Suspension velocity of irregularly shaped particle groups in pneumatic conveying
Inpneumatic conveyingIn gas-solid two-phase flow, most of the materials transported are irregularly shaped particle groups.
1. The influence of irregularly shaped particles on suspension velocity: Among materials of the same weight, spherical particles have the highest suspension velocity, while irregularly shaped particles have correspondingly lower suspension velocities. This is because the resistance coefficient of irregularly shaped particles is greater than that of spherical particles. Even for the same irregularly shaped particle, its drag coefficient varies due to its different orientations relative to the airflow. Therefore, in order to utilize the suspension velocity formula for spherical particles already obtained above, it is necessary to convert irregularly shaped particles into equivalent spheres. The diameter d of a volume equivalent sphereeAs the particle size of irregularly shaped materials, it is used for correction calculation.
According to the general expression of fluid dynamics (resistance) obtained earlier, when in the same pipeline and fluid medium, and both are in a suspended state, the floating weight WsBalance with fluid resistance. If we follow the formula, thenFor irregularly shaped particles (volume v)
2. The suspension velocity of particle groups in pneumatic conveying and classification selection refers to the movement of a large number of particles within a certain range. Due to the fluid displacement caused by the falling particles, additional upwelling flow is generated. At this point, particle settling is not only subject to fluid resistance, but also to interference resistance from other particles due to the large number of particles, that is, particle group settling is subject to both direct and indirect resistance. Direct acting resistance refers to the friction and collision between particles and between particles and the pipe wall, resulting in resistance; Indirect resistance refers to the fluid displacement caused by particles falling, resulting in additional upward flow resistance.
The resistance in these two aspects is related to the integral number o of the particle population (which is the ratio of the particle volume v to the air volume V, i.e. q=V/V). The larger the volume fraction, the slower the settling (i.e. suspension) velocity. When the volume fraction is the same, the finer the particles and the more particles there are, on the one hand, the larger the surface area of the particles, the higher the resistance, and on the other hand, the more opportunities for friction and collision between particles, the higher the resistance, and the lower the settling velocity. So the interference settling velocity of the particle group, that is, the suspension velocity (vn) of the particle group, is smaller than the settling velocity (vo) of a single particle.
When the volume fraction q is within the range of 5% -25%, v can be calculated according to the following formula:
VN = V (1 - φ)B
Therefore,Pneumatic conveying systemIt is a complex engineering project that involves multiple fields such as fluidization, aerodynamics, and particle science. Choosing a manufacturer with rich experience is necessary to make transportation more efficient and stable.