The aim of this research work to analyse the performance of the proposed solar tunnel dryer and photovoltaic (PV) system to dry star fruit. Star fruit (Averrhoa carambola L.) is a native fruit in the north eastern states of India. Due to its rich nutritional composition and medicinal property, the demand for this fruit increased nationally. The proposed design consists of a tunnel type drying chamber and thermal storage unit. Paraffin wax (PCM) was used as a thermal storing material mounted in the tunnel dryer chamber to use the thermal energy at off sunshine hours. The thermal insulation coating on the outer surface of the solar drying chamber enhances the thermal performance of the tunnel dryer. The overall efficiency of this proposed design was analysed. The results indicated that drying of star fruit occurred in the falling rate period, where no constant rate period of drying rate was observed. The quality analyses data revealed that higher values of TPC (47.59 mg GAE/gram of sample) and DPPH (73.59 μ mol of TE/gram of sample) are obtained in the samples dried in solar dried as compared to open sun-dried samples. Sensory analysis (taste, aroma and flavour) carried out on slices of star fruit indicated that the solar-dried slices provided better scores compared to open sun-dried samples.

Solar is abundant, renewable and sustainable energy source that attracted many renowned researchers across the globe. Solar drying is a promising drying technology for fruits and vegetables in developing countries. In this study, a low-cost solar dryer was designed and developed with moisture monitoring and temperature controlling system. The experimental setup consists of modified thermal collector and plenum chamber. Black turmeric (Curcuma caesia) slices (2 mm) was carried out for thin layer drying kinetics and results were compared with open sun drying and tray drying. The drying kinetics of the slices was tested by five thin-layer drying models. Among the empirical models investigated, the modified page model satisfactorily described the drying behavior of black turmeric slices with higher R 2 (0.9988) and lower χ 2 (0.0032) values. In addition to that, experiments were also conducted to study the effect of drying conditions on Color, TPC, TFC and Antioxidant activities. The low-cost dryer could be useful in the food industry/ farmers/small scale industry as a means of saving time and minimizing product quality damage.

The development and performance of a modified force convection solar dryer (MFCSD) for drying elephant apple slices have been presented in this research. The MFCSD consists of two solar collectors and a drying chamber of 20 kg drying capacity. The secondary collector is integrated with thermal energy storage unit using a phase change material-paraffin wax. Performance analysis of the MFCSD was studied for drying elephant apple (Dillenia indica) slices. The proposed design enhanced the collector thermal efficiency by 12% as compared to a conventional glass collector. Drying of elephant apple slices in MFCSD will limit exergy losses and increase exergy efficiency. The estimated uncertainty of the collector chamber and the drying unit of the proposed MFCSD were obtained as ±3.3% and ±1.0%. Quality analysis (proximity analysis and textural properties) of the fresh as well as samples dried in open sun drying, tray drying, and MFCSD was carried out. The contents of carbohydrates (47.85 ± 2.66) and protein (21.24 ± 1.68) were high in samples dried in MFCSD when compared to samples dried in other two methods. The ash content of the sample dried in MFCSD was found to be 10.25 ± 0.15%, which was higher than samples dried in tray dryer. The payback period for drying elephant apple in MFCSD is 2.56 years, which is lower than the lifetime period (20 years) of the dryer. Practical ApplicationsA traditional method practiced by small farmers for drying high-value perishable fruits is conventional open sun drying (OSD). Owing to slow drying rate and excessive heating, products dried under the open sun lose their nutritious and medicinal qualities. The present work details the construction of a low-cost solar dryer for the drying of elephant apple. The aim of the drying kinetics to develop the architecture aspects of the solar dryer is to refine the drying systems. The results showed that the performance of modified force convection solar dryer (MFCSD) assisted with thermal storage could improve the quality of dried elephant apple slices and reduce drying time in comparison with an OSD method and a tray drying method. MFCSD would Abbreviations: A, area (m 2 ); Cv, air volume heat capacity (J/kg K); A % , ash percentage (%); Cp, dry air heat capacity (J/kg K); Exeff, exergy efficiency (kW); Ex in , input exergy (kW); Ex loss , exergy loss (kW); F, mass flow rate of dry air (kg/s); Fc, fiber content in the drying sample; F % , sample fat (%); H, humidity (%); hc, convective heat transfer coefficient (W/m 2 K); M i , initial moisture content; m i , sliced elephant apple initial mass (g); m oven , mass of sliced-dried sample using oven (g); m s , mass of sliced sample dried in MFCSD (g); M t , moisture content at time (t); T, temperature ( C); Vd, dry air volume in dryer (m 3 ); W, weight (g).