Intelligent Compressed Air: How do Vortex Tubes Work

A vortex tube is an interesting device that has been looked upon with great fascination over the last 89 years since its discovery by George Ranque in 1928. What I’d like to do in this article is to give some insight into some of the physics of what is happening on the inside.

With a Vortex Tube, we apply a high pressure, compressed air stream to a plenum chamber that contains a turbine-looking part that we call a generator to regulate flow and spin the air to create two separate streams. One hot and one cold.

Below is an animation of how a Vortex Tube works:

Function of a Vortex Tube


The generator is a critical feature within a vortex tube that not only regulates flow and creates the vortex spinning action, it also aligns the inner vortex to allow its escape from the hot end of the vortex tube. Note the center hole on the photo below. This is where the cooled “inner vortex” passes through the generator to escape on the cold air outlet.

Vortex generator

Once the compressed air has processed through the generator, we have two spinning streams, the outer vortex and the inner vortex as mentioned above.  As the spinning air reaches the end of the hot tube a portion of the air escapes past the control valve; and the remaining air is forced back through the center of the outer vortex.  This is what we call a “forced” vortex.

If we look at the inner vortex, this is where it gets interesting.  As the air turns back into the center, two things occur.  The two vortices are spinning at the same angular velocity and in the same rotational direction.  So, they are locked together.  But we have energy change as the air processes from the outer vortex to the inner vortex.

If we look at a particle that is spinning in the outer vortex and another particle spinning in the inner vortex, they will be rotating at the same speed.  But, because we lost some mass of air through the control valve on the hot end exhaust and the radius is decreased, the inner vortex loses angular momentum.

Angular momentum is expressed in Equation 1 as:

L = I * ω

L – angular momentum
I – inertia
ω – angular velocity

Where the inertia is calculated by Equation 2:

I = m * r2

m – mass
r – radius

So, if we estimate the inner vortex to have a radius that is 1/3 the size of the outer vortex,  the calculated change in inertia will be 1/9 of its original value.  With less mass and  a smaller radius, the Inertia is much smaller.  The energy that is lost for this change in momentum is given off as heat to the outside vortex.

Adjustments in output temperatures for a Vortex Tube are made by changing the cold fraction and the input pressure.  The cold fraction is a term that we use to show the percentage of air that will come out the cold end.  The remaining amount will be exhausted through the hot end. You can call this the “hot fraction”, but since it is usually the smaller of the two flows and is rarely used, we tend to focus on the cold end flow with the “cold fraction”.  The “Cold Fraction”  is determined by the control valve on the hot end of the Vortex Tube. The “Cold Fraction” chart below can be used to predict the difference in temperature drop in the cold air flow as well as the temperature rise in the hot air flow.

Vortex Tube Cold Fraction

By combining the temperature drops expressed above with the various flow rates in which Vortex Tubes are available, we can vary the amount of cooling power produced for an application. The above cold fraction chart was developed through much testing of the above described theory of operation. The cold fraction chart is a very useful tool that allows us to perform calculations to predict vortex tube performance under various conditions of input pressure and cold fraction settings.

The most interesting and useful part about vortex tube theory is that we have been able to harness this physical energy exchange inside a tube that can fit in the palm of your hand and which has a multitude of industrial uses from spot cooling sewing needles to freezing large pipes in marine applications to enable maintenance operations on valves to be performed.

We would love to entertain any questions you might have about vortex tubes, their uses and how EXAIR can help you.

John Ball
Application Engineer

Twitter: @EXAIR_jb

Vortex Tube Cold Fractions – An Explanation

Vortex Tube Family

At EXAIR we’ve been a pioneer in the compressed air market for the past 34 years.  We’ve brought engineered nozzles to the market which reduce compressed air consumption while maintaining performance, laminar flow Air Knives, pneumatic conveyors, atomizing nozzles, air-assisted static eliminators, and a slew of other products.  One of these “other” products is our Vortex Tube, which we manufacture in various sizes while also using as a basis for our Cold Guns, Adjustable Spot Coolers, Mini Coolers, and Cabinet Coolers – all of which are built on the same Vortex Tube technology.

