In this paper, an intensified spray-drying process in a novel Radial Multizone Dryer (RMD) is analyzed by means of CFD. A three-dimensional Eulerian–Lagrangian multiphase model is applied to investigate the effect of solids outlet location, relative hot/cold airflow ratio, and droplet size on heat and mass transfer characteristics, G-acceleration, residence time, and separation efficiency of the product. The results indicate that the temperature pattern in the dryer is dependent on the solids outlet location. A stable, symmetric spray behavior with maximum evaporation in the hot zone is observed when the solids outlet is placed at the periphery of the vortex chamber. The maximum product separation efficiency (85 wt %) is obtained by applying high G-acceleration (at relative hot/cold ratio of 0.75) and narrow droplet size distribution (45–70 µm). The separation of different sized particles with distinct drying times is also observed. Smaller particles (<32 µm) leave the reactor via the gas outlet, while the majority of big particles leave it via the solids outlet, thus depicting in situ particle separation. The results revealed the feasibility and benefits of a multizone drying operation and that the RMD can be an attractive solution for spray drying technology.

In order to develop an alternative spray drying technology, a high drying rate in a smaller volume must be achieved. In this paper, results of CFD study are presented, carried out to investigate the possibility of spray drying in a novel design vortex chamber. The model is validated against experimental data, that makes a good agreement with an average error of 7% with only air and 24% with water spray. Results of temperature fields and droplet impact positions are discussed. The computations demonstrate that vortex chamber spray dryer can be an attractive solution for drying technology. Keywords: CFD; spray drying; vortex chamber; atomization;

This research presents 3D steady-state simulations of a skim milk spray drying process in a counter-current configuration dryer. A two-phase flow involving gas and discrete phase is modeled using the Eulerian–Lagrangian model with two-way coupling between phases. The drying kinetics of skim milk is incorporated using the Reaction Engineering Approach. The model predictions are found to be in accordance with the experimental temperature measurements with a maximum average error of 5%. The validated computational model is employed further to study the effects of nozzle position, initial spray Sauter Mean Diameter (SMD), air inlet temperature, and feed rate on the temperature and moisture profiles, particle impact positions, drying histories, and product recovery at the outlet. The location of the nozzle upwards (≈23 cm) resulted in maximum product recovery and increased the mean particle residence time at the outlet. A similar trend was observed for the highest feed rate of 26 kg/h owing to the increased spray penetration upstream in the chamber. The maximum evaporation zone was detected close to the atomizer (0–10 cm) when the spray SMD is 38 µm, whereas it shifts upstream (40–50 cm) of the dryer for an SMD of 58 µm. The high air inlet temperature resulted in enhanced evaporation rates only in the initial 10–20 cm distance from the atomizer. The results obtained in this study are beneficial for the development of the novel vortex chamber-based reactors with a counter flow mechanism.

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Conventional co-current spray dryers are widely used in the dairy industry to produce milk powder. These dryers are known for their high capital costs and low thermal efficiencies and are responsible for almost 27-55% of the total energy consumption of the dairy industries. In comparison to co-current dryers, countercurrent dryers have higher thermal efficiencies but they are not employed in the food industry due to the risks of product degradation.The conventional spray dryers used in the food industry suffer from multitude of disadvantages. They operate at relatively low air temperatures to avoid product degradation, which results in small drying rates [13]. Furthermore, the terminal velocities of the particles result in small gas-solid slip velocities, restricting the heat and mass transfer. The advent of multi-stage spray dryers (two or three stages) with integrated fluidized beds has improved the energy efficiency of the process by 13% [13][14][15][16][17]. Nevertheless, the drying systems are still far from beingThe evolution of a vortex chamber technology is a Radial Multizone Dryer (RMD) [44][45][46][47], shown in Figure 1.1-b. In this configuration, hot air enters axially into the central zone while the vortex is created via relatively cold airflow entering the RMD via the tangential channels; see Figure 1.1a. The process intensification is developed as an outcome of both: multizone drying operations with high and low temperature air feeding zones, and high-G acceleration. Consequently, the drying occurs in two steps: (i) the majority of drying takes Chapter 6 summarizes the conclusions drawn in the previous chapters and provides recommendations for future research.Experimental investigations of the atomization and counter-current spray drying process 9 Chapter 2 EXPERIMENTAL INVESTIGATIONS OF THE ATOMIZATION AND COUNTER-CURRENT SPRAY DRYING PROCESSThis chapter presents an experimental analysis of a counter flow spray drying process using water and skim milk as a feed. The study is performed by examining the droplet size distribution of sprays and the temperature profiles in the dryer. The influence of air inlet temperature, air mass flow rate, feed flow rate, and droplet size on air temperatures in the dryer is evaluated. The evaporation and deposition zones are found to be highly dependent on droplet sizes. The obtained results show that it is possible to achieve efficient contact between hot air and spray in a small volume using a counter-current mechanism.