## 6 CFD Analysis of Drying as a Mechanically Aided Process
### Optimization of Drying Chamber Geometry and Air Flow  
The geometric configuration of a drying chamber and the internal airflow patterns play a critical role in determining the efficiency, uniformity, and quality of food drying processes such as spray drying, fluidized bed drying, and spouted bed drying. Poor design may result in flow recirculation, wall deposition, non-uniform temperature distribution, particle agglomeration, and thermal degradation of the product. CFD has become an essential tool for analyzing and optimizing these systems, allowing detailed visualization of airflow, temperature, moisture gradients, and particle trajectories [123]. Figure 3 illustrates transient airflow behavior and mesh deformation in a spray drying chamber at different time steps, providing insight into the dynamic fluid-structure interaction and the importance of mesh resolution in unsteady CFD simulations.  
Role of Geometry in Drying Performance  
Drying chamber geometry directly influences RTD, contact efficiency between drying air and product, and powder recovery. Key design goals include minimizing dead zones and flow separation, promoting uniform residence times, and preventing product fouling or wall deposition. Geometric parameters such as chamber height-to-diameter ratio, air inlet positioning, plenum and distributor plate design, cone angle, and exhaust duct orientation all contribute to drying performance. Even small geometric modifications can significantly alter airflow behavior and, consequently, product quality and energy consumption [124].  
CFD-Based Analysis of Airflow Dynamics  
CFD simulations solve the Navier-Stokes equations coupled with turbulence models (e.g., \(\mathrm{k}\)-\(\epsilon\), RANS, or LES) to provide a high-resolution picture of airflow dynamics within the chamber. These simulations offer insights into velocity fields, streamlines, TKE, and the formation of vortices or stagnation zones. In spray dryers, for instance, airflow may be axial, tangential (swirling), or radial; CFD helps determine the configuration that ensures optimal droplet dispersion, evaporation kinetics, and powder collection [123].  
In fluidized bed systems, CFD is used to evaluate the uniformity of airflow through perforated distributor plates. Simulations help ensure balanced pressure drop, prevent  
Figure 3: Unsteady CFD simulation of airflow and dynamic mesh adaptation in a spray drying chamber at various time steps. Top: Velocity contours; Bottom: Adaptive mesh behavior. Source: [PERSON] et al. (2025) [123]. [Reproduced under CC BY 4.0 license from _ChemEngineering_, MDPI].  
channeling or slugging, and promote homogeneous suspension and mixing of particles. The analysis may also consider the effects of plenum shape and inlet geometry on air distribution and energy efficiency [125].  
Optimization Strategies Using CFD  
Geometry optimization through CFD involves refining chamber contours, adjusting inlet nozzle orientation, and tuning plenum and exhaust designs to achieve desirable flow patterns. Specific strategies include:  
* Reducing recirculation and energy losses through smoother transitions and optimized chamber tapers,
* Improving dispersion by selecting appropriate inlet angles and nozzle sizes,
* Enhancing drying uniformity with balanced airflow from distributor plates,
* Minimizing powder loss or fouling through optimized exhaust duct design.  
Multi-objective optimization frameworks are often employed to balance competing goals, such as reducing energy consumption, minimizing residence time variance, and maximizing product quality. CFD results are frequently combined with DoE and response surface methodology to explore the design space efficiently and determine optimal process windows [73,83].