Vortex Tubes Create Freeze Seals For Maintenance on Water Lines

Freeze plugs or Freeze seals are regularly used in nuclear reactor fluid systems to drain or isolate components that, for various reasons, cannot be conveniently isolated by valving. Once they are isolated, they are able to perform maintenance or upgrades without shutting down an entire system.

The United State Navy utilizes a large vortex tube to supply -50°F cooled air stream into a freeze jacket around the pipe. A time frame is chosen based on pipe size and fluid in the pipe to verify they are generating adequate cooling.  Temperature monitoring is put in place, flow through the pipe is stopped, and cooling of the freeze seal begins.  The water near the walls of the pipe freezes first.  Next, the frozen liquid continues towards the center until a solid plug of ice exists.  The freeze seal is then subcooled to a pre-determined temperature at which point the freeze is considered equivalent to a shut valve. Between the Ice plug and the small bit of pipe shrinkage at the point of cooling these seals are able to hold back thousands of pounds! (See drawing below, Shrinkage exaggerated for viewing)

Vortex Based Freeze Seal

In the attached photo bellow, (Provided by the U.S. Navy, photo by John Lenzo) this is a Freeze seal training Rig! You will see three colored lines, Blue is the cold air flow supplied by the vortex tube, red is the hot air from the vortex tube is exhausting away from the application location, and yellow is the pipe they are creating the freeze seal on. Surrounding that pipe is a jacket that holds the -50°F air in contact with the pipe.

With careful temperature monitoring in place and backup cooling methods on standby the work up stream can start.  Coolant flow throughout the rest of the system can now be reestablished.  Following the repair, flow will again be stopped for several hours while the freeze seal is given time to melt.  This ensures that the ice plug is not shot through the now repaired machine.

If you think you have an application that would benefit from Vortex tube technology, give us a call! We have a team of Application Engineers in from 7AM-4PM EST M-F! Or shoot us an email to techelp@exair.com and one of those Engineers will reach out to you!

Jordan Shouse
Application Engineer

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Freeze Seal Image Provided by the U.S. Navy

Process Cooling Utilizing Vortex Tube Technology

Vortex Tube Theory

What is a Vortex Tube? How long have they been around? How do they work? Vortex Tubes have been around since 1928 with what may seem as an accidental existence by the developer George Ranque. George accidentally discovered the phenomenon while studying physics at Ecole Polytechnique in Paris France. Ranque was performing an experiment on a vortex-based pump to vacuum up iron fillings; during the experiment he noticed that warm air was being expelled out of one side and cold air out of the other when he inserted a cone into one end of the vortex. In 1931 Ranque filed for a patent for the vortex tube and two years later presented a paper on it.

George’s vortex tube was all but lost and forgot about until 1947 when the German physicist Rudolph Hilsch published a paper on the device. This paper became widely read and exposed the vortex tube to the industrial manufacturing environment. This paper revived what was thought to be lost and led the vortex tube into what we see today.

As to how they work, these are a phenomenon of physics and the theoretical math behind them has yet to be proven and set in stone. But the basics are this, high pressure compressed air (typically 100 PSIG) is fed into a chamber which contains a generator. The generator takes that high pressure air and spins it at a very high rate of speed. As the air spins it starts to heat up on the inner walls of the vortex tube as it moves towards the control valve. A part of that hot air exits at that valve. The rest of the air which has now slowed down is forced back up the tube through the center of the first high speed air stream. The middle stream of slower air gives up energy in the form of heat to the outer faster moving air. And because of this the inner stream exits the opposite end as extremely cold air! (Check out image below for a visual representation)    

How a Vortex Tube Works

Now the question is how can this technology be integrated into a production process? See below for applications.

Cold Air Gun Application

A few months ago, a high-performance knitted products manufacturer called. They operate 128 Spindle motors on circular sock machines (CSM) that require couplings. These couplings use hi-speed, hi-temperature bearings that have been failing regularly and prior to the predicted run life. This was resulting in loss of production while the circular sock machines are down and the bearings are replaced. Additional costs associated with refurbishing the failed bearing include labor and new bearings. The average cost of a failed circular sock machines bearing including lost production was around $1925.00 and on average they were seeing 180 premature failures each year.

My recommendation was using a Cold Gun with the dual outlets to spread the cooling around the bearing. They had tried fans and electric blowers and they noticed no benefits. However, when they placed the 3925 on the largest trouble maker that was burning bearings at the highest rate, they noticed a prolonged lifetime of over 260%!!!

