Basic theory of pneumatic conveying Principles of air flow conveying in vertical pipelines Composite fabric information

Suppose the airflow velocity of pure air in the pipeline is v. When transporting fibers in the pipeline, the void ratio of the fiber medium is ε, then the flow rate permeating through the voids of the fiber medium is v/ε. When the flow velocity v is small, the fiber does not When v gradually increases, the entire fiber medium expands and increases ε, and the fiber begins to rise. However, due to the increase in ε in the upper part, the v/ε value decreases, so the fiber falls again. This phenomenon of rising and falling It is called fluidization, but the fibers remain in the pipe and cannot achieve the purpose of transportation. When v continues to increase and exceeds the terminal speed v_T of the fiber medium, it will no longer fall after rising and continue to move, forming a transportation process.
Assuming that during pneumatic conveying, the movement speed of the fiber in the pipe is v_f, which is generally lower than the air flow speed v, and the relative speed between the two is v-v_f , where During the normal and stable transportation process of vertical pipelines, v-v_f =v_T, that is, v=v_T +v_f . Because v_f =v-v_T, when the fiber medium is suspended in the vertical pipe, v_f =0, which makes the fiber medium in The airflow velocity that produces suspension in vertical ducts is called suspension velocity. It can be seen that the suspension velocity is numerically equal to the settling velocity (terminal velocity), that is, when the air flow velocity reaches the free settling terminal velocity (terminal velocity), the fiber medium is suspended in the vertical pipe. When the air flow velocity is greater than the terminal velocity of the fiber medium, Only when the final speed v_T can normal transportation of vertical pipelines be carried out. The air flow velocity is generally controlled at 1.5 to 2.0 times the terminal velocity.
When transporting fiber media in vertical pipelines, if the flow rate is reduced to a certain extent, there will be more fiber media in some sections and less fiber media in some sections. In the section with more fibers, ε is smaller. The flow rate v/ε of air passing through the gaps in the fiber medium is relatively high, causing surging phenomena, resulting in uneven flow. If the flow rate decreases further, blockage will occur. Whenever spiral motion occurs in a vertical pipe, blockage is likely to occur due to the increase in friction on the pipe wall and the energy consumption of the spiral motion, requiring an increase in the conveying speed.
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