Theory of operation for an EXAIR Vortex Tube

The principle behind a Vortex Tube is rooted in the Ranque-Hilsch effect which takes place inside of the tube.  As a compressed air source is fed into the Vortex Tube, the air flows through a generator and begins to spin down the length of the tube, “hugging” the ID of the tube.  When this spinning air contacts a deliberate obstruction at the end of the tube, it is forced to reverse directions, which requires a change in diameter to the vortex.  The original vortex must decrease in diameter, and in order to do so, it must give off energy.  This energy is shed in the form of heat, and a portion of the incoming air is directed out of the tube with a drastically reduced temperature via what is called the “cold end”.  Another portion of the air escapes through the “hot end” of the tube, resulting in a cold airflow at one end, and a hot airflow at the other end of the tube.

Small, but powerful, Vortex Tubes really are a marvel of engineering.  And, like most useful developments in engineering, Vortex Tube technology begs the question “How can we control and use this phenomena?”  And, “What are the effects of changing the amount of air which escapes via the cold end and the hot end of the tube?”

EXAIR Vortex Tube Performance Chart

These answers are found in the understanding of what is called a cold fraction.  A cold fraction is the percentage of incoming air which will exhaust through the cold end of the Vortex Tube.  If the cold fraction is 80%, we will see 80% of the incoming airflow exhaust via the cold end of the tube.  The remaining airflow (20%) will exhaust via the hot end of the tube.

For example, setting a model 3210 Vortex Tube (which has a compressed air flow of 10 SCFM @ 100 PSIG) to an 80% cold fraction will result in 8 SCFM of air exhausting via the cold end, and 2 SCFM of air exhausting through the hot end of the Vortex Tube.  If we change this cold fraction to 60%, 6 SCFM will exhaust through the cold end and 4 SCFM will exhaust through the hot end.

But what does this mean?

Essentially, this means that we can vary the flow, and temperature, of the air from the cold end of the Vortex Tube.  The chart above shows temperature drop and rise, relative to the incoming compressed air temperature.  As we decrease the cold fraction, we decrease the volume of air which exhausts via the cold end of the Vortex Tube.  But, we also further decrease the outlet temperature.

This translates to an ability to provide extremely low temperature air.  And the lower the temperature, the lower the flow.

Red box shows the temperature drop in degrees F when an EXAIR Vortex Tube is operated at 100 PSIG with an 80% cold fraction.

With this in mind, the best use of a Vortex Tube is with a setup that produces a low outlet temperature with good cold air volume.  Our calculations, testing, and years of experience have found that a cold fraction of ~80% can easily provide the best of both worlds.  Operating at 100 PSIG, we will see a temperature drop of 54°F, with 80% of the incoming air exiting the tube on the cold end (see red circle in chart above).  For a compressed air supply with a temperature of 74°F-84°F (common compressed air temperatures), we will produce an output flow with a temperature between 20°F and 30°F – freezing cold air!

With a high volume and low temperature air available at an 80% cold fraction, most applications are well suited for this type of setup.  When you order a Vortex Tube from EXAIR we will ship it preset to ~80% cold fraction, allowing you to immediately install it right of the box.

The cold air from an EXAIR Vortex Tube is effective to easily spot cool a variety of components from PCB soldering joints to CNC mills, and even complete electrical control panels.  Contact an Application Engineer with application specific questions or to further discuss cold fractions.

Lee Evans
Application Engineer

Vortex Tube Cools Glue On A Paper Folding Machine

I recently worked on a cooling application with an engineering company who designed a paper folding machine for their customer. As the paper enters the machine, it travels over a series of rollers or “plows” that folds the paper into the desired design. At the last step a heated glue is applied to the edge so the paper stays folded. After the paper leaves the folder it is sent to a stack machine to be processed and packaged for shipment. It was at this area they were starting to see some issues arise as the glue was retaining heat, causing it to leak onto the dividers of the stacker or other finished papers.

Example of a paper folding machine

To try and remedy the situation, the customer had installed an air nozzle to blow compressed air across the last fold and while this did work somewhat, they had to operate at really low pressure so they didn’t cause the paper to move while trying to cool the glue. This slowed the process down, which was negatively affecting their production output, so they reached out for assistance on a more reliable solution.

