A mathematical model of ozone distribution over walnut layer in a vibrating dryer

Abstract

The most energy-intensive and time-consuming process in walnut processing technology is drying. As a rule, the moisture content is about 35-45 % during harvesting. Such conditions do not allow for storage and processing since high humidity creates favorable conditions to develop microbiological and enzymatic processes, which cause an intensive decrease in product quality. According to international standards, the moisture content should be decreased to 10 %. Including ozone in the composition of the drying agent allows for improving the energy performance of the drying process. One means for intensifying the drying process is the vibrational impact on the material layer. These two intensifying factors significantly improve the energy performance of the drying process. The article aims to increase the intensity and quality indicators of the drying process by developing a mathematical substantiation of the ozone distribution over the layer depth in a convective-vibration dryer using a comprehensive vibration-ozonating effect. The impact of the ozone-air mixture depends on distribution features and absorption by the entire layer in the drying chamber. The sorption and the ozone content in the coolant flow influence the ozone absorption parameters. A ratio characterizing the surface area blown with ozone can also be increased by transforming the walnut layer from stationary to quasi-boiling due to applying vibrational impact to the processed material. For the first time, the theoretical and experimental results made it possible to evaluate the performance of the ozone generator and the distribution law for ozone concentration depending on coolant velocity and vibration acceleration for the drying chamber. The obtained data showed that ozone concentration in the coolant at the inlet and outlet of the drying chamber is proportional to the vibration acceleration of the latter. The velocity of the drying agent of 8.5 m/s was achieved at the maximum magnitude of vibration acceleration for the concentration of 22.1–32.2 mg/m3 . It was found that the average discrepancy in the ozone concentration range in the ozone-air mixture is achieved when leaving the dryer at 8–10 %, confirming the reliability of the developed mathematical model. It was also found that the average discrepancy in the range of ozone concentration in the ozone-air mixture when leaving the dryer is 8-10%, which confirms the adequacy of the developed mathematical model and the expediency of its further use. The article is devoted to solving the urgent problem of intensifying the convective process of drying walnuts with a comprehensive vibration-ozonating effect and a mathematical description of the ongoing process.