Going Outside The Box With Vortex Tubes

Among EXAIR’s comprehensive line of Intelligent Compressed Air Products, the Vortex Tube stands out as a unique, and fascinating, solution for a variety of applications requiring a flow of cold air:

  • Cabinet Cooler Systems: clean, cold air to protect electrical and electronic components housed in an enclosure.  Installs in minutes; no moving parts; reliable & maintenance free.
  • Cold Gun Aircoolant Systems:  Direct, focused flow of cold air to replace messy coolant in machining, cutting, drilling, grinding, etc., applications.  Integral magnet base for quick & easy installation; single or dual outlet hose kits; standard or High Power to meet any need.  Optimized flow for maximum cooling and freeze prevention.
  • Adjustable Spot Cooler: Similar to the Cold Guns in many ways, but with variable performance for specific applications.  Cold air to -30°F (-34°C) on demand.
  • Mini Cooler: Similar to the Cold Guns and Adjustable Spot Coolers – magnetic base mounting and single or dual outlet hose kits, but more compact.  Lower flows for smaller jobs.

Then there are the Vortex Tubes themselves…at the heart of all of these products, but perfectly capable all on their own.  In fact, in certain situations, “plain old” Vortex Tubes have been used to do the exact same jobs as all of the above products.  They can even be customized, in and of themselves, to meet specific installation, operation, and/or performance needs:

  • High Temperatures: It should come as no surprise that cold air is often needed because a heat-sensitive item is located in a high heat environment.
    • Vortex Tubes come standard with plastic Generators and Buna o-rings, which are good for ambient temperatures up to 125°F (52°C).
    • High Temperature Vortex Tubes are fitted with brass Generators and Viton o-rings for environments where the temperature can reach 200°F (93°C).
High Temperature Vortex Tubes are suitable for use in environments up to 200F (93C).
  • Preset temperature & flow: Many times, the ability to adjust the performance of a Vortex Tube is a big benefit, but occasionally it’s a liability.
    • I know none of your co-workers are like this (nor are mine) but I’ve heard of people who think they “know better” and are prone to tampering with something that is (or WAS) working just fine, thank you very much.
    • Perhaps you actually DO know better, through experimentation and experience, the optimal performance setting for your application.  Let’s say, for example, you install Vortex Tubes on a line of your products, and a technician has to “dial it in” to a specific Cold Fraction.
    • Any Vortex Tube can be fitted with a drilled orifice (or “Hot Plug”) to replace  the Hot Valve, which presets performance to a specific, non-adjustable value.  If you know the Cold Fraction you need, it’s as easy as that.  If not, it’s as easy as getting a stock Vortex Tube, setting the Cold Fraction where you want it, securing the Hot Valve in position (piece of tape works just fine,) and sending it in.
Preset Vortex Tubes feature a fixed plug, replacing the Hot Valve shown in this picture.

If you’ve got any other specific requirements – special materials, fittings, custom flow/temperature parameters, etc., give me a call; let’s talk.

Russ Bowman
Application Engineer
EXAIR Corporation
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Vortex Tubes: What is a Cold Fraction & How to use it to Your Benefit

Vortex Tubes

EXAIR has wrote many different articles about how Vortex Tubes work and the applications in which they are used.  The idea of making cold air without any freon or moving parts is a phenomenon.  This phenomenon can generate cold air to a temperature as low as -50 oF (-46 oC).  In this article, I will explain the adjustment of the Vortex Tube to get different temperatures and cooling effects in reference to the Cold Fraction.

To give a basic background on the EXAIR Vortex Tubes, we manufacture three different sizes; small, medium, and large.  These sizes can produce a range of cooling capacities from 135 BTU/hr to 10,200 BTU/hr.  The unique design utilizes a generator inside each Vortex Tube.  The generator controls the amount of compressed air that can enter into the Vortex Tube.  As an example, a medium-sized Vortex Tube, model 3240, will only allow 40 SCFM (1,133 SLPM) of compressed air to travel into the Vortex Tube at 100 PSIG (6.9 bar).  While a small-sized Vortex Tube, model 3208, will only allow 8 SCFM (227 SLPM) of compressed air at 100 PSIG (6.9 bar).  EXAIR manufactures the most comprehensive range from 2 SCFM (57 SLPM) to 150 SCFM (4,248 SLPM).

