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

Email: johnball@exair.com
Twitter: @EXAIR_jb

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

Email: johnball@exair.com
Twitter: @EXAIR_jb

A Solution for This and a Solution for That – Solving Problems Throughout the Plant

EXAIR’s 15 extensive product lines solve problems in production processes everyday. From cooling to laser lens protection (as you will see below) to static elimination, general shop housecleaning, conveying and air conservation –  we would like to help solve your problems.

Last week, I got an email from a customer.  It was late in the day, and I was spent from a busy day.  The customer was emailing for (2) reasons. First, they wanted to express their appreciation for our efforts several months ago regarding an application for a Vortex Tube. Over the course of a couple of weeks, we shared information and ideas back and forth regarding the Vortex Tube technology, how it works, and the various considerations when choosing the appropriate model.  They ended up purchasing a unit and put it into operation.  The application involved a plastic tubing cutting process and in this instance both the cold and hot air streams could be utilized to improve the process. The process involves heating up the material so it would lose its memory set, and then a cooling operation to improve the material cutting and handling.  Below is an excerpt from the recent email:

capture

How_A_Vortex_Tube_Works

The Vortex Tube takes in compressed air, and creates a Cold Stream and a Hot Air Stream

The second reason for the email was that he needed help with another application and based on the success of the initial collaboration, he knew he could trust in EXAIR to help find a solution that would work.  The new application involves protecting a camera lens from debris created during a wire cutting laser process. The lens is getting hit with spatter and damage is starting to occur. Our collaboration has begun, and we are looking at the Super Air Knife and Flat Super Air Nozzle as possible solutions, each of them providing a strong air flow to direct the debris away from the lens.

To discuss your application and how an EXAIR Intelligent Compressed Air Products can help your process, feel free to contact EXAIR and one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web
Like us on Facebook
Twitter: @EXAIR_BB

The Adjustable Spot Cooler Is Ideal For Small Parts Cooling

I recently worked with a customer who was trying to cool some small part housings after they leave a wash system. The parts are currently placed in a wash tray where they travel down a conveyor belt and into the washer where they are heated to around 160°F. As the parts exit the washer, the belt is stopped so the parts can be left to cool before an operator places the parts into their dryer system. This cooling process was taking about 15 minutes before the operator was able to safely handle the parts. This cooling delay was negatively affecting their production cycle. They were looking to eliminate the 15 minute cooling cycle by incorporating some type of air cooling system so the parts could be quickly processed to the dryer. They wanted to standardize on a single device as they manufacturer a variety of part shapes with the largest being a valve housing that measures close to 2″ x 2″.

The customer was able to send a few photos of their parts and after reviewing the information sent, I recommended they use our Model # 3925 Adjustable Spot Cooler System with dual point hose kit. Incorporating a Vortex Tube, the Adjustable Spot Cooler is able to produce cold air temperature as low as -30°F, based on ambient supply temperature. The unit features a temperature control valve that allows for simple adjustments of the temperature of the exhausting cold air as well as the volume of air being discharged.  The system includes 2 additional generators which provide more or less airflow volume through the device as well as cooling capacity (Btu/hr.) for even  more control. The dual hose kit separates the cold air into two separate airstreams to provide for a wider coverage area or in this particular case, the customer would be able to treat both sides of the housing for even cooling. The magnetic base makes for easy installation without having to make expensive modifications to their existing setup.

3925 Adjustable Spot Cooler

3925 Adjustable Spot Cooler System – for wider coverage areas with no moving parts to wear out or replace.

EXAIR offers a wide variety of spot cooling products for use in many industrial settings. For help selecting the best product to fit your needs, give me a call, I’d be glad to help.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

 

The Adjustable Spot Cooler Provides High Flexibility and Effectiveness

A customer emailed me with some questions about the using the EXAIR spot cooling technology for use on PEEK material being machined in a Swiss Turning machine. Typically, apart from drilling and parting, coolants are not necessary for thermoplastic machining operations.  In order to obtain the best surface finish and tightest tolerances, keeping the cutting area cool is required.  The ideal goal was to provide sub-zero air to the cutting area, while being quiet and easy to operate.  After reviewing the various EXAIR spot cooling products, it was determined that the Adjustable Spot Cooler System would satisfy all of the requirements.

asc-single-point-2

Model 3825 Adjustable Spot Cooler System

The Adjustable Spot Cooler System shown above is capable of producing temperatures from -30°F to room temperature, with just the turn of a knob.  Included in the package are (2) additional generators, which allow for more or less cold air flow rate, depending on the application cooling needs.  With the magnetic base, the system can be easily positioned, and the flexible hose allows for precise aim of the cold air flow. And, sound levels are kept below 75 dBA.

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Model 3825 Used in a Turning Operation

To recap, the Adjustable Spot Cooler System provides adjustable cold air temperature with the simple turn of a knob, includes additional generators to provide wide ranging flow rates, has a magnetic base to allow for positioning anywhere, on any machine, and has a flexible hose for directing the cold air wherever it is needed.

I would say that it is a Very Adjustable Spot Cooler.

