Basic theory of pneumatic conveying Settlement and terminal velocity of fiber media
In engineering, the flow that contains gas (vapor) phase, liquid phase and solid phase medium at the same time in the flowing medium is called two-phase flow. Obviously, two-phase flow problems can be divided into gas (steam)-liquid two-phase flow, gas-solid two-phase flow and liquid-solid two-phase flow. In cotton pneumatic conveying and gas dust removal devices, the flowing medium contains air, cotton or impurities at the same time, which is a solid-gas two-phase flow.
Since there are two interfaces in two-phase flow, in addition to the energy exchange between the two-phase overall interface and the outside world, there is also energy exchange between the two-phase interface, making this problem more complex than single-phase flow. It’s much more complicated.
1. Settlement and terminal velocity of fiber media
In completely still air, cotton clumps and cotton dust accelerate downward due to the action of gravity with an initial velocity of zero. Due to the acceleration, The sinking speed is getting faster and faster, and the resistance of the air to it is getting bigger and bigger. Until the two are balanced, the cotton dust sinks at the same speed. The speed at this time is called the “free settling terminal velocity” of the cotton dust, referred to as ” “Terminal velocity” is represented by vT.
Cotton dust can be transported only when the air flow velocity in the pipeline is greater than the terminal velocity of cotton dust. When the airflow velocity is lower than the terminal velocity, the cotton dust will settle at the bottom of the pipe. Only by increasing the power can the cotton dust be pushed forward.
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