籽棉团悬浮速度的理论算法与试验验证

Theoretical algorithm and experimental verification of seed cotton ball suspension velocity

针对常规悬浮速度理论值与测试值偏差大的问题,该研究以常规悬浮速度理论为基础,通过量纲分析法和力平衡原理,建立籽棉团物理属性与阻力系数之间的关系,提出一种轻软可压缩颗粒悬浮速度理论模型。在棉田测试单颗棉桃完全开裂时所含籽棉团直径,确定气力输棉管道最小直径,并通过管流雷诺数和绕流雷诺数计算确定阻力系数。用体积法测试籽棉团密度,用等密变径法制备6种不同密度、18种不同直径的球形籽棉团试样并进行悬浮速度试验测试。结果表明,单颗棉桃全开裂时直径变化范围在38~54 mm之间,此范围内管流和绕流雷诺数都大于500,阻力系数为0.44;籽棉团松散密度范围为20~90 kg/m^(3),半压实密度范围为90~220 kg/m^(3);籽棉团悬浮速度测试值从直径比(籽棉团直径与管道直径之比)大于0.6开始与常规悬浮速度理论值偏离,直径比等于1时籽棉团悬浮速度测试值不等于0。采用该研究提出的理论算法时,得到的籽棉团悬浮速度分布特征和大小与测试结果基本吻合,平均相对误差为4.6%,并通过方差分析验证了该研究提出的理论算法的有效性。这为籽棉、羊毛和驼绒等轻软可压缩物料的气力输送系统和装置的改进设计提供理论算法。

In order to solve the problem of the deviation between the conventional theoretical results and the experimental results of the suspension velocity of LASC(Light And Soft Compressible)seed cotton ball,the relationship between the physical properties of LASC seed cotton ball and the resistance coefficient were established by using the dimensional analysis method and the force balance principle,then the theoretical algorithm of LASC seed cotton ball suspension velocity was proposed based on the conventional particle suspension velocity theory.Then,the diameter of LASC seed cotton ball containing a completely cracked single cotton peach were tested in the cotton field,and the minimum diameter of pneumatic cotton conveying pipeline was determined,and the drag coefficient was determined by calculating and analyzing the Reynolds number of pipe flow and around flow.Spherical LASC seed cotton ball with 6 types of densities and 18 types of diameters were prepared by using equal density variable diameter method and the suspension velocities were tested.When the LASC seed cotton balls were just in completely suspended and stabilized at the middle of the glass tube on the test platform,then the suspension speed of the LASC seed cotton balls were calculated according to the relationship between frequency recorded by the frequency modulator and inlet wind speed,and following results were obtained.When a single cotton ball was fully cracked,the value range of the diameter of the seed cotton balls were between 38-54 mm,then the average diameter of the seed cotton ball and the minimum diameter of the cotton conveying pipe were determined to be 50 mm,so the both Reynolds numbers meet the conditions of 500<Re,and the resistance coefficient C was determined to be 0.44;The loose density of LASC seed cotton ball were between 20-90 kg/m^(3),and the semi-compacted density of LASC seed cotton ball were between 90-220 kg/m^(3);The suspension velocity takes the maximum value,when the diameter ratio dc/D was close to 0.45.If the diameter ratio dc/D was less than 0.6,the test data was basically close to the theoretical suspension velocity value,and the average relative errors were nearly 5%.While the value of dc/D was greater than 0.6,the measured values of LASC seed cotton ball suspension velocities starts to deviate from the conventional particle suspension velocity theory,and the test value of the suspension velocities of the LASC seed cotton balls were not equal to zero when the diameter ratio dc/D=1.After using the theoretical algorithm proposed in this paper,the distribution characteristics and size of the suspension velocities of the LASC seed cotton ball were close to that of the experimental results,with an average relative error of 4.6%.The results of variance analysis also shown that there were highly significant differences between the measurement areas with different densities,this indicating that the density change occurs a large impact on the suspension velocity.While there were no significant difference in the measurement areas with the same density,and this indicating that the theoretical calculation value and the test value had small fluctuation and were basically close to each other.Which also verifies the effectiveness of the test approach and theoretical algorithm proposed in this paper.This provides a theoretical algorithm and experimental method for the further improvement of the pneumatic conveying system and device of LASC particles such as seed cotton,wool and cashmere.