The Trick To Adding Sound Levels Of Multiple Sources

If I put a 10 pound weight on a scale, the scale will read 10 pounds. If I put another 10 pound weight next to it, the scale with now read 20 pounds.

If I have $10 bill in my pocket…well, that’s a LOT more cash than I usually carry. But if I somehow come into possession of another $10 bill and put it in my pocket, now I have $20. And it probably won’t be for long.

If there’s an EXAIR Model 1100 Super Air Nozzle supplied with compressed air at 80psig, and my Sound Level Meter is reading a level of 74 dBA, and I hook another one up right next to it, my Sound Level Meter now reads about 78 dBA.

Wait, what? Did we just break math there? You, and your ears, will be happy to know that there’s perfectly valid math behind the third (as well as the first two) statements above. The third one’s just a little different, that’s all.

See, sound power (that’s “how loud” sound is, as measured at the point of generation) and sound pressure (“how loud” it is, as measured at the point where it’s heard) are both quantified in units called decibels. And, unlike mass or wealth (the first two examples above), which are linear & additive, measurement of sound power & pressure is done on a logarithmic scale. That means simple arithmetic won’t work…we have to use a logarithmic equation to ‘add’ those sound levels together. It looks like this:

Combined Sound Level (dBA) = 10 x log10[10SL1/10 + 10SL2/10 + 10SL3/10 …]

Where “SL1”, “SL2”, “SL3”, etc., are the sound levels, in decibels, for the “noisemakers” in question. So, for the two Model 1100 Super Air Nozzles, generating 74 dBA each:

10 x log10[1074/10 + 1074/10] = 77.65 dBA

And just to prove the math works, we made a video of a real live test:

All EXAIR Intelligent Compressed Air Products are engineered & manufactured to be safe, efficient, and as quiet as possible. If you’d like to find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Maximum Effort!!! The Two Types of Vortex Tube Generators

I am a fan of just about all things MCU (Marvel Cinematic Universe) and have always found Deadpool to be entertaining. Anytime I see a Max Cold Temp or Max Refrigeration mention when discussing or reading about a Vortex Tube I go to a miniature cut scene where Deadpool is saying Maximum Effort as they are fighting the bad guys in Deadpool 2. Enough about my love for MCU, let’s get more into my nerd love for Vortex Tubes.

When it comes to Vortex Tubes and getting the most out of them, EXAIR are the subject matter experts. If you aren’t sure what a Vortex Tube is or how it works, we’ve blogged about that, today’s blog is going to focus more on why you would select a Maximum Cold Temp vs a Maximum Refrigeration Vortex Tube and what actually changes.

Vortex generator

The difference lies in the generator that is inside the Vortex Tube. The reason to choose between the two lies with the application for the tube. In the event that the tube will be used for spot cooling or cooling a small chamber, Maximum Refrigeration generators are desired because you will generally work at a 50% cold fraction or higher. The maximum refrigeration value possible is achieved under set variables such as operating pressure, cold fraction, and incoming compressed air temperature. To see how these effect the cooling performance, check out our blogs on de-rating a Vortex Tube (Part 1Part 2). The bulk of applications that I have worked on over the 10+ years I have been part of EXAIR utilize the Maximum Refrigeration Vortex Tube because customers desire to get a product, small area, or component below ambient air temperatures and are going to be operating in the 50% to 80% cold fraction area in order to provide the performance needed.

EXAIR Vortex Tube Performance Chart

The other small fraction of applications that really need to get the lowest air temperature; in order to get that small component or spot down to -50°F (-46°C) will utilize the Maximum Cold Temperature generators. These will be the 3400 series Vortex Tubes or the “-C” versions. While max cold temperature models are less common, they regularly solve applications for temperature stress testing parts and freeze seals. Maybe you aren’t sure if the Maximum Refrigeration or Maximum Cold Temp is the one you need. That’s where the Application Engineer Team here comes in, hit us up first, and then we can also showcase just how simple it is to change the generator in a Vortex Tube out and give an idea of how many turns out from closed on the Hot Valve you will be to get close to the performance needed.

It truly is just that simple, no internal moving parts, just change out one internal component, and adjust the Hot Valve. To understand how easy that is, check the video below and you can see how big of a swing one can see with adjustments.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Rudolf Hilsch, Shining a Light on the Vortex Tube

The Vortex Tube is also known as the Ranque – Hilsch tube is a device that takes a single source of compressed gas and splits it into two streams a hot and a cold. The Vortex Tube was invented in 1933 by French physicist Georges J. Ranque, however his findings never really went main stream until Physicist Rudolf Hilsch improved the design and published a widely read paper in 1947 on the device, which he called a Wirbelrohr. (Original publication in German can be found here.)

The Original drawing from Rudolf Hilsche’s 1947 Publication.

Compressed air is supplied into the tube where it passes through a set of nozzles that are tangent to the internal counter-bore. The design of the nozzles force the air to spin in a vortex motion at speeds up to 1,000,000 RPM. The spinning air turns 90° where a valve at one end allows some warmed air to escape. What does not escape, heads back down the tube in the inner stream where it loses heat and exhausts through the other end as cold air.

