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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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