莲子物料空气动力学特性与壳仁分离装置试验

为获得莲子物料的空气动力学特性,研究合适的莲子分选工艺参数,该文针对莲子剥壳后混合物料的风力分选技术进行研究。首先,对混合物料各组分的空气动力学特性进行理论分析与试验,得出莲仁、莲壳、碎仁的悬浮速度变化范围分别为11.230~14.680、2.511~4.891、6.505~7.865 m/s,合适的壳仁分离气流速度范围为7.865~11.230 m/s,修正了莲子物料的形状系数。然后,设计制造了莲子负压壳仁分离装置,通过试验确定了装置的优化分离工艺参数为:入料管倾斜角60°,分离通道倾斜角35°,分离通道气流速度7.881 m/s,入料管长度220 mm,进料量6颗/次,开展检测试验,结果表明清选率达98.283%。研究结果可为莲子壳仁分离设备研发提供理论依据。

Aerodynamic characteristics of lotus seed mixtures and test on pneumatic separating device for lotus seed kernel and contaminants

Abstract: Lotus seed hulling is the first process in rough processing, which is removing the tough shell that covers lotus seed kernel. Generally, it can utilize the mechanical processing method. After processing, the mixtures of lotus seed kernel, lotus seed shell, kernel debris and a small amount of imperfectly shelled lotus seed can be yielded. Because the lotus seed shell, kernel debris and other contaminants are easy to block the entrance of next working position (kernel coring process), a separating process for shell and kernel after the hulling process would be necessary and crucial. Pneumatic separating method is commonly used in separating equipment in agriculture products. However, there is limited academic research on pneumatic separating technology for lotus seed mixtures. In this paper, a negative pressure, pneumatic separating method was proposed to separate lotus seed kernel and shell. Firstly, the density parameter, the moisture content and the shape parameter of lotus seed mixture constituent were measured. The test results showed that the density parameters of lotus seed kernel, lotus seed, shell and kernel debris were 1 080, 1 042, 1 210 and 1 163 kg/m3 respectively, the moisture content of lotus seed kernel, unhulled lotus seed (with imperfectly shelled lotus seed), shell and kernel debris were 7.35%, 3.91%, 12.36% and 12.45% respectively. The shape of lotus seed kernel, lotus seed and the imperfectly shelled lotus seed could be abstracted as the spherical, and the grain diameter could be represented by maximum cross section. Secondly, the theoretical analysis and aerodynamics characteristics test of lotus seed mixtures were carried out. The results showed that the drag coefficient of lotus seed mixtures was within the Newton area, and the drag coefficient was 0.44. The ranges of theoretical suspension velocity of lotus seed kernel, lotus seed and imperfectly shelled lotus seed calculated were 14.134-16.115, 14.745-17.327 and 15.763-17.623 m/s respectively. The ranges of actual suspension velocity of lotus seed kernel, lotus seed shell, kernel debris, lotus seed and lotus seed which is shelled imperfectly were 11.230-14.680, 2.511-4.891, 6.505-7.865, 12.573-16.289 and 12.533-16.017 m/s respectively. The range of suitable air flow velocity for separation was confirmed as 7.865-11.23 m/s. There was no overlaps between the ranges of suspension velocity of lotus seed kernel and contaminants such as kernel debris and shell. Therefore, it's suitable to use pneumatic separating method to separate lotus seed kernel and contaminants. According to the comparison of test results and theoretical calculation results, the shape correction coefficient of products which was used in theoretical calculation was corrected. The ranges of shape correction coefficient of lotus seed kernel, lotus seed and lotus seed which was shelled imperfectly were 1.46-1.76, 1.29-1.66, 1.65-1.81 respectively. Thirdly, the negative pressure, pneumatic separating device for lotus seed kernel and shell, which matched the lotus seed huller with multiple working positions, had been designed and manufactured. This device consists of centrifugal fan, separation channel, cyclone separator, frame and inverter. Single factor test and orthogonal test were carried out. The effect law of factors on test indices was studied through the single factor test, and the influential factor and level were identified. The key parameters of separating processing of the device, which was identified and corrected by the orthogonal test, were as follows: inclination angel of inlet tube was 60°, inclination angle of separation channel was 35°, air flow velocity of separation channel was 7.881 m/s, length of inlet tube was 220 mm, and feed rate was 6 grains every time. Verification test on the optimum scheme was carried out and the result showed that the separating ratio could reach 98.283%. The result of this study in this paper can be taken as theoretical basis and reference for the research and development on separating equipment for lotus seed kernel and contaminants.