chamber, which can predict the whole spray drying process i.e., from the liquid feed stock entering into the dryer to the end product, thereby resulting in cost effective and economic spray drier designs [1, 5]. The modeling of spray flows and the spray drying has been studied for many years now, which is done to predict the characteristics of the spray drying end products, e.g. particle size, shape, density or porosity. The previous studies mainly concern the systems of whole milk, salt solution, colloids or other materials for which the physical and thermal properties are well tabulated. The simulation of polymer or sugar solution spray drying is not studied so far because of unknown drying behavior of these materials and unavailability of properties. The present study deals with the modeling and simulation of polyvinylpyrrolidone (PVP)/water and mannitol/water spray flows, with an aim to predict the effect of drying conditions on the evolution of droplet properties. The synthesis, applications of PVP and mannitol, and the motivation to choose these systems are elaborated in the following paragraphs. PVP is a water-soluble polymer made from the monomer N-vinylpyrrolidone [6, 7].
3 Fig. 1.2: Chemical structure of polyvinylpyrrolidone (C 6 H 9 NO) n [8]. It is a unique polymer providing a remarkable combination of properties that no other molecule is yet able to match. PVP offers a variety of properties, such as good initial tack, transparency, chemical and biological inertness, very low toxicity as well as high media compatibility and cross linkable flexibility. PVP was first synthesized by Prof. Walter Reppe and a patent was filed in 1939 for one of the most interesting derivatives of acetylene chemistry. Soluble PVP is obtained by free-radical polymerization of vinylpyrrolidone in water or 2-propanol, yielding the chain structure as shown in Fig. 1.2. There exists several grades of PVP, which are classified based on molecular weight, and spray drying technology is used in production of all types of PVPs [8]. PVP was initially used as a blood plasma substitute and later in a wide variety of applications in medicine, pharmacy, cosmetics and industrial production [9]. It is used as a binder in many pharmaceutical tablets; it simply passes through the body when taken orally. PVP binds to polar molecules exceptionally well, owing to its polarity. This has led to its application in coatings for photo-quality ink-jet papers and transparencies, as well as in inks for ink jet printers. PVP is also used in personal care products, such as shampoos and toothpastes, in paints, and adhesives that must be moistened, e.g. old-style postage stamps and envelopes [10]. It has also been used in contact lens solutions and in steel-quenching solutions. PVP is the basis of the early formulas for hair sprays and hair gels, and still continues to be a component of some [10]. As a food additive, PVP is a stabilizer and has E number E1201 [9]. In year 2006, the total world wide production of PVP was 31,000 tonnes, out of which 47% was used in cosmetics and 27% in pharmaceuticals [9]. Figure 1.3 [11] shows the scanning electron microscope (SEM) images of PVP powder produced via spray drying. In the evaporation and drying of PVP dissolved in water droplet, the molecular entanglement prior to solid layer formation is observed, which is different from the colloids, silica or salt in water droplet where crust formation is found. It is observed that the spray drying yields hollow or solid particles with spherical or non-spherical shape but the initial droplet size, gas temperature and velocity and other drying conditions show enormous effect on the final powder characteristics such as flowability, particle density,
Page 1: INAUGURAL-DISSERTATION zur Erlangun
Page 5: Dreams can never become a reality w
Page 8 and 9: II ial direction). Earlier studies
Page 10 and 11: IV DQMOM wird die Tropfengrößen-
Page 13 and 14: Contents Abstract . . . . . . . . .
Page 15 and 16: List of Tables 4.1 Initial weights
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Page 19 and 20: List of Figures XIII 4.27 Effect of
Page 21: 1. Introduction Drying has found ap
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Page 31 and 32: 2. Mathematical Modeling Spray cons
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Page 37 and 38: 2.2. Euler - Lagrangian Approach 17
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Page 41 and 42: 2.3. Euler - Euler Approach 21 quan
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Page 45 and 46: 2.3. Euler - Euler Approach 25 of t
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Page 49 and 50: 2.4. Single Droplet Modeling 29 col
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3.3. Numerical Performance 53 where
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4. Results and Discussion Results p
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4.1. One-dimensional Evaporating Wa
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4.2. Two-dimensional Evaporating Wa
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4.3. Single Bi-component Droplet Ev
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4.4. Two-dimensional Evaporating PV
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5. Conclusions and Future Work The
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101 proved UNIFAC-vdW-FV method for
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Appendix
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106 A. Nomenclature Symbol Unit Des
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108 A. Nomenclature S n S g S l Vec
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110 A. Nomenclature List of Abbrevi
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Bibliography [1] K. Masters: Spray
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BIBLIOGRAPHY iii [24] K. D. Squires
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BIBLIOGRAPHY v [49] D. L. Marchisio
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BIBLIOGRAPHY vii [72] G. M. Faeth:
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BIBLIOGRAPHY ix [95] C. Cercignani,
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BIBLIOGRAPHY xi [119] R. O. Fox: Hi
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BIBLIOGRAPHY xiii [142] R. Clift, J
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BIBLIOGRAPHY xv [170] G. Brenn, L.
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BIBLIOGRAPHY xvii [197] M. Stieß:
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BIBLIOGRAPHY xix [222] I. S. Grigor
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