Corona discharge characteristics, ionic wind and ozone concentration in a multi-needle-to-mesh electrode system for seed drying

Ionic wind and ozone generated by corona discharge have demonstrated significant potential for applications in non-thermal processing, especially in the low-temperature drying and sterilization of agricultural products. In this study, a corona discharge plasma drying platform was established to evaluate the discharge characteristics of a multi-needle-to-mesh electrode system, as well as the ionic wind characteristics and ozone concentration during seed drying. The effects of applied voltage and electrode configuration - electrode gap (d), mesh aperture (D), and hole spacing (L) - on V-I characteristics, ionic wind velocity, and ozone concentration were systematically investigated. Based on the electrical characteristics, optimal parameters were selected to conduct drying experiments on Capsicum annuum L. seeds, with comparisons made against 50 ℃ hot air drying and natural air drying. The results indicate that positive corona discharge promoted streamer formation at an electrode gap of d = 25 mm. At 15 kV, the positive corona current, ionic wind velocity, and ozone concentration were significantly higher than those under negative polarity. A mesh electrode with an aperture of D = 3 mm and a hole spacing of L = 30 mm was more conducive to generating ionic wind and active species such as ozone. Drying experiments demonstrate that under optimal electrical parameters, the initial drying rate of Capsicum annuum L. seeds was 0.11 g/min, approximately 1.8 times that of hot air drying. This enhancement is primarily attributed to the disruption of the saturated vapor boundary layer on the material surface by the strong ionic wind. Additionally, over the same 2-hour drying period, the specific energy consumption (SEC) of plasma drying was 18.2 kJ/g, substantially lower compared to hot air drying (33.8 kJ/g). This study confirms the application potential of multi-needle-to-mesh corona discharge technology in the drying of heat-sensitive agricultural products and provides a theoretical basis for the parameter design of drying equipment.