Controlling Temperature and Flow in a Vortex Tube

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A few weeks ago, we looked at the Vortex Tube and provided a general overview of the device (see that blog here.)  In a nutshell – a Vortex Tube uses an ordinary supply of compressed air as a power source, creating two streams of air, one hot and one cold – resulting in a low cost, reliable, maintenance free source of cold air for spot cooling solutions.

One of the features of the Vortex Tube is that the temperature of the cold air and the cold air flow rate is changeable. The cold air flow and temperature are easily controlled by adjusting the slotted valve in the hot air outlet.

Vortex Tube Hot Valve Adjustment
Hot Valve Adjustment for a Vortex Tube

Opening the valve (turning it counterclockwise) reduces the cold air flow rate and the lowers the cold air temperature.  Closing the valve (turning it clockwise) increases the cold air flow and raises the cold air temperature.

VT Adjustment Table

As with anything, there is a trade off – to get higher a cold air flow rate, a moderate cold air temperature is achieved, and to get a very cold air temperature, a moderate air flow rate is achieved.

An important term to know and understand is Cold Fraction, which is the percentage of the compressed air used by the Vortex Tube that is discharged through the Cold End.  In most applications, a Cold Fraction of 80% produces a combination of cold flow rate and and cold air temperature that results in the maximum refrigeration or cooling output form a Vortex Tube.

For most industrial applications – such as process cooling, part cooling, and chamber cooling, maximum refrigeration is best and the 32XX series of Vortex Tubes are preferred.  For those applications where ‘cryogenic’ cooling is needed, such as cooling lab samples, or circuit testing, the 34XX series of Vortex Tube is best.

To set a Vortex Tube to a specific temperature, simply insert a thermometer into the cold air exhaust and adjust the hot valve.  Maximum refrigeration, at 80% Cold Fraction, is achieved when the cold air temperature drop is 50°F (28°C) from the incoming compressed air temperature. See the video posted here for measuring and lowering and the cold air temperature.

For those cases when you may be unsure of the required cold air flow rate and cold air temperature to provide the needed cooling in an application, we would recommend an EXAIR Cooling Kit.  The Cooling Kit contains a Vortex Tube, Cold Air Muffler, Air Line Filter, and a set of Generators that will allow for experimentation of the full range of air flows and temperatures possible.

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EXAIR Vortex Tube Cooling Kit

To discuss your application and how a Vortex Tube or any EXAIR Intelligent Compressed Air Product can improve your process, feel free to contact EXAIR, myself, or one of our other Application Engineers. We can help you determine the best solution!

Brian Bergmann
Application Engineer

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Vortex Tube Cooling: One Vortex Tube, Multiple Targets, Will This Work?

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I had this question posed to me the other day. The customer asks, “I have three, small, enclosed spaces that are all within about five feet of each other. I’d like to put vortex tube cooling into each space. Can I do it with one vortex tube or will I have to use three of them?”

Imagine if you will, the cold air output of a single vortex tube being split three ways and ducted into each of these small chambers. While it is definitely technically possible to do, it isn’t always a feasible idea from the point of view of lost cooling power. Also, anytime that you can split up the effect you are trying to create whether that be cooling with a Vortex Tube or blowing off a large target that has many features to it, generally it is better practice to divide the application solution up to be applied over multiple, smaller units rather than one large one.

In this customer’s case, he wanted to save money on the purchase of multiple vortex tubes by purchasing one model 3230 vortex tube and plumbing the cold air output to his three cooling chambers. The problem is that the ambient temperature outside the boxes is rather hot and also contains high humidity. How exactly is this a problem?  You might ask. The problem is in all of the heat lost in cooling down the cold air distribution pipe (the pipe, hose or tube delivering the cold air into the chambers) that lies outside each box. That results in a net temperature gain (higher temperature) of the cold air you are trying to use for cooling the chambers or enclosures. With that lost cooling power, the customer runs a risk of not having sufficient cooling power to offset the heat load in each chamber. There is also the issue of back-pressure being presented to the Vortex Tube itself from the cold air distribution piping. When subjected to back-pressure, vortex tubes will lose their cooling capacity. Finally, there is the problem of getting equal cooling power delivered to each chamber. In this case, the solution of piping cold air to each chamber would cause an un-even distribution of the cold air with the closest chamber receiving the lion’s share of the cooling, leaving the other two under-cooled.

So, what is a better way to do this?  The method I suggested to the client was to use three of our model 3208 (8 SCFM) vortex tubes, allowing for direct connection of the vortex tube cold air output to each chamber. The cold air no longer has to cool down the cold air piping thus leaving more cooling power for each chamber, there is no back-pressure issue, and finally and probably most importantly would be the total air consumed would only be 24 SCFM in this case (3 x 8 SCFM) vs. 30 SCFM with a single larger vortex tube. That is a 20% savings on compressed air use in a straight up comparison. Depending on how many hours a day the system would be used, the difference in purchase price could be made up by lower operating cost in less than a year.

Neal Raker
Application Engineer
nealraker@exair.com