## 4 Conclusions  
**Stage I:** IAH had a significant impact on both s and \(E_{s}\) of spray drying/evaporation of model solution of distilled water. The ambient IAH increased the s significantly compared to experiments conducted at lower values. \(E_{s}\) was also influenced by the FR but the effect  
Figure 14: SEM images of model MD powders in Stage III of the research. L, M, H signifies the low, medium or high level of drying air humidity; 80, 100, 120 signifies the drying air temperature; 10, 20, 30 signifies the feed solution concentration. was the most visible at the lowest value (0.16 mL/s). At higher FR, irrespective of the inlet air temperature, the effect was less significant as the same energy input was needed to evaporate the same amount of water. Obtained results highlight potential improvements in the drying process while modifying FR regardless of the drying temperature or air humidity. The approach presented in this stage has the potential to reduce energy consumption in order to lower operational costs. **Stage II:** The evidence from this stage of the research suggests that the decreased IAH to the medium (1.1-1.3 g/m\({}^{3}\)) or low (0.1-0.3 g/m\({}^{3}\)) levels of the medium level led to the production of model maltodextrin powders of the most satisfying \(R_{p}\), MC and \(a_{w}\). In order to enhance the mass and heat transfer, especially when spray drying at ambient IAH, and in consequence improve powders' properties, it was important to increase the IAT. **Stage III:** Presented results proved that it was possible to optimize maltodextrin solutions spray drying due to the application of the dehumidified air. The findings imply that lowered IAH in combination with increased IAT supported more efficient mass and heat transfer, leading to production of powders with more satisfactory \(R_{p}\), lower MC and \(a_{w}\). It was also concluded that increasing FC was favorable in order to lower MC and \(a_{w}\), as there was less total moisture to evaporate. When taking into consideration the highest \(R_{p}\), the lowest MC, and \(a_{w}\), the conditions that were the most optimal for spray drying of maltodextrin solutions were inlet air temperature of 120 \({}^{\circ}\)C, inlet air humidity of 0.1 g/m\({}^{3}\) and feed solution concentration of 29.571%. This three-stage research adds substantially to fundamental knowledge on the impact of drying air humidity in spray drying based on the use of model materials. These findings have important implications for optimizing process parameters in order to enhance powder properties and at the same time lower operational costs. However, as this study has only investigated the distilled water evaporation and maltodextrin solutions spray drying, further experimental investigation should be taken into consideration to validate results with real food matrices. Conceptualization, A.B.-D. and K.S. ; methodology, A.B.-D. and K.S. ; formal analysis, A.B.-D., A.J. and K.S. ; investigation, A.B.-D. and K.S. ; data curation, A.B.-D.; writing--original draft preparation, A.B.-D. and A.J. ; writing--review and editing, A.B.-D. and K.S. ; visualization, A.B.-D.; supervision, K.S. ; project administration, A.B.-D.; funding acquisition, A.B.-D. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Science Center, Poland (in Polish: NCN--Narodowe Centrum Nauki), program: PRELUDIUM-20, grant number 2021/41/N/ST8/01742 (\"Investigation on the role of drying air humidity in shaping the conditions of spray drying\", in Polish: \"Badanie roli wilgotnosci powietrza suszacego w ksztaltowaniu warunkow suszenia rozpylowego\"). Not applicable. The original contributions presented in this study are included in the article. Further inquiries can be directed at the corresponding author.