If you’re a regular reader of the EXAIR Blog, you likely know that you can get cold (and hot) air from a Vortex Tube. You probably also know that there are ways to get more or less flow, and higher or lower temperatures. Today, I wanted to write about vortex tube operation. First, let’s recall the basics:
To change the cold (or hot) air flow AND temperature (you can’t do one without the other), all you have to do is manipulate the Control Valve, or Hot Valve, as it’s oftentimes referred to because of its location at the ‘Hot’ end of the Vortex Tube. Essentially, as you open it, more hot air exits, meaning there’s less air to go to the ‘Cold’ end. By increasing the ‘Hot’ flow, more kinetic energy (in the form of heat) is carried away. And, since more energy (heat) is given off, the energy (heat) in the cold flow decreases as well, so you get colder air…and less of it as the hot flow increases. We can use the data in EXAIR’s Vortex Tube Specification and Performance Tables to calculate the cold (and hot) flows and temperatures at different positions of the Hot Valve. Let’s say we have a Model 3210 Vortex Tube that uses 10 SCFM when supplied at 100psig:
Let’s assume the compressed air supply temperature is 70°F and the Hot Valve is open wide enough to allow 40% of the Model 3210’s 10 SCFM (or 4 SCFM) worth of compressed air consumption out. That means that 60% (or 6 SCFM) are going to go out of the cold end. We call this condition a 60% Cold Fraction:
And, at that 60% Cold Fraction, the cold air is going to be 86°F colder than the supply of 70°F, which means that the 6 SCFM of cold flow is going to be -16°F. If the Hot Valve is opened further, to allow 5 SCFM out the hot end (and hence the other 5 SCFM will go out the cold end), that 5 SCFM of cold flow will now be 100°F colder than the 70°F supply, or -30°F. That’s as low as you can go with a 3200 Series Vortex Tube…they have a Cold Fraction range of 50-80%.
Now let’s say you want even COLDER air. You can simply replace the generator (shown to the left) in the Model 3210 to make it a 3400 Series Vortex Tube. If you replace its 10-R Generator with a 10-C Generator, you’ll now have a Model 3410, and you’ll be able to adjust your Vortex Tube to the 20-50% Cold Fraction range. The difference between R and C-style generators is the center hole size. The hole sets up proper internal pressure conditions to work better in each temperature range. In short, the generator type optimizes the temperature drop for each working condition.
You’re still working with a compressed air consumption of 10 SCFM, so, while the air gets colder, the flow decreases. At a 30% Cold Fraction, for example, you’ll get -48°F air (70°F – 118°F), but only 3 SCFM (30% of 10 SCFM) of the total flow going in.
If you need a -48°F net air temperature, but cannot accommodate such a reduction in flow, using a generator with a higher consumption rating is how you get around such an issue. If you were to replace that 10-C Generator with a 30-C, now it is a Model 3430 with triple the original flow of model 3410. Readjustment of the hot valve would be necessary to get back to a 30% Cold Fraction. That means the air flow will be the same temperature (-48°F) but it’s going to be 9 SCFM (instead of 3 SCFM.)
All you need to change the Cold Fraction of an EXAIR Vortex Tube is a flat-head screwdriver. If it’s something you’re going to be doing more frequently, our Adjustable Spot Coolers have a Temperature Control Knob that works the Hot Valve and may be a better choice for an application.
The Adjustable Spot Coolers also come with three different generators, so you can get the different flows at the same temperature, or vice versa, as described above. If you have an application requiring cold (or hot) air flow, on demand, you’re looking for an EXAIR Vortex Tube. For help picking the right one, give me a call.
Russ Bowman, CCASS
Application Engineer
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