To discuss spot cooling and your application, we ask you to contact EXAIR and one our  Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web
Like us on Facebook
Twitter: @EXAIR_BB

Cooling a Thermal Manikin After a Fire

Not to be persnickety, but there is a difference between mannequins, life size model for displaying or tailoring clothes, and manikins, an anatomical model used for testing and teaching, usually with movable joints. (The enunciation is exactly the same though).  A lab designed a test for thermal protective clothing.  They had a manikin that was 6 feet in height and had 120 copper slug sensors located all over its body. The sensors would record the temperature gradients on the surface of the manikin, representing skin exposure to heat.  They would dress their manikin with thermal protective clothing from head to toe and expose it to intense fires at various temperatures and exposure times.  After each test was completed, they would record the results and cool the manikin to 26 deg. C before they started the next fire test.  These results were used for safety limits to protect wearers from second and third degree burns, very important in keeping firefighters safe.

Fire Suit under test

Fire Suit under test

In their application, they were looking to cool the sensors on the manikin as quickly as they can to increase test cycle rates. Initially they used a “cool down” area fitted with fans to blow air across the manikin.  The problem was that it took too long to cool to the 26 deg. C mark required in their testing protocol.  They decided to manually use an air gun to blow compressed air across the sensors to increase cooling.  This did reduce the cycle time, but because of the force created by the air gun, some sensors would shift and be out of calibration.  This was a huge concern for the test lab.

The design of the copper slug sensor has a small piece of copper set inside a silicone holder. To isolate the copper metal, there are small ruby spheres between the holder and copper slug.  This creates an air gap around the copper slug to help increase sensitivity to temperature changes.  A thermocouple is attached to the back side of the copper slug for analytical measurements.

Adjustable Spot Cooler

Adjustable Spot Cooler

After they discussed their application with me, I suggested the model 3725 Adjustable Spot Cooler. This base unit comes without a magnetic base and hose kit, which makes it lighter in weight. The customer could easily attach it directly to their compressed air line, replacing the air gun that was damaging the sensors.  The Adjustable Spot Cooler incorporates the Vortex Tube which makes standard compressed air into cold air.  With a turn of a knob, they could control the temperature and the velocity of the cold air.  This feature was key in determining just the right amount of force to not affect the calibration of the sensors.  An added benefit of the Adjustable Spot Cooler is if you reduce the amount of outlet cold air, the temperature will decrease even more.  This feature allowed the customer to reach their target much more quickly and without damaging the sensors.

If you need to cool things down in your application, you can contact an Application Engineer at EXAIR. We have many different styles and combinations of Vortex Tubes and Spot Coolers to give you the right form of cooling, whether it is a mannequin or a manikin.

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

 

DDI-2007-Burning Man by Interpretive Arson.  Common License.

Vortex Tube Cold Fractions

Vortex Tubes are the perfect solution when dealing with a variety of spot cooling applications. They use compressed air to produce a cold air stream and a hot air stream, with temperatures ranging from as low as -50°F  up to +260°F (based on ambient supply temperature) and providing as much as 10,200 Btu/hr. of cooling capacity. By simply adjusting the valve in the hot end of the Vortex Tube, you are able to control the “cold fraction” which is the percentage of air consumed by the vortex tube that is exhausted as cold air versus the amount of air exhausted as hot air. Our small, medium and large Vortex Tubes provide the same temperature drop and rise, it’s the volume of air that changes with the various sizes.

Vortex Tubes

Vortex Tubes are available in small, medium and large sizes with various flows and cooling capacities.

When looking at the below performance chart, you will see that “Pressure Supply” and “Cold Fraction %” setting all play a part in changing the performance of the Vortex Tubes. Take for example, an operating pressure of 100 PSIG and cold fraction setting of 20%, you will see a 123°F drop on the cold side versus a 26°F temperature rise on the hot side. By the using the same Vortex Tube and keeping the operating pressure at 100 PSIG but changing the cold fraction to 80%, you will now see a 54°F temperature drop on the cold side and a 191° rise at the hot end.

Vortex Tube Performance Data

Vortex Tube Performance Chart

We’ve looked at how the cold fraction changes the temperature, but how does it change the flow for the various Models?

Say you are using a Model # 3240 Medium Vortex Tube which consumes 40 SCFM @ 100 PSIG. Again with the cold fraction set at 80% (80% of the consumed compressed air out of the cold end), you would flow 32 SCFM at the cold air exhaust.

40 SCFM x 0.8 (80% CF) = 32 SCFM

Using the same Model # 3240 Medium Vortex Tube but now with a 20% cold fraction (20% of consumed compressed air out of the cold end), you would flow 8 SCFM at the cold exhaust.

40 SCFM x 0.20 (20% CF) = 8 SCFM

As you can see, to achieve the colder air temperatures, the volume of cold air being exhausted is reduced as well. This is important to consider when making a Model selection. Some other considerations would be the operating pressure which you can see also has a significant effect on performance. Also the compressed air supply temperature because the above temperatures are temperature differentials, so in the example of the 80% cold fraction there is a 115F temperature drop from your inlet compressed air temperature.

If you need additional assistance, you can always contact myself or another application engineer and we would be happy to make the best selection to fit your specific need.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

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