CFD-DEM Simulation of Paddy Drying in Lifting Screw Conveyor of Harvester

doi:10.13304/j.nykjdb.2021.0056

Abstract

Abstract:

In order to prevent the newly harvested paddy from mildewing due to the high moisture content， a method of direct drying paddy in lifting screw conveyor of combine harvester was proposed by combining far infrared and hot air. The internal heating scheme of installing the infrared heater in the center of the screw conveyor and the external heating scheme of setting the infrared heater on the outer of the screw conveyor were designed. The paddy movement， heat and mass transfer process and fluid flow in the screw conveyor were simulated by coupling method of discrete element methodologies （DEM） and computational fluid dynamics （CFD）. The simulation results were verified by the paddy drying experiment of external heating scheme. The results showed that： the variation trends of simulated and experimental values were consistent and the maximum relative error between the simulated and experimental value was 8.34%， which meaned that the simulation method was acceptable； under different conditions of screw conveyor rotate speed， hot air temperature， hot air speed and feed rate， the dehydration rate of the external heating scheme was at least 2.91% faster than those of the internal one， which showed that the drying effect of the external heating scheme was better than that of the internal one； the increasing temperature of the paddy decreased with the increase of the screw conveyor rotate speed， hot air speed and feeding amount， while increased with the increase of the hot air temperature； the paddy dehydration rate decreased with the increase of the screw conveyor rotate speed and feed rate， and increased with the increase of the hot air temperature and hot air speed. Above results provided theoretical basis for the design and optimization of drying paddy in lifting screw conveyor of combine harvester.

Key words: lifting screw conveyor, paddy drying, far infrared-hot air, CFD-DEM

摘要：

针对联合收割机刚收获的稻谷由于含水率较大而易霉变的问题，提出了利用远红外联合热风将稻谷在收割谷物提升搅龙中直接干燥的方法。设计了红外加热器安装在搅龙中心的内加热和安装在搅龙外筒上的外加热2种方案，采用CFD-DEM耦合方法对稻谷运动、传热传质过程以及搅龙内的流场进行了仿真分析，并采用外筒加热方案试验对仿真结果进行了验证。结果表明：模拟值和试验值变化趋势一致，最大相对误差仅为8.34%，试验和仿真结果基本吻合；在不同搅龙转速、热风温度、热风风速和喂入量条件下，外加热方案脱水速率比内加热方案至少快2.91%，说明外加热方案干燥效果优于内加热方案；谷粒的升温随着搅龙转速、热风速度和喂入量的增大而减小，随着热风温度的增大而增大；谷粒脱水速率随着搅龙转速和喂入量的增大而减小，随着热风温度和热风速度的增大而增大。上述研究结果为联合收割机谷物提升搅龙中集成干燥装置的设计及干燥过程的优化提供了理论依据。

关键词: 提升搅龙, 稻谷干燥, 远红外-热风, CFD-DEM

CLC Number:

S226.6

Pinglu CHEN, Shihua XIAO, Jing XU, Muhua LIU. CFD-DEM Simulation of Paddy Drying in Lifting Screw Conveyor of Harvester[J]. Journal of Agricultural Science and Technology, 2022, 24(5): 93-101.

陈平录, 肖石华, 许静, 刘木华. 收割机提升搅龙中干燥稻谷的CFD-DEM数值模拟[J]. 中国农业科技导报, 2022, 24(5): 93-101.

Figures/Tables 16

Fig.1 Structure of drying device in combine harvesterNote：1—Inlet （hot air inlet）； 2—Shaftless screw conveyor； 3—Infrared heating tube； 4—Shell； 5—Outlet （exhaust outlet）； 6—Screw conveyor.

Fig.2 Paddy particle simulation model

Table 1 Material parameters of particle model

材料 Material	密度Density/（kg·m^-3）	弹性模量Hear modulus/（N·m^-2）	泊松比 Poisson’s ratio
稻谷 Paddy	1 086	8.65×10⁷	0.25
钢 steel	7 850	7×10⁹	0.29

Table 2 Contact parameters of particle model

接触形式

Form of contact

恢复系数

Coefficient of restitution

静摩擦系数

Coefficient of static friction

动摩擦系数

Coefficient of rolling friction

Fig.3 Water distribution in in drying device at t=1.0 s

Fig.4 Temperature distribution in drying device at t=1.0 s

Fig.5 Movement and water content distribution of paddy particles at different time

Fig.6 Temperature and movement distribution of paddy particles at different time

Fig.7 Change of particles quantity in drying unit

Fig.8 Change of paddy particles moisture content

Fig.9 Temperature change of paddy particles

Fig.10 Change of dry-down rate with screw conveyor rotation speed

Fig.11 Change of dry-down rate with hot air temperature

Fig.12 Change of dry-down rate with hot air velocity

Fig.13 Change of dry-down rate with feed amount

Fig.14 Comparison between experimental and simulation results of the external heating scheme

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