Simple Air Permeation Experiment 1

[jrt20839]

I am working on an air permeation experiment to show the difference in air permeation between three fabrics. If you use lab testing equipment, you get air perm values of 221 CFM, 86.6 CFM, and 35.6 CFM respectively. I tried a set-up with a ping pong ball in a clear tube and a fan blowing up on it across the fabric, hoping that you would be able to see a difference in height, but it wouldn't work. The fan wouldn't even blow confetti around when the fabric barrier was in place. Does anyone have any ideas why this is not working?

 

[1gibson]

Because the air is not going through the cloth. You need a differential pressure, not just a fan.

Shop vac (vacuum side) pulling from top of the tube may work.

 

[MiketheEngineer]

If the "holes" are small and I am sure they are - when the air hits - it becomes very turbulent. It can actually almost "clog" the hole and very little air will actually get through.

As noted - you really need a wind tunnel or equal.

 

[Ron]

As Mike says...head loss through the orifice.

 

[berkshire]

If you are going to put a ping pong ball in a tube for a meter, as soon as the air flow lifts the ball , it will take it out of the end of the tube. You need a tapered tube for a meter. even if it as simple as a tapered saw cut in one side of the tube.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[chicopee]

Instead of a fan which has CFM values based on RPM and not on static pressure values, try a blower which has CFM's based on static pressures.

 

[MintJulep]

Your experiment set up is worthless because the material under test determines the performance of the test equipment.

You need something that can either:

Establish a fixed and known pressure drop across the sample, then measure cfm.

or

Establish a fixed and know flow through the apparatus, then measure the pressure drop across the sample.

 

[Ron]

Aw come on MJ...don't sugar coat it.

 

[jrt20839]

The whole idea is not to use this set up to gain data. It is to create a visual demonstration that can be used at trade shows and the like to illustrate the differences in fabric performance.

 

[MintJulep]

People like me attend trade shows. We see things like your proposed demonstration experiment and listen to sales reps try to explain how it's meaningful.

Then we conclude that your company doesn't know what it's doing and don't ever buy anything.

You want people to come to your booth, hire some pretty girls.

 

[vpl]

But, Mint, even if they hire pretty girls, aren't you're still going to walk away once the sales rep gives you the impression the company doesn't know what it's doing?

They should save the salary money and figure out a test that demonstrates what they're trying to show.

Even if you get the blower installed the right way, what is the blowing confetti or ping pong ball going to prove? If the fabric permeability only works under certain conditions, then how is the OP's company going to ensure that in actual applications customers are getting the permeability they want?

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.