Tag: air entrainment

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 EXAIR Air Jets?

Published on by Russ BowmanLeave a comment

For over 40 years now, EXAIR has been making engineered Air Nozzles and Air Jets for a wide range of industrial and commercial applications. Basically, if you need to blow air onto, into, towards, or through something, we’ve got something for that.

Our Super Air Nozzles seem to “get all the press” (based on an unscientific survey of the EXAIR Blog), and maybe they should, with their ease of installation onto the end of a pipe or tube that someone who’s never thought about the cost of compressed air has been using as a cheap to make but expensive to operate blowoff.

Compression fittings and Model 1100 Super Air Nozzles transformed the part ejection from “loud and wasteful” to “quiet and efficient.”

Like our engineered Super Air Nozzles, our Air Jet products use the Coanda effect to entrain enormous amounts of free air from the surrounding environment. While the Super Air Nozzles do this via an array of small holes recessed between a series of fins, the Air Jet uses an internal annular ring nozzle to draw the free air through its throat. There are a number of applications where either a Super Air Nozzle or an Air Jet can be used efficiently, safely, and quietly. Some jobs, however, benefit from the specific design of one or the other. Since this is an Air Jets blog, I’m going to focus on them:

  • Powerful, directed air stream. This makes EXAIR Air Jets ideal for part ejection, chip removal, and part drying.
Model 6013 Brass High Velocity Air Jet (left) blows rinse water off beverage cans on a high speed conveyor. An array of Model 6013SS SS High Velocity Air Jets (right) dries a finned component after washing.
  • Reliable and efficient blowoff. With no moving parts, as long as you supply them with clean compressed air, they’ll operate darn near indefinitely, maintenance free. And they’ll use a LOT less of that compressed air than similarly sized open-ended blowoff devices too, thanks to engineering:
Compressed air enters through the 1/8 MNPT fitting and discharges into the throat via an annular ring gap, where the Coanda profile of the plug directs the air towards the jet outlet (1). This primary, high velocity flow pulls in air from the entrainment plenum (2), creating a total developed flow up to 25 times the compressed air flow (3).
  • Safe to use. EXAIR Air Jets, like the rest of our Intelligent Compressed Air Products, are compliant with OSHA Standard 1910.242(b) which limits the downstream pressure at the nozzle or opening of a compressed air device used for cleaning purposes to 30psi. If you cover the entire outlet opening, the air simply flows out the entrainment plenum.
  • Remote positioning. Since both the inlet and outlet can be ducted, you can fit a 1″ ID hose over the entrainment plenum and run the other end to the location where you want to draw airflow from. This is beneficial if, for example, you want to position the Air Jet in a contaminated area, but want to eliminate any of that contamination from the Air Jet’s developed airflow. You can also fit a 1/2″ ID hose over the outlet to direct the airflow elsewhere.
  • Adjustability. For the Adjustable Air Jet, it’s right there in the name: the Plug can be threaded into, or out of, the body to reduce, or increase the annular ring nozzle’s gap, and hence, the airflow and force applied. There’s a micrometer gap indicator so you can set – and reset – the performance to different levels, as required. The High Velocity Air Jet’s annular ring nozzle gap is fixed with a shim (they come with a 0.015″ thick shim installed) but Shim Sets, containing one each of a 0.006″ and 0.009″ thick shim, can be used to make gross adjustments to the airflow and force applied. You can regulate the air supply pressure to either the Adjustable or High Velocity Air Jets to very precisely “dial in” the performance.
A 0.006″ or 0.009″ thick shim from the 6313 Air Jet Shim Set (top left) can be installed in a High Velocity Air Jet (bottom left) to put the Air Jet in a whole new performance band. You can do this to an Adjustable Air Jet (right) by turning the knurled ring on the plug to set (and reset) the air gap and hence the performance.
  • Materials of construction. Both the Adjustable and High Velocity Air Jets come in brass for general purpose applications, or 303SS for use in areas with high heat or corrosive elements in the environment.
The brass Air Jets (top) are rated for installation in areas with ambient temperatures up to 275°F, while the 303SS models (bottom) are good to 400°F.

If you’d like to find out more about EXAIR Air Jets, or how any of our Intelligent Compressed Air Products can help you get the most out of your compressed air system, give me a call.

Russ Bowman, CCASS

Application Engineer
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What Makes EXAIR’s Super Air Knife so Efficient

Published on by codybiehleLeave a comment

EXAIR Super Air Knives have been designed to improve upon performance characteristics of our original Standard Air Knife design, which was already a very good performer itself. The Super Air Knife design improves air consumption and noise exposure levels. Since they use less air, they cost less to operate. Because they operate quieter, they can contribute to a quieter environment and increase safety for your personnel. 

Compressed air is such a common utility in manufacturing environments (and more) that many of us take it for granted and may not be the best stewards of its use.  EXAIR Super Air Knives are the most efficient compressed air knife on the market today and help us all to use our compressed air more wisely.

If you have homemade air knives, pipe with drilled holes or manifolds with multiple nozzles, you are in a position to play the hero and save your company compressed air and money. 

Implementing a design which uses the free air surrounding us all, is a significant feature making the Super Air Knife efficient. This is done by utilizing entrainment to move the surrounding ambient air and amplify the blast of compressed air.

