الفهرس 
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Abstract
Objectives: The main objectives of this research work are to design, construct, and operate two different solar active driers (Modified-Quonset and Lean-to structural forms). Methodology & Results: Thermal performance analysis of the two solar dryers, drying characteristics of thin layer of Stevia leaves, and comparing experimentally between the active (solar driers) and passive solar drying (natural-sun drying) modes were also tested, examined and evaluated. Moreover, the effect of drying process on the three different physical and chemical components (pigments, primary components, and anti-oxidant) had measured before and after the drying process for the three different modes of drying operation. Two different experiments of drying Stevia plants using completed plants and the leaves only were employed for the drying process using two different solar driers (Modified-Quonset and Lean-to and natural-sun drying as control unit) during the experimental work from 25th to 28th of September 2016. Whilst, the second drying experiment using the same solar driers conducted from 7th to 8th of October 2016. The obtained results revealed that, the completed Stevia plants dried from the initial moisture content of 73.56% wb to 7.55% wb within 36 hours with drying rate of 30.03 g/hr using the Modified-Quonset solar drier. While, the initial moisture content reduced from 73.56% wb into 5.35% wb within 12 hour which, achieved drying rate of 90.9 g/hr using the Lean-to solar drier. The moisture content of completed Stevia plants using natural-sun drying reduced from 73.56% wb into safety level of 5.01% wb through 77 hours with drying rate of 15.6 g/hr. For the duration of the experimental work, the hourly average thermal efficiencies for the Modified-Quonset and Lean-to solar driers, respectively, were 62.59% and 68.23%. The diurnal average solar drying efficiencies for the two solar driers during this research work were 26.19% and 29.71%, respectively. Therefore, the drying efficiency of the Lean-to solar drier was greater than that of the Modified-Quonset solar drier by 13.44%. The obtained results revealed that, the drying process using the two different solar driers improved, enhance, and protect the majority of Stevia quality after accomplished of drying process. The very important content in the Stevia plants as a glycoside species, is the total sugar, which on an average slightly reduced (26.40%) due to drying process using the two solar driers as compared with the natural-sun drying when the total sugar reduced by 45.18%. aled that, the drying process using the two different solar driers improved, enhance, and protect the majority of Stevia quality after accomplished of drying process. The very important content in the Stevia plants as a glycoside species, is the total sugar, which on an average slightly reduced (26.40%) due to drying process using two solar driers (Modified- Quonset and Lean-to structural forms) as compared with the natural sun drying when the total sugar reduced by 45.18% Furthermore, another important component in the Stevia plants is the anti-oxidant contents particularly when the dried product is used as natural drugs.