Physics of Fluid Flow

There is a whole science within hydraulics that deals with fluid flow.

The concept of boundary layer physics plays a major role.

When a fluid fills a pipe, the layer of molecules adjacent to the pipe have an affinity for the material of the pipe.

They sort of stick to it.

Forming the...

"Boundary Layer" And this stickiness affects how a fluid flows through the pipe.

In actuality, the fluid does not flow through the pipe but through the pipe coated with the boundary layer of the fluid/pipe interface.

Thus every pipe that conducts fluid is actually smaller than it appears depending on the thickness of this boundary layer.

If the pipe is already very small, then the proportion of the pipe that is occupied by this boundary layer is relatively larger and thus the bore smaller, and has more of an effect on how well the fluid flows.

As we know, the smaller the pipe, the greater pressure is needed to force a given volume to flow in a given amount of time.

I.e. the flow rate is diminished.

In syringes as used for endo we are dealing with two adverse factors.

• First the needle is very small.
• Second the cement is very thick

and technically is not a fluid at all but a suspension of zinc oxide and other particles in eugenol.

To a great extent, what determines the pressure needed to attain a given flow rate is the ability of these particles to roll or tumble past one another as they move past the particles in the boundary layer. i.e. it helps if the particles themself are round and smooth vs. large and jagged.

Thus it takes a great deal of pressure to get a thick mix of ZOE to flow through a small needle.

This is all but impossible to attain with normal hypodermic type syringes.

Some device to give us a mechanical advantage must be used.

Lever handle devices and screw type devices such as the Precision Endo Multi-Mode syringe, have been used in the past to solve this problem.

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