Development and performance evaluation of wind field automatic control system for raisin drying room

The existing traditional natural raisin drying room, although it has a high green grade rate for grape drying, the disadvantage is that long drying cycle and uneven product quality. Therefore, a wind field automatic control (WFAC) system was proposed to address the above problems. The WFAC system was built based on the traditional natural drying room by installing blowing fans and exhausting fans, the working principle of the system is to use HMI software to monitor and display the environmental information in the drying room and remotely control the operating parameters of different fans to adjust the wind field by the wireless network communication system, thus increasing the utilisation rate of natural wind in the grape drying. The CFD simulation experiments were conducted, and the simulation results showed that when the fan was combined with two blowing fans and one exhausting fan (TBI + OEO), the fan wind speed was 8 m s−1, and the fan vertical installation distance was 1206 mm, the corresponding wind field uniformity in the drying room was the best, which was 0.721. Based on the simulation optimisation results, the grape drying field experiment was conducted, and the results showed that the efficiency of grape drying in the TBI + OEO drying room was the highest and the drying cycle could be shortened by up to 7 days compared to the traditional drying room. Additionally, the green grade rate of raisin by hanging string in the TBI + OEO drying room was the highest, up to 78%, which was 4% higher than that in the traditional raisin drying room. Overall, the WFAC system designed and optimised in this study performed well in improving the efficiency and quality of grape drying. The results of this study can provide a theoretical basis for drying room structure improvement and industrial product condition control.