Influence of pore structure on steam disinfection heat and mass transfer in Yunnan red loam

Abstract

The obstacles to the continuous cropping of Chinese herbs in Yunnan have become increasingly prominent. Many soil-borne diseases can infect the roots of crops, affect the growth of crops, and eventually lead to quality and yield reduction. Soil steam disinfection can still be used as one of the first methods to solve the problem of continuous cropping obstacles of Chinese herbs such as Panax notoginseng. However, the steam will condense into a large amount of liquid water when it is cold, which will cause soil pore blockage and seriously affect the steam diffusion efficiency. Therefore, it is necessary to study the influence mechanism of the pore structure of Yunnan red loam on heat and mass transfer of steam disinfection. The experimental research was conducted on steam disinfection's heat and mass transfer patterns under different soil pore structure conditions. Image processing technology was used to collect accurate soil profiles and to establish real soil pore structure analysis. Then, fluid simulation technology was used to simulate the heat and mass transfer process and trend of steam distribution within the soil profile under different soil pore structures. The results showed that the steam heat flow of <2 mm, 2–4 mm and 4–6 mm treatments were uniformly diffused in the form of matrix flow in a 1/4 ellipse, and the effective disinfection range was 18 cm horizontal distance and 20 cm vertical distance, in which the highest temperature could reach more than 90 °C. The steam heat flow of the 6–8 mm and >8 mm treatment groups diffused irregularly in large pore steam flow. Therefore, some devices for breaking soil and rotary tillage need to finely rotate the soil in the future. The end effector's disinfection pipe spacing can refer to the effective disinfection range.