Vortex Tube Exploded View

After the compressed air goes through the generator, the pressure will drop to slightly above atmospheric pressure.  (This is the “engine” of how the Vortex Tube works).  The air will travel toward one end of the tube where there is an air control valve, or Hot Air Exhaust Valve.  This valve can be adjusted to increase or decrease the amount of air that leaves the hot end.  The remaining portion of the air is redirected toward the opposite end of the Vortex Tube, called the cold end.  By conservation of mass, the hot and cold air flows will have to equal the inlet flow as shown in Equation 1:

Equation 1: Q = Qc + Qh

Q – Vortex Inlet Flow (SCFM/SLPM)

Qc – Cold Air Flow (SCFM/SLPM)

Qh – Hot Air Flow (SCFM/SLPM)

Cold Fraction is the percentage of air that flows out the cold end of a Vortex Tube.  As an example, if the control valve of the Vortex Tube is adjusted to allow only 20% of the air flow to escape from the hot end, then 80% of the air flow has to be redirected toward the cold end.  EXAIR uses this ratio as the Cold Fraction; reference Equation 2:

Equation 2: CF = Qc/Q * 100

CF = Cold Fraction (%)

Qc – Cold Air Flow (SCFM/SLPM)

Q – Vortex Flow (SCFM/SLPM)

Vortex Tube Charts

EXAIR created a chart to show the temperature drop and rise, relative to the incoming compressed air temperature.  Across the top of the chart, we have the Cold Fraction and along the side, we have the inlet air pressure.  As you can see, the temperature changes as the Cold Fraction and inlet air pressure changes.  As the percentage of the Cold Fraction becomes smaller, the cold air flow becomes colder, but also the air flow becomes less.  You may notice that this chart is independent of the Vortex Tube size.  So, no matter the generator size of the Vortex Tube that is used, the temperature drop and rise will follow the chart above.

Vortex Tube Example

How do you use this chart?  As an example, a model 3240 Vortex Tube is selected.  It will use 40 SCFM of compressed air at 100 PSIG.  We can determine the temperature and amount of air that will flow from the cold end and the hot end.  The inlet pressure is selected at 100 PSIG, and the Hot Exhaust Valve is adjusted to allow for a 60% Cold Fraction.  Let’s use an inlet compressed air temperature to be 68 oF.  With Equation 2, we can rearrange the values to find Qc:

Qc = CF * Q

Qc = 0.60 * 40 SCFM = 24 SCFM of cold air flow

The temperature drop from the chart above is 86 oF.  If we have 68 oF at the inlet, then the temperature is (68 oF – 86 oF) = -18 oF.  So, from the cold end, we have 24 SCFM of air at a temperature of -18 oF.  For the hot end, we can calculate the flow and temperature as well.  From Equation 1,

Q = Qc + Qh or

Qh = Q – Qc

Qh = 40 SCFM – 24 SCFM = 16 SCFM

The temperature rise from the chart above is 119 oF.  So, with the inlet temperature at 68 oF, we get (119 oF + 68 oF) = 187 oF.  At the hot end, we have 16 SCFM of air at a temperature of 187 oF.

With the Cold Fraction and inlet air pressure, you can get specific temperatures for your application.  For cooling and heating capacities, these values can be used to calculate the correct Vortex Tube size.  If you need help in determining the proper Vortex Tube to best support your application, you can contact an Application Engineer at EXAIR.  We will be glad to help.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Controlling Temperature and Flow in a Vortex Tube

VT_air2

A few weeks ago, we looked at the Vortex Tube and provided a general overview of the device (see that blog here.)  In a nutshell – a Vortex Tube uses an ordinary supply of compressed air as a power source, creating two streams of air, one hot and one cold – resulting in a low cost, reliable, maintenance free source of cold air for spot cooling solutions.

One of the features of the Vortex Tube is that the temperature of the cold air and the cold air flow rate is changeable. The cold air flow and temperature are easily controlled by adjusting the slotted valve in the hot air outlet.

Vortex Tube Hot Valve Adjustment
Hot Valve Adjustment for a Vortex Tube

Opening the valve (turning it counterclockwise) reduces the cold air flow rate and the lowers the cold air temperature.  Closing the valve (turning it clockwise) increases the cold air flow and raises the cold air temperature.

VT Adjustment Table

As with anything, there is a trade off – to get higher a cold air flow rate, a moderate cold air temperature is achieved, and to get a very cold air temperature, a moderate air flow rate is achieved.

An important term to know and understand is Cold Fraction, which is the percentage of the compressed air used by the Vortex Tube that is discharged through the Cold End.  In most applications, a Cold Fraction of 80% produces a combination of cold flow rate and and cold air temperature that results in the maximum refrigeration or cooling output form a Vortex Tube.

For most industrial applications – such as process cooling, part cooling, and chamber cooling, maximum refrigeration is best and the 32XX series of Vortex Tubes are preferred.  For those applications where ‘cryogenic’ cooling is needed, such as cooling lab samples, or circuit testing, the 34XX series of Vortex Tube is best.

