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

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

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

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

The difference between a mold and a die? EXAIR Vortex Tubes can help in both applications.

Vortex Tubes

What is the difference between a mold and a die?  A mold is a form that shapes a liquid material into a sold piece.  It requires time for the liquid material to harden and take shape.  A die is a form that shapes a solid piece through brute force.  This can be either through stamping or through metalworking.  I will illustrate examples of both and how the Vortex Tubes were able to improve cycle times.

Mold Example: An automotive company was making plastic gas tanks through blow molding.  Liquid plastic is oozed into a mold, and just before it hardens, air is injected to create a cavity inside while the mold shapes the gas tank.  The warm tank was then placed in a fixture to cool.  Once hardened, then it could be handled and processed for the next operation.  The problem was that it took 3 minutes to harden; creating a bottleneck.  EXAIR suggested two pieces of a model 3250 Vortex Tubes to blow cold air into each cavity of the gas tanks.  This cooling process decreased the hardening time from 3 minutes to 2 minutes.  This improved productivity by 33%.

Movie Film

Die Example: A reel manufacturer was using a die stamping machine that would create the sprocket holes in the outer edge of a 35mm film.  These holes were used to advance the reel strip through printers, projectors, and processing machines.  The stamping die would heat up from the brute force of the cutting edge making the hole.  This would cause issues with the quality of the plastic film reel.  For this application, EXAIR recommended the model 5315 Cold Gun System.  This product is a modified version of the Vortex Tube that includes a magnetic base, muffler, and a dual flexible outlet hose.  They would blow the cold air on both sides of the die to keep them cool.  They were able to increase speeds and also noticed that the die stayed sharper 20% longer before they had to be reworked.

1/4 ton of refrigeration in the palm of your hand

Both customers were intrigued with the EXAIR Vortex Tubes as they can generate cold air by only using compressed air.  They do not use refrigerants, moving parts, or motors to wear.  These simple devices are very compact and can fit into tight places.  EXAIR Vortex tubes offer cooling capacities from 275 BTU/hr to 10,200 BTU/hr.  They can be configured in different styles to best suite your application.

Whether you are using a mold or a die in your process, a Vortex Tube may benefit you.  Heat causes slowdowns and bottlenecks.  With both customers above, the EXAIR Vortex Tubes were able to increase their productivity and decrease their downtime.  If you believe that temperature is affecting your process, you can contact an Application Engineer to discuss how we can help.

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

 

Photo:  Reel Film Cinema By JanBabyCreative Commons CC0 Public Domain

EXAIR Vortex Tubes are for a Variety of Cooling Applications

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 me a call.

Steve Harrison
Application Engineer
Send me an email
Find us on the Web 
Follow me on Twitter
Like us on Facebook

Keep Small Parts Cool with EXAIR’s Mini Cooler

As they always say, “big things come in small packages”. Oftentimes, some of the things that have the most value or quality are quite small. Jewelry or diamonds certainly come to mind as some high-quality items that are relatively small in size. One little product we have at EXAIR is the Mini Cooler. Don’t let the word “Mini” fool you. EXAIR’s Mini Cooler packs a powerful punch while using minimal compressed air and not taking up valuable space on your shop floor.

minicoolerWFAM_500
Single and Dual Point Mini Cooler

The Mini Cooler is a proven, reliable way to reduce downtime and increase productivity on a wide variety of operations involving small parts where heat is causing a problem. With just an ordinary supply of compressed air as the power source, the Mini Cooler uses Vortex Tube technology to produce a 20°F (70°F compressed air temp) stream of cold air. This cold air can be directed to the part to prevent heat build-up that can cause premature tool wear, affect part tolerances and improve product finish. The Mini Cooler consumes just 8 SCFM of compressed air when operated at 100 PSIG, making it an ideal solution when available compressed air is at a premium.

The Mini Cooler can be used for a wide variety of applications, many of which we’ve blogged about here before. This application discusses a manufacturer that made surf casting bags used by fishermen fishing straight off of the beach. They had problems with the needle overheating and breaking which in turn damaged the finished product. Not only were they wasting materials, but also time spent periodically replacing the needles on the sewing machines. A focused stream of cold air from the Mini Cooler was all it took to remedy the situation.

Another application that I had the pleasure of seeing while visiting in Hungary was at a manufacturer of cataract lenses. They were using both the Adjustable Spot Cooler and the Mini Cooler in the milling process of the lenses. The cold air from the Mini Cooler replaced expensive and messy liquid coolant and was capable of maintaining a consistent temperature on the lens to prevent warping.

IMG_1951
Mini Cooler used to maintain a low temperature on cataract lenses during inspection.

The Mini Cooler is available with both single and dual cold outlets, depending on the part needing to be cooled. The kit will include the Mini Cooler, a swivel Magnetic Base for precise mounting and positioning, either a Single or Dual Point Hose Kit, and a Manual Drain Filter with a mounting bracket included. If you’re experiencing heat related troubles on a small application, take advantage of EXAIR’s Unconditional 30-Day Guarantee and give the Mini Cooler a try. You’ll be HEATED if you don’t!

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

Do You Need 30 Days for Testing?

Not long ago while checking out of a motel my laptop bag that was attached to the handle on my suitcase fell forward and the impact shattered the screen on the laptop.  Upon turning the computer on I realized that a new screen was in order.

I waited until I arrived at home and found what I thought to be the correct monitor and quickly ordered it.  It arrived two days later and I painstakingly took the laptop apart and exposed the mounting frame.  The removal of the broken screen and the installation of the new was not too difficult but the cable connector was less than robust and was very tight.  Carefully I worked it back and forth and it came free.

Installation and reassembly went quickly and then I powered up the machine.  I was only greeted with a series of very loud and annoying beeps.  At that point I shut it down and called the company I purchased the screen from and described the issue.  They determined that the resolution of the screen was incorrect for my laptop and that I needed a different model.  They said I could return the incorrect one and upon inspection receive a credit less the return shipping.  At that point I ordered the correct screen and packaged up the wrong one and dropped it off at the parcel delivery service.

The new model arrived and it installed easily and worked perfectly.  I waited patiently and never did see a refund so I called the company and they said that it was an oversight on their end and that it would be corrected within 48 hours.  Sure enough they issued the credit and money was credited back to my account with one exception, the 40% restocking fee!

I can tell you that EXAIR is not that way!  If you order the wrong item or are not satisfied for any reason and the item was purchased within the last 30 days we will facilitate the return and ZERO restocking fee. There are a multitude of reasons our customers would want to take advantage of our 30 day guarantee and we make it a simple transaction if you need to take advantage of it too. Testing is one reason a customer would use this 30 days, other customers may have ordered incorrectly or released product inadvertently, they may have wanted a small sample for a meeting or demonstration at a customers location.

30 day money back guarantee
EXAIR Guarantee

If you want to discuss any EXAIR product, I would enjoy hearing from you…give me a call.

Steve Harrison
Application Engineer
Send me an email
Find us on the Web 
Follow me on Twitter
Like us on Facebook