Things Are Not Always As They Seem

A magician got a job on a cruise ship, entertaining the passengers on deck throughout the day, and performing a big nightly after dinner show. The Captain sat in the front row, and brought his pet parrot to see the show every night. After a couple of performances, the parrot started to figure out some of the magician’s tricks, and would cry out “The card’s up his sleeve!” “The ball’s in his other hand!” “There’s a fake bottom in the box!”  This irritated the magician to no end, but despite his protests, the Captain continued to bring the parrot to every show.

Then one night, the ship hit an iceberg and sank. The magician and the parrot ended up in the same lifeboat, where they sat, quietly glaring at each other. Hour upon hour passed in complete silence. Just before dawn, the parrot finally said “OK; I give up. What did you do with the ship?”

Magicians, of course, are the masters of all things “not as they seem,” using sleight-of-hand to create illusions or distractions. That means we see what they want us to see, we’re entertained, and their mission is accomplished.

The laws of physics mean that things are not always as they might seem as well. This morning, I had the pleasure of discussing an Air Knife application with a customer who intended to mount a Standard Air Knife as close as possible to his material, in order to provide the highest possible force from the air flow. The thought was, the closer the better, right? Well…

It turns out, this Air Knife was tested at distances from 3mm – 30mm (about 1/8” – 1”) from the target. The amount of force applied actually INCREASED with the distance over that range. His thinking was, with the velocity of the air flow being the highest, right at the outlet of the Air Knife, this would be where the force was greatest too. And, all other things being equal, this would be true.

The velocity of the air flow exiting our Air Knives can be as high as 13,000 feet per minute, and it’s not slowing down one bit over an inch of travel…not to any degree that we have an instrument to measure, anyway. The Standard Air Knife, however, entrains air from the surrounding environment…in fact, at 6″ away, it’s actually entrained 30 TIMES the amount of air that’s being supplied from your compressed air system. This is a TREMENDOUS increase in the mass flow rate. So, if you have a BUNCH more air hitting the target at the same speed, it’s going to exert a proportionately higher force.

How Std AK works

After explaining this to my customer (who installs these on chemical processing machinery), he was then able to enlighten HIS clients to the benefits of letting a little physics do the heavy (or not so heavy) lifting. In this case, the unexpected increase in force they got by moving the Air Knife about ½” away meant they could actually lower their compressed air supply pressure, conserving a great deal of air in this continuous blowing application.

Do you want to know how EXAIR, our Intelligent Compressed Air Products, and the laws of physics can work wonders in your facility, give us a call. No sleight-of-hand or prestidigitation required, but we’re willing to learn!

Russ Bowman
Application Engineer
EXAIR Corporation
(513)671-3322 local
(800)923-9247 toll free
(513)671-3363 fax

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