Design and performance evaluation of an innovative medium-scale solar dryer with heat recovery based-latent heat storage: Experimental and mathematical analysis of tomato drying

The processing industry faces a significant challenge in reducing drying times for large quantities of food. To address this issue, a medium-scale direct solar dryer with a 50 kg capacity was designed and built, and its performance was meticulously assessed. The dryer was equipped with a heat recovery system (HRS) and a phase change material (PCM) that stored latent heat, specifically paraffin wax. Locally available materials were used to construct the prototypes, which underwent two sets of experiments under identical conditions. The experiments involved testing empty solar dryers and then drying tomatoes as the load. Results showed that the HRSPCM consistently maintained an average air temperature of 5 degrees C higher during the day and an extension of 1 to 8 degrees C higher for 5 h at night compared to the conventional dryer. Moreover, the HRSPCM demonstrated superior thermal efficiency over the non-improved dryer, averaging 21%. Drying tomatoes with the HRSPCM resulted in a 50% decrease in total dehydration time, reducing the moisture content from 93.5% to 13.5% in 20 h, while the non-improved dryer took 40 h for the same quantity. The study also modeled moisture transfer from tomato slices using Fick's second law and calculated the effective diffusivity. The 'Verma et al.' and 'Two-terms' models were found to be the most suitable for describing the air-drying of the product in HRSPCM and conventional prototypes, respectively. The study demonstrated the system's superior capacity for high-volume drying operations compared to existing methods described in the literature, providing strong evidence for its usefulness in large-scale processes.