Recently, I had a customer ask me about our Adjustable Spot Cooler and how to change the cold flow and cooling capacity. In this video, I will demonstrate how to change the generator to accomplish both. Watch below:
John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb
EXAIR has written many different articles about how Vortex Tubes work and the applications in which they are used. The idea of making cold air without freon or moving parts is a phenomenon. This phenomenon is the Vortex Tube. It can generate cold air to a temperature as low as -50 oF (-46 oC). In this article, I will explain the adjustment of the Vortex Tube to get different temperatures and cooling effects with reference to the Cold Fraction.
To give a basic background on the EXAIR Vortex Tubes, we manufacture them in three different body sizes: small, medium, and large. These sizes can produce a range of cooling capacities, from 135 BTU/hr to 10,200 BTU/hr (34 Kcal/hr to 2,570 Kcal/hr). The unique design utilizes a generator inside each Vortex Tube. The generator controls the amount of compressed air that can enter the Vortex Tube as well as initiating the spinning of the air inside. As an example, a medium-sized Vortex Tube, model 3240, will only allow 40 SCFM (1,133 SLPM) of compressed air to travel into the Vortex Tube at 100 PSIG (6.9 bar). While a small Vortex Tube, model 3208, will only allow 8 SCFM (227 SLPM) of compressed air at 100 PSIG (6.9 bar). EXAIR manufactures the most comprehensive range, from 2 SCFM (57 SLPM) to 150 SCFM (4,248 SLPM).
After the compressed air goes through the generator, the pressure will drop to slightly above atmospheric pressure. (This is the “engine” of how the Vortex Tube works.) The air will travel toward one end of the tube, where there is an air control valve, or Hot Air Exhaust Valve. This side of the Vortex Tube will blow hot air. This valve can be adjusted to increase or decrease the amount of air that leaves the hot end. The remaining portion of the air is redirected toward the opposite end of the Vortex Tube, called the cold end. By conservation of mass, the hot air and cold air flows will have to equal the inlet flow, as shown in Equation 1:
Equation 1:
Q = Qc + Qh
Q – Vortex Inlet Flow (SCFM/SLPM)
Qc – Cold Air Flow (SCFM/SLPM)
Qh – Hot Air Flow (SCFM/SLPM)
The percentage of inlet air flow that exits the cold end of a vortex tube is known as the Cold Fraction. As an example, if the Hot Air Exhaust Valve of the Vortex Tube is adjusted to allow only 20% of the air flow to escape from the hot end, then 80% of the air flow is redirected toward the cold end. EXAIR uses this ratio as the Cold Fraction; reference Equation 2:
Equation 2:
CF = Qc/Q * 100
CF = Cold Fraction (%)
Qc – Cold Air Flow (SCFM/SLPM)
Q – Vortex Inlet Flow (SCFM/SLPM)
EXAIR created a chart to show the temperature drop and rise relative to the incoming compressed air temperature. Across the top of the chart, we have the Cold Fraction, and along the side, we have the inlet air pressure. As you can see, the temperature changes as the Cold Fraction and inlet air pressure changes. As the percentage of the cold fraction becomes smaller, the cold air flow becomes colder, but the amount of cold air flow becomes less. You may notice that this chart is independent of the Vortex Tube size. So, no matter the size of the Vortex Tube that is used, the temperature drop and rise will follow the chart below.
How do you use this chart? As an example, we can select a model 3240 Vortex Tube. It will use 40 SCFM (1133 SLPM) of compressed air at 100 PSIG (6.9 Bar). We can determine the temperature and amount of air that will flow from the cold end and the hot end. For our scenario, we will set the inlet pressure to 100 PSIG, and adjust the Hot Exhaust Valve to allow for a 60% Cold Fraction. Let’s say the inlet compressed air temperature is 68oF. With Equation 2, we can rearrange the values to find the Cold Air Flow, Qc:
Qc = CF * Q
Qc = 0.60 * 40 SCFM = 24 SCFM of cold air flow
The temperature drop shown in the chart above is 86oF. If the inlet temperature is 68oF, the temperature of the cold air is (68oF – 86oF) = -18oF. So, at the cold end, we will have 24 SCFM of air at a temperature of -18oF. For the hot end, we can calculate the flow and temperature as well. From Equation 1,
Q = Qc + Qh or
Qh = Q – Qc
Qh = 40 SCFM – 24 SCFM = 16 SCFM
The temperature rise shown in the chart above is 119oF. So, with the inlet temperature at 68oF, we get (119oF + 68oF) = 187oF. So, we have 16 SCFM of air at a temperature of 187oF coming out of the hot end.
With the Cold Fraction and inlet air pressure, you can get specific temperatures for your application. For cooling and heating capacities, flow and temperature can be used to calculate the correct Vortex Tube size for your application. If you need help determining the proper Vortex Tube to best support your application, you can contact an Application Engineer at EXAIR. We will be glad to help.
John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb
Some names in science instantly feel larger than life. Newton. Einstein. James Clerk Maxwell often sits just outside that spotlight, but his influence runs deep in modern engineering. If you work with compressed air, heat, or energy transfer, you are already working with ideas that trace directly back to Maxwell.
Maxwell was a 19th century Scottish physicist best known for a set of equations that unified electricity and magnetism. Those equations helped make electric motors, power generation, and modern communications possible. Less discussed, but just as important, was his work on gases and thermodynamics. Maxwell was one of the first scientists to explain that temperature and pressure come from the motion and energy of individual gas molecules, not just from the bulk properties of air.
