Study of airflow induced by regular particles in freefall through tubes


Workplace air quality is not only important for ensuring good health for workers but also equipment and industrial machinery. Belt conveyance, a major industrial transport system, is associated with dust generation as a result of the airflow induced by free-falling particles. According to past research reviews, dust emissions in industrial conveyor belts is a non-linear process influenced by numerous factors including particle sizes, height, and mass flow rate. To this end, numerous studies have been proposed to study the induced airflow patterns in materials transfer processes. However, few experimental studies have been proposed to study the effects of tube characteristics on the induced airflow.

Herein, Dongxue Wang (Master Degree Candidate) and Dr. Xiaochuan Li from the China University of Mining and Technology experimentally investigated the airflow induced by regular particles in freefall through tubes. Specifically, the effects of tube diameter, mass flow rate, drop height, and particle sizes were examined. First, the authors examined the relationship of the materials particles and energy transfer between the air and the material. The main objective was to establish effective design and optimization strategies for dust suppression in industries. The work is currently published in the Advanced Powder Technology journal.

Based on the experiment, free fall of regular particles was initiated through tubes of different diameters. Regular grain particles such as mung and millet were chosen for the study. Different tube parameters provided different cross-sectional areas and Buckingham theorem for results analysis. Results showed that induced airflow was mainly influenced by the mass flow rate of the free-falling particles attributed to the cumulative energy effect. Similar observations were reported for previous studies. On the other hand, height drop and gravitational potential energy were responsible for maintaining airflow within the tubes.

The relationship between the total drag coefficient and the induced airflow velocity was clarified. For instance, an increase in the induced airflow velocity, drop height, and mass flow rate of the particles due to a total drag coefficient in the range of 0.62-0.94 was observed. The minimum and maximum particle dispersion occurred at 3.247 mm and 9.223 mm respectively. Within this range, an increase in the power coefficient and exponent of a fitted curve for induced airflow velocity was also noted. Consequently, larger diameter tubes exhibited smaller total drag coefficients and relative particle proportions. When the tube diameter decreased from 200 mm to 120 mm, the induced airflow velocity and quantity increased, after which they decreased with a further decrease in the tube diameters. Finally, a semi-empirical equation of the induced airflow velocity of free-falling regular particles was developed. This equation was used to predict accurately the airflow quantity under different operation conditions and establish their actual deviations.

In summary, the study experimentally investigated the airflow induced by freefall of regular particles in different diameter tubes. The influence of various factors such as drop height, total drag coefficients, and mass flow rate on induced airflow velocity were clarified. Most importantly, a semi-empirical equation for accurate prediction of the quantity of induced airflow was established. Dr. Xiaochuan Li, said the study highlights important insights that will advance the design and optimization of high-performance dust suppression strategies for industrial applications.


Wang, D., & Li, X. (2020). Study of airflow induced by regular particles in freefall through tubes. Advanced Powder Technology, 31(1), 169-180.

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