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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Leaks and Why They Matter

Leaks can be discussed quite frequently around industrial environments. These can be refrigerant leaks, water leaks, gas leaks, even information leaks. All of these leaks have one thing in common, they all cost the company money in the end. I often think about several classic cartoons when I hear about leaks being fixed as they are found. They can become a little overwhelming like the “Squirrel” from the movie Ice Age 2.

1 – Ice Age 2 – Scrat – Mission Impossible

When it comes down to it, not many leaks create good results, that is why I want to take a second and educate on the costs your facility may be seeing from compressed air leaks. The leaks within an industrial environment can often account for up to 30% of the total compressed air generated.

So let’s take a look at that, the cost of compressed air is derived from the kWh cost the facility pays to the utility company. Here in the Midwest the average cost is around $0.08 / kWh. The equation to convert this to cost per cubic foot of compressed air is shown below. This formula assumes that the compressor generates four standard cubic feet of compressed air per horsepower of compressor. Again this is an industry acceptable assumption.

The size of a leak will determine how much compressed air is wasted, most of these leaks are not even to the audible range for the human ear which leads them to be undetected for long periods of time. A leak that is equivalent to a 1/16″ diameter orifice can result in an annual loss of more than $836.50 USD. While the scale of this number when compared to the annual revenue of a company may be small, the fact remains that this single leak would more than likely not be the only one. This isn’t the only way leaks will cost money though.

Leaks can also generate false demand which can result in pressure drops on a system. When the pressure on a production line drops this could result in unscheduled shutdowns. Often, when a pressure drop is observed the quick answer is to increase the header pressure which causes even more energy to be utilized and even more compressed air will be pushed out of these leaks. That increase in system pressure comes at a price as well. When increasing a system pressure by 2 psi the compressor will consume an additional percent of total input power. This again will hit the bottom line and result in lower efficiency of operation for the facility.

If you hear that distinct hiss of compressed air leaks when you are walking through your facility, or even if you don’t hear the his and you know that a leak detection action plan is not being practiced and want to find out the best ways to get one in place, contact us. We are always willing to help you determine how to lower the leaks in your facility as well as reduce the system pressure required to keep your lines up and running by implementing engineered solutions at the point of use.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

1 – Ice Age 2 – Mission Impossible Scrat – retrieve from YouTube – https://www.youtube.com/watch?v=S-HniegbnFs

 

Super Air Amplifiers Provide Safe Air During Mine Rescue Missions

superairamp(2)

I have recently had the pleasure of working with a customer developing a method of delivering air to trapped miners during a multi-man mine rescue mission. The federal government mandates that in the event of an explosion, miners must have a safe place to retreat for a minimum of 96 hours. This system will provide them with a supply of air during that period of time. In the initial stages, they had tried using some old venturis left over from a previous project. While this did work, they weren’t as effective or efficient as they needed. Through a little bit of research, they found EXAIR.

Generally, the Super Air Amplifier utilizes a source of compressed air. In this case, instead of using compressed air as the source, they’re using cryogenic liquid air. That air passes through a series of cold plates and heat exchangers and gets to the Super Air Amplifier at about 70°F. This air is then carried into the chamber, giving the miners a source of clean air.

superairamp(1)
Model 120021 in prototype

EXAIR Super Air Amplifiers utilize a patented shim design that allows the unit to entrain ambient air at a rate of up to 25:1 from the compressed air supply. This balanced outlet airflow minimizes wind shear, producing sound levels that are typically three times quieter than other air movers. The Super Air Amplifiers are supplied with a .003” slotted air gap and can be adjusted by replacing the shim with a thicker .006” or .009” shim or by regulating the air pressure supplied to it. In addition to making gross adjustments to the airflow by changing the shim thickness, flow can also be dialed in by regulating the air pressure supplied. All Super Air Amplifier Kits come complete with the a properly sized Auto-Drain Filter to keep the air clean and dry, a Pressure Regulator to “dial” in the airflow, and a shim set. When the filter is installed just upstream of the Super Air Amplifier, there is no need to perform any regular maintenance. With no moving parts to wear out, you can expect many years of reliable operation.

Do you have a cooling or drying application that could benefit from a Super Air Amplifier? Contact an Application Engineer today to find out how EXAIR can help you save compressed air in your application!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

EXAIR Standard Air Knives™: Overview

Standard Air Knife

EXAIR manufactures three different styles of Air Knives; Super, Standard, and the Full Flow.  In this blog, I will be discussing the Standard Air Knives.

The Standard Air Knife uses a Coanda profile for blowing.  The Coanda effect was named after a Romanian aerodynamic pioneer, Henri Coanda, where he found a fluid phenomenon.  He stated that “a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops” (1).  Being that air is a fluid, it will react in the same way.

Compressed air flows through the inlet (1) to the Standard Air Knife, into the internal plenum. It then discharges through a thin gap (2), adhering to the Coanda profile (3) which directs it down the face of the Air Knife. The precision engineered & finished surfaces optimize entrainment of air (4) from the surrounding environment.

The EXAIR Standard Air Knife creates a high velocity air stream along an engineered profile.  So, as the air “hugs” the profile, a low pressure is created which will draw in ambient air.  What does this mean for you?  It will use less compressed air to save you money.  For the Standard Air Knife, it has an amplification ratio of 30:1.  (For every 1 part of compressed air, 30 parts of ambient air is drawn into the stream).  We can use less compressed air and bring in more of the free ambient air to create a strong blowing force.  This design makes the product very efficient.

We stock the Standard Air Knives in various lengths from 3” to 48” (76mm to 1219mm) in two materials, aluminum or 303 stainless steel.  The unique design is very compact; so, it can fit into tight places for blowing and cooling.  The aluminum version uses a plastic shim to set the gap.  They come standard with a 0.002” (0.05mm) shim installed.  We have additional shims to make the Standard Air Knife more versatile.  The shim set will include a 0.001”, 0.003”, and a 0.004” thickness shim (.03mm, .08mm, and 0.1mm respectively) for controlling the air flow from a small breeze to a blast.  The shims are color coded for easy verification.  The stainless steel Standard Air Knife comes with a stainless steel shim for higher temperatures or chemical resistance.

Standard Air Knife Kit

We do offer the Standard Air Knives in kits for a more complete package.  The kit will include the Air Knife, a filter, regulator and the above-mentioned shim set.  The filter will remove the debris and liquid water from the compressed air line to optimize the air knife as well as keeping your product clean.  The regulator is used to make “fine” adjustments to the blowing force.  The shim set is used as a “coarse” adjustment to the blowing force.  Together, you can “dial” in the right amount of air required to do the job without wasting compressed air.

Universal Mounting System

For easy mounting, we do offer a Universal Air Knife Mounting System.  This kit is used to position your air knife securely and precisely.  It comes with a bracket and an articulated arm that can reach up to 30” (762mm).  You can direct the Standard Air Knife in any position to maximize the effectiveness.  It is easy to use as seen in this video: CLICK HERE.

With the today’s cost to make compressed air, it is important to do it as efficiently as possible.  The Standard Air Knife has the ability to give you the effective blowing to remove debris, dry parts, or cool objects without using a large amount of compressed air.  As another feature, the Standard Air Knife is quiet.  It only has a sound level of 83 dBA at 80 psig (5.5 bar).  So, by using this EXAIR product, you are not creating a noise nuisance in the work environment.  If you have any questions about the Standard Air Knife or if you would like to discuss an application, you can contact an Application Engineer at EXAIR.

 

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

 

  1.  Wikipedia – Caonda effect.