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.
Vortex Tubes are the perfect solution when dealing with a variety of spot cooling applications. They use compressed air to produce a cold air stream and a hot air stream, with temperatures ranging from as low as -50°F up to +260°F (based on ambient supply temperature) and providing as much as 10,200 Btu/hr. of cooling capacity. By simply adjusting the valve in the hot end of the Vortex Tube, you are able to control the “cold fraction” which is the percentage of air consumed by the vortex tube that is exhausted as cold air versus the amount of air exhausted as hot air. Our small, medium and large Vortex Tubes provide the same temperature drop and rise, it’s the volume of air that changes with the various sizes.
When looking at the below performance chart, you will see that “Pressure Supply” and “Cold Fraction %” setting all play a part in changing the performance of the Vortex Tubes. Take for example, an operating pressure of 100 PSIG and cold fraction setting of 20%, you will see a 123°F drop on the cold side versus a 26°F temperature rise on the hot side. By the using the same Vortex Tube and keeping the operating pressure at 100 PSIG but changing the cold fraction to 80%, you will now see a 54°F temperature drop on the cold side and a 191° rise at the hot end.
We’ve looked at how the cold fraction changes the temperature, but how does it change the flow for the various Models?
Say you are using a Model # 3240 Medium Vortex Tube which consumes 40 SCFM @ 100 PSIG. Again with the cold fraction set at 80% (80% of the consumed compressed air out of the cold end), you would flow 32 SCFM at the cold air exhaust.
40 SCFM x 0.8 (80% CF) = 32 SCFM
Using the same Model # 3240 Medium Vortex Tube but now with a 20% cold fraction (20% of consumed compressed air out of the cold end), you would flow 8 SCFM at the cold exhaust.
40 SCFM x 0.20 (20% CF) = 8 SCFM
As you can see, to achieve the colder air temperatures, the volume of cold air being exhausted is reduced as well. This is important to consider when making a Model selection. Some other considerations include the operating pressure which also has a significant effect on performance. The compressed air supply temperature is important because the above temperatures are temperature differentials, so in the example of the 80% cold fraction there is a 115F temperature drop from your inlet compressed air temperature.
If you need additional assistance, you can always contact myself or another application engineer and we would be happy to make the best selection to fit your specific need.
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.