That shift in thinking matters in industrial applications. Compressed air is not just pressure in a pipe. It is stored energy made up of countless fast-moving molecules. When that air expands, the energy redistributes. Sometimes it becomes work. Sometimes it becomes heat. Under the right conditions, it can separate into hot and cold streams. That is where the Vortex Tube enters the conversation.
A Vortex Tube takes compressed air and introduces it into a chamber where it spins at extremely high velocity. As the air rotates, energy separates within the flow. Hot air migrates toward the outer wall while cold air remains closer to the center. The result is two air streams at dramatically different temperatures, created without moving parts or electricity.
Because of this behavior, the Vortex Tube is sometimes nicknamed Maxwell’s Demon. The name comes from a famous thought experiment Maxwell proposed to explore how energy and entropy behave at the molecular level. In the experiment, a tiny demon selectively allows faster, hotter molecules to move one way and slower, cooler molecules another. While the Vortex Tube is not violating any laws of physics, the visual result feels similar. Energy appears to be sorted within the air stream, producing distinct hot and cold outputs from the same supply.
What makes this more than a clever analogy is that the Vortex Tube operates entirely within the principles Maxwell helped define. The cold air is not created from nothing. It comes from redistributing energy already present in the compressed air. The geometry of the tube and the controlled expansion guide that separation in a predictable and repeatable way.
At EXAIR, Vortex Tubes are used every day for spot cooling, enclosure cooling, and process temperature control. They are valued because they are compact, reliable, and well suited for industrial environments where electrical cooling is impractical or undesirable. With no moving parts to wear out, they offer a simple solution built on solid physics.
Maxwell’s broader legacy is his system-level thinking. He did not study heat, energy, or motion in isolation. He focused on how they interact. That same mindset is essential when designing compressed air solutions today. A Vortex Tube is not just a cold air device. It is part of a complete compressed air system where flow, pressure, temperature, and efficiency all matter.
James Clerk Maxwell never saw a modern factory floor, but his work is still there. Every time compressed air expands, transfers energy, or changes temperature, it follows rules he helped explain. That is why his ideas have endured for more than a century.
The next time you see a Vortex Tube producing cold air with no moving parts, it is worth remembering that it is not a trick. It is applied physics, rooted in Maxwell’s work, and still doing practical, reliable work in industry today.
Tyler Daniel, CCASS
Application Engineer
E-mail: TylerDaniel@EXAIR.com
EXAIR’s Vortex Tubes are a great product for many cooling applications. When supplied with a clean and moisture-free source of compressed air, they will generate two streams of airflow, one hot and one cold. They are a low-cost and reliable solution, capable of producing temperatures ranging from -50°F to +260°F. We have flow rates from 2 SCFM to 150 SCFM, producing refrigeration over 10,000btu/hr.
We also have several other product lines that are great for cooling, like our Air Knives or Air Amplifiers. So, why would you choose a Vortex Tube? Our Air Knives and Amplifiers cool primarily by moving large volumes of ambient air. If you have a 400°F part that needs cooling to under 100°F, then hitting it with large amounts of 70°F ambient air is going to rapidly bring the temperature down. This does mean that there is a limit to how low of a temperature you can achieve with these products; our Air Knives and Amplifiers won’t be able to cool below ambient temperatures. Our Vortex Tubes, on the other hand, with temperatures as low as -50°F, can provide much more powerful cooling and targeted cooling.
Now you have determined that a Vortex Tube is right for you, you’ll need to decide between our two different series: 32XX and 34XX. The difference between the two model types comes down to the Cold Fraction, which is determined by where the Control Valve is positioned. When you open the Control Valve (by turning it counterclockwise, as shown by the blue arrow in the photo to the right), it decreases the Cold Fraction, which leads to a reduced flow and a significant drop in temperature in the cold air discharge. Conversely, closing the Control Valve (by turning it clockwise, indicated by the red arrow) boosts the cold air flow, but causes a smaller temperature drop. This ability to adjust is crucial for the Vortex Tube’s flexibility.
You can set the Cold Fraction as low as 20%, which means that a small portion (20% to be precise) of the supply air is sent to the cold end, resulting in a significant temperature drop. On the flip side, you can crank it up to 80%, meaning that most of the supply air heads to the cold end, but the temperature drop won’t be as drastic. Our 34XX Series Vortex Tubes are designed for cold fractions between 20–50 %, while the 32XX Series caters to 50–80 % Cold Fractions.
So how do you select the right model for you? To determine this, you need to know what temperature and flow will best serve your application. For most situations, the ~20°F produced by an 80% cold fraction is sufficiently cold. At this cold fraction, you will get the most flow (80% of the inlet supplied). Applications like welding or brazing benefit from higher flows. When your starting temperature is hundreds of degrees Fahrenheit, there is little difference in blowing -20°F air vs +20°F. What you need is more volume to strip away the heat as quickly as possible. In this instance, a 32XX series is the way to go.
If you need lower flow, or to achieve freezing temperatures, then the 34XX series would be the best choice. A chocolate maker took advantage of the lower flow rates offered by this type of Vortex Tube as they didn’t want the airflow to disturb the surface of the chocolate as it cooled, affecting the finish. The greater temperature drop allowed for rapid cooling without reducing quality.
Vortex Tubes can produce higher levels of noise than our Knives and Amplifiers, so we would always recommend using hot and cold mufflers with them. This will ensure they stay within OSHA sound standards. And just like with all EXAIR products, it’s a good idea to use a pressure regulator with a gauge right where you’re using it. This is especially crucial for Vortex Tubes if you want to get an accurate temperature.
Whatever your cooling application, our Vortex Tubes will likely be able to help. If you would like to discuss it, please give us a call!
Al Wooffitt
Application Engineer
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