Tag: entrainment ratio

Venturi Effect in Use

Published on by jasonkirbyLeave a comment

The Venturi effect describes the phenomenon where a fluid, such as air or water, accelerates as it passes through a constricted section, resulting in a decrease in pressure. This occurs because the fluid is drawn into the narrower area, and the increase in velocity leads to a corresponding drop in pressure. The effect is named after Giovanni Battista Venturi, who first articulated this principle in 1797.

A perfect example of the Venturi Effect can be found in our Air Amplifiers. Compressed air enters through the air inlet and flows into an annular chamber, where it is accelerated through a small ring nozzle. This high-velocity primary airstream follows the Coanda effect, guiding it toward the outlet. As a result, a low-pressure zone forms at the center, drawing in a significant volume of surrounding air into the primary flow. The mixture of the primary airstream and the surrounding air is then expelled from the Air Amplifier at a high volume and velocity.

The Venturi Effect is represented in amplification ratios. A ratio represents the relationship between two quantities, indicating how many times one value is contained within another. In the case of the Super Air Knife, this ratio illustrates the volume of ambient air that is drawn in alongside the primary flow of compressed air. With an impressive amplification ratio of 40:1, the Super Air Knife incorporates 40 parts of ambient air for every single part of compressed air, making it one of the most efficient air-operated knives available. This addition of mass enhances the device’s ability to deliver a powerful force, enabling it to perform more effectively in various applications.

The Venturi effect is integral to various EXAIR products designed for cooling, drying, and cleaning, alongside our vacuum generators. If your facility has a process that could benefit from an Intelligent Compressed Air solution, please reach out to us. We would be pleased to discuss your specific application and develop a solution that not only lowers your compressed air expenses but also enhances worker safety.

Jason Kirby
Application Engineer
Email: jasonkirby@exair.com
Twitter: @EXAIR_jk

Amplification Ratio: Super Air Knives

Published on by John BallLeave a comment
Super Air Knife

Earlier, I wrote a blog about how entrainment works with EXAIR products by using two phenomena, Coanda Profile and the Venturi Effect.  You can find it here, “Entrainment: how it works and why EXAIR products use it.”  In this blog, I will cover the Super Air Knife specifically and how it uses the Venturi Effect to entrain the surrounding air. 

This Venturi Effect is named after Giovanni Venturi, who discovered that by increasing the velocity through an orifice, the surrounding fluid will move with it, generating a lower pressure.  The higher the velocity, the lower the pressure.  When you have a low pressure, the surrounding air will fill that void and move into the airstream.  The amount of ambient air that gets “pulled” into the airstream is the entrainment, and this amount as compared to the inlet flow is the Amplification Ratio. 

So, what does this mean?  The definition of a ratio is the relationship between two amounts showing the number of times one value is contained within the other.  For the Super Air Knife, it is a value that shows the amount of ambient air that is drawn in along with the primary, compressed air flow.  With an amplification ratio of 40:1, that means that there are 40 parts of ambient air for every 1 part of compressed air, which helps make them the most efficient compressed air operated Air Knives available on the market.  By adding mass, the Super Air Knife will give a hard-hitting force to do more “work”. 

Most people think that compressed air is free, but it is most certainly not.  Because of the amount of electricity required to produce compressed air, it is considered to be a fourth utility for manufacturing plants.  To save on utility costs, it is important to use compressed air as efficiently as possible.  So, the higher the amplification ratio, the more efficient the compressed air product.  Manufacturing plants that use open fittings, copper tubes, and drilled pipes for blowing are not efficient.  These types of products generally have a very low amplification ratio, somewhere between 2:1 to 5:1.  When EXAIR began manufacturing in 1983, we knew that there was a better way of saving compressed air by increasing the amplification ratios of our various air moving products.

I like to explain things in everyday terms.  For this analogy, we can use the amplification ratio as represented by gas mileage.  Like your car, you want to get the most distance from a gallon of gas.  With your compressed air system, you want to get the most utilization for the compressed air being expended.  With an EXAIR Super Air Knife, it has a 40:1 amplification ratio; or, in other words, you can get 40 MPG.  But, if you use drilled pipes, copper tubes, etc. for blowing, then you are only getting 2 to 5 MPG, so to say.  If you want to get the most “mileage” for the money you spend on creating compressed air, you want to check the “fuel efficiency” of your blow-off components.

EXAIR manufactures many blow-off items with high amplification ratios to save compressed air. EXAIR can help “tune up” your blow-off systems to make them efficient and safe by contacting an Application Engineer.  We will be happy to help you.  

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

Entrainment: How it Works and Why EXAIR Products are Engineered to Use it.

Published on by John BallLeave a comment
EXAIR Super Air Nozzle entrainment

Because of the large amount of energy required to run an air compressor, the pneumatic system is considered the fourth utility in a manufacturing plant.  And saving this commodity and using it as efficiently as you can, should be a priority.  EXAIR has many products that can save energy by using less compressed air.  And the story behind this is entrainment explained by Bernoulli’s equation. 

