Fluidics, Boundary Layers, And Engineered Compressed Air Products

Fluidics is an interesting discipline of physics.  Air, in particular, can be made to behave quite peculiarly by flowing it across a solid surface.  Consider the EXAIR Standard and Full Flow Air Knives:

Compressed air flows through the inlet (1) to the Full Flow (left) or Standard (right) 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 serve to optimize the entrainment of air (4) from the surrounding environment.

If you’ve ever used a leaf blower, or rolled down the car window while traveling at highway speed, you’re familiar with the power of a high velocity air flow.  Now consider that the Coanda effect can cause such a drastic redirection of this kind of air flow, and that’s a prime example of just how interesting the science of fluidics can be.

EXAIR Air Amplifiers, Air Wipes, and Super Air Nozzles also employ the Coanda effect to entrain air, and the Super Air Knife employs similar precision engineered surfaces to optimize entrainment, resulting in a 40:1 amplification ratio:

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

As fascinating as all that is, the entrainment of air that these products employ contributes to another principle of fluidics: the creation of a boundary layer.  In addition to the Coanda effect causing the fluid to follow the path of the surface it’s flowing past, the flow is also affected in direct proportion to its velocity, and inversely by its viscosity, in the formation of a boundary layer.

High velocity, low viscosity fluids (like air) are prone to develop a more laminar boundary layer, as depicted on the left.

This laminar, lower velocity boundary layer travels with the primary air stream as it discharges from the EXAIR products shown above.  In addition to amplifying the total developed flow, it also serves to attenuate the sound level of the higher velocity primary air stream.  This makes EXAIR Intelligent Compressed Air Products not only as efficient as possible in regard to their use of compressed air, but as quiet as possible as well.

If you’d like to find out more about how the science behind our products can improve your air consumption, give me a call.

Intelligent Compressed Air: Utilization of the Coanda Effect

Henri Coanda was a Romanian aeronautical engineer most known for his work developing what is today known as the Coanda effect. The Coanda effect is the propensity of a fluid to adhere to the walls of a curved surface. A moving stream of fluid will follow the curvature of the surface rather than continuing to travel in a straight line.  This effect is used in the design of an airplane wing to produce lift. The top of the wing is curved whereas the bottom of the wing remains straight. As the air comes across the wing, it adheres to the curved surface, causing it to slow down and create a higher pressure on the underside of the wing. This  is referred to as lift and is what allows an airplane to fly.

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The Coanda effect is also the driving force behind many of EXAIR’s Intelligent Compressed Air Products. Throughout the catalog you’ll see us talking about air amplification ratios. EXAIR products are designed to take advantage of this phenomenon and entrain ambient air into the primary air stream. Compressed air is ejected through the small orifices creating air motion in their surroundings. Using just a small amount of compressed air as the power source, Super Air Knives, Air Nozzles, and Air Amplifiers all draw in “free” ambient air amplifying both the force and the volume of airflow.

Entrainment
EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

Super Air Knives provide the greatest amount of air amplification at a rate of 40:1, one part being the compressed air supply and 40 parts ambient air from the environment. The design of the Super Air Knife allows air to be entrained at the top and bottom of the knife, maximizing the overall volume of air. Super Air Nozzles and Super Air Amplifiers also use this effect to provide air amplification ratios of up to 25:1, depending on the model.

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

The patented shim design of the Super Air Amplifier allows it to pull in dramatic amounts of free surrounding air while keeping sound levels as low as 69 dBA at 80 psig! The compressed air adheres to the Coanda profile of the plug and is directed at a high velocity through a ring-shaped nozzle. It adheres to the inside of the plug and is directed towards the outlet, inducing a high volume of surrounding air into the primary air stream. Take a look at this video below that demonstrates the air entrainment of a Super Air Amplifier with dry ice:

Utilizing the Coanda effect allows for massive compressed air savings. If you would like to discuss further how this effect is applied to our Super Air Knives, Air Amplifiers, and Air Nozzles give us a call. We’d be happy to help you replace an inefficient solution with an Engineered Intelligent Compressed Air Product.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

Custom Air Amplifiers To Meet Most Any Requirement

When I think of “special” in regard to Air Amplifiers, I’m more inclined to think of the applications they can be used in. I mean, the Air Amplifier itself is about as straight-forward as an engineered compressed air product can be:

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

Considering the simplicity of the product itself, they can be used for a large variety of “typical” applications:

  • Cooling
  • Drying
  • Cleaning
  • Ventilation
  • Fume Exhausting
  • Dust Collection

There are no shortage of “special” applications either.  They’re used successfully in Air Operated Conveyance applications (when the stronger vacuum head of a Line Vac isn’t required) and we’ve even got a customer who uses one instead of an E-Vac Vacuum Generator for a “pick & place” operation…they’re picking up small, porous fiber discs (sort of like a coffee filter) one at a time, and the E-Vac wanted to pick up a good part of the whole stack, no matter how low they turned the pressure.  And of course, I can’t think of anything more special about Air Amplifiers than this:

You have to read it to believe it.  Follow the link and click on “Case Study: Roaring Banana Breath”

With fifteen distinct models to choose from in a range of sizes (3/4″ to 8″,) materials (aluminum or Stainless Steel) and even a High Temperature model that’s rated to 700°F (374°C), we’ve still made a fair number of Custom Air Amplifiers too…thirty-four, to be exact, as of this writing.