After further discussing the process with the design company, I recommended they use our Model # 3908 Small Vortex Tube Cooling Kit. The Vortex Tube Cooling Kits include the Vortex Tube, cold muffler, tubing, filter separator and all of the generators to change the flow rate and cooling capacity of the Vortex Tube during operation. The temperature drop from the supply air temperature and the volume of air being exhausted can be controlled by adjusting the valve in the hot end to change the cold fraction (the percentage of air being exhausted out of the cold end versus the amount of air being exhausted out of the hot end).

Items included in a Vortex Tube Cooling Kit

By incorporating the Cooling Kit into the process, the customer would be able to experiment with the airflow and temperature to achieve an acceptable balance, providing enough cold air to cure the glue, while not disrupting the process. If you have a similar process you would like to discuss, please contact an application engineer at 800-903-9247 for assistance.

Justin Nicholl
Application Engineer

The Folding Machine 4 image courtesy of Ms. Tharpe via creative commons license

EXAIR Manufactures Custom Vortex Tubes

EXAIR is based in Cincinnati, OH and it is where we design and manufacture our products. Since we are the manufacturer, we can design and build custom product when your application demands particular features. Vortex Tubes are the foundation of our cooling products and can be customized to suit your needs in many ways…

Vortex Family

The EXAIR Vortex Tube uses compressed air to generate a cold air stream at one end and a hot air stream at the other end.  This phenomenon in physics is also known as the Ranque-Hilsch tube.  It can generate very cold or very hot air without any moving parts, motors, or Freon.  Thus; making it low cost, reliable, and maintenance free.  The EXAIR Vortex Tube can generate

  • Air temperatures from -50 to +260 deg. F (-46 to +127 deg. C).
  • Flow rates from 1 to 150 SCFM (28 to 4,248 SLPM)
  • Refrigeration up to 10,200 BTU/hr (2,570 Kcal/hr)

Cooling or Heating with the Vortex Tube

With a wide range of cooling and heating applications, the EXAIR Vortex Tubes can be an ideal product for you.  They are used for cooling electronics, CCTV cameras, and soldered parts.  They are also useful for setting hot melts, gas sampling, and environmental chambers.  With its very compact and versatile design, it can be mounted in tight places to apply heated or cold air to your process.  The Vortex Tubes are used for improving process times in cooling, protecting equipment, or setting specific temperature requirements.  If you need a Vortex Tube to be more specific to your application, EXAIR can manufacture a proprietary product in the following ways:

Preset Vortex Tubes – the standard Vortex Tube has a screw on the hot end to adjust the cold and hot air temperatures.  To make the Vortex Tube tamper-resistant, EXAIR can replace the screw with a preset hot valve.  If you can supply the temperature and flow requirements for your application, EXAIR can determine the correct diameter hole to give you a consistent temperature and flow from the Vortex Tube.

Materials – The standard Vortex Tubes has a maximum temperature rating of 125 deg. F (52 deg. C).  For elevated ambient temperature, we offer a brass generator which will increase the temperature rating to 200 deg. F (93 deg. C).  If other materials are needed for food, pharmaceutical, or chemical exposure, we can also offer stainless steel for the hot plug, cold cap, and generator. I have seen Vortex Tubes made entirely from 316SS and even one made with a brass body. There are EXAIR Vortex Tubes with special material o-rings and hot valves or with customized muffler assemblies.

Fittings – Our standard units have threaded connections on the Vortex Tube to connect fittings and tubing.  In certain applications to improve mounting and assembly, special fittings may be required for ease of installation.  EXAIR can attach or modify these parts to the Vortex Tube to meet your requirements.

At EXAIR, we pride ourselves with excellent customer service and quality products.  To take this one step further, we offer specials to accommodate your applications.  As a manufacturer of the Vortex Tubes, we can work with our customers to generate a custom product with high quality, fast delivery, and a competitive price.  So, if you do need a special Vortex Tube to give you a specific temperature, ease of mounting, or a proprietary product for your OEM design, you can discuss your requirements with an Application Engineer.  We will be happy to help you.

