4LZ-0.8型水稻联合收割机清选装置气固两相分离作业机理

为解决小型水稻联合收割机脱净率和损失率问题,提高脱粒清选质量,利用两相流动力学理论,分析了4LZ-0.8型水稻联合收割机脱粒清选分流筒中气流和杂物颗粒两相流动的规律。建立了杂物颗粒流的运动微分方程,导出了分离筒中杂物漂浮速度计算的一种方法,通过比较不同粒径、密度的物料的悬浮速度,得到了杂物颗粒最高速度与气流速度之比随气流速度变化的关系曲线,气流和杂物在分流筒及吸风管中运动时的压力损失随气流速度变化呈现先降后升的规律,压力损失中以加速损失和摩擦损失为主,各约占30%和26%。压力损失曲线存在最小值,此时的气流速度定义为经济气流速度。在喂入量为0.8 kg/s,谷草比为3:1脱粒条件下的经济的清选气流速度9.2 m/s,压力损失为630 Pa。该研究为4LZ-0.8型水稻联合收割机脱粒清选部件的参数优化设计及风机的选择提供了理论依据。

Gas-solid two-phase separation operation mechanism for 4LZ-0.8 rice combine harvester cleaning device

Abstract: Using the theory of two-phase flow dynamics, the law of two-phase flow formed by airflow and sundry grain in the threshing cleaning shunt tube of the 4LZ-0.8 type of rice combine harvester is studied in this paper. The movement differential equation of sundry grain flow is established and the sundry suspension speed is deduced. A method for calculating the suspension velocities of the particles with different sizes and densities is analyzed in the paper. The curve of the ratio of the highest sundry particle velocity to the air velocity varying with air velocity is obtained. The pressure loss in the air and debris flow in shunt tube is analyzed, and the most economical cleaning air velocity under a certain mass flow is calculated. All of these provide a theoretical basis for the parameter design of 4LZ-0.8 type of rice combine harvester's threshing cleaning parts. Material in the flow field is subjected to aerodynamic drag and the role of its own gravity which are related to the size of the pneumatic resistance, the velocity of airflow relative to sundry, the density of material, the shape and so on. When the airflow resistance equals to material gravity, the material in the air keeps in the stable state of suspension. The velocity of the material in a stable floating state is known as the floating velocity (or terminal velocity), and it is only related to the density and shape of the material itself. Taking advantage of the nature that the floating pneumatic resistance is equal to the gravity when material floating, the relationship of the Reynolds number and floating resistance coefficient would be reached. Taking logarithm of both sides of the relationship expression of debris floating and floating resistance coefficient, with logarithm of floating Reynolds number as the horizontal axis, and logarithm of floating resistance coefficient as the vertical axis, the curves for a given dynamic viscosity and density of air are drawn, and a set of straight lines with the same slope can be obtained for the particles with given sizes and densities. Draw the logarithm curve of resistance coefficient and Reynolds number in the same coordinate system, and by the intersections of the curve and each line, the particles with different sizes and densities can get suspended Reynolds number, and floating velocity is obtained after the corresponding computation. In addition, this paper has studied the pressure loss in the process of cleaning, and analyzed various influence factors of pressure loss and their effects on the quantitative relationship of pressure drop. In order to compare the various pressure drops, ascension pressure drop, acceleration pressure drop, suspension pressure drop, friction pressure drop and the total pressure drop curve were drawn in the same coordinates. The velocity corresponding to the lowest pressure in total pressure drop curve can be defined as economic speed, i.e. when cleaning with the speed, pressure loss in the flow separation barrel is minimal. The results can provide the reference for aspirated cleaning of other crops.