Abstract

In this experimental study, the performance of an evacuated U-tube solar collector (ETSC) combined with an indirect solar dryer is investigated, and the obtained results are compared with conventional open sun drying (OSD) to determine the optimal method for drying neem leaves. The ETSC dryer reduces the initial moisture content from 68.1% (db) to 8.34% (db) in 7 h, whereas it takes 13 h in the OSD. The average efficiencies of the collector and dryer are 61.22% and 29%, respectively. Furthermore, eleven different mathematical models are compared with non-linear regression analysis for describing the drying behavior of neem leaves. Among all examined models, the one suggested byVerma et al., is found to be the most suitable fit for the drying kinetics of the neem leaves in an ETSC dryer with the coefficient of determination (R2) value of 0.9994, root mean square error (RMSE) of 0.01002, and chi-squared error (χ2) of 0.0001673; the Modified Henderson and Pabis model gives the best correlation in the OSD with the R2°value of 0.9984, RMSE value of 0.0153, and χ2of 0.000237. Further, quality analysis of the dried leaves is carried out; the highest value of color change in the dried samples is found in the OSD, and Total phenolic content (TPC) values are found to be more in the leaves dried by the ETSC. The images obtained from the scanning electron microscope (SEM) reveal that the OSD samples contain more pores in their microstructure comparedto ETSC-dried samples. The X-Ray diffraction (XRD)analysis indicates that ETSC-dried neem leaves have a longer shelf life. The Fourier-transform infrared spectroscopy (FTIR)analysis shows thepresence of amino acids and phenolic content in the driedneem samples, making its suitability for use inthe production of drugs by pharmaceutical industries.

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