I won’t bore you with all the details – I can’t, actually, because some of them are proprietary* – but here are some “regular” examples of “special” accommodations:

  • Connections: EXAIR Air Amplifiers have smooth bores on the inlet & outlet plenums that you can hose clamp a hose (or round duct) to if you need to get air flow from, or to, one place or another.  Sometimes, though, they’re going in to an existing system, so we’ve made them with flanges (150#RF and Sanitary Tri-Clamp, for example) or threads (NPT or BSPP.)  If you want to use something other than a standard hose or duct line, we can help.
  • Material of construction: Our durable, lightweight aluminum Super & Adjustable Air Amplifiers are just fine an awful lot of the time.  Our type 303 Stainless Steel Adjustable Air Amplifiers will hold up to heat and corrosives.  We’ve also in PTFE (Teflon™) as well as a range of metal alloys to meet specific corrosion or wear conditions.  If your environment calls for a little something extra, we can help.
  • Assembly: Super Air Amplifiers are fitted with a stock shim that gives you published performance.  We’ve got other thicknesses, though, if you need more (or less) flow, though.  Adjustable Air Amplifiers are, well, adjustable…you just thread the plug in/out of the body until you get the results you want.  Sometimes the user knows what shim they want in a Super Air Amplifier, or what gap their Adjustable Air Amplifier needs to be set to, and we can assemble it accordingly.  If you have a ‘tried-and-true’ performance setting and want it met right out of the box, we can help.
  • Assembly, part 2: Good engineering practices call for lubrication on O-rings and threaded connections, and we use high quality, general purpose compounds when assembling our Air Amplifiers.  These are detrimental, however, in certain situations (silicone exclusion areas, I’m looking at you.) If certain chemicals or compounds are prohibited by your application, we can help.

*Let’s say you’ve done the “heavy lifting” to call out one (or more) of these special design features.  If we make a custom product (and that’s not just Air Amplifiers, by the way) using directions based on your time and labor, we’ll treat that product as proprietary to you, and you alone.

EXAIR has 208 catalog pages worth of Intelligent Compressed Air Products on the shelf…8 of those pages are our Air Amplifiers.  If you want to talk about customizing one to meet your needs, give me a call.

Russ Bowman
Application Engineer
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Air Amplifiers – What is an Amplification Ratio?

On Friday my colleague, Russ, blogged about the Super Air Amplifier (see that BLOG here, including a video demo)  In discussing the Air Amplifiers, the topic of amplification was mentioned. Today, I’d like to expand a bit further the amplification aspect of the Air Amplifier performance.

As the name of the device implies, the compressed air used by the Air Amplifier is added to, and thus ‘amplified’, the total output flow of the unit. Depending on the size and type of Air Amplifier, the amplification ratio starts at 12:1 and goes up to 25:1, with the ratio being the output flow to the compressed air usage.

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Super Air Amplifier and Adjustable Air Amplifier

EXAIR offers (2) types- the Super Air Amplifier and the Adjustable Air Amplifier.  The Super Air Amplifier uses a patented shim technology to maintain a precise gap, which controls the compressed air flow and expansion through the unit.  As the expanded air flows along the Coanda profile, a low pressure area is created at the center which induces a high volume flow of surrounding air into the primary air-stream.  The combined flow of primary and surrounding air exhausts from the Air Amplifier in a high volume, high velocity flow.  The larger diameter units have a greater cross sectional area with larger low pressure areas, resulting in greater amplification ratios.

The Below table shows the amplification ratios.

SuperAirAmplifierPerformance

The Adjustable Air Amplifier does not use a shim, but rather has an infinitely adjustable gap, allowing for fine adjustment of performance.  Force and flow is changed by turning the exhaust end to adjust the gap, and is then locked into place. The method of the amplification is the same as for the Super Air Amplifier, and the amplification ratios are similar and shown below.

AdjustableAirAmplifierPerformance

The Super Air Amplifiers and Adjustable Air Amplifiers are ideal for use in applications and processes that require cooling, drying and/or cleaning of parts, or the ventilation of confined areas or weld smoke or the exhausting of tank fumes.

If you have questions regarding the Air Amplifier, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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What’s So “Super” About The Super Air Amplifier?

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of free air from the surrounding environment.

“Free air” from the surrounding environment?  You might think it’s too good to be true, and if you think you’re getting something for nothing, you’re right.  If you consider, though, that it’s oftentimes preferable to work smarter, not harder, then the use of engineered compressed air products is too good NOT to be true.  Case in point: the Super Air Amplifier.

