Henri Coanda: June 7, 1886 – November 25, 1972

Compressed air flows through the inlet (1) to the Standard Air Knife, into the internal plenum. It then discharges through a thin gap (2), adhering to the Coanda profile (3) which directs it down the face of the Air Knife. The precision engineered & finished surfaces optimize entrainment of air (4) from the surrounding environment.

How did a past inventor help generate efficient compressed air products for EXAIR?  In the early 20th century, Henri Coanda who was a Romanian aeronautical engineer built an experimental Coanda-1910 airplane.  There are some debates if the airplane actually flew, but he invented a curved surface for a wing to generate a Coanda effect. The Coanda effect is the “tendency of a fluid jet to stay attached to a convex surface”1.   Thus, a moving stream of fluid will follow the curvature of the surface rather than continuing to travel in a straight line.  The Wright Brothers who flew the first airplane in the state where EXAIR is located, Ohio, used the Coanda effect to create lift.  With a curved profile, the air will adhere to the surface, causing a low pressure which makes the airplane fly.

EXAIR also uses this Coanda profile to make some of our Intelligent Compressed Air Products™.  Like an airplane wing, our curved surface will create a low pressure.  How does this help?  Well, higher pressure will always travel to lower pressure.  Instead of lift, we use the low air pressure to entrain ambient air.  This ratio of entrained air to compressed air is what we call the amplification ratio.  The higher the amplification ratio, the higher the efficiency for a blowing device. Two main compressed air products that EXAIR manufactures use this type of profile; Air Knives and Air Amplifiers.  I will cover both below. 

The Air Knives that use the Coanda profile blows air along the length of the knife at a 90o angle from the exit.  We offer two types; the Standard Air Knife and the Full Flow Air Knife.  The Standard Air Knives are made in Aluminum or Stainless Steel with blowing widths up to 48” (1219mm).  The inlet ports are at each end; so, the overall length is 1” (25.4mm) longer than the blowing length.  The Full Flow Air Knives have a port, or ports, on the backside.  Like the name states, the air blows out the entire length of the air knife.  The maximum length is 36” (914mm).  Both types use the Coanda profile to generate a low pressure as the air exits the gap and “hugs” the curve (reference photo above).  This low pressure draws ambient air into the air stream at a 30:1 amplification ratio for both the Standard Air Knife and Full Flow Air Knife.  So, for every one part of compressed air, we entrain 30 parts of ambient air.  Besides efficiency, it also adds mass to the air stream for a hard-hitting force.  With the engineered profile, the airstream is laminar which gives a consistent force across the entire length and makes them quiet.  Not only will they save you money by using less compressed air, but they are also OSHA safe.    

Super Air Amplifier – flow region

The Air Amplifiers use the Coanda profile in a circular form to pull in large amounts of free surrounding air.  The Coanda effect is able to generate a low pressure in the center to blow air for cooling, cleaning or removing welding smoke and debris efficiently and quietly.  The Air Knives above will blow a flat stream of air while the Air Amplifiers will blow a conical air stream.  They can reach amplification ratios up to 25:1. The Super Air Amplifiers use a patented shim to increase efficiency.  Unlike fans, they blow a laminar air stream for quick cooling.  They do not have any moving parts or motors to wear, so they are very quiet.  EXAIR manufactures five different sizes from ¾” (19mm) to 8” (203mm).  The Adjustable Air Amplifiers have a plug that can be adjusted to control the blowing from a breeze to a blast.  For cleaning surfaces, this is a nice feature to “dial” in the correct amount of blowing force.  We also manufacture five different sizes ranging from ¾” (19mm) to 4” (102mm).  Both types can be ducted to remove debris, heat or smoke. 

Utilizing the Coanda effect allows for massive compressed air savings. Whether it is a flat or round air stream, EXAIR can do this with high amplification ratios.  If you would like to discuss further how our Air Knives or Air Amplifiers can help you in your application, please contact us. An Application Engineer will be happy to help you replace your inefficient blowing devices.  History has given us a way to increase efficiency for blowing compressed air.  Thank you, Henry Coanda. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

1note – Wikipedia – Coanda effect

What Is A Coanda Profile?

The big thing that sets engineered products like EXAIR Intelligent Compressed Air Products apart from other devices is the engineering that goes into their design.  Several principles of fluidics are key to those designs:

The one I wanted to discuss today, though, is the Coanda Effect, what it means for our engineered compressed air products, and what they can do for you:

The Coanda effect is named after Henri Coandă, who was the first to use the phenomenon in a practical application…in his case, aircraft design.  He described it as “the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops.”  Put simply, if fluid flows past a solid object, it keeps flowing along that surface (even through curves or bends) and pulls surrounding fluid into its flow.  Here’s a demonstration, using an EXAIR Super Air Amplifier and a plastic ball:

What’s interesting here is that the Super Air Amplifier is not only DEMONSTRATING the Coanda effect, it’s also USING it:

Air Amplifiers use the Coanda Effect to generate high flow with low consumption.

