Tag: spot cooling systems

Vortex Tubes: What is Cold Fraction?

Published on by John BallLeave a comment

EXAIR has written 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 of physics that has been referred to by many names including Ranque Tube, Ranque-Hilsch Tube and Maxwell’s Demon.  The modern name is Vortex Tube.  It can generate cold air to a temperature as low as -50 oF (-46 oC) simply by spinning compressed air at high RPM.  In this article, I will explain the adjustment of the Vortex Tube to get different temperatures and cooling effects with reference to the Cold Fraction.

To give a basic background on the EXAIR Vortex Tubes, we manufacture them in three different body sizes: small, medium, and large.  These sizes can produce a range of cooling capacities, from 135 BTU/hr to 10,200 BTU/hr (34 Kcal/hr to 2,570 Kcal/hr).  The unique design utilizes a generator inside each Vortex Tube.  To read more about the type of generators, you can find this here: Maximum Effort!!! The Two Types of Vortex Tube Generators. The generator controls the amount of compressed air that can enter the Vortex Tube as well as initiating the spinning of the air inside.  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 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).

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 side of the Vortex Tube will blow hot air.  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 air 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)

The percentage of inlet air flow that exits the cold end of a vortex tube is known as the Cold Fraction.  As an example, if the Hot Air Exhaust 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 is 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 Inlet Flow (SCFM/SLPM)

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 the amount of cold air flow becomes less.  You may notice that this chart is independent of the Vortex Tube size.  So, no matter the size of the Vortex Tube that is used, the temperature drop and rise will follow the chart below.

EXAIR Vortex Tube Performance Chart

How do you use this chart?  As an example, we can select a model 3240 Vortex Tube.  It will use 40 SCFM (1133 SLPM) of compressed air at 100 PSIG (6.9 Bar).  We can determine the temperature and amount of air that will flow from the cold end and the hot end.  For our scenario, we will set the inlet pressure to 100 PSIG, and adjust the Hot Exhaust Valve to allow for a 60% Cold Fraction.  Let’s say the inlet compressed air temperature is 68oF.  With Equation 2, we can rearrange the values to find the Cold Air Flow, Qc:

Qc = CF * Q

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

The temperature drop shown in the chart above is 86oF.  If the inlet temperature is 68oF, the temperature of the cold air is (68oF – 86oF) = -18oF.  So, at the cold end, we will have 24 SCFM of air at a temperature of -18oF.  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 shown in the chart above is 119oF.  So, with the inlet temperature at 68oF, we get (119oF + 68oF) = 187oF.  So, we have 16 SCFM of air at a temperature of 187oF coming out of the hot end.

With the Cold Fraction and inlet air pressure, you can get specific temperatures for your application.  For cooling and heating capacities, flow and temperature can be used to calculate the correct Vortex Tube size for your application.  If you need help 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

EXAIR Mini Cooler Is Ideal For Small Spot Cooling Applications

Published on by Russ BowmanLeave a comment

It was 23 °F (minus 5 °C) when I walked out the door this morning, and it was a shock to my system. The primary reason for that shock was the heat (generated from my house’s furnace) that maintains a comfortable temperature inside my home. Relief from that cold came when the internal combustion of gasoline that powers my car’s engine provided heat to the coils that the cabin fan passes air through on its way to the vents that maintain a comfortable temperature inside my car. Heat is a good thing this time of the year.

Heat, however, isn’t always a good thing. Just a few short months ago, I walked out of the building here at quitting time and the 100 °F (37.8 °C) temperature similarly shocked my system. The reason for that was I had just walked out of a comfortably air-conditioned building…and relief came when my car’s trusty air conditioning system started blowing refrigerated air from the same vents that heated air comes out of during these winter months.

Heat from processes like machining, welding, soldering, brazing, electrical losses, rotating or reciprocating equipment, etc., causes problems as well, and it’s not simply a matter of comfort. Removing heat from these processes is critical to sustained operation. Sometimes, a great amount of heat has to be removed. Power plants that generate electricity, for example, have massive pumps that send thousands of gallons of water per minute through huge heat exchangers that condense steam from turbines so that it can be boiled again to keep those turbines spinning.

On the other end of that spectrum are equipment like industrial sewing needles, lens grinders, skitters or small cutting tools, and soldering guns, just to name a few. These can all be successfully addressed with a focused stream of cold air…just like you get from an EXAIR Mini Cooler.

EXAIR Model 3308 Mini Cooler System w/ Dual Point Hose Kit is used to remove heat from this UHMW Polyethylene part, and the cutting tool. This not only keeps the plastic from melting, but also extends the tool life.