The Coanda Effect is the “work smarter, not harder” part of the Super Air Amplifier

Simple and low cost, (hey, “engineered” doesn’t necessarily mean “complex and expensive”) the EXAIR Super Air Amplifier uses a small amount of compressed air to generate a tremendous amount of air flow through entrainment.  How much do they pull in?  Depending on the model, they entrain air at rates of 12:1 (for the 3/4″ Model 120020) to 25:1 (4″ & 8″ Models 120024 & 120028, respectively.)  The larger diameters mean there’s more cross sectional area to entrain air, so there is indeed efficiency to scale, size-wise.  There are a couple of great visuals in this video, if you want to see the entrainment in action (1:50) or the difference that the entrainment makes (1:30):

 

Where can you use a Super Air Amplifier?  The easy answer is, anyplace you want a consistent, reliable air flow.  The pressure supply can be regulated from a “blast to a breeze,” depending on the needs of your application.  The patented shim can be replaced for even higher performance, while maintaining the efficiency that makes it so valuable.  The balanced flow makes for incredibly quiet operation…no more noisy fans, blowers, or open-end compressed air pipes.  The body (3/4″ to 4″ sizes) is cast with a 2-hole flange for ease of installation.

When can you use a Super Air Amplifier?  Another easy answer: anytime you want.  If you need a continuous air flow, there are no moving parts to wear or electrical components to burn out.  Supply them clean, dry air, and they’ll run darn near indefinitely, maintenance free.

Alternately, if you need intermittent air flow, starting & stopping operation is as simple as opening & closing a valve in the compressed air supply line.  They produce rated flow immediately, and cut it off just as fast.

Some of the more popular applications are ventilation/exhaust, cooling, drying, cleaning, and dust collection.  There are five distinct models to choose from, and they’re all in stock.  We’re also happy to discuss special requirements that might lead to a custom product too.  Our Application Engineers work with Design & Production all the time to meet specific needs of particular situations.

If you’d like to find out more about letting the Super Air Amplifier, or any of EXAIR’s Intelligent Compressed Air Products work smarter for you, give me a call.

Russ Bowman
Application Engineer
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Video Blog: Which EXAIR Air Knife Is Right For You?

The following short video explains the differences between the 3 styles of Air Knives offered by EXAIR – The Super, Standard and Full-Flow. All of these Models are IN STOCK, ready to ship, with orders received by 3:00 PM Eastern.

If you need additional assistance choosing your EXAIR Air Knife, please contact an application engineer at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

EXAIR Blogs This Week Are Almost As Cool As Shark Week

Yes, ALMOST. This week, the EXAIR Blog has featured some excellent explanations of the science behind the operation of compressed air products. On Tuesday, John Ball posted the best explanation of SCFM vs ACFM that I’ve come across, and I’ve been explaining this to callers for almost four years now. I’m using his blog to perfect my “elevator pitch” on this topic. It will still likely require a building with more than ten floors, but I think that’s OK.

Also on “Two Blog Tuesday,” (this week only; I’m not trying to start anything) Dave Woerner’s gem of a blog detailed the terminology associated with pressure measurement, and why we use “psig” (g = gauged) – in a nutshell, the compressed air inside the pipe doesn’t care what the pressure outside the pipe is. And, since he mentioned it, I might add that most of agree that we care even less about how a certain NFL team’s footballs were (or were not) properly inflated.

Brian Farno’s “One Blog Wednesday” entry was a quite useful (if not alphabetical…OK; now I AM trying to start something) list of some common terms and expressions we use on a regular basis while discussing the operation and performance of EXAIR compressed air products. If you liked his photo demonstration of the Coanda effect with the foam ball & Super Air Amplifier, I encourage you to experience the Coanda effect for yourself, if you have access to a leaf blower and a volleyball:

I mention these earlier blogs to get to the point of MY blog today…a bit of theory-to-practice, if you will. Once you’ve gotten a decent understanding of these principles (or have the above links bookmarked for quick reference,) we can apply it to what’s needed for the proper operation of a compressed air product itself.

With a working knowledge of air flow (SCFM) and compressed air supply pressure (psig,) we can more easily understand why certain pipe sizes are specified for use with particular products. For instance, the longer the Super Air Knife and/or the longer the run of piping to it, the larger the pipe that’s needed to supply it:

This table comes directly from the Installation & Operation Instructions for the Super Air Knife.
This table comes directly from the Installation & Operation Instructions for the Super Air Knife.

The reasons for this are two-fold: First, the pipe…longer runs of pipe will experience more line loss (a continuous reduction in pressure, due to friction with the pipe wall…and itself) – so, larger diameter pipe is needed for longer lengths. For another practical demonstration, consider how much faster you can drink a beverage through a normal drinking straw than you can through a coffee stirrer. Not as dramatic as the leaf blower & volleyball (you really want to try it now, don’t you?) but you get my point.

Second, the Air Knife…the longer the Air Knife, the more air it’s going to use. And, if it’s longer than 18”, you’ll want to feed it with air at both ends…line loss will occur in the plenum as well.

In closing, I want to leave with another video, shot right here at EXAIR, showing the actual reductions in pressure due to line loss through different lengths, and diameters, of compressed air supply line to a Super Air Knife.

If you ever have any questions about compressed air use, or how EXAIR products can help you use your compressed air more efficiently, safely, and quietly, please give us a call.

Russ Bowman
Application Engineer
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