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
Twitter: @EXAIR_jb

Choosing the Right Vortex Tube – Max Refrigeration vs. Max Cold Temperature

The Vortex Tube is a low cost, reliable, maintenance free way to provide cooling to a wide variety of industrial spot cooling problems.


There are two (2) popular uses for the Vortex Tubes.  One is to spot cool a warm item as fast as possible.  The other is to chill an item to as low a temperature as possible. Because these are very different requirements, different Vortex Tube configurations exist to handle each.

For those applications of spot cooling, we recommend the 3200 series of Vortex Tubes. They are designed to be most efficient at providing maximum refrigeration, which is a function of high cold air flow rate and moderate temperature differential of the cold air to the warm item.

And for those applications of chilling an item to a very low temperature at low flow rate , we recommend the 3400 series of Vortex Tubes.  They are designed to be most efficient at providing maximum cold air temperatures, but with a lower cold air flow rate.

An important parameter for the Vortex Tubes is the Cold Fraction.  By adjusting the hot valve on a vortex tube, the amount of air that is discharged through the cold end changes. When expressed as a percentage of the total compressed air that is supplied to the vortex tube, we get the Cold Fraction.  For example, if the hot valve is adjusted so that for every 10 parts of compressed air supplied, we get 7 parts of cold air, then we have a 70% Cold Fraction. When you know the Cold fraction setting and the compressed air supply pressure, you can use the Vortex Tube Performance tables and get the cold air discharge temperature.

Using the table below left, at 100 PSIG compressed air pressure and a 70% Cold Fraction, we can expect the cold air discharge temperature drop to be 71°F.  With 70 ° compressed air temperature, the cold air will be at -1°F.

Vortex Tube Charts
Vortex Tube Performance Tables

The 3200 series of Vortex Tubes are for use in the 50-80% Cold Fraction range, and the model 3400 series is designed for use in the 20-50% Cold Fraction ranges, to maximize the performance of each.

In summary, the selection of the Vortex Tube that best meets the application needs is based on the desired cold air flow rate, and the temperature of air desired. Once these are known, using the tables can provide the information needed to select the best option.

For those applications where we are unsure what will work best, we offer the EXAIR Cooling Kits, that include a Vortex Tube (small, medium, or large) and an array of Generators, to allow the configuration of the full range of Vortex Tubes within each size family.

  • Model 3908 – Small Vortex Tube Cooling Kit – build models 3202, 3204, 3208, and 3402, 3404, 3408
  • Model 3930 – Medium Vortex Tube Cooling Kit – build models 3210, 3215, 3225, 3230, 3240, and 3410, 3415, 3425, 3430, 3440
  • Model 3998 – Large Vortex Tube Cooling Kit – build models 3250, 3275, 3298, 3299, and models 3450, 3475, 3498, 3499


If you have questions about Vortex Tubes or any of the 16 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
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The Theory of the Vortex Tube

There are many theories regarding the dynamics of a vortex tube and how it works. Many a graduate student has studied them as part of their research requirements.


The Vortex Tube was invented by accident in 1928, by George Ranque, a French physics student. He was performing experiments on on a vortex-type pump that he had developed and noticed that warm air exhausted from one end and cold air from the other! Ranque quickly stopped work on the pump, and started a company to take advantage of the commercial possibilities for this odd little device that produced both hot and cold air, using only compressed air, with no moving parts. The company was not successful, and the vortex tube was forgotten until 1945 when Rudolph Hilsch, a German physicist, published a widely read paper on the device.

A vortex tube uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of the two air streams is adjustable with a valve built into the hot air exhaust.  Temperatures as low as -50°F (-46°C) and as high as 260°F (127°C) are possible.

Here is one widely accepted explanation of the physics and the phenomenon of the vortex tube.VT

Compressed air is supplied to vortex tube and passes through nozzles that are tangent to to an internal counterbore (1). As the air passes through it is set into a spiraling vortex motion (2) at up to 1,000,000 rpm. The spinning stream of air flows down the hot tube in the form of a spinning shell, like a tornado (in red). The control valve (4) at the end allows some of the warmed air to escape (6) and what does not escape reverses direction and heads back down the tube as a second vortex (in blue) inside of the low pressure area of the larger warm air vortex. The inner vortex loses heat and exits the through the other end of as cold air (5).

It is thought that that both the hot and cold air streams rotate in the same direction at the same angular velocity, even though they are travelling in opposite directions. A particle of air in the inner stream completes one rotation in the same amount of time that an air particle in the outer stream. The principle of conservation of angular momentum would say that the rotational speed of the inner inner vortex should increase because the angular momentum of a rotating particle (L) is equal to the radius of rotation (r) times its mass (m) times its velocity (v).  L = r•m•v.  When an air particle moves from the outer stream to the inner stream, both its radius (r) and velocity (v) decrease, resulting in a lower angular momentum. To maintain an energy balance for the system, the energy that is lost from the inner stream is taken in by the outer stream as heat. Therefore, the outer vortex becomes warm and the inner vortex is cooled.

At EXAIR, we have harnessed the cooling power of the vortex tube, and it can be found and utilized in such products as Spot Coolers, Cabinet Coolers, and the Vortex Tube themselves.

Harnessing the cooling power of the vortex tube 

If you have questions about Vortex Tubes, or would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
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Cool Small Parts and Tools, with Clean, Cold Air

Do you need a proven way to reduce downtime and increase productivity on a variety of operations involving small parts where heat is a problem?  EXAIR‘s Mini Cooler produces a stream of 20°F (-7°C) cold air to prevent heat build up and blow away chips and debris.

Especially effective on high speed operations, the Mini Cooler helps to prevent burning, melting, and heat related breakage, and while doing so, at a quiet 76 dBA sound level. Better yet, all done with no moving parts to wear out.

Mini Cooler Cooling a Small Mill Operation

Some popular applications for the Mini Cooler are – small tool cooling, needle cooling, blade cooling, and lens grinding.

There are several advantages to take note of – low cost, increased production rates, better tolerances, and quiet and compact.


The Mini Cooler Systems are available with One or Two Cold Outlets, and also include a 1″ wide Flare Nozzle Tip, and a Manual Drain Air Filter to clean the air, ensuring long, trouble free operation.

Using just 8 SCFM of 100 PSIG compressed air, the Mini Cooler will not tax your compressed air system.  Its small size allows it to fit in areas where larger systems could not fit.  The powerful magnetic base sticks to any ferrous surface and and provides up to 100 pounds of pull force.

If you have any questions about the Mini Cooler, the Adjustable Spot Cooler, Cold Gun or any EXAIR compressed air product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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