## 3 Results and Discussion  
### Stage I  
Drying Air Consumption and Specific Energy Consumption  
Drying air consumption (s) was the highest for the variants at the lowest FR (0.16 mL/s) at 80 \({}^{\circ}\)C and 100 \({}^{\circ}\)C using the air of ambient humidity (9-10 g/m\({}^{3}\)) (Figure 1A). Irrespective of IAT and IAH, \(s\) decreased with increased FR. However, IAH was crucial to lower the \(s\), as more drying air was needed to evaporate water efficiently due to a lower drying rate at higher IAH. It can be noted that ambient air humidity increased \(s\) substantially in comparison to variants processed at lower IAH, underlining the importance of air dehumidification in evaporation efficiency during spray drying and, in consequence, in the optimization of the process. [PERSON] et al. (2003) concluded, based on their simulation, that the air consumption and evaporation efficiency depend on IAT; however, in this study, the effect of IAH and FR were more prominent [13]. As energy conservation is a crucial aspect of any process considerations in the industry, obtained results can be usefully employed in the modification of drying parameters in order to minimize the \(s\) or to indicate the importance of the heat recovery in order to reduce the operational cost and the impact on the environment.  
Figure 1: (**A**) Drying air consumption (\(s\)); (**B**) specific energy consumption (\(E_{s}\)) during spray drying/evaporation of distilled water at different inlet air temperature (80–120 \({}^{\circ}\)C), inlet air humidity (0.1–10 g/m\({}^{3}\)), and feed rate (0.16–0.83 mL/s) (Stage I); blue areas indicate the experiments where not-evaporated water was observed inside the drying chamber. The gradient of blue, orange and red color indicate the increasing inlet air temperature, while blue color demonstrates the lowest level, orange the middle level and red the highest level of inlet air humidity.  
The specific energy (\(E_{s}\)) consumption during spray drying is crucial to evaluate the economic aspects of the process. Optimization of the \(E_{s}\) can be consequently performed by increasing total solids content in the liquid feed, increasing IAT or by decreasing the outlet air temperature [14]. It can be observed that \(E_{s}\) was the most influenced by IAH and FR (Figure 1B). [PERSON] et al. (2018) noted as well that \(E_{s}\) was influenced by IAH while spray drying vitamin C and that lowering IAH enabled to lower \(E_{s}\)[15]. In this research the effect of the FR was the most significant at the lowest value (0.16 mL/s), but it should be noted that \(E_{s}\) increased substantially at these values with increasing IAH. The effect of increased \(E_{s}\) was less prominent at higher FR irrespective of IAT. This phenomenon occurred since the same energy input was required to evaporate the same amount of water, which points to the possible improvement of the drying process that can be introduced in order to optimize the process irrespective of drying temperature and drying air humidity. [PERSON] et al. (2019) and [PERSON] et al. (2020), who studied the spray drying with the application of dehumidified air of honey and apple juice concentrate, concluded that FR has to be relatively low to evaporate water efficiently at low IAT of 80 \({}^{\circ}\)C [8; 16]. However, the researchers spray dried materials of high solids content in comparison to distilled water, which require different approaches. [PERSON] et al. (2017), who optimized the spray drying conditions for the production of the powder consisting of gum Arabic and MD, noted that increasing FR enabled to increase the mass and heat transfer, thus at the end it improved the energy efficiency of the process, confirming the data obtained in this research [17]. The blue areas presented in Figure 1A,B indicates the experiments where droplets of water were observed inside of the drying chamber. This phenomenon demonstrates that at the highest FR independently of other variables, water was not evaporating, indicating not efficient heat transfer.