Tarek J. Jamaleddine

Application of Computational Fluid Dynamics for Simulation of Drying Processes: A Review

In recent years, computational fluid dynamics (CFD) has been used increasingly to improve process design capabilities in many industrial applications, including industrial drying processes. Drying of food and beverage products, industrial and municipal wastewater sludge, and other manufacturing and environmental products is done regularly in order to enhance the quality and life span of these products and to facilitate their use, storage, and transportation. With recent advancements in mathematical techniques and computer hardware, CFD has been found to be successful in predicting the drying phenomenon in various types of industrial dryers, which utilize all forms of drying operations including spray, freeze, and thermal drying techniques. The CFD solutions are being used to optimize and develop equipment and processing strategies in the drying industry, replacing expensive and time-consuming experimentations. However, a comprehensive review on the application of CFD for the design, study, and evaluation of industrial dryers is not yet available. A comprehensive review of the current literature on the use of CFD models in both industrial and lab-scale drying applications is presented in this article. The use of Eulerian-Eulerian and Eulerian-Lagrangian models in the study of the drying kinetics for gas–solid multiphase flow systems is fully discussed. Merits and disadvantages of using various CFD models in the design of industrial dryers are illustrated and the scope of their applicability is also discussed.

Drying of Sludge in a Pneumatic Dryer Using Computational Fluid Dynamics

A control volume–based technique implemented in FLUENT computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for wet PVC and sludge material in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENT capability to account for mixture properties and to simulate the drying rate for surface moisture evaporation. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Initially, the model was validated against experimental data in the open literature for polyvinyl chloride (PVC) particles. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. In addition, mixture inlet conditions such as the particle moisture content and gas turbulent intensity were examined. The model showed high sensitivity to the turbulent conditions at the mixture inlet for the gas phase; high turbulent intensities were needed to disperse the particulate phase in the dryer reasonably well. The numerical model demonstrated the successful implementation of a commercial CFD code with user-defined heat and mass transfer models for complex multiphase flows.

The Drying of Sludge in a Cyclone Dryer Using Computational Fluid Dynamics

A control volume-based technique implemented in FLUENT (ANSYS Inc., Canonsburg, PA) computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for sludge material in a large-scale cyclone dryer. The drying characteristics of sludge at the dryer inlet were obtained from a previous study on the drying of sludge in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENTs capability to account for mixture properties and to simulate the constant and falling rate drying periods. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. Numerical predictions for the multiphase flow hydrodynamics showed a highly diluted region in the dryer core and a higher concentration of particles close to the wall region, an indication of nonuniform distribution of particles at a cross-sectional area. The numerical predictions for the hydrodynamic profiles qualitatively depicted the flow behavior natural to these designs. The work demonstrated the successful application of CFD in the design stage of a combined pneumatic-cyclone dryer model.

Numerical Simulation of Pneumatic and Cyclonic Dryers Using Computational Fluid Dynamics

Drying is inherently a cross and multidisciplinary area because it requires optimal fusion of transport phenomena and materials science and the objective of drying is not only to supply heat and remove moisture from the material but to produce a dehydrated product of specific quality (Mujumdar, 2004)[1]. There are two main modes of drying used in the heat drying or pelletization processes; namely, direct and indirect modes. Each mode of drying has its merits and disadvantages and the choice of dryer design and drying method varies according to the nature of the material to be handled, the final form of the product, and the operating and capital cost of the drying process. The drying of various materials at different conditions in a wide variety of industrial and technological applications is a necessary step either to obtain products that serve our daily needs or to facilitate and enhance some of the chemical reactions conducted in many engineering processes. Drying processes consume large amounts of energy; any improvement in existing dryer design and reduction in operating cost will be immensely beneficial for the industry. With the advance in technology and the high demands for large quantities of various industrial products, innovative drying technologies and sophisticated drying equipment are emerging and many of them remain to be in a developmental stage due to the ever increasing presence of new feedstock and wetted industrial products. During the past few decades, considerable efforts have been made to understand some of the chemical and physical changes that occur during the drying operation and to develop new methods for preventing undesirable quality losses. It is estimated that nearly 250 U.S. patents and 80 European patents related to drying are issued each year (Mujumdar, 2004)[1]. Currently, the method of drying does not end at the food processing industry but extends to a broad range of applications in the chemical, biochemical, pharmaceutical, and agricultural sectors. In a paper by Mujumdar and Wu (2008)[2], the authors emphasized on the need for cost effective solutions that can push innovation and creativity in designing drying equipment and showed that a CFD approach can be one of these solutions. The collective effort of their research work along with other researchers in the drying industry using mathematical