Bernoulli’s principle explains how a high velocity fluid can generate a low pressure.  (You can read more about Bernoulli’s principle HERE.)  Let’s start by looking at Equation 1.

Equation 1:

P + d * V2/2 = C 

P – pressure

d – density of the fluid

V – velocity

C – a constant

As you can see from Equation 1, when the velocity goes up, the pressure must go down.  When we have a lower pressure, then the surrounding fluid will fill that void.  Since air is a fluid, we can use high velocity to entrain the surrounding ambient air.  The free air will add to the compressed air to give the airstream mass for a hard-hitting force.  This ratio of ambient air to compressed air is called entrainment.  The higher the entrainment, the more efficient the product.  Bernoulli’s Principle can be applied in two ways; as a Coanda and as a Venturi.  EXAIR uses both methods in our products for creating low-pressure effects. 

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 optimize entrainment of air (4) from the surrounding environment.

The first way is from a Coanda profile.  Coanda, named after Henri Coanda, noticed that a fluid would “hug” a curved surface.  (You can read more about Henri Coanda HERE.)  The high velocity air going around the curved surface will generate a low pressure above it.  You can imagine an airplane wing generating that low pressure to fly.  We use this with our FullFlow and Standard Air Knives, our Air Wipes, and our Air Amplifiers.  With a Coanda profile, we can get an amplification ratio up to 30:1, which means that for every 1 part of compressed air, 30 parts of ambient air is entrained.  We are able to create an efficient blow-off device by using the Coada profile. 

To generate even lower pressure, this can be done by a Venturi.  This phenomenon is named after Giovanni Venturi, who discovered that by increasing the velocity through an orifice, the surrounding fluid will move with it, generating a lower pressure.  (You can read more about Giovanni Venturi HERE.)  Remember the higher the velocity, the lower the pressure from Equation 1 above.  We use the Venturi effect on our Super Air Knives, E-Vacs, Line Vacs, and Super Air Nozzles.  As compared to our FullFlow and Standard Air Knives, the Super Air Knives can generate an amplification ratio of 40:1.  As an engineered product, we were able to increase efficiency even further. 

EXAIR has been manufacturing Intelligent Compressed Air® products since 1983.  We can provide solutions that are efficient, effective, and safe for blow-off systems.  In comparison, the other blow-off devices are like incandescent light bulbs, while EXAIR products are like LED light bulbs.  Entrainment of free ambient air can save you a lot of money when using your compressed air system.  If you would like to discuss solutions to use less compressed air and improve your bottom dollar, an Application Engineer at EXAIR is available to help.   

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

What’s So Great About Air Entrainment?

Published on by Russ BowmanLeave a comment

Air entrainment is the phenomenon that occurs when air (or any gas) under pressure is released from a device in such a way that a low pressure is generated in the immediate area of the air (or gas) discharge.  Air (or gas) from the surrounding environment is then pulled (or entrained) into the discharged air stream, increasing its volumetric flow rate.  EXAIR Corporation has been engineering & manufacturing compressed air products to take maximum advantage of this phenomena since 1983…and we’ve gotten better & better at it over the past 36 years.

Obviously, the first thing that’s so great about air entrainment is…free air flow.  Every cubic foot that’s entrained means that’s a cubic foot that your compressor didn’t have to spend energy compressing.  Considering the EXAIR Super Air Knife’s entrainment ratio of 40:1, that makes for a VERY efficient use of your compressed air.

Another thing that’s so great about air entrainment is…it’s quiet.  As you can see from the graphic at the top of this blog, the Super Air Knife entrains air (the lighter, curved blue arrows) into the primary compressed air stream (the darker, straight blue arrows) from above and below.  The outer layers of the total developed flow are lower in velocity, and serve as a sound-attenuating boundary layer.  The sound level of a Super Air Knife (any length…here’s why) is only 69dBA.  That means if you’re talking with someone and a Super Air Knife is running right next to you, you can still use your “inside voice” and continue your conversation, unaffected by the sound of the air flow.

I always thought it would be helpful to have more than just a graphic with blue arrows to show the effect & magnitude of air entrainment.  A while back, I accidentally stumbled across a stunning visual depiction of just that, using a Super Air Knife.  I had the pleasure of talking with a caller about how effective a Super Air Knife might be in blowing light gauge paperboard pieces.  So I set one up in the EXAIR Demo Room, blowing straight upwards, and tossed paper plates into the air flow.  It worked just as expected, until one of the paper plates got a little closer to the Super Air Knife than I had planned:

As you can see, the tremendous amount of air flow being entrained…from both sides…was sufficient to pull in lightweight objects and ‘stick’ them to the surface that the entrained air was being drawn past.  While it doesn’t empirically prove the 40:1 ratio, it indisputably demonstrates that an awful lot of air is moving there.

If you’re looking for a quiet, efficient, and OSHA compliant solution for cleaning, blow off, drying, cooling…anything you need an even, consistent curtain of air flow for – look no further than the EXAIR Super Air Knife.  If you’d like to discuss a particular application and/or product selection, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
Visit us on the Web
Follow me on Twitter
Like us on Facebook