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Soil-borne diseases of crops are becoming more and more serious due to the direct return of crop straw and root stubble and the application of many pesticides. In this study, the field experiment was carried out using the self-developed controlled combustion thermal contact killing device. The harmless disposal of stubble/straw was realized for the effective prevention and control of soil-borne diseases. The temperature distribution of flue gas was obtained in the smoke channel and along the grate direction. The temperature increasing level of the preheated air was also determined after passing along the heat exchanger under four conditions. The killing rate of pathogenic fungi and bacteria in soil was evaluated after thermotactic killing. The incidence rate, disease grade and disease index of maize plants were counted to separate and purify the stem base and root of maize plants, and then the morphology was identified preliminarily. Furthermore, the composition and number of microbial communities were determined by molecular biological identification, in order to evaluate and monitor the incidence of soil-borne diseases. Laboratory test results showed that the thermal contact temperature (117-167 ℃) and the air supply temperature (62-172 ℃) were regulated effectively, when the feed speed was 360, 720, 1 080 and 1 800 kg/h. The temperature distribution of flue gas in the smoke channel increased first and then decreased, and the maximum temperature of the furnace reached 479 ℃ during stable combustion, which was beneficial to the combustion efficiency at a high level. The isolation of fungi and bacteria in the thermal contact showed that the bacteria were more resistant to temperature than fungi. The killing rates of bacteria and fungi at 117 ℃ were 53.33% and 33.33%, respectively. Both killing rates reached more than 86% at 132 ℃. There was the relatively consistence at 153 ℃ and 167 ℃, where the killing rate reached 100%, indicating the deep killing. According to the killing rate of colonies combined with the soil organic matter and equipment energy efficiency, 1 080 kg/h was selected as the optimal treatment for the soil-borne diseases of maize after field experiment. The field experiment showed that the corn stem base of the thermal contact treatment group was normal bluish yellow, the root was white, and the ear leaves grew upward, compared with the control group. While the corn stem base of the control group was dark brown, soft and hollow, the root was black brown rot, and the ear leaves withered and drooped. Furthermore, Fusarium spp., Magnaporthiopsis spp., Gaeumannomyces spp., Alternaria spp., Trichoderma spp., and Talaromyces spp. were isolated from the stem base and root of maize. Among them, 44 strains of fungi were isolated from the control group, where only 3 strains were isolated after thermal contact. The fungus strain and speecies of microbial communities (such as Fusarium spp) that caused soil-borne diseases were significantly reduced for the better crop growth. The thermal contact can effectively slow down the soil-borne diseases in the continuous cropping of crops. This finding is of great significance to realize the green prevention and control of soil-borne diseases in crop continuous cropping. [ABSTRACT FROM AUTHOR]

The interior of the molten pool is a complex high temperature environment, and the internal high temperature flue gas flow process has an important impact on the smelting effect Aiming at the flow process of high temperature flue gas in the molten pool, the growth of bubbles generated by high temperature flue gas injection, the change of velocity in the rising process and the change of temperature in the molten pool, as well as the gas liquid two phase mixing state in the molten pool during continuous injection at different speeds were analyzed by numerical simulation. The results show that the bubbles generated by high temperature flue gas injection grow larger at the nozzle of the spray gun, the initial shape is semi circular and gradually becomes elliptical. It rises close to both sides of the spray gun pipe wall. During the rising process, the lower boundary is concave inward and rises in an 11 umbrella cap shape11. The higher the rising height is, the deeper the inward depression is, and it breaks into multiple small bubbles when it rushes out of the liquid level. The velocity of high temperature flue gas with different injection speeds decreases rapidly in the process of generating bubbles at the nozzle of the spray gun. The velocity of the generated bubbles is basically stable at 0.25 m/s. When the bubbles move in the molten pool, their internal temperature drops rapidly to 300 K in a short time, and there is an obvious gradient change in the internal temperature field. Within 1 s, the higher the injection speed of high temperature flue gas, the better the gas liquid two phase mixing state in the molten pool. [ABSTRACT FROM AUTHOR]