Tag: cold air

EXAIR Vortex Tubes are for a Variety of Spot Cooling Applications

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Vortex tube
Cooling or Heating with the Vortex Tube

EXAIR Vortex Tubes are a low cost, reliable and maintenance free solution to a wide variety of industrial spot cooling problems.  They only requirement is a supply of compressed air as the power source.  Vortex Tubes have no moving parts and can produce temperatures that range from -50°F to +260°F (-46°C to +127°C).

Vortex Tubes produce two air streams one cold and one hot, the percentage of cold air flow from the inlet flow is referred to as the cold fraction.  The cold fraction is adjustable by the hot valve on the hot discharge side of the vortex tube.  Adjusting the hot valve results in both air temperature and air volume changes. The colder the air becomes, the volume of that cold air declines. So for very cold temperatures, a smaller volume of air is produced compared to a warmer air temperature.

For the vast majority of industrial cooling applications a larger volume of cool air will provide more efficient cooling than a lesser amount of very cold air.  Generally speaking the highest Btu/Hr values are in the 70-80% cold fraction range.

The exception to this would be in labs or special cases where the coldest temperatures are desired.  Adjusting a Vortex Tube is easy, simply insert a thermometer/thermocouple in the cold air exhaust and set the temperature by adjusting the valve on the hot end of the Vortex Tube.  You will know when you reach max refrigeration (80% cold fraction) as the cold air temperature will be 50°F (28°C) lower than the compressed air supply temperature.

EXAIR Vortex Tubes are constructed from stainless steel.  This ensures excellent wear resistance, corrosion resistance and assures years of reliable operation.  They are offered in 3 different size ranges (small, medium & large).  There are generators located inside the tube (user serviceable) that will change the volumetric flow.  The generators are available in a plastic construction or brass construction for high temperature applications.  The ranges 2 SCFM – 8 SCFM are designated as small Vortex Tubes, 10 SCFM – 40 SCFM are medium and 50 SCFM – 150 SCFM are large.  This feature allows you to customize or change your Vortex Tube for greater flexibility in a wide range of applications.

vortex_generator
Vortex generator

Large Vortex Tubes are specified when a high flow of cold air is needed. There are 16 models to choose from in total.  Capable of providing 3,400 BTU/HR up to 10,200 BTU/HR of cooling power.  These have been used to cool high heat loads that are centrally located or to help cool samples of gases for testing.

Medium Vortex Tubes are the most popular – there are twenty to choose from, depending on the cold air flow rate and temperature you’re looking for. These can produce temperatures as cold as -40°F (-40°C) when set to a 20% Cold Fraction (which is the percentage of total supply air that’s directed to the cold end) and cold air flows as high as 32 SCFM when set to an 80% Cold Fraction, which will produce a cold air temperature of about 20°F (-7°C). Some common uses are cooling ultrasonic welds and brazed joints.

The Medium Vortex Tubes are so popular, in fact, that they’re incorporated into our Adjustable Spot Cooler and Cold Gun Systems. They come ready-to-go with mufflers, cold air hose kits, and magnetic bases, so they couldn’t be easier to use.

Adjustable Spot Cooler

Cold Gun Lineup

Small Vortex Tubes are great when low flows (less cooling power) will succeed, or if compressed air supply is limited.  There are 12 models in total to choose from. These are specified for much smaller applications, like cooling the needle of a sewing machine, small drill bits, etc. You can also get one with a cold air hose & magnetic base…that’s the Mini Cooler System.

Mini Cooler

If you would like to discuss Vortex Tubes, Spot Cooling, efficiency of your compressed air usage, quieter compressed air products and/or any EXAIR product,  I would enjoy hearing from you…give us a call.

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How To Make Compressed Air Get Cold…A Couple Of Different Ways

Published on by Russ BowmanLeave a comment

The Vortex Tube makes cold air for the same reason that a can of compressed air gets cold when I clean my computer keyboard, right?

