Entrainment: What is it?

By definition, entrainment is a form of the verb, entrain, which is fluid that is swept along into an existing moving flow.   Whenever there is a discussion about fluid dynamics, the 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 incompressible fluids, but under certain conditions, it can be significant for gas flows as well.  I would like to discuss how EXAIR uses the Bernoulli’s equation for entrainment to maximize efficiency within your compressed air system.

This relationship between pressure as compared to flow and velocity came to be known as the 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. Bernoulli realized that the sum of kinetic energy, flow energy, and potential energy is a constant during steady flow.  He wrote the equation like this:

Equation 1:

P/r + V2/2 + gz = constant

P – Pressure

r – density

V – velocity

g – gravitational constant

z – height difference

 

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.

Since we know the criteria to apply the Bernoulli’s equation with compressed air, let’s look at some EXAIR products.  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.  Remember from the equation above, as the velocity increases, the pressure has to decrease.  When the pressure decreases, the surrounding air will move toward the low pressure.  That low pressure will sweep the ambient air into the air stream; called entrainment.

Compressed air is expensive, but the ambient air is free.  The more ambient air we can entrain, the more efficient the blowing device is.  As an example, 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.  By adding mass to the flow stream, it will reduce the compressed air usage, saving you money, and allow for better cooling and a stronger blowing force.  For a drilled pipe, the amplification ratio is generally only two to three times.

We use this principle for many of our products like the Air Amplifiers, Safety Air Guns, Air Nozzles, Air Knives, and Gen4 Static Eliminators. Daniel Bernoulli was able to find a relationship between velocities and pressures, and EXAIR was able to use 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

Cooling Parts? Super Air Amplifiers May Be For You

Super Air Amplifier Family

When working with a cooling application, many customers will immediately look to the Vortex Tube and Spot Cooling product lines. While this may be the best solution for some applications, cold air is not always the best method that we have available for cooling. EXAIR’s Super Air Amplifiers are very effective at reducing the temperature of a part without requiring cold air, when the temperature differential between the Super Air Amplifier’s airflow and the temperature of the part is significant. Due to their ability to entrain large amounts of ambient air, we can move a lot of volume of air across the surface of the part and quickly lower the temperature.

I like to compare this to blowing on a hot cup of coffee just as it’s been brewed. The temperature of the air coming from your mouth is around 98.6°F, the same as your body temperature. Coffee can be as hot as 185°F when fresh. Due to the temperature differential between your breath and the hot coffee, we’re able to achieve a reasonable amount of cooling just by simply blowing across the surface. Typically, when the target temperature of the hot part or material needs to be around ambient temperature or higher, a Super Air Amplifier can be a good choice. 

While many applications utilize the outlet flow of the Super Air Amplifier to blow off, clean or cool a part or material, the ability of the Super Air Amplifier to entrain large amounts of ambient air can also be utilized to convey light materials or to draw in dust, smoke, or fumes from the surrounding environment. As the plugs on the exhaust side of the Super Air Amplifiers come in sizes of ¾”, 1-1/4”, 2”, 4”, and 8” the exhaust flow can be ducted with standard size hose.

EXAIR’s Super Air Amplifiers utilize a patented shim design to maintain critical positioning of component parts. This allows a precise amount of compressed air to be released at exact intervals toward the center of the Super Air Amplifier. This creates a constant, high velocity outlet flow across the entire cross-sectional area. Free, ambient air is entrained through the unit, resulting in high amplification ratios. The balanced outlet airflow minimizes wind shear to produce sound levels far lower than other similar air movers.

Patented Super Air Amplifier Shims

Super Air Amplifiers are supplied with a .003” thick shim that is ideal for most applications. Flow and force can be increased by replacing the shim with a thicker .006” or .009” shim. The flow of air is also controlled by adjusting the input pressure supplied to the amplifier. Higher pressures increase both the force and flow, while lower pressures decrease both force and flow. All Super Air Amplifiers are available in kits that come with a shim set as well as a suitably sized pressure regulator and auto-drain filter.

EXAIR has a solution for you if you need to move A LOT of air. Reach out to an Application Engineer today if you have an application that you believe could be served with a low-cost, simple solution!

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

Proper Filtration Eliminates the Need for Maintenance of Super Air Amplifier in Brewing Application

EXAIR’s Super Air Amplifiers utilize a patented shim design to maintain critical positioning of component parts. This allows a precise amount of compressed air to be released at exact intervals toward the center of the Super Air Amplifier. This creates a constant, high velocity outlet flow across the entire cross-sectional area. Free, ambient air is entrained through the unit, resulting in high amplification ratios. The balanced outlet airflow minimizes wind shear to produce sound levels far lower than other similar air movers.

As with any EXAIR Product, we always recommend the installation of a particulate filter. If there is any oil present in your air supply, an oil filter is also recommended after the particulate filter. Nearly all of our products have no moving parts to wear out and will never require maintenance so long as they’re supplied with clean, condensate free, oil-free air. If the air is not filtered prior, anything contained within the air is going to be passed through into your process. Debris could  also eventually clog up the tight orifices in the product itself. Eventually the debris/oil will end up clogging it up and stop performing as it should. This leads to downtime while the root cause of the issue is sorted out, and subsequent maintenance of the product that has been clogged.

I recently worked with a brewing company that had a machine with one of our ¾” Model 120020 Super Air Amplifiers installed. It was used on a canning line and would dry off the cans after a washing operation before being marked with a date code. Up until recently it had worked just fine without any issues. Now they were noticing residual moisture leftover on the cans that was preventing a legible date code from being marked on the outside. Further investigation led them to determine that the outlet flow from the amplifier had been reduced to almost nothing. Since their compressor delivers oil-free air and they used stainless steel piping, they didn’t think it was necessary to install a filter.

The Super Air Amplifier is a maintenance-free product, when supplied with clean, condensate free air of course. After removing the plug from the body, they noticed a significant amount of oil present inside the plenum chamber and around the shim. This was clogging up the nozzle and restricting airflow through the unit. The photo below shows the inside of the amplifier prior to cleaning. The fine-toothed shim at the bottom is hardly even noticeable. In looking upstream, they noticed an oiler that was necessary for many of the other pneumatic components of the machine. This same air supply was being used to supply the compressed air to our Super Air Amplifier.

At our instruction, they installed an oil-filter on a new line dedicated just to this amplifier. And after cleaning the Super Air Amplifier the problem drying off the cans immediately stopped and they were back up in running in no time. Now that they had removed the oil from their air supply, this issue won’t return and they can begin operating the way we intend it to, maintenance free!

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

Rotational molding: EXAIR Super Air Amplifiers compared to fans

Super Air Amplifier Family

A customer contacted EXAIR to find a better way to cool a die in a rotational molding facility.  Rotational molding, or Rotomolding, involves a heated hollow mold which is filled with plastic material. It is then slowly rotated (usually around two perpendicular axes), causing the softened material to disperse and cling to the walls of the mold. In order to maintain an even thickness throughout the part, the mold has to continue to rotate during the heating phase. After the desired timing sequence, the heating is turned off to allow the material to harden. 

This particular company was making plastic containers.  To try and improve the cycle rate between each container, they were using two fans (reference photo below) for cooling.  Time is money in this industry, and they wanted to target the fans to improve cooling.  They mentioned that water jackets for cooling would affect the life of the molds due to thermal shock.  So, they needed to cool with air; and EXAIR had a solution for them; the Super Air Amplifiers.

The Super Air Amplifiers as compared to fans are compact, easy to use, and very effective in cooling.  The capacity to cool is determined by the mass of air and the temperature difference. Since the mold is heated to 650oF (343oC) and the ambient air is 80oF (27oC), we have a good temperature difference for cooling.  For this application, I recommended to replace their fans with our model 120024 4” Super Air Amplifiers.  Each one can move 2,190 SCFM (6,1977 SLPM) of air while only needing 29.2 SCFM (826 SLPM) of compressed air at 80 PSIG (5.5 Bar). 

I also recommended to add one piece of a model 120022 2” Super Air Amplifier for cooling the inside of the mold.  Because the opening in the center of the mold is relatively small, a fan would take up most of the area.  Thus, not allowing the hot air to escape.  Since the 2” Super Air Amplifier is much smaller, they were able to place the air stream in the center allowing the hot air to escape around the edge of the hole.  With this combination, we were able to cool the mold 25% faster than the fans.  EXAIR did a comparison video between a Super Air Amplifier and a fan for cooling.  Watch it here.  

To expand on the comparison, EXAIR Super Air Amplifiers and electrical fans are designed to move air.  Fans use motors and blades to push the air toward the target.  There are mainly two types, centrifugal fans and axial fans.  The customer above was using axial fans.  The air enters from directly behind the fan, and the blades “slap” the air forward to the target. This creates a turbulent and loud air noise.  The EXAIR Super Air Amplifiers does not use any blades or motors to push the air.  They use a Coanda profile with a patented shim to create a low pressure to draw the air.   (You can read more about it here: Intelligent Compressed Air: Utilization of the Coanda Effect.)  So, they create laminar air flow which is much quieter. 

Super Air Amplifier – flow region

In physics, it is easier to pull than it is to push.  The same goes for moving air.  Fans are designed to “push” the air and the Super Air Amplifiers are designed to “pull” the air.  This method of pulling makes it simple to create a laminar flow in a small package which is more efficient, effective, and quiet.  With the patented shims inside the Super Air Amplifiers, they maximize the amplification by “pulling” in large amounts of ambient air while using less compressed air.  More air means better cooling.  If you want to move away from blower systems or axial fan systems to get better cooling, drying, cleaning, and conveying; you can contact an Application Engineer for more details about our Super Air Amplifiers. 

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