## Can I Use a Vortex Tube and an Air Knife Together?

This concept does seem a really cool idea. Taking the cold output flow from a Vortex Tube and pumping it into an Air Knife to get the advantage of the Air Knife to amplify the cold air volume. That would be really cool if that were the way it actually worked. The idea that you can take two really interesting products and combine them together like this has intrigued many would be problem solvers who have called or e-mailed us about the idea.

The problem is that the idea does not work and I would like to explain why.

There are two issues that you have working against the idea:

1. The Vortex Tube is a device that works on a pressure differential between its inlet and both outlets (hot and cold). The more extreme the pressure differential, the more effective it is at producing cold air. For example, when 100 PSIG is measured at the inlet and there are zero restrictions to hot and cold flows. This provides for a very strong 7.8:1 ratio of pressure differential across the Vortex Tube. And so, when you place a restriction to that cold end flow (an Air Knife in this example), you raise the pressure at the cold air outlet. When you raise the outlet pressure, the pressure ratio lessens to a point when 20 PSIG is reached at the outlet, the Vortex Tube function is rendered useless for practical purpose. Given the fact that our Super Air Knife only really begins to move a large volume of air at 20 PSIG, you have a mis-match of useful pressures from Vortex Tube outlet to Air Knife inlet.

2. Let us imagine for a moment that you could produce a reasonable cold compressed air flow and feed it into an Air Knife. The manner in which our compressed air operated Air Knives work is that they have a primary flow of compressed air, 1 part. That 1 part pulls in 30 to 40 parts of ambient air from around the immediate area of the Air Knife body. What ends up happening is with an amplification ratio of even 30:1, the output flow becomes highly diluted with the temperature of the secondary, ambient air becoming the majority of the overall output flow temperature. So, you have just made a whole lot of effort to pipe cold air to an Air Knife that ends up producing only a negligible effect in terms of temperature drop.

Perhaps some day we will be able to work around this little problem of back pressures and air entrainment so the two devices could actually be used together. But until then, it is only a fantasy.

Neal Raker
Application Engineer
nealraker@exair.com

## 2 thoughts on “Can I Use a Vortex Tube and an Air Knife Together?”

1. J wegener says:

What if you put the air knife before the vortex tube? i.e. don’t connect their air supply lines; but have the 30:1 amplication of the air knife pulling in cold ambient air from the vortex output?

1. Kirk Edwards says:

The Amplification Ratios 40:1 in the case of our Super Air Knives, and 30:1 from our Standard and Full flow air knives can be a great tool to create the most powerful blast of air for cooling, cleaning and drying!

We have seen people use vortex tubes to try to lower the ambient air temperature around a blow off device that entrains that air, and since there are 30 parts of ambient air for every 1 part of compressed air the cooler the ambient air the better the cooling effect will be on your product! So the logic checks out, however if the ambient air temps are much hotter than the cold air flow from the vortex tube that cold air isn’t going to last very long as air does not hold a temperature differential (Delta T) very well. So if your ambient temp is lets say 80F and the cold air from the Vortex tube is 20F, your end result will still be closer to the 80F side of the spectrum. Will it help a little, yes but it’s probably not going to produce impressive results. This is to say, it is difficult to introduce the cold air from a Vortex Tube in a way that the air knife grabs only that cold air.

Give an application engineer a call! We have worked with customers to design a “Cold” Air knife using several of our Vortex tubes in the past! They are not as efficient as the Super air knives etc. but they tend to get the job done! 1-800-903-9247 or 513-671-3322.