Vortex Tubes: What is a Cold Fraction?

Have you ever needed a source of cold air but don’t want to invest in a costly chiller? INTRODUCING Vortex Tubes! Vortex Tubes use compressed air and contain no moving parts to create a cold and hot stream of air from either end of the device. Using the valve located on the hot stream a vortex tube can achieve temperatures as low as -50°F (-46°C) and temperatures as high as 260°F (127°C).

When the vortex tube is supplied with compressed air the air flow is directed into the generator that causes spin into a spiraling vortex at around 1,000,000 rpm. This spinning vortex flows down the neck and wall of the hot tube. The control valve located on the end of the hot tube allows a fraction of the hot air to escape and what does not escape reverses direction and travels back down the center of the tube and exhausts out of the cold end. Inside of the low-pressure area of the larger outer warm air vortex, the inner vortex loses heat as it flows back to the cold end of the vortex and as it exits the vortex expels cold air. The absolute temperature drop that occurs during this process is going to be controlled by the cold fraction of the Vortex Tube and the supply pressure.

The brass screw used to control the cold fraction of a vortex tube

The cold fraction is defined as the amount of the inlet supply air that will exit out of the cold end of the vortex tube. An example would be if I had 10 SCFM supplied to a vortex tube with 60% cold fraction, then 6 SCFM would be exiting the cold discharge. Cold based on the amount of air you allow out of the hot end of the vortex tube you can control the temperature drop of the cold air. A smaller cold fraction which only allows a small amount of air to exit the cold discharge will result in a larger temperature drop; and vise versa a larger cold fraction will result in a much smaller temperature drop.

Table the shows the temperature drop and rise in correlation with the cold fraction and pressure

Here a EXAIR we have designed our vortex tubes to operate optimally at both a high cold fraction and a low cold fraction. The 32XX series designed to give you the best refrigeration, which means it will work well for cold fractions ~60% – 80%. This will give you a smaller temperature drop with more air flow which allows you to keep things cool much easier. This contrasts with the 34XX series which is designed more optimal performance at lower temperatures; this means the optimal cold fraction would be ~20% to 40%. Cold fractions this low will produce very little air flow but the temperature will be very cold (as low as -50°F). This is useful if you need to get an item down to a very low temperature.

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Tried and True Products with Modern Performance and Safety Features

Over Labor Day I got the chance to take my dad and his friend climbing in Seneca Rocks West Virginia for the first time in a very long time. Seneca Rocks is a large Quartzite knife edge located in the Monongahela National forest on route 33. The majority of climbing there is what is known as Trad Climbing, which is just short for traditional climbing and is where one must place their own protection to clip the rope into (also pray it holds when you fall). Trad climbing requires a strong mental fortitude and precise physical movements as you jam different parts of your body into various sized cracks.

Me on the left and my Dad’s friend at the trail head for the hike to “the walls”.

In the ever-expanding world of new technology and advancements of outdoor adventure gear, all trad climbers stick with the same gear that was used some 30+ years ago. Although the materials and performance have improved the very principle and mechanics behind them has not. In this case the old saying “If it ain’t broke don’t fix it!” rings true. Sometimes when it comes to a solution, whether its hanging 200’ in the air or updating a process line, traditional is a great choice due to its simplicity and effectiveness.

Compressed air has been around since 1799 but the idea has been around since 3rd Century B.C. making it one of the oldest utilities next to running water. When it comes to manufacturing applications it’s about as tried and true as you can get, so why not look into our engineered products to help you solve your issues. Their simplicity and effectiveness remain, while their efficiency, safety and performance have been engineered to modern day needs.  These modern needs have insisted that products be safer and more efficient then they were 30+ years ago.  

One example of this is EXAIR’s Vortex Tube. Vortex tubes where discovered in 1931 and were exposed to industrial manufacturing in 1945. EXAIR improved upon them when the company began in 1983. Today they are still used for various cooling applications such as replacing mist coolant on CNC machines, cooling down plastic parts during ultrasonic welding, and keeping electrical cabinets cool so they don’t overheat.

Another example is air nozzles, nozzles are used for many different purposes like cleaning or cooling parts. If you are using nozzles from 30 years ago because they are effective, there is a good chance you can improve you r efficiency and increase safety for your personnel with EXAIR’s engineered Super Air Nozzles. They are designed in a variety of styles to fit your needs from tiny micro nozzles to massive cluster nozzles to blow off or cool  a multitude of parts and processes. 

Sub-zero air flow with no moving parts. 3400 Series Vortex Tubes from EXAIR.

