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Simulation of superhead steam spray drying using computational fluid dynamics

Authors
Publication Date
Keywords
  • Transfert De Chaleur
  • Transfert De Masse
  • Modele Numerique
  • Sechage
Disciplines
  • Computer Science
  • Design
  • Mathematics
  • Physics

Abstract

This paper presents a numerical simulation and experimental validation of a spray dryer using superhead steam instead of air, modeled with a computational fluid dynamics (CFD) code. The model describes momentum, heat and mass transfers between two phases (discrete phase of droplets and continuous gas phase) through a finite volume method. For the simulation, droplet size distribution is represented by 6 discrete diameters classes, fitting to an experimental distribution, injected at the initial velocity from the nozzle orifice. This model is able to predict the most important features of the dryer : fields of gas temperature and gas velocity inside the chamber, droplets trajectories and eventual deposits on the walls. The results are compared to a pilot scale dryer. Considering that there is no risk of powder ignition in steam, we operated at a rather high inlet temperature (973K). It appears that experimental and predicted values of temperature inside the chamber are in agreement. After experimental validation, the model can be used for chamber design, or scale up. Using superhead steam as drying medium instead of air shows a high volumic evaporation rate and can allow high energy recovery and better environment control. / Dans ce travail, un modèle bidimensionnel monophasique a été élaboré sous PHOENICS permettant d'évaluer les champs de température et de vitesse dans la chambre de séchage. Les transferts de chaleur et de matière entre les phases liquide et vapeur sont obtenus grâce à des termes sources imposés explicitement. Ces termes, qui traduisent les bilans macroscopiques des échanges entre les deux phases, sont estimés séparément par un programme écrit en PASCAL. Le recours à ce modèle simplifié permet de tester aisément de nouvelles configurations de séchoirs et de se prononcer rapidement sur l'efficacité du traitement thermique effectué.

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