John Ball
Application Engineer

Twitter: @EXAIR_jb

EXAIR Cabinet Cooler Systems Vs. Refrigerant-Based Panel Cooling Options

If you’ve got an electrical enclosure that needs heat protection, you’ve got a good number of options at your disposal. Frankly, if any one of them were the “be-all and end-all” solution, the rest of us would be looking for something else to do. Fact is, there are certain situations where one particular method makes more sense than the others, and other situations where one method just won’t work but several others will.

In industrial and commercial settings, these situations will often present conditions where there is indeed an ideal solution. Today, we’ll explore the ones where the choice comes down to a compressed air-operated EXAIR Cabinet Cooler System or refrigerant-based panel cooling.  Let’s consider:

Environment – Now, we’re all going to make sure we protect our gear from the elements, as much as is humanly possible. Your company’s computer server is likely a lot closer to the climate controlled office spaces than the welding or grinding stations. But what happens when sensitive electronics need to be in close proximity to the machinery they’re controlling? And that machinery isn’t in climate controlled office spaces?

EXAIR NEMA 4 Cabinet Cooler System on an enclosure in a hot steel mill.

Even if an A/C type panel cooler would fit on this box, it would be problematic:

  • See all that dust on the ducts? And the belt? And the rails? And the…well, everywhere? Yeah; would be in the filters, condenser coils, the compressor motor bearings and eventually, inside the panel.
  • They make condensate. The big thing about air conditioners is that they lower the humidity…and that water has to go somewhere. Even if a small drain line is easy enough to run, what happens when it gets clogged (that dust is going to find its way here too, by the way)?
  • They’re sensitive to vibration. Every fastener, every brazed joint, every electrical connection, risks cyclical failure if they’re shaken about.

EXAIR Cabinet Cooler Systems are impervious to all of these conditions:

  • The only air they use comes straight from your compressed air supply. We even provide Automatic Drain Filter Separators to make sure this is clean & dry.
  • There are no moving parts. Vibration is not a problem.
  • We offer different levels environmental considerations to meet most any challenge:
    *NEMA 12 (dust tight, oil tight) are ideal for general industrial environments.
    *NEMA 4 (splash resistant) keep liquids out too, and are indoor/outdoor rated.
    *NEMA 4X (corrosion resistant) also keep liquids out, and are stainless steel construction. They’re also available in 316SS construction for the most exacting, harshest, and critical environments such as food service, pharmaceutical, or highly corrosive atmospheres.
    *High Temperature Cabinet Cooler Systems are specified for installation in areas where ambient temperatures exceed 120°F (52°C.)

Location – Sometimes, there’s just not room to mount an air conditioner. The compressor, and, especially, the condenser coils have to take up a finite amount of space, by design.

When there’s no room to use a bulky air conditioner, a compact EXAIR Cabinet Cooler System is ideal.

EXAIR Cabinet Cooler Systems have a small footprint…a NEMA 12 550 Btu/hr system, for example, installs through a ½ NPS knockout, is under 6” tall, and just over 1” in diameter.

Reliability – We talk to callers all the time about the frustration of:

  • Having to replace a burned out Variable Frequency Drive because their panel cooler failed.
  • Constantly resetting controls that have tripped due to an overheat condition because they missed, or don’t have time for, their panel cooler’s maintenance.
  • Down time and lost production while waiting for replacement parts…or a whole new panel cooler.

Even in less aggressive environments, filters and coils can slowly accumulate dirty buildup, which reduces the unit’s cooling power.  Then, a heat wave hits early in the season, and your machine trips out (if you’re lucky) or burns out (if you’re not) -either way, that part or process you were in the middle of is scrap, and you’re back to step one.

EXAIR Cabinet Cooler Systems are not affected by this – in fact, a system with thermostat control may just sit there dormant through the winter, and “spring” (pun intended) into action when that first heat wave rolls through.  And it’ll be just as powerful as that last hot day, the previous autumn.

