抄録
The pressure drop due to horizontal-to-vertical and vertical-to-horizontal bends was measured in an experiment on pneumatic conveying. The ratio of the additional pressure gradients at the inlet and outlet of the bend is defined as the factor showing the effect of the bend on the pressure drop. The experimental conditions are as follows:
Pipe diameter (I. D.)=40mm
Bend curvature to pipe diameter ratio=12.3, 20.5
Particle size=2.9mm (Large particle), 0.18mm (Small particle)
Loading ratio defined as the particle to air mass ratio=2, 5, 8
Bulk air velocity=15, 20, 25m/s
Experiments were also made on particles with a mixed size of the above two kinds. The results are summarized as follows:
(1) The effect of mixed size on the pressure drop is negligible in the constant velocity region of a straight pipe.
(2) The pressure gradient ratio π decreases as the loading ratio increases. The ratio π is always larger than one for the large particles. The ratio π becomes smaller than one for the small and mixed particles at a large loading ratio. This is due to the fact that those particles tend to slide on the bend pipe wall.
The ratio π of the mixed particles shows the same tendency as the large particles at a low loading ratio and the same tendency to the small particles at a high loading.
(3) In the case of large particles, it is possible to calculate the particle velocity at the bend outlet and pressure drop after the bend by using the data of the additional pressure drop at the outlet.
