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Old Jan 28th 2016, 02:35 PM   #1
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Membrane driving a fluid

Hello, I've been struggling with a flow issue on a design I am working on. The design is to deliver a viscous material through a nozzle that exits out of the side of one end of a reservoir that is roughly rectangular. The material is covered on its top surface by a thin metallic foil (which acts like a diaphragm) and above it is a pressurized gas. I have done many experiments with variations of the design of the foil to get it to squeeze the paste in a lateral direction from the side opposite of the nozzle first, so as to not block the nozzle entrance with the foil before all of the paste can be squeezed out of the reservoir. Am I fighting the pressure differential of the paste which is a minimum at the entrance to the nozzle and much higher at the opposite end? If this is a pressure differential issue, are there simple ways to make the pressure closer to constant within the volume of drug. Note, the reservoir is very small (~0.8cc) and the viscosity is very high (approximately that of toothpaste) so the pressure differential due to gravity is negligible and mostly due to viscosity of the fluid and a very small nozzle (around 0.4mm diameter X 25mm long). Any thoughts?
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Old Jan 29th 2016, 05:28 AM   #2
MBW
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A couple of ideas

Perhaps reinforce the diaphragm with a wire round the edge,
then have a small ledge just above the nozzle to catch the wire.
have the wire strong enough to hold the diaphragm under normal load
but deform as the last few drops are squeezed out.
Might also help if, instead of a diaphragm, you enclose the fluid entirely in a bag.
If possible manufacture bag and nozzle as one item, this can then be inserted into the pressure chamber.
The pressure chamber will then be reusable, just the bag and nozzle being replaced.
I've no idea if these ideas are feasible, but hopefully they might help.
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