Availability – Let’s say you installed some new equipment recently, and its first exposure to the heat of summer created one of the frustrating situations above.  An air conditioner-type panel cooler will require:

  • “Invasive surgery” on your enclosure. Most of these require a sizeable rectangular hole for installation.
  • These systems can pull 5 amps or more, which might mean a dedicated circuit breaker & wiring.
  • Many are built-to-order, so you might have to wait, depending on their assembly schedule.  And they might be busy, because if the heat just started causing you problems, you’re probably not the only one.
  • Once it’s received, installed, and wired up, you may still have to wait for the compressor’s oil (special oil for use with refrigerant) to settle before you start it up the first time.

EXAIR Cabinet Cooler Systems are stock products.  We ship same day, across the country, with orders received by 3pm EST.  They install in minutes, and most of the preparation can be done today, so you’re ready to install when it comes in tomorrow – which isn’t a big deal…most Cabinet Cooler Systems weigh only 5lbs or less, so expedited shipping isn’t near as painful to your wallet as a big box full of electric motor, copper coil, and refrigerant.

Environment (friendly, that is) – No matter how well they’re built, a refrigerant system is going to leak sooner or later.  And every whiff through an aging seal, or sudden loss through a failed tube, will contribute to the ozone depletion that today’s strict controls and high attention to CFC’s are trying to prevent.

Our Cabinet Cooler Systems are solely compressed air operated…the only thing they exhaust is the air from inside the enclosure.

Durability – Refrigerant leaks. Electric motors wear out.  Coils corrode.  Filters clog.  A GOOD warranty on an air conditioning type panel cooler is two years.  And it won’t cover environmental effects.

All EXAIR Compressed Air Products have a Five Year Built To Last Warranty.  But if you supply your Cabinet Cooler System with clean, dry air, it’s going to run darn near indefinitely, maintenance free.

Don’t trust your critical electronics to anything less than the assurance provided by an EXAIR Cabinet Cooler System. If you’d like to find out which one(s) are right for your needs, give me a call.

Russ Bowman
Application Engineer
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BTU/hr. vs. Cold Air Temperature


Way back in 1983 the founder of EXAIR began producing Vortex Tubes.  Using only compressed air, these small devices produce extremely cold air through the Ranque-Hilsch effect.  As the compressed air enters the Vortex Tube, it begins to spin, reaching over 1,000,000 rpm.  When the spinning airflow reaches the end of the tube, an adjustable percentage is forced to change directions and decrease in diameter.  This decrease in diameter requires a decrease in energy, which the airflow does in the form of heat.  What is left is a hot airstream from one end of the tube and a cold airstream from the other.

An EXAIR Vortex Tube

A key component in the creation of the Vortex Tube effect is the apparatus which starts the spinning of the air inside the tube.  At EXAIR we refer to this piece as the generator, and we can significantly impact the performance of the Vortex Tube based on the dimensional characteristics of this component.

By changing one dimension of the generator we can increase or decrease the total volume of air which flows through the Vortex Tube; and by changing another dimension we can “force” a certain percentage of air to exit the hot end of the Vortex Tube.  These small dimensional changes will result in either a high volume of very cold air, or a low volume of INSANELY cold air.  So, how is this possible?

EXAIR Vortex Tube Performance Chart

To thoroughly answer this, we have to look at something called cold fraction.  A cold fraction is the percentage of air which enters the Vortex Tube and exhausts through the cold end.  An 80% cold fraction will direct 80% of the air which enters the Vortex Tube to exhaust through the cold end.  For example, using a 10 SCFM Vortex Tube with an 80% cold fraction will produce 8 SCFM of flow through the cold end of the tube and 2 SCFM of flow through the hot end of the tube.

Adjusting the cold fraction of a Vortex Tube is as simple as turning the brass valve on the hot end of the tube.  The more the valve is opened, the lower the cold fraction.  As the valve is opened it allows more air to “escape” the Vortex Tube through the hot end, resulting in a lower flow (and also lower temperature air) from the cold end of the tube.  These cold fractions determine the temperature drop of the incoming compressed air, and therefore the outlet temperature of the cold air from the Vortex Tube.  But, this adjustment limited, based on the geometry of the generator mentioned above.

An EXAIR Cooling Kit, complete with Vortex Tube, cold air muffler, generator kit, and automatic drain filter separator.

