Experimental investigation of drying neem (Azadirachta indica) in an evacuated tube solar dryer: Performance, drying kinetics and characterization

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 by Verma 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 (chi 2) of 0.0001673; the Modified Henderson and Pabis model gives the best correlation in the OSD with the R2 degrees value of 0.9984, RMSE value of 0.0153, and chi 2 of 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 compared to ETSC-dried samples. The X-Ray diffraction (XRD) analysis in-dicates that ETSC-dried neem leaves have a longer shelf life. The Fourier-transform infrared spectroscopy (FTIR) analysis shows the presence of amino acids and phenolic content in the dried neem samples, making its suit-ability for use in the production of drugs by pharmaceutical industries.

Automated summary

This experimental study investigates the performance of an evacuated U-tube solar collector (ETSC) combined with an indirect solar dryer for drying neem leaves. It compares the results with conventional open sun drying (OSD) and finds that the ETSC dryer reduces moisture content more efficiently in 7 hours compared to the OSD in 13 hours. Various mathematical models are used to describe the drying behavior of neem leaves, and the most suitable fit is determined. Quality analysis shows that the leaves dried by the ETSC have higher total phenolic content and fewer pores in their microstructure compared to OSD-dried leaves. XRD analysis indicates that ETSC-dried neem leaves have a longer shelf life, and FTIR analysis suggests their suitability for drug production in the pharmaceutical industry.