**1. Introduction**

Lemongrass (*Cymbopogon citratus*), also known as oil grass, silky heads, or citronella grass, is a popular annual crop for spices and medicinal herbs. The species is an herbaceous plant with long, thin leaves, and belongs to the Cymbopogon genus that is geographically distributed over various regions in India, America, Africa, Australia and Europe [1]. The use of lemongrass is diverse. At the family scale, lemongrass in both fresh and dried forms, is used as a spice in Vietnamese and Thai cooking, and for treatment of the common cold [2]. In Chinese and Indian medicine, the plant has been widely utilized as a tranquilizer and anti-inflammatory medicine. Tea made from lemongrass is also commonly consumed in Brazil, Cuba, and Argentina as a treatment for catarrh, rheumatism, and sore throat [3]. At larger scale, lemongrass is often cultivated and harvested to produce citronella oil and citronella-derived products such as mosquito repellant, soap, and perfume. The broad variety of uses of lemongrass is due to its valuable and numerous biological properties, which have been extensively studied and documented, including antifungal, antibacterial, antioxidant, anti-carcinogenic, and anti-rheumatic activities [3,4].

Lemongrass in general, and lemongrass oil in particular, is known for its abundant citral component, which is composed of geranial and neral. The content of citral in lemongrass essential oil varies from 40 to 82%, and is considered as an important quality indicator for utilization in medicine, food, herbicides, and cosmetics [5]. Lemongrass is also rich in aromatic compounds, which have been demonstrated to exhibit anticancer activity (myrcene and limonene) and pain-relieving properties (myrcene and limonene). Regarding antimicrobial properties, citral, mycrene, geranial, and gereniol—which are found in lemongrass in large proportions—have been shown to inhibit *Desulfovibrio alaskensis* (gram-negative bacteria), *Campylobacter jejuni* (enteritis-causing bacteria), *Escherichia coli* O157 (diarrhea-causing bacteria), and *Listeria monocytogenes* [6,7]. Other components with beneficial properties include limonene (antioxidant capacity), β-myrcene (gout prevention), citronellol (anti-fungal properties), and methyl heptentone (anti-diabetes, allergy, and anti-cancer) [6].

Similar to other aromatic plants, the nutritional quality of raw lemongrass cannot be maintained for an extended period of time, highlighting the need for the food industry to find a way to produce low-moisture lemongrass and select a suitable preservation method [8]. Drying, which involves the process of moving water inside the materials onto the surface and removing surface water by evaporation, is a common and efficient preservation technique [9]. Drying could prevent multiplication of spoilage-causing micro-organisms and minimize the occurrence of chemical reactions inside the material, in turn prolonging the shelf-life of the product and resulting in higher economic value than direct use of raw materials. Among many feasible methods of separating moisture from materials (such as convection drying, vacuum drying, freeze drying, and fluidized bed drying), thin layer hot air convection drying has proven to be a simple and cost-effective method [10]. However, to develop an efficient drying system for a particular product, the determination of suitable drying models for raw materials is required. Accurate modeling of material behavior during the drying process contributes to the development of dried products by predicting the drying process of materials based on the moisture balance of the material, from which improvements to existing drying system can be made [10].

Although lemongrass has been extensively studied with regards to its biological activities and chemical composition, literature concerning drying kinetics of lemongrass is still limited. To the best of our knowledge, two notable attempts have been made to model lemongrass behavior in drying processes [11,12]. The study of Coradi et al. (2014) suggested the appropriateness of the two-term model in describing the drying kinetics of lemongrass, demonstrated by a low value of the average estimated error (SE) and average relative error (P) [11]. However, only four typical models were taken into account in their study: modified Page, logarithmic, two-term and Midilli models. On the contrary, Simha (2016) fitted experimental data to an extensive pool of ten drying models, showing that the Midilli model is the most suitable drying kinetics model for both lemongrass and *Adathoda vasica* leaves [12]. However, the drying method of choice in this study was microwave drying, which lacks applicability and is energy-inefficient at larger scale.

Given the scarcity of studies on lemongrass drying kinetics and the significance of the thin layer convection-drying technique, this study aimed to determine the kinetic profile that characterizes convective drying of lemongrass material. In addition, the effective moisture diffusion coefficient, activation energy of the material, and other important parameters resulting from the present study can act as a precursor for further investigation regarding the mass transfer and moisture removal occurring during the drying process under various drying conditions.

#### **2. Materials and Methods**

#### *2.1. Materials and Methods*
