Thin-Layer Convective Solar Drying and Mathematical Modelling of the Drying Kinetics of Marrubium vulgare Leaves

Mohammed Benamara^1,2, Boumediene Touati³, Said Bennaceur⁴, Bendjillali Ridha Ilyas^5,*
1 Department of Electrical Engineering, Institute of Technology, University Center Nour Bachir, El Bayadh, 32000, Algeria
2 Laboratory of Energetics in Arid Zones (ENERGARID), Team of Solar Resources and Its Applications, Tahri Mohamed University, Béchar, 08000, Algeria
3 Department of Material Sciences, Faculty of Exact Sciences, Laboratory of Energetics in Arid Zones (ENERGARID), Team of Solar Resources and Its Applications, University of Tahri Mohammed, Béchar, 08000, Algeria
4 Department of Material Sciences, Faculty of Exact Sciences, Laboratory for the Development of Renewable Energies and Their Applications in Saharan Areas (LDREAS), Tahri Mohamed University, Béchar, 08000, Algeria
5 Laboratory of Electronic Systems, Telecommunications and Renewable Energies, Department of Electrical Engineering, University Center Nour Bachir, El Bayadh, 32000, Algeria
* Corresponding Author: Bendjillali Ridha Ilyas. Email: email
(This article belongs to the Special Issue: Recent Advance and Development in Solar Energy)

Energy Engineering https://doi.org/10.32604/ee.2025.072641

Received 31 August 2025; Accepted 11 November 2025; Published online 05 December 2025

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Abstract

This study explores the thin-layer convective solar drying of Marrubium vulgare L. leaves under conditions typical of sun-rich semi-arid climates. Drying experiments were conducted at three inlet-air temperatures (40°C, 50°C, 60°C) and two air velocities (1.5 and 2.5 m·s⁻¹) using an indirect solar dryer with auxiliary temperature control. Moisture-ratio data were fitted with eight widely used thin-layer models and evaluated using correlation coefficient (r), root-mean-square error (RMSE), and Akaike information criterion (AIC). A complementary heat-transfer analysis based on Reynolds and Prandtl numbers with appropriate Nusselt correlations was used to relate flow regime to drying performance, and an energy balance quantified the relative contributions of solar and auxiliary heat. The logarithmic model consistently achieved the lowest RMSE/AIC with r > 0.99 across all conditions. Higher temperature and air velocity significantly reduced drying time during the decreasing-rate period, with no constant-rate stage observed. On average, solar input supplied the large majority of the thermal demand, while the auxiliary heater compensated short irradiance drops to maintain setpoints. These findings provide a reproducible dataset and a modelling benchmark for M. vulgare leaves, and they support energy-aware design of hybrid solar dryers for medicinal plants in sun-rich regions.