Airflow re-entrainment of particulate contamination deposited on a surface: applied to the case of a heap of powder.
Laure Alloul-Marmor, doctorate thesis of the University of Paris XII, 238 p., defended on the 11th April 2002.
Resuspension of particulates from a powder deposit to a turbulent airflow is important in many fields like nuclear safety, environmental air pollution, sediment transport by wind or surface contamination in semiconductor operations. The objective of our work is to contribute to the understanding and quantification of the main factors that govern the particle reentrainment from a pile deposit exposed to a turbulent airflow.
Therefore, a review and analysis has been conducted about this subject. We describe forces and parameters, which operate in the reentrainment, and numerous theoretical and experimental studies, which cover different aspects of the phenomena. Then, a program of experiments has been carried out in which the reentrainment of polydisperse powder of different sizes (mean diameter in the range from 5 to 60 μm) from a powder deposit exposed to an horizontal airflow (air velocity in the range 0,5 to 10 m/s) has been studied. After the evaluation of our experimental methodology, the influence of eight factors on the reentrainment has been investigated using the designs of experiments. These parameters are related to the deposit, the powder particles, the surface, the airflow and the environment. Results from this study are discussed. Then, we propose a relative classification of these parameters about the resuspension. Finally, a semi-empirical formula which describes the reentrained fraction as a function of a dimensionless particle diameter which depends on the two relevant factors of réentraînement (the particle size distribution and the air friction velocity), is proposed.
It is hoped that our work will be of interest to all engineers in charge of safety analysis in the nuclear industry, and more, to all people involved in the particle reentrainment by airflow.