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• W2264768809 abstract "Spray drying is one of the most widely used drying techniques to convert liquid feed into a dry powder. The modeling of spray flows and spray drying has been studied for many years now, to determine the characteristics of the end products, e.g. particle size, shape, density or porosity. So far, the simulation of polymer or sugar solution spray drying has not been studied because drying behavior as well as properties are unknown. Previous studies concentrated on the systems of milk, salt solution, colloids or other materials for which the thermal and physical properties are well tabulated.The present study deals with the modeling and simulation of polyvinylpyrrolidone (PVP)/water and mannitol/water spray flows. PVP is a polymer, widely used as a pharmaceutical excipient, and mainly manufactured by BASF under several patented names, whereas mannitol is a sugar, which is used in dry powder inhalers and tablets. Experimental studies have shown that the powder properties of PVP and mannitol are significantly influenced by the drying conditions. The growing importance of PVP or mannitol powders and the inability of existing studies to predict the effect of drying conditions on the properties of the end product have prompted the development of a new reliable model and numerical techniques.Evaporating sprays have a continuous phase (gas) and a dispersed phase, which consists of droplets of various sizes that may evaporate, coalesce, or breakup, as wellas have their own inertia and size-conditioned dynamics. A modeling approach which is more commonly used is the Lagrangian description of the dispersed liquid phase.This approach gives detailed information on the micro-level, but inclusion of droplet coalescence and breakup increase computational complexity. Moreover, the Lagrangiandescription coupled with the Eulerian equations for the gas phase, assuming a point-source approximation of the spray, is computationally expensive. As an alternative to Lagrangian simulations, several Eulerian methods have been developed based on the Williams’ spray equation. The Euler – Euler methods are computationally efficient and independent of liquid mass loading in describing dense turbulent spray flows.The objective of this thesis is the modeling and simulation of spray flows and spray drying up to the onset of solid layer formation in an Euler – Euler framework. The behavior of droplet distribution under various drying conditions in bi-component evaporating spray flows is examined using, for the first time, direct quadrature method of moments (DQMOM) in two dimensions. In DQMOM, the droplet size and velocitydistribution of the spray is modeled by approximating the number density function in terms of joint radius and velocity. Transport equations of DQMOM account for dropletevaporation, heating, drag, and droplet–droplet interactions.At first, an evaporating water spray in nitrogen is modeled in one dimension (axial direction). Earlier studies in spray flows neglected evaporation or considered it through a simplified model, which is addressed by implementing an advanced droplet evaporation model of Abramzon and Sirignano, whereas droplet motion and droplet coalescence are estimated through appropriate sub-models. The assumption of evaporative flux to be zero or computing it with weight ratio constraints was found to be unphysical, which is improved by estimating it using the maximum entropy formulation. The gas phase is not yet fully coupled to the DQMOM but its inlet properties are taken to compute forces acting on droplets and evaporation. The simulation results are compared with quadrature method of moments (QMOM) and with experiment at various cross sections. DQMOM shows better results than QMOM, and remarkable agreement with experiment.Next, water spray in air in two-dimensional, axisymmetric configuration is modeled by extending the one-dimensional DQMOM. The DQMOM results are compared with those of the discrete droplet model (DDM), which is an Euler – Lagrangian approach. Droplet coalescence is considered in DQMOM but neglected in DDM. The simulation results are validated with new experimental data. Overall, DQMOM shows a much better performance with respect to computational effort, even with the inclusion of droplet coalescence.Before extending DQMOM to model PVP/water spray flows, a single droplet evaporation and drying model is developed, because most of the evaporation models available in the literature are valid for salts, colloids or milk powder. The negligence of solid layer formation effects on the droplet heating and evaporation is addressed, and treatmentof the liquid mixture as the ideal solution is improved by including the non-ideality effect. The PVP or mannitol in water droplet evaporation and solid layer formationare simulated, and the results are compared with new experimental data, which shows that the present model effectively captures the first three stages of evaporation and drying of a bi-component droplet.Finally, PVP/water spray flows in air are simulated using DQMOM including the developed bi-component evaporation model. Simulation results are compared with new experimental data at various cross sections and very good agreement is observed.In conclusion, water and PVP/water evaporating spray flows, and preliminary stages of PVP/water and mannitol/water spray drying, i.e., until solid layer formation, are successfully modeled and simulated, and show good agreement with experiment." @default.
• W2264768809 created "2016-06-24" @default.
• W2264768809 creator A5017007801 @default.
• W2264768809 date "2013-01-01" @default.
• W2264768809 modified "2023-09-28" @default.
• W2264768809 title "Numerical Simulation of Bi-component Droplet Evaporation and Dispersion in Spray and Spray Drying" @default.
• W2264768809 doi "https://doi.org/10.11588/heidok.00015937" @default.
• W2264768809 hasPublicationYear "2013" @default.
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