The Mini Cooler uses the Vortex Tube phenomenon to generate cold air from compressed air, with no moving parts, on demand. Since it’s a physical phenomenon, as opposed to a direct transfer of heat, the Mini Cooler is generating cold air at rated flow & temperature as soon as you open the supply of compressed air to it. You can turn it on & off as often, or as seldom, as needed. There are no moving parts to wear or electrical components to burn out. With a compressed air consumption of only 8 SCFM @100psig, even fairly small compressors (as low as 3HP for some) can operate a Mini Cooler continuously.

If an application requires a higher rate of cooling, other Vortex Tube operated products are available from stock:

If you’re not sure which Cooling Product fits your needs, EXAIR Application Engineers are standing by to help specify the right one for you…give me a call.

Russ Bowman, CCASS

Application Engineer
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Adjustable Spot Cooler from EXAIR

Published on by Jordan T Shouse2 Comments

The Adjustable Spot Cooler is a low cost, reliable, maintenance free way to provide spot cooling to a myriad of industrial applications. Simply turn the knob, and the temperature can be changed to suit the needs of the process. The Adjustable Spot Cooler delivers precise temperature settings from -30 °F (-34 °C) to room temperature.

Adjustable Spot Cooler
Adjustable Spot Cooler

The Adjustable Spot Cooler utilizes the Vortex Tube technology that converts compressed air into a cold air stream. To learn more about EXAIR vortex tubes, click here.

  • It can produce temperatures form -30 °F to +70 °F (-34 °C tp +21 °C)
  • Parts included for flow rates of 15, 25 and 30 SCFM (425, 708, 850 SLPM.) The unit comes from the factory set at 25 SCFM (708 SLPM)
  • It can produce refrigeration up to 2,000 BTU/hr (504 Kcal/hr.)

A swivel magnetic base allows for easy mounting and portability, you can move it from machine to machine as needed. The flexible cold air outlet tubing holds its position and is easy to aim. Most importantly, there are no moving parts or CFC’s, ensuring maintenance free operation.

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The Adjustable Spot Cooler maintains critical tolerances on machined plastic parts
How the Adjustable Spot Cooler Works

The Adjustable Spot Cooler incorporates a vortex tube to convert a supply of compressed air (1) into two low pressure streams, one hot and one cold. With the turn of a knob, the temperature control valve (2) allows some hot air to flow through a muffling sleeve and out the hot air exhaust (3). The opposite end provides a cold air stream (4) that is muffled and discharged through the flexible hose, which directs it to the point of use. The swivel magnetic base (5) provides easy mounting and portability.

The Adjustable Spot Cooler can produce a wide range of air flows and temperatures as determined by the temperature control valve knob setting and the generator installed. The generator controls the total SCFM (SLPM) of compressed air consumption, and is easy to change. From the factory, the 25 SCFM (708 SLPM) generator is installed, producing up to 1,700 BTU/hr (429 Kcal/hr) of cooling. For less cooling, the 15 SCFM (425 SLPM) generator can be installed, providing up to 1,000 BTU/hr (252 Kcal/hr) of cooling. And for more cooling, the 30 SCFM (850 SLPM) generator can be installed, providing up to 2,000 BTU/hr (504 Kcal/hr) of cooling.

Adjustable Spot Cooler Specifications

Two (2) Systems are available as shown below, and include the 15 and 30 SCFM (425 and 850 SLPM) generators, a filter separator, and either a single or dual point hose kit.

3825_3925 adj spot cooler

If you have any questions on how our Adjustable Spot Cooler can help save you money give us a call! One of our application engineers will be happy to assist!

Jordan Shouse
Application Engineer

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VIDEO Blog: Vortex Tubes and Cooling Kits

Published on by Jordan T ShouseLeave a comment

EXAIR manufactures three sizes of Vortex Tubes, small, medium & large.  Each size can produce a range of cooling power that can be changed by installing a different generator that will change the volume output capability of that Vortex Tube.

If a different cooling capacity is desired, other generators are available by either purchasing them individually or by purchasing one of the (3) highly versatile Vortex Tube Cooling Kits designated as the 3908 (small), 3930 (medium) or 3998 (large).  The Kits include the Vortex Tube, Filter Separator, Vinyl Tubing, Tubing Adapter, Tube Clamps, Cold End Muffler (Optional Hot End Muffler Available) and Both “R” & “C” Generators.

If you would like to discuss Vortex Tubes, their Generators, or any of EXAIR’s safe, quiet & efficient compressed air products, I would enjoy hearing from you…give me a call or shoot me an email!

Jordan Shouse
Application Engineer

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