The enhanced run life of the circular sock machines was noticed immediately as the non-cooled circular sock machine bearings continued to fail at a much higher rate when compared to the positions with the Cold Air Guns installed.

Based on the average cost of a failed circular sock machine bearings including lost production ($1925.00) and an average of (180) premature failures each year, their estimated annual savings using the Cold Gun is $346,500.00 on just the 12 high fail rate machines they have put these on to date. They are expecting to place a Cold Gun on every circular sock machine within 5 years focusing on the high fail rate machines first. 

If you think you have an application that would benefit from Vortex tube technology, give us a call! We have a team of application Engineers in from 7AM-4PM EST M-F! Or shoot us an email to techelp@exair.com and one of those Engineers will reach out to you!

Jordan Shouse
Application Engineer

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Vortex Tubes Video – How Fast Can They Produce Cold Air?

Today’s video is going to showcase for you just how fast an EXAIR Vortex Tube or spot cooling product produces cold air to published values. The answer may surprise you. Take a couple minutes and watch, then if you have any questions or want to discuss it further, please contact an Application Engineer.

A Vortex Tube produces cold air instantly, cools down the temperature probe in seconds!

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

How Vortex Tubes Work

A vortex tube is an interesting device that has been looked upon with great fascination over the last 89 years since its discovery by George Ranque in 1928. What I’d like to do in this post is to give some insight into some of the physics of what is happening on the inside.

With a Vortex Tube, a high pressure compressed air stream id fed into a plenum chamber that contains a turbine-looking part called a generator. The generator serves to regulate flow and spin the air to create two separate streams. One hot and one cold.

Below is an animation of how a Vortex Tube works:

Function of a Vortex Tube

The generator also provides the pathway for the cold air to escape. This is where the cooled “inner vortex” passes through the generator to escape from the cold air outlet.

Vortex generator

Once the compressed air has moved through the generator, we have two spinning streams, the outer vortex and the inner vortex as mentioned above.  As the spinning air reaches the end of the hot tube, a portion of the air escapes past the control valve (the gold triangle in the animation above); and the remaining air is forced back through the center of the outer vortex.  This is what we call a “forced” vortex.

If we look at the inner vortex, this is where it gets interesting.  As the air turns back into the center, two things occur.  The two vortices are spinning at the same angular velocity and in the same rotational direction.  So, they are locked together.  But we have energy change as the air processes from the outer vortex to the inner vortex.

If we look at a particle that is spinning in the outer vortex and another particle spinning in the inner vortex, they will be rotating at the same speed.  But, because we lost some mass of air through the control valve on the hot end exhaust and the radius is decreased, the inner vortex loses angular momentum.

Angular momentum is expressed in Equation 1 as:

L = I * ω

L – angular momentum
I – inertia
ω – angular velocity

Where the inertia is calculated by Equation 2:

I = m * r2

m – mass
r – radius

So, if we estimate the inner vortex to have a radius that is 1/3 the size of the outer vortex,  the calculated change in inertia will be 1/9 of its original value.  With less mass and  a smaller radius, the Inertia is much smaller.  The energy that is lost for this change in momentum is given off as heat to the outside vortex.

Adjustments in output temperatures for a Vortex Tube are made by changing the cold fraction (with the control valve) and the input pressure.  The cold fraction is a term that we use to show the percentage of air that will come out the cold end.  The remaining amount will be exhausted through the hot end. You can call this the “hot fraction”, but since it is usually the smaller of the two flows and is rarely applied, we tend to focus on the cold end flow with the “cold fraction”.  The “Cold Fraction”  is determined by the control valve on the hot end of the Vortex Tube. The “Cold Fraction” chart below can be used to predict the difference in temperature drop in the cold air flow as well as the temperature rise in the hot air flow.

Vortex Tube Cold Fraction

By combining the temperature drops expressed above with the various flow rates in which Vortex Tubes are available, we can vary the amount of cooling power produced for an application. The above cold fraction chart was developed through much testing of the above described theory of operation. The cold fraction chart is a very useful tool that allows us to perform calculations to predict vortex tube performance under various conditions of input pressure and cold fraction settings.

The most interesting and useful part about vortex tube theory is that we have been able to harness this physical energy exchange inside a tube that can fit in the palm of your hand and which has a multitude of industrial uses from spot cooling sewing needles to freezing large pipes in marine applications to enable maintenance operations on valves to be performed.

We would love to entertain any questions you might have about vortex tubes, their uses and how EXAIR can help you.

Jordan Shouse
Application Engineer

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