Pulsatile flow generator

This pulsatile flow generator produces a pulsating water flow by using flexible tubes, a collapsible elastic bladder and a fluid supply. This is a rare phenomenon which still isn't fully understood. What makes this phenomenon unique is the fact that it can generate a pulsatile flow without any use of difficult mechanical engines. There are existing pulsatile flow generators but none of them are as frugal and easy to build as this one. They are also expensive and none of them are based on principle of flow limitation occurring in collapsible tubes.

The fluid reservoir is connected to the collabsible bladder. The lower end of the bladder is connected to a flexible tube made of synthetic rubber or PVC. The first bit of the flexible tube that begins at the lower end of the bladder is 'U' shaped by using an elastic connector or a wire spiral. The end of the flexible tube were the water flows out is open to the atmospheric pressure. If the vertical height from the reservoir to the bladder is less than from the ground to the bladder and during a certain flow rate the bladder performs an interesting phenomenon of collapsing and opening along with the generation of a pulsatile flow of the liquid. The cause of this phenomenon can be explained by the functioning of the Starling resistor which produces self-excited oscillations caused by fluid-structure interaction in an elastic tube due to sudden stoppage of flow. This pulsatile flow generator can actually be seen as a modification of the Starling resistor.

As liquid starts filling the collabsible bladder a pressure drop inside the bladder causes the bladder to collapse and cutting off the fluid flow into the 'U' shaped tube (sudden stoppage of flow). As a result, a pulsatile flow is produced because of the continuously collapsing bladder. As the collapsing goes on the ‘U’ shaped tube strikes down with strong force pulling the spring down which was supporting the ‘U’ shaped tube from above. The force generated can be recorded directly with a dynamometer connected to the upper limb of the 'U' shaped tube.

The flow rate can be adjusted to change the frequency of the collapsing bladder (collapse per minute). As the flow rate increases, the frequency decreases. Consequently, the flow rate is inversely proportional to the frequency.

The velocity of the fluid at which it enters the bladder is lower than the velocity at which the fluid leaves the construction at the end of the flexible tube. Still, the flow rate remains the same.

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