Blinded T-bends flow patterns in pneumatic conveying systems

Abstract

Blinded T bends are commonly used in pneumatic conveying systems. The main benefit of this design is that a loose bed of particles accumulates in the blinded pocket of the fitting, allowing particle-particle collision while experiencing a change in the direction of the flow. Such collisions are intended to reduce erosion of the construction material and attrition of the conveyed particles. Since prior research showed that particles will not necessarily accumulate in a blinded T, a series of experiments were conducted to evaluate the effect of the operating parameters on the critical point in which the blinded T becomes effective. In this study we investigate the effect of gas velocity, solid loading ratio, orientation and bend geometry on the critical point using 1.5″ and 2″ pneumatic conveying systems. The experiments were conducted with NaCl with mean particle diameter of 0.85mm, glass spheres with mean particle diameter of 1mm, plastic beads with mean particle diameter of 4mm, polystyrene beads with mean particle diameter of 2mm and cement powder. The blinded T arrangement also varies in depths of the blinded leg. To investigate these phenomena we conducted attrition experiments with NaCl for practical implications. It was found that both the conveying air velocity and the depth of the blinded pocket affect the filling of the blinded T bend. In addition, correlation for the filling of the bend as well as one for complete particle deposition is suggested with respect to the geometry of the bend and the operating conditions.