**4. Conclusions**

Our research has identified a mathematical model suitable to describe the behavior of sliced lemongrass subjected to convection drying. In addition, the moisture diffusion coefficient and the activation energy of the material were computed. The results show that higher drying temperature is associated with shorter drying time and faster moisture removal rate. During the drying process, only initial and falling-rate periods occurred, with the absence of a constant-rate period. The Weibull model was found to be the most suitable model describing thin-layer drying by hot air.

The effective moisture diffusivity of the dried material at different temperatures was calculated and the results ranged from 7.64089 × 10−<sup>11</sup> m2/s to 1.47784 × 10−<sup>10</sup> m2/s. The moisture diffusion capability of the lemongrass material peaked at 65 ◦C. The calculated activation energy of lemongrass was relatively high, at 38.34 kJ/mol, indicating that more energy is needed to separate moisture from the material by drying. This may be related to the structure of the lemongrass, which consists of many layers resulting in tight links among water molecules and in turn low evaporability. These results sugges<sup>t</sup> that moisture removal from the lemongrass should also take into account the remaining content of essential oils and aromatic compounds in the material.

**Author Contributions:** Investigation, T.V.L.N., D.M.N. and T.D.L.; supervision, L.G.B.; writing—original draft, T.V.L.N.; writing—review & editing, D.C.N.

**Funding:** This research is funded by Tien Giang Department of Science and Technology, Vietnam.

**Acknowledgments:** The authors would like to thank Nguyen Tat Thanh University for permission and providing facilities during the research period.

**Conflicts of Interest:** The authors declare no conflict of interest.
