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.
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.
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 Visit us on the Web Follow me on Twitter Like us on Facebook
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.
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.
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.
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.
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.
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.
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
