Even if you’re a casual reader of our blogs, you already know that EXAIR Application Engineers LOVE to preach efficiency in the use of compressed air…it’s our “bread and butter;” the very nature of our business. This year, we’re celebrating thirty-five years of leading the way in the development of efficient, safe, and quiet compressed air products. Our track record of success as a solutions provider across a diverse range of industrial and commercial applications is well documented in our blogs, as well as Knowledge Base and Case Study Libraries. We devote considerable resources (engineering, research & development, product testing, etc.) to making certain that EXAIR Intelligent Compressed Air Products cost less to operate, and perform better, than whatever you’re using right now.
Strange as it may seem, though, sometimes our products are EXTREMELY popular in cases where they INCREASE a facility’s consumption of compressed air…by replacing something that DOESN’T use compressed air at all:
*I’ve written before about how our Large Maximum Cold Temperature Vortex Tubes have replaced liquid nitrogen rigs in freeze sealing operations. Now, a Vortex Tube directs a portion of its air supply to (usually) unusable hot exhaust, in order to generate the usable flow of cold air. When compared to the costs of liquid nitrogen and the resources involved to get it where it needs to be, though, the cost of the compressed air needed to operate the Vortex Tube is indeed the practical solution.
*Line Vacs are probably THE prime example of the value of using compressed air where it wasn’t used before…replacing a “bucket and ladder” operation:
*Then there are the situations that just come down to time. In large spaces, our Super Blast Safety Air Guns can be used to “sweep” the floor in a fraction of the time it takes an operator with a push broom.
To make a long story just a little bit longer…if you’re using compressed air, you can use it better with EXAIR’s engineered compressed air products. And there are plenty of practical applications where you’re not using compressed air right now too. If you’d like to find out more about either one, give me a call.
I wish I could quantify that, but we keep finding more and more applications for them:
Vortex Tubes are used all the time for cooling applications, down to MINUS 40 degrees (Fahrenheit OR Celsius…that’s the point where they’re both the same; no math required.) They also produce a HOT air flow, which we usually call “exhaust,” but some users actually use IT for heating, and call the COLD flow the “exhaust.”
Our E-Vac Vacuum Generators are popular for “pick-and-place” jobs…hook one up to a Vacuum Cup and you can move parts around all day long. One time, though, I helped a
customer who needed to “pick-and-place” individual small pieces of woven fabric, a lot like a coffee filter. Even our smallest E-Vac, supplied from a Pressure Regulator cranked all the way down, was too much…it would still pick up most of the stack. We found they could use a Model 120020 3/4″ Super Air Amplifierjust fine…the Pressure Regulator was still cranked all the way down, and it picked them up one at a time.
Our Super Air Knives are perfect for blow off, drying, and cooling applications…whether you’re trying to rid your product of dirt/debris, water, or heat, a laminar curtain of adjustable air flow is a “textbook” solution. But I recently had the pleasure of helping a customer who needed to KEEP SOMETHING IN PLACE and called to ask about an Air Knife. They had small cups running single-file down a conveyor belt, with an overhead brush roller pushing down on them at one point so they could be treated on one side. Without something holding them in place, the tooling would simply push them off the side of the conveyor. It required frequent adjustment because they run different sized cups…and they almost always lost some cups when they switched to a different size, while “dialing in” the brush tension. By installing a Model 110036 36″ Aluminum Super Air Knife in place of the brush, they can hold any size cup in place with the downward air flow “curtain.” No more lost product when they don’t get the brush adjustment just right!
If you have a compressed air application you’d like to discuss, give me a call. Perhaps we’ll find the next level of versatility!
If you look into the history or even the definition of a vortex tube, you’re likely to find mention of a physicist named Rudolf Hilsch. Born December 18th, 1903, Hilsch was a German physicist, professor, and manager of the Physics Institute of the George August University of Göttingen. He received a doctorate degree by the age of 24 and spent his career furthering the advancement and understanding of numerous phenomena of physics.
Although Hilsch didn’t invent the Vortex Tube (the original inventor was a physicist by the name of Georges J. Ranque), he is entwined with their history thanks to a paper he published in 1947. According to lore, this paper significantly changed the understanding and performance capabilities of the vortex tube, eventually being marked as the precursor for identifying a vortex tube as a real potential cooling device. (I’ve made attempts to find this 1947 publication properly translated into English, but to no avail. If you have it or find it, please email it to me at LeeEvans@EXAIR.com! (Original publication in German can be found here.)
Given that vortex tubes are a known EXAIR solution, it seems reasonable that today, on Hilsch’s birthday, we give recognition to this influential physicist and his mark on thermodynamic fluid flow technology. And, although we at EXAIR are connected to Hilsch through vortex tubes, everyone alive has been influenced by his work. This is because Hilsch and a partner (physicist Robert Wichard Pohl) constructed the first semiconductor amplifier in 1938, prompting Hilsch to prove (in 1939) that solid-state electronics are possible. This work paved the way for transistor and solid-state electronics technology as we know it today. Without Hilsch and his life’s work, not only would we not have vortex tubes, we likely would have any electronic devices we use every day.
Here’s to you Rudolf Hilsch. Thank you for your work, your discoveries, and your achievements.
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.
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.
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.
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.
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?”
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.
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.
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.
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).
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.
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…
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)
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.