Hello!

I believe that there must be a relation between pressure, (hydraulic)
diameter, and certain fluid properties which decide wheter a fluid flow or
not through a certain channel. For example, if you have a small syringe
needle then you need to apply pressure before fluid flows out. Can anyone
tell me something about functions or relations on this topic? Or where to
look for answers probably?

Thanks,
MeV

MeV wrote:

Hello!

I believe that there must be a relation between pressure, (hydraulic)
diameter, and certain fluid properties which decide wheter a fluid flow or
not through a certain channel. For example, if you have a small syringe
needle then you need to apply pressure before fluid flows out. Can anyone
tell me something about functions or relations on this topic? Or where to
look for answers probably?

Viscosity.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

"MeV" wrote in message ...
I believe that there must be a relation between pressure, (hydraulic)
diameter, and certain fluid properties which decide wheter a fluid flow or
not through a certain channel. For example, if you have a small syringe
needle then you need to apply pressure before fluid flows out. Can anyone
tell me something about functions or relations on this topic? Or where to
look for answers probably?

As Al, says, look up viscosity. A good place to start is here.

www.google.com

For very small bore tubes, such as needles, capillary action may have
some effect. Look that up also. Though that is likely to be more of
a perturbation than the main effect. And it rapidly becomes unimportant
as the tube cross section becomes larger.
Socks

I would say surface tension. Just like some for some tents. The gaps in the
woven structure are normally the tiny for water to breakthrough, but when
you toch the tent water seeks through since the gaps grow under influence of
the increased tension. So I did the following calculation:

square gap of 0,4x0,4mm makes 1,6exp-7 square meter. A 4mm water column
provides 40N per square meter so the available force in this case is
6,4exp-6 N

The maximum length in a 0,4mm square is 0,4 x sqrt(2) = 0,57mm
surface tension of water is 73mN/meter so the required force to break the
surface tension would be 4,1exp-5 N

Conclusion in this case would be the water doesn't enter the channel. Right?

MeV
wrote in message
om...
"MeV" wrote in message
...
I believe that there must be a relation between pressure, (hydraulic)
diameter, and certain fluid properties which decide wheter a fluid flow
or
not through a certain channel. For example, if you have a small syringe
needle then you need to apply pressure before fluid flows out. Can
anyone
tell me something about functions or relations on this topic? Or where
to
look for answers probably?

As Al, says, look up viscosity. A good place to start is here.

www.google.com

For very small bore tubes, such as needles, capillary action may have
some effect. Look that up also. Though that is likely to be more of
a perturbation than the main effect. And it rapidly becomes unimportant
as the tube cross section becomes larger.
Socks