Diagram showing how the Super Air Knife works

Air Entrainment is the phenomenon that occurs when air/gas under pressure is released from a device in such a way that a low pressure is generated in the immediate area of the gas discharge.  Gas from the surrounding environment is then pulled into the discharged air stream, increasing its volumetric flow rate. Using this principle, a Super Air Knife increases the air flow without increasing the amount of compressed air used.

This phenomenon is prevalent in many of EXAIR’s products but shines the brightest with EXAIR’s Super Air Knife. The Super Air Knife Sports the highest entrainment ratio out of all of the products with a whopping 40:1 ratio, this makes for a very efficient use of compressed air. With an air consumption of only 2.9 SCFM per inch of air curtain at 80 psig then the air knife would be moving 116 SCFM per inch of air curtain. That’s a lot of air!

Also the fact that entraining ambient air is just moving the ambient air with the energy within compressed air makes process is extremely quiet. This is because 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 at any length is only 69dBA.  That’s about as loud as someone talking at normal speech 3’ away from you.

Entrainment demonstration using a Super Air Knife

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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People of Interest: Daniel Bernoulli

Published on by John BallLeave a comment

Daniel Bernoulli

Whenever there is a discussion about fluid dynamics, Bernoulli’s equation generally comes up. This equation is unique as it relates flow energy with kinetic energy and potential energy. The formula was mainly linked to non-compressible fluids, but under certain conditions, it can be significant for gas flows as well. My colleague, Tyler Daniel, wrote a blog about the life of Daniel Bernoulli (you can read it HERE). I would like to discuss how he developed the Bernoulli’s equation and how EXAIR uses it to maximize efficiency within your compressed air system.

In 1723, at the age of 23, Daniel moved to Venice, Italy to learn medicine. But, in his heart, he was devoted to mathematics. He started to do some experiments with fluid mechanics where he would measure water flow out of a tank. In his trials, he noticed that when the height of the water in the tank was higher, the water would flow out faster. This relationship between pressure as compared to flow and velocity came to be known as Bernoulli’s principle. “In fluid dynamics, Bernoulli’s principle states that an increase in the speed of fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluids potential energy”1. Thus, the beginning of Bernoulli’s equation.

Bernoulli realized that the sum of kinetic energy, potential energy, and flow energy is a constant during steady flow. He wrote the equation like this:

Equation 1:

Bernoulli’s Equation

Not to get too technical, but you can see the relationship between the velocity squared and the pressure from the equation above. Being that this relationship is a constant along the streamline; when the velocity increases; the pressure has to come down. An example of this is an airplane wing. When the air velocity increases over the top of the wing, the pressure becomes less. Thus, lift is created and the airplane flies.

With equations, there may be limitations. For Bernoulli’s equation, we have to keep in mind that it was initially developed for liquids. And in fluid dynamics, gas like air is also considered to be a fluid. So, if compressed air is within these guidelines, we can relate to the Bernoulli’s principle.

  1. Steady Flow: Since the values are measured along a streamline, we have to make sure that the flow is steady. Reynold’s number is a value to decide laminar and turbulent flow. Laminar flows give smooth velocity lines to make measurements.
  2. Negligible viscous effects: As fluid moves through tubes and pipes, the walls will have friction or a resistance to flow. The surface finish has to be smooth enough; so that, the viscous effects is very small.
  3. No Shafts or blades: Things like fan blades, pumps, and turbines will add energy to the fluid. This will cause turbulent flows and disruptions along the velocity streamline. In order to measure energy points for Bernoulli’s equation, it has to be distant from the machine.
  4. Compressible Flows: With non-compressible fluids, the density is constant. With compressed air, the density changes with pressure and temperature. But, as long as the velocity is below Mach 0.3, the density difference is relatively low and can be used.
  5. Heat Transfer: The ideal gas law shows that temperature will affect the gas density. Since the temperature is measured in absolute conditions, a significant temperature change in heat or cold will be needed to affect the density.
  6. Flow along a streamline: Things like rotational flows or vortices as seen inside Vortex Tubes create an issue in finding an area of measurement within a particle stream of fluid.

Super Air Knife has 40:1 Amplification Ratio

Since we know the criteria to apply Bernoulli’s equation with compressed air, let’s look at an EXAIR Super Air Knife. Blowing compressed air to cool, clean, and dry, EXAIR can do it very efficiently as we use the Bernoulli’s principle to entrain the surrounding air. Following the guidelines above, the Super Air Knife has laminar flow, no viscous effects, no blades or shafts, velocities below Mach 0.3, and linear flow streams. Remember from the equation above, as the velocity increases, the pressure has to decrease. Since high-velocity air exits the opening of a Super Air Knife, a low-pressure area will be created at the exit. We engineer the Super Air Knife to maximize this phenomenon to give an amplification ratio of 40:1. So, for every 1 part of compressed air, the Super Air Knife will bring into the air streamline 40 parts of ambient “free” air. This makes the Super Air Knife one of the most efficient blowing devices on the market. What does that mean for you? It will save you much money by using less compressed air in your pneumatic application.

We use this same principle for other products like the Air Amplifiers, Air Nozzles, and Gen4 Static Eliminators. Daniel Bernoulli was able to find a relationship between velocities and pressures, and EXAIR was able to utilize this to create efficient, safe, and effective compressed air products. To find out how you can use this advantage to save compressed air in your processes, you can contact an Application Engineer at EXAIR. We will be happy to help you.

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

  1. Wikipedia https://en.wikipedia.org/wiki/Bernoulli%27s_principle