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Battling Heat Transfer

If you haven’t read many of my blogs then this may be a surprise. I like to use videos to embellish the typed word. I find this is an effective way and often gives better understanding when available.  Today’s discussion is nothing short of benefiting from a video.

We’ve shared before that there are three types of heat transfer, more if you go into sub-categories of each. These types are Convection,  Conduction, and Radiation. If you want a better understanding of those, feel free to check out Russ Bowman’s blog here.  Thanks to the US Navy’s nuclear power school, he is definitely one of the heat transfer experts at EXAIR.  If you are a visual learner like myself, check out the video below.

The Application Engineering team at EXAIR handles any call where customers may not understand what EXAIR product is best suited for their application. A good number of these applications revolve around cooling down a part, area, electrical cabinet, or preventing heat from entering those areas.  Understanding what type of heat transfer we are going to be combating is often helpful for us to best select an engineered solution for your needs.

Other variables that are helpful to know are:

Part / cabinet dimensions
Material of construction
External ambient temperature
If a cabinet, the internal air temperature
Maximum ambient temperature
Desired temperature
Amount of time available
Area to work with / installation area

Understanding several of these variables will often help us determine if we need to look more towards a spot cooler that is based on the vortex tube or if we can use the entrained ambient air to help mitigate the heat transfer you are seeing.

If you would like to discuss cooling your part, electrical cabinet, or processes, EXAIR is available. Or if you want help trying to determine the best product for your process contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

Video Source: Heat Transfer: Crash Course Engineering #14, Aug 23, 2018 – via CrashCourse – Youtube – https://www.youtube.com/watch?v=YK7G6l_K6sA

Cooling With Compressed Air: Air Knife vs. Vortex Tube Products

One of the popular applications for the EXAIR Super Air Knife is cooling. When mounted so that the air flow sweeps across the surface of a product, the laminar nature of the air flow works to maximize the contact time with the surface, which also maximizes the heat transfer…which means better product cooling than, say the turbulent air flow from a fan or blower.

Still, it’s common for us to get questions about how to provide even faster cooling.  Well, the two main variables in heat transfer are the time the air is in contact with the product, and the difference in temperature between the product surface and the air.

We’ve already touched on “time in contact”…sweeping the laminar flow across the surface at as low of an angle as you can, against the direction of travel, is ideal.  Combine that with the extraordinarily high air flow due to the entrainment level of the Super Air Knife, and you get an awful lot of air in contact with the surface, for a (relatively) long time.

Super Air Knives cool steel casting from 1,725°F (940°C) to 200°F (93°C) in under 20 minutes.

The difference in temperature, though, is a little trickier to deal with.  Because the developed flow from the Super Air Knife is mostly entrained ambient temperature air from the surrounding environment, you’re at the mercy of that ambient temperature.  One of the most common question – of the common questions about faster cooling – is, can you feed a Super Air Knife with cold air from a Vortex Tube?  The answer is no, for two big reasons:

  • The Vortex Tube’s cold flow can’t be back pressured, which would happen if you fed it through the plenum of a Super Air Knife and tried to make it come out the 0.002″ gap.
  • Even if it did work, the entrained air which, remember, makes up most of the flow, is still room temperature…meaning the total developed flow is a lot closer to room temperature than however cold the air you fed the Super Air Knife would be.

If the surface area to be blown on, to effect the desired cooling, is suitably sized, a Vortex Tube can be installed at a low angle to sweep its flow across.  The cold air flow from a Vortex Tube can also be distributed to more than one point, to cover more surface area.  That’s exactly what we do with our Dual Point Hose Kits for our Adjustable Spot Coolers, Mini Coolers, and Cold Gun Aircoolant Systems:

Dual Point Hose Kits can distribute air to both sides of a part, or onto a wider surface, than a single point discharge.

In fact, both the Single and Dual Point Hose Kits have a variety of tips they can be fitted with for tighter, or broader, flow patterns:

In some cases, multiple Vortex Tube products can be used, and, in other situations, the cold air can be directed through a manifold of some sort:

There are numerous methods to distribute the cold air flow from a lone, or a series of, Vortex Tubes.

Applications like the two on the right above (setting molten chocolate in molds, and keeping those white plastic parts during ultrasonic welding, respectively,) commonly start out as Air Knife inquiries, but the need for refrigerated air leads to creative Vortex Tube solutions.

If you’d like to discuss whether your application is best served by a Super Air Knife or a Vortex Tube Spot Cooling Product, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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