Numerical modelling of solar dryers focusing on heat exchangers and solar collectors – comparing flat and rib designs with varying airflows

Abstract

Solar drying is an effective method for food preservation; however, conventional solar dryers often suffer from limited heat transfer and non-uniform airflow, which increases drying time and reduces product quality. These limitations are largely associated with the use of flat absorbers and heat exchangers that restrict turbulence development and weaken thermal performance. To address this issue, the present study optimizes a solar dryer by integrating ribbed surfaces in both the absorber and the heat exchanger to enhance the thermal performance of the dryer. A validated computational fluid dynamics (CFD) model was employed to investigate four dryer configurations under airflows ranging from 15 l/s to 45 l/s. The numerical analysis evaluated collector outlet temperature, absorber surface temperature, collector thermal efficiency, heat exchanger effectiveness, turbulent kinetic energy, and dissipation rate. Among the investigated designs, configuration S, defined as the optimized geometry incorporating ribs in both the collector absorber and heat exchanger, demonstrated the best overall performance. The maximum collector efficiency of 91.74 % was obtained at 35 l/s for configuration S, while the heat exchanger effectiveness reached 35 % at 20 l/s. Airflows below 15 l/s resulted in excessive temperature rise, whereas airflows above 35 l/s reduced the outlet temperature and negatively impacted drying performance. The optimal operating condition was identified at 25 l/s for configuration S, achieving a collector efficiency of 88.63 % and a heat exchanger effectiveness of 33.65 %. Overall, the results confirm that rib integration significantly improves dryers’ thermal performance, providing a promising design approach for developing efficient, practical, and sustainable solar drying systems.