Thermal Death Kinetics Of Storage Pests And Heating Uniformity Of Controlled Atmosphere/Heating Block Systems

Pest infestations in stored grains such as corn, wheat and rice make a huge damage and loss of the products. Among these pests, the rice weevil, Sitophilus oryzae(L.), is one of the most destructive and widespread pests and is urgently needed to get controlled. The conventional heat treatment and emerging dielectric heat treatment technologies such as RF and microwave could effectively control postharvest insect pests in agricultural products. Because the controlled efficiency of pests depends on treated temperature, holding time and heating rate, studying the thermal death kinetics of target pests as influenced by temperatures, heating times and heating rates could provide a theoretical guidance for developing effective postharvest heat treatment protocols.Heating block system could accurately control temperature, heating time and heating rate and simulate the heating processing environment of conventional heat treatment and emerging dielectric heat treatment, which was widely used to study the thermal death kinetics of treated pests. This paper mainly used the heating block system to study the thermal death kinetics of rice weevil under different temperatures, holding times and heating rates. Besides, a controlled atmosphere system was combined with the heating block system to increase the treatment efficiency and a finite element software COMSOL was used to simulate the temperature distribution of heating block treatment chamber in the treatment processing when added controlled atmosphere, so as to propose the best working condition for improving the heating uniformity and providing a technology guidance for the heat and controlled atmosphere combination treatment. The main research contents and conclusions are as follows:(1) Studied the thermal death kinetics of rice weevil. Rice weevils that are destructive and widespread pests in corn, wheat and rice products were chosen as target insects. Heating block system was used to study the effects of temperatures(44 °C, 46 °C, 48 °C and 50 °C), hold times(0-130 min) and heating rates(0.1 °C/min, 0.5 °C/min, 1 °C/min, 5 °C/min and 10 °C/min) on the mortalities of rice weevils. The experimental results showed that the relationships between rice weevil mortality and temperatures, holding times and heating rates were obtained, a thermal death kinetics model of rice weevil was developed, and the lethal time was predicted under diffrent temperature insect mortality levels(95%, 99% and 99.99%) using the kinetic model.(2) Controlled atmosphere/heating block system was built. The system combined heating with controlled atmosphere treatment to increase the treatment efficiency could accurately control gas flow, gas concentration, temperature, heating rate and holding time, but slight non- uniformity of temperature and heating rate was observed in the treatment chamber.(3) Improved the heating uniformity of heating block and controlled atmosphere system. Using the finite element software COMSOL, the heating uniformity of heating block treatment chamber was analyzed when adding controlled atmosphere at different heating rates, pest positions, air admission ways, air temperatures and air speeds to determine the best working condition. The simulation results showed that indirect air admission way, a lower pest position, a higher air temperature, a slower air speed and heating rate would largely improve the temperature uniformity in the heating block treatment chamber.