CHU Jiawei, HU Liqun, HAN Zhenqiang, SHAO Wei
(School of Highway, Key Laboratory for Special Area Highway Engineering of Ministry of Education,Chang’an University, Xi’an 710064, China)

Abstract

Objective In order to improve the characteristics of graded gravel materials, the study explores the influence of the material bin discharge phase on the uniformity of granular materials in the plant mixing construction process. The findings offer valuable insights for optimizing the discharge process and achieving superior material mixing.

Methods In this paper, the vertical segregation index S_v, center percentage difference P_c, and grid uniformity index σ_g metrics were developed to evaluate vertical, horizontal, and grid-generated particle uniformity. The grid uniformity index was defined as quantifying the uniformity of granular material distribution within a defined grid. By calculating the standard deviation of particle counts in each grid, a measure of how evenly granular materials are distributed was obtained. The vertical segregation index measures the extent of vertical segregation within the material, which calculates the difference between the mean Z-coordinate of particles within a single layer. When S_v was equal to 0, vertical uniformity was considered good. When S_v is less than 0, it indicates that particles in this grade tend to be in the lower part of the material. Conversely, when S_v is greater than 0, it suggests that particles in this grade tend to be in the upper part of the material. Center percentage difference assesses the distribution of granular material in the center region of the container versus the peripheral region. It calculates the difference in the central percentage of two types of particles. A P_c value of 0 indicates perfect material uniformity. A P_c value greater than 0 indicates that the particles involved in the calculation are more concentrated in the core region of the material, and A Pcvalue less than 0 suggests that the particles involved in the calculation are distributed around the periphery of the material. Secondly, the discrete element method (DEM) and a multi-factor Box-Behnken response surface model, containingthree continuous factors, were employed to examine the uniformity of granular materials during the discharge process. Thirdly, using particles with radii of 6mm and 10 mm, an initial uniform material distribution was established. By varying the funnel’s inclination angle (α), funnel outlet size ( L), and inter-particle rolling friction coefficient (μ), simulations were conducted to explore different segregation scenarios and identify the most uniform particles. Furthermore, the reliability of the fitted equations obtained from the response surface experiments was conducted through an additional 17 sets of simulation experiments. Finally, according to the results of numerical simulation, the parameters of silo were optimized and conducted via the fitting results.

Results and Discussion Based on the simulations conducted above, an analysis was performed to determine the correlation between the indicator values and the corresponding factors. Regression analysis was then performed using the response surface method, equations were fitted using quadratic functions. Non-significant factors were eliminated to establish a suitable regression equation. For the three indicators corresponding to S_v , P_c, and σ_G , the R-squared values of the respective equations were 95. 1%, 99. 16%, and 98. 46%, respectively. Fixing two parameters among them allowed the generation of curves that illustrated the relationships between the parameters and the indicators. Additionally, a 95% confidence interval for regression analysis errors was provided. Within the results of the regression equation, the variables S_v and μ exhibited a close correlation, while the varia ble Pc and σ_G were more sensitive to L. By computing the indicators from 17 sets of validation experiments and applying them to the error analysis of the regression equation mentioned above, it was evident that all indicator values were obtained from the validation experiments fall within the predicted range. The regression equation accurately predicted the results of discrete element simulation. In conclusion, the relationships between various judgment indicators and influencing factors, with a reliability of 95%, have been obtained. The following results showed that the horizontal homogeneity did not change with the increase of funnel inclination, and the grid partition homogeneity increased and the vertical homogeneity decreased with the funnel outlet size and inter-particle rolling friction coefficient fixed. Upon fixing the funnel inclination angle and inter-particle rolling friction coefficient increasing the funnel outlet size enhanced horizontal and grid partition uniformity, with a temporary decrease and subsequent improvement in vertical uniformity. In addition, upon fixing the funnel outlet size and inclination angle, an increase in inter-particle rolling friction coefficient led to decreased grid partition and vertical uniformity, while improving horizontal uniformity. To optimize discharge parameters for achieving a uniform mixture, the regression equations underwent multifactor response prediction, and recommended values for reliability analysis parameters were provided based on a 95% confidence level.

Conclusion In this paper, several new segregation assessment criteria and recommendations for the modification of silo funnel shape parameters were reported. These evaluation metrics assessed the uniformity of the mixed material from various perspectives, including the degree of uniformity in the horizontal and vertical directions, as well as the uniformity of grid differentiation. The proposed criteria provided a comprehensive framework for evaluating and enhancing the uniformity of material distribution in material bin discharge phase. Based on the numerical simulations analyzing, it was found that various influencing factors in the simulation experiments had significant correlations with the response indicators, indicating that the metrics had a valuable reference significance. Therefore, to improve the uniformity of graded crushed stone, for particles with an inter-particle rolling friction coefficient of approximately 0. 07, discharge funnel parameters for the batching plant including a funnel’ s inclination angle α = 55° and a funnel outlet length L = 400 mm were recommended. Due to the constraints of the experimental methods for obtaining three-dimensional particle coordinates, the quantitative validation of the discrete element simulation proposed in this study faces challenges when compared to physical experiments. The chosen theoretical models and parameter ranges have limitations in representing real-world situations and need further refinement. In summary, optimizing the discharge phase of material bins during the construction process of a mixing station is crucial for achieving uniform material distribution. The uniformity of graded crushed stone materials is a key factor influencing the quality of road construction. The simulation results obtained in this study provide a basis for improving the design of discharge hoppers in the field of road construction and enhancing construction quality.

Keywords: silo; pavement material; uniformity; discrete element

Get Citation:CHU J W, HU L Q, HAN Z Q, et al. Mixing uniformity of particles of different particle sizes during blanking condition of silo[J]. China Powder Science and Technology, 2024, 30(1): 79-89.

Received: 2023-07-04,Revised:2023-11-10,Online:2023-12-16。

Funding Project:中央高校基本科研项目,编号:300102211307。

First Author:褚嘉玮(1999—),男,硕士生,研究方向为路面基层材料研发。 E-mail: cjw@chd.edu.cn。

Corresponding Author:胡力群(1971—),男,教授,博士,交通部交通科技英才,博士生导师,研究方向为路面结构与材料。 E-mail: hlq123@126.com。

DOI:10.13732 / j.issn.1008-5548.2024.01.008

CLC No: U414; U415; TB4              Type Code:A

Serial No:1008-5548(2024)01-0079-11