At EXAIR we produce multiple styles of Vortex Tube generators which produce different cold fraction bandwidths.  Our “C” style generators are better suited to produce a cold fraction between 0-60%, and our “R” style generators are better suited to produce a cold fraction between 40-100%.  These cold fractions are independent of airflow volume, allowing for different outlet temperature ranges with the same inlet compressed air volume.  (You will notice some overlap of cold fraction in the 40-60% range.  Generally, our practice is to use “R” style generators down to 50% cold fraction.)

So, which one is better?

The answer depends on the target temperature needed in the application.  If the absolute coldest temperature is necessary, such as when trying to reach more of a cryogenic type of temperature on a small component or for a test, a “C” style generator may be the best choice.  But, if maximum cooling power is needed, the “R” style generator will prove to have an advantage.  It may seem counter-intuitive at first, but extremely low temperature air from a “C” style generator at less volume will produce less cooling effect than the moderately low temperature air at higher volume from an “R” style generator.

To illustrate this effect, let’s take a look at calculating BTU/hr. of a Vortex Tube.  This is done in the following steps:

  1. Determine inlet airflow to the Vortex Tube.
  2. Determine cold flow value at specified cold fraction.
  3. Use the cold fraction chart to determine temperature drop of incoming compressed air.
  4. Subtract temperature drop from the temperature of the incoming air.
  5. Determine the ΔT between the temperature of the air you are producing and the required temperature in the application.
  6. Place these values into the refrigeration formula shown below.


1.0746 x Cold Flow in SCFM (step 2 value) x ΔT in °F (step 5 value) = BTU/hr.


Now, using the process above, let’s compare a “C” style Vortex Tube and an “R” style Vortex Tube in terms of BTU/hr.  For this exercise we will compare a model 3425 “C” style Vortex Tube with a model 3225 “R” style Vortex Tube, using a supply pressure of 100 PSIG and a compressed air temperature of 70°F.

Calculations for model 3425 “C” style Vortex Tube

  1. Determine inlet airflow to the Vortex Tube.
    1. 25 SCFM
  2. Determine cold flow value at specified cold fraction.
    1. With a range of 0-60%, we will utilize a value of 40% for this comparison. This will yield a cold flow volume of 10 SCFM.
  3. Use the cold fraction chart to determine temperature drop of incoming compressed air.
  4. Subtract temperature drop from the temperature of the incoming air.
    1. At a supply pressure of 100 PSIG and 40% cold fraction, the temperature drop will be 110°F. With a compressed air temperature of 70°F we will have an outlet temperature of -40°F.
  5. Determine the ΔT between the temperature of the air you are producing and the required temperature in the application.
    1. An application using a “C” style generator will normally have a low target temperature, such as 0°F. This will yield a ΔT of 40°F.
  6. Place these values into the refrigeration formula shown below.


1.0746 x Cold Flow in SCFM (10 SCFM) x ΔT in °F (40°F) = 430 BTU/hr.


Calculations for model 3225 “R” style Vortex Tube

  1. Determine inlet airflow to the Vortex Tube.
    1. 25 SCFM
  2. Determine cold flow value at specified cold fraction.
    1. With a range of 50-100%, we will utilize a value of 70% for this comparison. This will yield a cold flow volume of 17.5 SCFM.
  3. Use the cold fraction chart to determine temperature drop of incoming compressed air.
  4. Subtract temperature drop from the temperature of the incoming air.
    1. At a supply pressure of 100 PSIG and 70% cold fraction, the temperature drop will be 71°F. With a compressed air temperature of 70°F we will have an outlet temperature of -1°F.
  5. Determine the ΔT between the temperature of the air you are producing and the required temperature in the application.
    1. For most applications using an “R” style generator we aim for a target temperature of 95°F. This will yield a ΔT of 96°F.
  6. Place these values into the refrigeration formula shown below.


1.0746 x Cold Flow in SCFM (17.5 SCFM) x ΔT in °F (96°F) = 1,805 BTU/hr.


In this comparison we have proven that although the “C” style Vortex Tube will produce a lower temperature airflow, it will not produce a greater cooling effect in an application.  Maximum cooling is achieved with the “R” style generator.  For this reason, 9 out of 10 applications utilize the “R” style 3200 series EXAIR Vortex Tube.  These units produce an extremely cold output air with high volume to effectively remove heat.  The “C” style units are also effective at removing heat, but are normally suited for applications aiming to achieve the lowest temperature airflow possible.