To set a Vortex Tube to a specific temperature, simply insert a thermometer into the cold air exhaust and adjust the hot valve.  Maximum refrigeration, at 80% Cold Fraction, is achieved when the cold air temperature drop is 50°F (28°C) from the incoming compressed air temperature. See the video posted here for measuring and lowering and the cold air temperature.

For those cases when you may be unsure of the required cold air flow rate and cold air temperature to provide the needed cooling in an application, we would recommend an EXAIR Cooling Kit.  The Cooling Kit contains a Vortex Tube, Cold Air Muffler, Air Line Filter, and a set of Generators that will allow for experimentation of the full range of air flows and temperatures possible.

gh_VTcoolingkit_750x696p
EXAIR Vortex Tube Cooling Kit

To discuss your application and how a Vortex Tube or any EXAIR Intelligent Compressed Air Product can improve your process, feel free to contact EXAIR, myself, or one of our other Application Engineers. We can help you determine the best solution!

Brian Bergmann
Application Engineer

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Vortex Tube Overview

VT_air2

A Vortex Tube uses an ordinary supply of compressed air as a power source, creating two streams of air, one hot and one cold – resulting in a low cost, reliable, maintenance free source of cold air for spot cooling solutions.

The EXAIR Vortex tubes are made of stainless steel, which provides resistance to wear, corrosion and oxidation – ensuring years of reliable, maintenance free operation

How_A_Vortex_Tube_Works

The cold air flow and temperature are easily controlled by adjusting the slotted valve in the hot air outlet.  Opening the valve reduces the cold air flow and the cold air temperature.  Closing the valve increases the cold air flow and and the cold air temperature.

EXAIR Vortex Tubes come in three sizes. Within each size, a number of flow rates, which are dictated by a small internal generator, are available. Selection of the appropriate Vortex Tube can be achieved either by knowing the BTU/hr (Kcal/hr) requirements or the desired flow and temperature requirements. Selection is then based on the specification table (BTU/hr or Kcal/hr is known) or the performance tables (flow and temperature is known.)

Capture
Vortex Tube Specification Tables

 

Cold Fraction
Vortex Tube Performance Tables

The performance of a Vortex Tube is reduced with back pressure on the cold air exhaust. Low back pressures up to 2 PSIG ( 0.1 Bar) will not change performance and a 5 PSIG (0.3 Bar) will change the temperature drop by approximately 5°F (2.8°C)

The use of clean air is essential, and filtration of 25 microns or less is recommended.  EXAIR offers filters with 5 micron elements and properly sized for flow.

A Vortex Tube provides a temperature drop to the incoming supply air.  High inlet temperatures will result in a corresponding rise in the cold air temperature.

EXAIR offers mufflers for both the hot and cold air discharge.  If the cold air is ducted, muffling may not be required.

For best performance, operation at 80 to 110 PSIG (5.5 to 7.6 Bar) of supply pressure is recommended. The Vortex Tubes have a maximum pressure rating of 250 PSIG (17.2 Bar) and a minimum requirement of 20 PSIG (1.4 Bar)

To discuss your application and how a Vortex Tube or any EXAIR Intelligent Compressed Air Product can improve your process, feel free to contact EXAIR, myself, or one of our other Application Engineers. We can help you determine the best solution!

Brian Bergmann
Application Engineer

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Cool Small Parts and Tools, with Clean, Cold Air

Do you need a proven way to reduce downtime and increase productivity on a variety of operations involving small parts where heat is a problem?  EXAIR‘s Mini Cooler produces a stream of 20°F (-7°C) cold air to prevent heat build up and blow away chips and debris.

Especially effective on high speed operations, the Mini Cooler helps to prevent burning, melting, and heat related breakage, and while doing so, at a quiet 76 dBA sound level. Better yet, all done with no moving parts to wear out.

minicooler_appli400
Mini Cooler Cooling a Small Mill Operation

Some popular applications for the Mini Cooler are – small tool cooling, needle cooling, blade cooling, and lens grinding.

There are several advantages to take note of – low cost, increased production rates, better tolerances, and quiet and compact.

minicoolerWFAM_500

The Mini Cooler Systems are available with One or Two Cold Outlets, and also include a 1″ wide Flare Nozzle Tip, and a Manual Drain Air Filter to clean the air, ensuring long, trouble free operation.

Using just 8 SCFM of 100 PSIG compressed air, the Mini Cooler will not tax your compressed air system.  Its small size allows it to fit in areas where larger systems could not fit.  The powerful magnetic base sticks to any ferrous surface and and provides up to 100 pounds of pull force.

If you have any questions about the Mini Cooler, the Adjustable Spot Cooler, Cold Gun or any EXAIR compressed air product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Adjustable Spot Cooler: How Cold Can You Go?

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

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