Performance of a hybrid compound parabolic concentrator solar dryer for tomato slices drying

In this study, a hybrid drying system incorporating a compound parabolic concentrator (CPC) solar collector and an electric auxiliary heater was developed to make advances in sustainable tomato drying. The proposed dryer was designed to operate in a combined mode with solar energy as the prime source of energy, and the auxiliary unit was only used in the cases with the absence of solar radiation or limitation in generated solar power. Experimental tests were carried out to investigate the drying performance at different levels of sample thickness, airflow rate, and drying temperature. Using image processing and high-performance liquid chromatography (HPLC) techniques, the quality of the dried products was also evaluated in terms of the changes in color, shrinkage, and vitamin C content. Results indicated that the average drying time was about 231 min, while the shortest time was obtained as 83 min, suggesting an improved performance compared to similar works. It was found that drying temperature is the key factor influencing the rate of color changes, and shrinkage is only affected by the thickness of tomato slices. The experimental data further showed that the destruction of vitamin C was mostly influenced by the drying air temperature and sample thickness. The maximum energy and exergy efficiencies of the solar collector were determined as 25 and 6% at the maximum and minimum airflow rates, respectively