But, no matter the style of generator installed into the Vortex Tube, the cold air output is useful for industrial applications.  Whether the need is for spot cooling electronic components, grinding wheels, milling and drilling equipment, or laser cutting heads, we have a Vortex Tube solution.  If you have an application and would like to discuss an EXAIR Vortex Tube solution, contact our Application Engineers.  We’ll be happy to help.

Lee Evans
Application Engineer

EXAIR Vortex Tubes: As Much Cold Air As You Need, As Cold As You Need It

If you’re looking for a reliable, consistent flow of cold air, there’s really no better way to produce it than with a Vortex Tube. There are no moving parts…the air flow and temperature from a particular model, set to a specific cold fraction, is only influenced by the compressed air supply pressure & temperature.

Pressure is easy to control…all you need is a suitable regulator.  Temperature CAN be a variable, depending on your type of compressor, if you have a dryer system (and what type it is,) and sometimes, ambient conditions…if, for example, a long pipe is run through a very hot environment like a foundry or a blast furnace operation.  In cases where supply pressure and/or temperature can be limitations, a higher capacity Vortex Tube, set to a lower Cold Fraction, may be specified.  Which brings me to the user inquiry that inspired today’s blog…

This particular customer uses our Model 3215 Vortex Tubes (15 SCFM, 1,000 Btu/hr) to provide cooling to analyzer systems that monitor certain quality parameters in their manufacturing processes.  The ability to precisely control the temperature in these systems makes for repeatable and accurate measurement of these parameters.   Their compressed air supply in this area is regulated to 80psig, they have a refrigerant-type dryer and climate-controlled facility, so their supply temperature is a consistent 70°F.  You couldn’t ask for better conditions for a successful Vortex Tube application, and they’ve worked great, for years.

Now, due to a plant expansion, they’re installing some of these analyzer systems in a location where the compressed air supply is limited to 60psig.  The required cooling capacity is going to be the same, so the Project Manager reached out to us to see if they could get the same amount of cooling with this new pressure limitation.  Here’s how they’re doing it:

We publish the rated performance of Vortex Tube products for a supply pressure of 100psig.  The Model 3215 Vortex Tube consumes 15 SCFM @100psig and, when set to an 80% Cold Fraction (meaning 80%…or 12 SCFM…of the 15 SCFM supply is directed to the cold end,) the cold air will be 54F colder than the compressed air supply temperature.  Here’s the performance table, so you can follow along:

EXAIR Vortex Tube Performance Table

Now, their supply is at 80psig.  Since air consumption is directly proportional to absolute supply pressure (gauge pressure PLUS atmospheric, which is 14.7psi at sea level,) we can calculate their units’ consumption as follows:

(80psig + 14.7psia) ÷ (100psig + 14.7psia) = 0.83 X 15 SCFM (@100psig) = 12.4 SCFM (@80psig)

So, with a 50°F temperature drop (from a supply @70°F,) they were getting 12.4 SCFM of cold air at 20°F.

As you can see from the table above, they’ll only get a 46°F drop at 60psig…and the flow won’t be as high, either.  So…we’ll need to get more air through the Vortex Tube, right?  Let’s use a little math to solve for what we need.

We still need 20°F cold air from 70°F compressed air, so, at 60psig, we’re looking at a Cold Fraction of ~70%.  And we still need 12.4 SCFM, so:

12.4 SCFM ÷ 0.7 = 17.7 SCFM @60psig (required supply)

Our Model 3230 Vortex Tube uses 30 SCFM @10opsig…at 60psig it’ll consume:

(60psig + 14.7psia) ÷ (100psig + 14.7psia) = 0.65 X 30 SCFM (@100psig) = 19.5 SCFM (@60psig)

That’s about 10% more flow than they needed, theoretically, which was close enough to start.  From there, they “dialed in” performance by regulating the supply pressure and Cold Fraction (see video, below):

If you’d like to find out more, or work through a cooling application, give me a call.

Russ Bowman
Application Engineer
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