水稻负压混流干燥室结构优化设计与试验.

Rice is a major food crop grown widely in south and northeast China, particularly on a total annual production of nearly 210 million tonnes with a high level of consumption. The rice must be dried in time to minimize the loss as a result of sprouting, molding, and bursting waists after harvest. A positive-pressure high-temperature dryer is mostly adopted for hot-air drying in the actual production at present, but it was easy to cause uneven drying and low quality of rice. A negative-pressure dryer can be expected to improve the uniformity of rice drying and further reduce the saturation temperature of materials with a high drying speed in low-temperature drying, while shortening the drying time for energy saving. The mechanism and arrangement of angle tubes determine the airflow in the chamber for the rice drying. In this study, an analytical model was established for the negative-pressure drying of rice in a vertical chamber using irreversible thermodynamics, in order to gain even air distribution for better drying efficiency and quality of the dried product. Combined with the mixed flow drying, a perforated air duct with variable diameter was designed to improve the air distribution in the air duct of the vertical chamber. FLUENT software was used to conduct the numerical simulation and experimental verification for the flow field in the drying chamber under the conditions of no- and full-load. The research results showed that the perforated air duct with variable diameter well improved the wind speed and flow in the pipe of the vertical chamber for the uniform drying of rice. A self-developed 5HSN-1 dryer with a negative-pressure circulation system was used to optimize the drying parameters. In a quadratic orthogonal rotation test with four factors and five levels, the regression model was established with the temperature of hot air, the wind speed, the speed of discharging roller, and the initial moisture content as the experimental factors, while the drying rate, and increment rate of waist burst as the test indices. The optimal combination of working parameters was as follows: the wind speed of 0.75 m/s, the hot air temperature of 40 ℃, the rotation speed of discharging roller of 3.2 r/min, the initial moisture content of 16.9%, the drying rate of 1.407%/h, the increment rate of burst waist of 0.574%. The relative error between the experimental and optimized values was 6.2%-7.4%. The model with excellent fitting can offer practical application for better comprehensive quality of rice drying. [ABSTRACT FROM AUTHOR]