Fundamental investigation of plug conveying of cohesionless particles in a vertical pipe (pressure drop and friction of a stationary plug)

A stationary packed bed of cohesionless particles is set up in a vertical pipe for the fundamental study of plug conveying. The effect of flow acceleration or deceleration on the pressure drop of the plug is investigated first. It is found that the pressure drop increases due to the flow acceleration and vice versa. Next, the following three kinds of experiments were made for the study of friction characteristics: 1. Friction between the plug and moving wall without air flow, 2. Friction between the plug and wall with downward air flow, 3. Friction between the plug and wall with upward air flow. The results are compared with the theory established in powder mechanics. The state of stress being of the active or passive case is discussed. Finally the problem of particles raining down from the back of the plug is studied. It is shown that the air velocity necessary to support the particles can be calculated based on a simple analysis of pressure distribution around the particles. Un lit stationnaire garni de particules disparates a ete place dans un tuyau vertical pour l'etude experimentale du transport bouchon. Dans un premier temps, on a etudie l'effet d'acceleration ou de ralentissement de l'ecoulement sur la perte de charge du bouchon. On a trouve que la perte de charge augmente a cause de l'acceleration de l'ecoulement et vice-versa. On a ensuite mene trois types d'experiences pour l'etude des caracteristiques de friction, soit: 1° friction entre le bouchon et la paroi mobile sans ecoulement d'air; 2° friction entre le bouchon et la paroi avec ecoulement d'air descendant; 3° friction entre le bouchon et la paroi avec ecoulement d'air ascendant. Les resultats sont compares a la theorie etablie en mecanique des poudres. L'etat de stress, de type actif ou passif, est examine. Enfin, on a etudie le probleme des particules tombant de l'arriere du bouchon. On montre que la vitesse de l'air necessaire pour soutenir les particules peut etre calculee a partir d'une simple analyse de la distribution de pression autour des particules.