That’s a common question, and since they both start with compress air and end up with cold(er) air, it’s not an unreasonable assumption.  But the answer is no; they’re not the same.   Both are curious physical phenomena, though:

Cans of compressed air get cold while they’re discharging because of a thermodynamic principle known as the adiabatic effect.  When you pressurize a gas by compressing it into a container, you’re putting all those molecules into a smaller volume of space…and you’re adding potential energy by the compression.  Then, when you release that gas back to atmospheric pressure, that energy has to go somewhere…so it’s given off in the form of heat – from the air inside the can, as the pressure inside the can decreases.  Now, the air that’s not under as much pressure as it was when you pushed the button on top of the can is going to start coming out of the can pretty soon.  I mean, there’s only so much air in there, right?  So, since it’s given off that energy immediately upon the drop in pressure, when it comes out of the can, it’s at a lower temperature than it was before you started spraying it out.

Vortex Tubes, on the other hand, generate a flow of cold air by a completely different phenomenon of physics called, maybe not so curiously, the Vortex Tube principle:

You can get a lot more cold air – and a much lower temperature – from a Vortex Tube than you can from a can of compressed air.

If you need a reliable and dependable flow of cold air, look no further than EXAIR’s comprehensive line of Vortex Tubes and Spot Cooling Equipment.  We’ve got 24 models of Vortex Tubes to choose from, as well as “out of the box” solutions for cooling applications like the Adjustable Spot Cooler, Mini Cooler, Cold Gun Aircoolant Systems. and, to protect your sensitive electrical and electronic enclosures from heat, Cabinet Cooler Systems.  If you’d like to find out more, give me a call.

Russ Bowman

Application Engineer
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Adjustable Spot Cooler: How Cold Can You Go?

Published on by Russ BowmanLeave a comment

I had the pleasure of discussing a spot cooling application with a customer this morning. He wanted to get more flow from his Adjustable Spot Cooler, but still keep the temperature very low.  He machines small plastic parts, and he’s got enough cold flow to properly cool the tooling (preventing melting of the plastic & shape deformation) but he wasn’t getting every last little chip or piece of debris off the part or the tool.

After determining that he had sufficient compressed air capacity, we found that he was using the 15 SCFM Generator. The Adjustable Spot Cooler comes with three Generators…any of the three will produce cold air at a specific temperature drop; this is determined only by the supply pressure (the higher your pressure, the colder your air) and the Cold Fraction (the percentage of the air supply that’s directed to the cold end…the lower the Cold Fraction, the colder the air.)

Anyway, the 15 SCFM Generator is the lowest capacity of the three, producing 1,000 Btu/hr of cooling. The other two are rated for 25 and 30 SCFM (1,700 and 2,000 Btu/hr, respectively.)

He decided to try and replace the 15 SCFM Generator with the 30 SCFM one…his thought was “go big or go home” – and found that he could get twice the flow, with the same temperature drop, as long as he maintained 100psig compressed air pressure at the inlet port.  This was more than enough to blow the part & tool clean, while keeping the cutting tool cool, and preventing the plastic part from melting.

Model 3925 Adjustable Spot Cooler System comes with a Dual Outlet Hose Kit, and three Generators for a wide range of cooling performance.

If you’d like to find out how to get the most from a Vortex Tube Spot Cooling Product, give me a call.

Russ Bowman
Application Engineer
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Intelligent Compressed Air: How do Vortex Tubes Work

Published on by John BallLeave a comment

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 article is to give some insight into some of the physics of what is happening on the inside.

With a Vortex Tube, we apply a high pressure, compressed air stream to a plenum chamber that contains a turbine-looking part that we call a generator 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 is a critical feature within a vortex tube that not only regulates flow and creates the vortex spinning action, it also aligns the inner vortex to allow its escape from the hot end of the vortex tube. Note the center hole on the photo below. This is where the cooled “inner vortex” passes through the generator to escape on the cold air outlet.

Vortex generator

Once the compressed air has processed 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; 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 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 used, 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.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb