What Makes EXAIR’s Super Air Knife so Efficient

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

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

Coandă Profiles

Here at EXAIR, Coandă is a household name that can be heard on any given day multiple times throughout the day. The Coandă effect is fairly easy to visualize with a ligthweight ball and some high velocity airflow. Take the video below for example. This 2″ Super Air Amplifier on a stand powered at 40 psig at the inlet easily lifts this hollow plastic ball and then suspends the ball due to the Coandă effect.

If you were able to see the airflow, you would see it impacting the surface of the sphere at all different points then following the profile of the sphere until it colides with itself and is forced to separate off the surface. The turbulent flow on the top is creating a downward pressure as well. The science behind this was all found and showcased by Henri Coandă. He showcased this with a propulsion device which used a domed hood with airflow to follow the curvature of the dome then exit off the sharp edge or where the separate air streams began to recombine causing a turbulent / low pressure area depending on the angle.

This stream of air following a surface begins to pull in all surrounding and impacted air molecules from around the stream which is called entrainment. This is a key factor for EXAIR products and one reason the Coandă profiles are a key characteristic to obtaining the peak performance and efficiency out of a compressed air product.

As the high velocity air stream exits the EXAIR model 1100 Super Air Nozzle the ambient air is entrained around the fins and angled surfaces of the nozzle.

Many EXAIR products utilize the Coandă principle to improve their efficiencies and performance. Below you can see the EXAIR product families containing Coandă profiles within their design which increases the ambient air entrainment resulting in an amplified air blowoff.

Super Air Wipes, Super Air Knives, Super Air Nozzles and Super Air Amplifiers use the Coanda principle to become some of the most efficient compressed air blowoff products available.

If you would like to discuss how the Coandă profile and EXAIR Intelligent Compressed Air Products® can help your process, please give us a call.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

People of Interest: Daniel Bernoulli (2/8/1700-3/17/1782)

Daniel BernoulliDaniel Bernoulli was born in the Netherlands in February of 1700. Mathematics was in his bloodline as the son of renowned Swiss mathematician, Johann Bernoulli. He and Johann’s brother, Jakob, both took jobs as professors at a university in Basel, Switzerland. Fittingly, Johann taught Daniel mathematics at a very young age. Daniel Bernoulli spent some time studying a variety of topics including philosophy, logic, and medicine. Daniel obtained his Bachelor’s Degree at the age of just 15, earning his Master’s Degree just one year later.

Daniel was well-known and was highly regarded among scholars throughout Europe. After spending some time teaching Botany, he switched to physiology topics in 1743. This continued for several years when in 1750 he was appointed to the chair of physics where he taught at Basel for 26 years. During this time, he also received a total of 10 grand prizes from the Paris Academy of Sciences for work he completed in astronomy, a variety of nautical topics, and magnetism.

Daniel is most commonly known for his work in developing what is now called Bernoulli’s Principle, which discusses the relationship between fluid speed and pressure. An increase in the speed of a fluid will occur simultaneously with a decrease in the fluid’s pressure or potential energy.

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.

The air entrainment properties of some of EXAIR’s Intelligent Compressed Air Products can be explained through Bernoulli’s Principle. As high-velocity air exits the nozzle of a Super Air Knife, for example, a low-pressure area is created that speeds up and draws in ambient air at an astonishing rate of 40:1. The same also occurs with the Super Air AmplifiersAdjustable Air Amplifiers, and Air Nozzles. To find out how you can utilize this advantage to save compressed air in your processes, give us a call. An Application Engineer will be happy to help assist you in determining the most suitable products for your application.

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