EXAIR Standard and Full Flow Air Knives also have Coanda profiles that the primary (compressed air) flow follows, and uses, to entrain “free” air from the surrounding environment:

Compressed air flows through the inlet (1) to the Standard Air Knife, into the internal plenum. It then discharges through a thin gap (2), adhering to the Coanda profile (3) which directs it down the face of the Air Knife. The precision engineered & finished surfaces optimize entrainment of air (4) from the surrounding environment.

EXAIR Air Wipes can be thought of as “circular Air Knives” – instead of a Coanda profile along the length of an Air Knife, an Air Wipe’s Coanda profile is on the ring of the Air Wipe, which entrains surrounding air into a 360° ring of converging air flow:

Air Wipe – How it works

So that’s the science incorporated in the design of our products.  But what does it mean to the user?

  • Efficiency.  Pulling in a tremendous amount of “free” air from the surrounding environment means minimal consumption of compressed air, while still getting a hard hitting, high velocity air flow.
  • Sound reduction.  This air entrainment also creates a boundary layer in the air flow, resulting in a much quieter air flow than you get from a simple open-end blow off.

EXAIR Corporation is committed to helping you get the most out of your compressed air system, and thanks to Mr. Coandă, that includes reducing your compressed air consumption and noise levels.  If you’d like to find out more, give me a call.

Russ Bowman, CCASS

 

 

 

Application Engineer
EXAIR Corporation
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Many Air Knife Materials and Shim Options to Suit Your Application

The EXAIR Super Air Knives are used in many applications ranging from part drying, to web cleaning, to conveyor blowoff, and many other uses. For most processes, the aluminum models provide the performance required and withstand the environmental conditions present.

Ambient temperature limits for the aluminum models is 180°F (82°C). EXAIR also offers the air knives in types 303 and 316 Stainless Steel, which increase the temperature limit to 800°F (427°C) and provides a great degree of corrosion resistance. For the harshest, most corrosive environments, an air knife constructed of Polyvinylidene Fluoride (PVDF) with a temperature limit to 275°F (135°C) is available.

Super Air Knives
Aluminum, Stainless Steel and PVDF Super Air Knives

But what can we do about those applications where the increased corrosion resistance isn’t needed and the temperatures do not approach anywhere near to 800°F (427°C)?

The solution to this situation is an aluminum air knife with a custom stainless steel shim. The aluminum material is rated to 400°F (204°C) and the shim is good to 800°F (427°C) so this knife can be used in those hotter environments up to 400°F (204°C). This option helps to keep the cost of the knife low, by utilizing the lower cost aluminum for the body and cap.

The table below details the materials of construction options for the Super Air Knife – a wide array of material offerings to suit even the hottest, harshest conditions.

Air Knife Temperature Table

We recommend consulting with an Application Engineer to review the application, process, and environmental conditions, and we can present best options.

And don’t forget, the shims can be further customized for special blowoff requirements. See the blog that my colleague, Russ Bowman, posted here.

If you have questions about Super Air Knives or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
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Standard Ion Air Knife Keeps Viewing Cover Clean

A manufacturer of high speed industrial machinery makes a sorting machine for seeds.  There’s a clear plastic cover for operators to see the seeds as they pass through the machine.  Many seeds are dense enough to move right on through, but some lower density seeds (canola, lettuce, and flax seed, specifically) bounce around a bit, and even the slight static charge that builds up as they move through causes them to cling to the inside of that viewing window.

This was a great fit for our Model 8406 6″ Gen4 Standard Ion Air Knife Kit…”fit” being the operative word.  While the Super Ion Air Knives are more efficient and quieter, there simply wasn’t very much room at all for mounting inside, so the smaller profile of the Standard Ion Air Knife made all the difference in the world.  Also, since they just need static dissipation of such a small area, and not much flow at all is required to blow off these lightweight seeds, the differences in compressed air consumption and sound level were not very much at all.

Profile-wise, a Gen4 Standard Ion Air Knife takes up less than half the space of a Gen4 Super Ion Air Knife.

For performance, efficiency, and dependability, look no further than EXAIR’s Gen4 Static Eliminator Products.  If you have a problem with static, we’ve got a solution.  Give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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