How a Vortex Tube Works

Both streams rotate in the same direction and at the same angular velocity. Due to the principle of conservation of angular momentum, the rotational speed of the inner vortex should increase. However, that’s not the case with the Vortex Tube. The best way to illustrate this is in Olympic Figure Skating. As the skater is wider, the spinning motion is much slower. As she decreases her overall radius, the velocity picks up dramatically and she spins much quicker. In a Vortex Tube, the speed of the inner vortex remains the same as it has lost angular momentum. The energy that is lost in this process is given off in the form of heat that has exhausted from the hot side of the tube. This loss of heat allows the inner vortex to be cooled, where it can be ducted and applied for a variety of industrial applications.

This Vortex Tube theory is utilized in basic Vortex Tubes, along with a variety of other products that have additional features specific for your application. EXAIR’s line of Cabinet CoolersCold GunsAdjustable Spot CoolersMini Coolers, and Vortex Tubes all operate off of this same principle.

If you’re fascinated by this product and want to give it a try, EXAIR offers an unconditional 30-day guarantee. We have them all in stock and ready to ship as well, same day with an order received by 2:00 ET. Feel free to get in contact with us if you’d like to discuss how a vortex-based product could help you in your processes.

Jordan Shouse
Application Engineer

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Rudolf Hilsche’s Publication Drawing provided by Die Zeitschrift für Naturforschung

(Photo Link https://zfn.mpdl.mpg.de/data/1/ZfN-1946-1-0208.pdf )

Top Ten Reasons Why EXAIR’s Super Air Knife Is So Super

1. Efficiency – With an air entrainment ratio of 40:1 (literally means it pulls in 40 SCFM of “free” air from the surrounding environment for every 1 SCFM of consumption), compressed air consumption is dramatically lower than any other blow off device.

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. Laminar air flow – My colleague John Ball did a bang-up job in a video blog explaining the fluid mechanics theory behind this. Operationally, laminar flow is is beneficial because it’s particularly conducive to generating a stripping or sweeping action, as opposed to the turbulent flow from an open blow off, a blower, or a fan.

3. Quiet operation – The high entrainment ratio that makes the Super Air Knife so efficient also makes for amazingly low sound levels. The outermost entrained air creates a boundary layer that attenuates the sound level of the higher velocity, hard hitting center flow.

4. Lengths available – Super Air Knives are stocked in lengths from 3″ to 9ft. Custom lengths can be made if you’re space-limited for installation, and custom shims can be installed if you want to shorten the curtain width of a stock Super Air Knife. Super Air Knives can also be coupled together for even longer lengths.

Air Knife Coupling Bracket Kits are available from stock for Aluminum, 303SS, and 316SS Super Air Knives.

5. Material of construction – No matter how aggressive the environment is, odds are, EXAIR has a Super Air Knife that’ll hold up to it. Durable aluminum models are good to 180°F (82°C). There are also two Types of Stainless Steel to choose from: 303SS for high strength, and 316SS for protection from chloride pitting corrosion & higher strength. Both 303SS & 316SS are good to 800°F (427°C). For exceptionally harsh environments, PVDF (Polyvinylidene Fluoride) constructed Super Air Knives have Hastelloy C-276 hardware & PTFE shims, which are resistant to UV light, inorganic chemicals, solvents, ozone, weather, fungi, chlorinated hydrocarbons, highly corrosive acids, weak bases, and salts. They’re good to 275°F (135°C).

6. Easy installation – Like all of our products, the Super Air Knives – from the 3″ to the 9ft models – are “user friendly” as far as mounting & installation goes. The Model 9060 Universal Air Knife Mounting System makes for quick installation and easy positioning. 24″ to 42″ Super Air Knives need to be plumbed to both ends…if you hard pipe the air supply, the Super Air Knife itself will essentially be as well supported as the piping. The same holds true for longer Super Air Knives with Plumbing Kits installed. 3″ Super Air Knives can even be fitted with Stay Set Hoses, and Magnetic Bases. And the 1/4″-20 tapped holes on the bottom of the body allow for a wide range of mounting solutions…anything you can put a bolt through, really.

The 9060 Universal Air Knife Mounting Systems are perfect for simple, fast installation and positioning.
Yes, that’s a door hinge. No, it wasn’t my idea ( but I kind of wish it was.)

7. Low maintenance – With no moving parts, they’ll run darn near indefinitely, maintenance free, as long as you supply them with clean, moisture free compressed air. Oh, and keep them clean, externally, if they’re in an area where environmental contaminants can build up on the precision finished surfaces that are essential to their air entrainment.

8. Reliability – Hand in hand with #7, no moving parts also means there’s not much that can stop them from working. They can operate continuously, if needed, or you can cycle them on & off as frequently as necessary to keep from using valuable compressed air, except when needed.

EXAIR’s award winning EFC Electronic Flow Control can be set to operate a Super Air Knife (or any of our Intelligent Compressed Air Products) in cycles as low as 0.1 seconds.

9. Static Eliminator option -The laminar, high velocity air flow is ideal for many blow off applications, but if static charge is a problem, an Ionizing Bar can be installed, turning the Super Air Knife into a Super Ion Air Knife:

10. Free stuff – OK; this last one is “super” for a limited time. Order a Super Air Knife between 11/1/22 and 12/31/2022, and get a FREE Safety Air Gun. Click here for details.

If you’d like to find out how the Super Air Knife – or any of our Intelligent Compressed Air Products can help you get the most out of your compressed air system, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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