The Legend of Rudolf Hilsch

It is thought that Georges Ranque, a French inventor, inadvertently discovered a key principle while developing early prototypes during the German occupation of France. These prototypes later attracted the interest of Rudolf Hilsch, a German physicist who was working on low-temperature refrigeration systems for military applications. Although Hilsch improved upon Ranque’s original design, he found that it did not surpass conventional refrigeration methods in achieving lower temperatures. Ultimately, the device became known as the Hilsch tube.

The Hilsch tube was constructed using a pair of modified nuts along with several other components. The horizontal section of the T-shaped fitting contains a specially machined element that fits tightly within the arm, featuring a spiral cross-section on the inside that differs from its external shape. At the spiral’s “step,” a small opening connects to the T’s leg, allowing air to enter through the leg and exit via this opening, creating a spiraling flow. The “hot” pipe measures approximately 14 inches in length with a half-inch internal diameter, and its far end is fitted with a stopcock to control the system’s pressure. In contrast, the “cold” pipe is about four inches long, also with a half-inch internal diameter, and its end that connects to the spiral piece includes a washer with a central hole of roughly a quarter of an inch in diameter. Various washers with different hole sizes can be utilized to adjust the system’s performance.

EXAIR’s Vortex Tube operates by channeling compressed air into a tube where it flows through nozzles positioned tangentially to an internal counter-bore. This innovative nozzle design induces the air to rotate in a vortex at speeds reaching up to 1,000,000 RPM. As the air spins, it makes a 90° turn, allowing a valve at one end to release some of the heated air. The remaining air continues down the tube, losing heat in the process, and ultimately exits through the opposite end as cold air.

Both streams in a Vortex Tube rotate in the same direction and at the same angular velocity, which would typically suggest that the rotational speed of the inner vortex should increase due to the conservation of angular momentum. However, this is not observed in practice. A useful analogy can be drawn from Olympic Figure Skating: when a skater extends her arms, her spinning slows down, but as she pulls them in, her rotational speed increases significantly. In the case of the Vortex Tube, the inner vortex maintains a constant speed because it has lost angular momentum. This loss manifests as heat, which is expelled from the hot side of the tube. Consequently, the inner vortex cools down, allowing the cooled air to be channeled for various industrial applications.

How the EXAIR Cabinet Cooler System Works

The theory behind the Vortex Tube is applied to standard Vortex Tubes and a range of other products designed with specific features tailored to your needs. EXAIR offers a variety of solutions, including Cabinet Coolers, Cold Guns, Adjustable Spot Coolers, Mini Coolers, and Vortex Tubes, all of which function based on this fundamental principle.

If you have questions about Rudolf Hilsch, or anything regarding EXAIR and our products, please do not hesitate to reach out.

Jason Kirby
Application Engineer
Email: jasonkirby@exair.com
Twitter: @EXAIR_jk

4 Mistakes Plants Might Be Making with Compressed Air (and How to Avoid Them)

Compressed air is one of the most versatile and expensive utilities in any plant. It powers tools, moves products, cools processes, and keeps production running smoothly. But it’s also one of the most commonly misused resources on the floor.

Small inefficiencies add up quickly, and many facilities are losing thousands of dollars a year without realizing it. The good news? Most of these issues are easy to fix once you know where to look, especially with engineered solutions from EXAIR.

Here are four of the most common mistakes plants make with compressed air, and how to avoid them.

1. Using Open Pipes Instead of Engineered Nozzles

The Mistake:
Blowing with open pipes or drilled tubes is still surprisingly common. It “kinda works,” but it’s incredibly inefficient, noisy, and unsafe.

Why It Matters:
Open pipes consume a massive amount of compressed air and can create dangerous dead-end pressure situations. They also produce high noise levels that can exceed OSHA limits.

How to Avoid It:
Switch to engineered air nozzles and knives like EXAIR’s Super Air Nozzles or the Super Air knife. These are designed to:

  • Reduce air consumption by up to 80%
  • Meet safety standards for dead-end pressure
  • Dramatically lower noise levels

The Result:
Immediate air savings, safer operation, and a quieter plant floor.

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

2. Running at Higher Pressure Than Necessary

The Mistake:
Many plants run their systems at higher pressure “just in case.” It feels safer—but it’s costing you.

Why It Matters:
Every 2 PSI increase in pressure can increase energy consumption by roughly 1%. Multiply that across your entire system, and the cost adds up fast.

How to Avoid It:
Use EXAIR’s pressure regulators to optimize pressure at the point of use instead of over-pressurizing the entire system.

The Result:
Lower energy bills and better control over your applications—without sacrificing performance.

EXAIR offers a range of Pressure Regulators capable of handling air flow of up to 700 SCFM.

3. Ignoring Compressed Air Leaks

The Mistake:
Leaks are often treated as “minor” issues and left unresolved.

Why It Matters:
Leaks can waste 20–30% of your compressed air output. That’s essentially money leaking out of your system 24/7.

How to Avoid It:

  • Conduct routine leak audits using the Model 9207 Ultrasonic Leak Detector
  • Fix worn fittings, hoses, and connections
  • Use efficient components that minimize unnecessary air use

Pairing leak reduction with efficient products from EXAIR ensures you’re not just fixing losses, you’re preventing new ones.

The Result:
Reduced compressor load, lower maintenance costs, and immediate energy savings.

4. Not Optimizing Airflow for the Application

The Mistake:
Using too much air—or the wrong type of airflow—for blowing, drying, or conveying applications.

Why It Matters:
Inefficient airflow leads to higher consumption, inconsistent performance, and unnecessary wear on equipment.

