Experiment on temperature field distribution characteristics of citrus huanglongbing hot air rapid treatment

Abstract: For the weak points of citrus huanglongbing (HLB) heat treatment by sunlight, such as long treatment period, low efficiency, serious dependence on natural condition, and large temperature difference in treatment enclosure, one citrus HLB hot air rapid treatment method was proposed. To solve the problem of large temperature difference in the heat treatment enclosure, an experimental platform was set up for analyzing the temperature field distribution characteristics of HLB hot air rapid treatment, which consisted of heat treatment enclosure, industrial hot air blower, paperless recorder and 12-channel temperature recorder. And the influence of air return duct existence or not, wind speed, hot air inlet position, outlet position, and inlet hot air temperature on the temperature field distribution of hot air treatment were investigated. The results showed that: (a) Return air duct had a significant impact on the cross section of middle and upper layer and the longitudinal section where the hot air inlet position existed in the enclosure, but had no significant effect on the cross section of lower layer and the longitudinal section where the hot air outlet position existed. When there was a air return duct, not only the uniformity was better in the enclosure, but also the energy consumption was lower than the condition without it. (b) Wind speed had a significant impact on each section in the heat treatment enclosure, and the average temperature of each section increased with the increase of wind speed. When the wind speed was 14.5 m/s, the uniformity of each section was better. (c) Hot air inlet position had a significant impact on each section in the heat treatment enclosure, and the uniformity of each section was better when the hot air inlet position was located at the lower layer of the enclosure. (d) Hot air outlet position had a significant impact on each section in the heat treatment enclosure, and the uniformity of each section was better when the hot air outlet position was located at the upper layer of the enclosure, which had a 90° angle with the inlet position. (e) Inlet hot air temperature had a significant impact on each section in the heat treatment enclosure, and the higher the inlet temperature, the faster the temperature rising in the heat treatment enclosure. When the uniformity and the rising speed of temperature in the enclosure were taken into consideration, 90 ℃ was the best temperature of inlet hot air. (f) The optimal parameters were that there was a return air duct, the wind speed was 14.5 m/s, the hot air inlet position was located at the lower layer of the enclosure, the hot air outlet position was located at the upper layer of the enclosure, which had a 90° angle with the inlet position, and the inlet hot air temperature was 90℃. Under the optimal parameters, the temperature in the treatment enclosure rising from 32 to 48 ℃ took about 9 min, and the temperature range of the whole enclosure was 3.9 ℃, which dropped by 14.1 ℃ compared to that under non-optimal parameters; and the temperature range of each section under the optimal parameters was also decreased. Under the optimal parameters, the effectiveness of rapid hot air treatment on the control of citrus HLB was proved, and the average reduction rate of bacteria concentration after treatment was 80.28%. The results provide a reference for the optimization design of large-scale HLB hot air treatment equipment.