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 few months ago I got a call from a major producer of high-performance knitted products who operates 128 Spindle motors on circular sock machines (CSM) that require couplings. These couplings use hi-speed, hi-temperature bearings that have been failing regularly, prior to the predicted run life. This was resulting in loss of production while the CSM is down and the bearings are replaced, repair costs associated with refurbishing the failed CSM bearing include labor, new bearings, lost production, etc. The average cost of a failed CSM bearing including lost production was around $1925.00 and on average they were seeing 180 premature failures each year.
My recommendation was using a 3925 Adjustable Spot Cooler System with the dual outlets to spread the cooling around the bearing. They had tried fans and electric blowers and they noticed no benefits. How ever 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 CSMs was noticed immediately as the non-cooled CSM bearings continued to fail at a much higher rate when compared to the positions with the Exair Spot Coolers installed.
Based on the average cost of a failed CSM bearing including lost production ($1925.00) and an average of (180) premature failures each year, their estimated annual savings using the Adj. Spot Cooler 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 3295 on every CSM within 5 years focusing on the high fail rate machines first.
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:
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.
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.
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.
EXAIR’s Vortex Tubes are a low-cost, reliable, and maintenance-free solution to a variety of industrial spot cooling problems. With just an ordinary supply of compressed air, the Vortex Tube produces two streams of air: one hot and one cold. This is achieved without any moving parts or refrigerants!!
The Vortex Tube is capable of achieving a temperature drop/rise from your compressed air supply ranging from -50°F to +260°F (-46°C to +127°C). Flow rates range from 1-150 SCFM (28-4,248 SLPM) and refrigeration of up to 10,200 Btu/hr. With all Vortex Tubes constructed of stainless steel, they’re resistant to corrosion and oxidation ensuring you years of reliable, maintenance-free operation.
In addition to providing a range of different Vortex Tubes available to ship same-day from stock, EXAIR also has a few options available for cases where a stock Vortex Tube may not be the right solution. The standard Vortex Tube is suitable for use in environments with ambient temperatures up to 125°F (52°C) due to the plastic generator and Buna o-rings. For more extreme environments and ambient temperatures up to 200°F (93°C), we install a brass generator and replace the Buna o-rings with Viton seals.
All standard Vortex Tubes are adjustable. A small valve is located at the hot air exhaust end of the tube. Using a flat-tipped screwdriver, you can adjust the amount of air that is permitted to exhaust from the hot end. As more air is allowed to escape, the temperature at the cold end of the tube drops even further. The volume of air at the cold end as the temperature drops will also decrease. The percentage of air exhausting from the cold end relative to the total air consumption is referred to as the cold fraction percentage. Lower cold fractions will produce lower temperatures, but there won’t be as much volume. Finding the proper setting for your Vortex Tube can take some adjusting.
As we all know, if there’s a knob to turn, button to press, or adjustment that can be made an operator is inevitably going to tinker with it. Day shift will blame the night shift, night shift blames the day shift, and it can present a problem when the Vortex Tube has been specifically tested and set to achieve the desired cold fraction. If you know the cold fraction you need, but would prefer to prevent it from being able to be adjusted, EXAIR can install a precisely drilled hot plug to set the cold fraction percentage to your specifications and eliminate any potential for it to be changed.
If you’d still prefer to keep the adjustability, but don’t have the capabilities to measure and set it yourself, we can also set any Vortex Tube to the desired cold fraction with the adjustable valve and send it to you ready to be installed. We’ll provide you with a special model number so you can rest assured that any time you need another it’ll come set to your specification.
At EXAIR, we’re committed to providing you with the best solution possible for your application. Sometimes that isn’t going to be achievable with a standard stock product. Just because you don’t see it in the catalog or on our website, doesn’t mean we can’t do it. If you have a unique application and would like more information on getting a special Vortex Tube, contact an Application Engineer today.