How to Avoid It:
Adopt engineered air amplification products like EXAIR’s Air Knives, Air Amplifiers, and Air Wipes. These devices entrain the surrounding air to:

  • Maximize output while minimizing compressed air use
  • Provide uniform, high-performance airflow
  • Improve drying, cleaning, and conveying efficiency

The Result:
Better process performance with significantly lower air usage.

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

Compressed air is too valuable to waste. The difference between an optimized system and an inefficient one often comes down to a few overlooked decisions.

By avoiding these common mistakes—and implementing engineered solutions from EXAIR—plants can:

  • Cut energy costs
  • Improve safety
  • Boost productivity
  • Extend equipment life

If your facility hasn’t evaluated its compressed air usage recently, now is the time. Even small changes can deliver fast, measurable results.

Jordan Shouse
Application Engineer
E: JordanShouse@exair.com
O: (513) 671‑3322
F: (513) 671‑3363
A: 11510 Goldcoast Dr Cincinnati OH 45249
www.exair.com

Find time on my calendar by scheduling a meeting here.

Safety Is Everyone’s Responsibility

That’s a direct quote that everyone at EXAIR hears at our regularly scheduled safety training meetings. While our machine tool operators & assembly technicians spend a lot more time “up close and personal” with devices that can hurt you if not used properly, we all work in the same building with them. That’s why EVERYONE is required to attend those meetings. I like the people I work with, so I REALLY like the level of confidence we all have that the company is looking out for us like that.

The confidence in safety that we have in working at EXAIR is built into our engineered Compressed Air Products as well. Compressed air is downright dangerous, so it’s imperative that you use it safely.

I spent 6 years & 23 days in the United States Navy, so I know full well that you can’t make anything “sailor proof” (no offense to you veterans of other branches, but I once got a letter of commendation from my Commanding Officer for fixing something that I’d broken myself) but I cannot figure out, for the life of me, how to violate OSHA’s Standard on using compressed air for cleaning, with an EXAIR Super Air Nozzle:

OSHA Standard 1910.242(b) says that if you use a compressed air device for cleaning, the static air pressure at the nozzle or opening must not exceed 30 PSI when dead-ended (blocked). Since the air from a Super Air Nozzle comes out of those holes recessed between those fins, there’s a (dare I say it?) sailor proof relief path to make sure that can’t happen.

In fact, all of our blowoff products comply with that standard:

The same design feature (the cap overhanging the body) makes our Flat Super Air Nozzle (left) and our Super Air Knife (right) OSHA Compliant.

Another danger associated with the use of compressed air is the noise level associated with introducing a high pressure gas to atmospheric pressure. If you use airguns or other blow offs without engineered nozzles, you likely know this already. EXAIR engineered Compressed Air Products solve this safety issue as well. Each of the products in the photos above has a very specific feature that causes the primary flow of compressed airflow to entrain a secondary airflow, which results in a much higher total developed airflow. That makes them EXTREMELY efficient — but it also forms a low velocity boundary layer around the hard-hitting air stream in the center, which attenuates the sound level.

In each of these EXAIR engineered compressed air products, the primary air stream following the curved surface causes entrainment. And efficiency. And sound attenuation.

The effectiveness of that low velocity boundary layer is so good that all of our Super Air Nozzles except the very largest ones are compliant with OSHA Standard 1910.95(a) for maximum allowable noise exposure (that limit is 90dBA, so you know.)

In closing, let me reiterate: compressed air is dangerous, so use it safely, and that starts with using safe compressed air products. Like EXAIR’s…we’re all about safety. If you’d like to find out more, I can talk about it all day, and sometimes I do…give me a call.

Russ Bowman, CCASS

Application Engineer
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Dude, Where’s My Safety Air Gun?

I am the poster child for misplaced items. A couple of years back, I lost the key to my truck. I looked for it for WEEKS (it’s not my daily driver) — and finally admitted defeat. A local locksmith offered mobile service, which was kind of expensive but not as bad as I thought, and made me a new key in about a half hour. He actually made two (my wife insisted) and having my truck back just in time for that spring’s mulch was well worth it. Knowing the location of the spare key is nice & comforting too.

Just last fall, I lost my glasses one fine Friday afternoon. I’m only moderately nearsighted, so it was just a mild-to-moderate inconvenience. After a quick trip to the eye doctor and a local business that makes glasses on the same day, I had two new pairs of glasses (my wife, again, insisted on the 2nd pair.) When I got home, my “lost” glasses were on the counter…she’d found them between the arm of the couch and the end table. Ironically, if I’d had a pair of glasses, I’d have found them easily since that’s one of the first places I looked, but was unable to see them with my compromised vision.

Last month, both of those incidents came to mind when the Press Release dropped for a new EXAIR product: our Model 5920 Air Cradle.

EXAIR’s new Air Cradle is a simple but innovative accessory designed to keep safety air guns and similarly sized tools within easy reach at workstations and machine centers.

It’ll hold up to 10lbs, so you can even leave the air supply hose hooked up. Using the Air Cradle means you won’t have to search for your Safety Air Gun, worry about it getting damaged or dropped, and you’ll be one step closer to having a well-organized work space.

Now, I’m not saying that if I had a “truck key cradle” or an “eyeglasses cradle” I wouldn’t have lost my keys or glasses…it’s important to note that one has to actually USE handy organizational tools to be organized…but it would’ve definitely lowered the chances of losing them.

I think it’s also important to note that the Air Cradle came about as a direct result of a customer or two asking about properly stowing their Safety Air Gun. We have regularly scheduled meetings where we discuss calls like that, and the Air Cradle was the direct result of such a conversation. If you have questions about compressed air in general, or EXAIR engineered compressed air products specifically, we’d love to hear from you…whether your call leads to a new product’s development or not!

Russ Bowman, CCASS

Application Engineer
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