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Gas-solid two-phase flow state in material pneumatic conveying device

Release time: 2019-11-22

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In the pneumatic conveying device, the material forms a gas-solid two-phase flow under the action of the conveying air flow. Obviously, due to the addition of materials in the two-phase flow, the material flow will be affected by factors such as air velocity, material characteristics and gas-solid ratio, and its motion state will change significantly. The movement state of the material particles is different in the vertical conveying pipe and the horizontal conveying pipe.
1. Movement state of the material in the vertical conveying pipe In the vertical conveying pipe of the pneumatic conveying device, because the air velocity is greater than the material suspending speed, the material powder particles continuously move upward. At the same time, due to the pneumatic conveying speed selected for pneumatic conveying, the laminar critical speed is generally greatly exceeded, and the two-phase flow is in a turbulent state. Therefore, in addition to the rise, the material particles are also affected by the component that moves vertically with the flow direction, and the material particles are conveyed Due to its size, irregular shape, and particles colliding with each other or with the tube wall, the material particles are constantly rotated and swayed by the uneven thrust of the airflow, so the material particles do not rise straight, but are irregular. The curve goes up. During the rise of two-phase flow during pneumatic conveying, due to many reasons such as friction, collision and adhesion between material particles and between the material and the pipe wall, and uneven air velocity distribution on the pipe section, the material is actually suspended and continuously rising The required air velocity is greater than the theoretically calculated rate of material particle suspension by HdFJ11.cOM. In the vertical conveying material pipe, the airflow resistance is on the same line as the gravity of the material particle group. However, due to the complexity of the actual vertical conveying particle flow movement, the material particle flow will be continuously disturbed by the force perpendicular to the direction of movement. Forms an irregular interlaced serpentine movement, so that the material particle flow forms a stable and evenly distributed two-phase flow in the vertical conveying pipe
2. The movement state of the material in the horizontal conveying pipe <When the gas-solid two-phase flow moves in the horizontal pipe of the pneumatic conveying device, the gravity direction of the material particles is perpendicular to the airflow direction, and the horizontal aerodynamic force component generated by the airflow velocity at this time It has no effect on the suspension of particles, but due to the existence of the following vertical component forces, the particles in the horizontal conveying pipe are still transported in a suspended state.
(1) Because the airflow in the horizontal conveying pipe is turbulent, the force generated by the vertical velocity of the turbulent airflow causes the particles to suspend. According to the test, the vertical velocity component of the turbulent state accounts for about 15% of the average velocity.
(2) The upper and lower air velocity of the particles at the bottom of the horizontal conveying pipe are different, the air velocity at the upper part of the particle is large, that is, the dynamic pressure is large, and the static pressure is small, while the velocity at the lower part of the particle is small, the dynamic pressure is small, and the static pressure is large. The static pressure difference causes the particles to suspend,
(3) The particles near the bottom of the tube roll forward under the impetus of the airflow in the tube. Due to the existence of gas viscosity, the air around the particles is driven to form a circular flow. In the upper part of the particle, the circulation flow is in the same direction as the airflow in the tube, and the flow velocity increases after superposition; in the lower part of the particle, the circulation flow is in the opposite direction to the airflow in the tube. After superposition, the velocity becomes smaller. As the velocity of the upper part of the particle increases, the dynamic pressure increases, and the static pressure decreases; while the velocity of the lower part of the particle decreases, the dynamic pressure decreases, and the static pressure increases. Therefore, there is a static pressure on the upper and lower particles. Poor, it creates a lift on the particles, and makes the particles suspended and rolling.
(4) Due to the irregular shape of the particles, the vertical component force generated by the air flow.
(5) Because the particles jump against each other or the particles collide with the pipe wall during the advance, the reaction force generated in the vertical direction is the component of the force. Under the effects of the above forces, the material particles will be suspended in the horizontal pipe and pushed forward with the airflow in a jumping manner, taking off and landing in sequence, and moving while floating.

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