Vortex Tubes Cool a UV Scanner

Copper smelting furnace

Safety is important when it comes to gas furnaces; and with large ovens, equipment is used to protect workers and equipment.  A copper company was using natural gas for smelting, and they had a UV scanner to monitor the flames.  If the burners go out, the scanner will turn off the gas valves to stop a potential explosion.   As with many instruments, it is important to keep the electronics cool for proper measurements.  In this case, they were having issues with accuracy from the high heat.  They contacted EXAIR for a solution. 

Air path flow for UV scanner

With their UV scanner, it was designed for a “cooling” device already.  This was basically compressed air that would blow around the instrument.  Because of the location, the compressed air was heating up to 125oF (52oC).  This heat would not cool the scanner properly, and it was causing unreliable readings and premature shutdowns.  They gave me the design specifications, and the scanner required 3.2 SCFM (90 SLPM) of air at atmospheric pressure with a maximum of 77oF (25oC).  I mentioned that we had the perfect solution to keep the UV scanner cool and operational; the EXAIR Vortex Tube.   This product can take elevated temperatures of compressed air and reduce it to lower temperatures.   It is a low cost, reliable, maintenance-free solution that uses compressed air to produce cold air as low as -50oF (-46oC).  With a range of cooling capacities from 135 BTU/hr to 10,200 BTU/hr, I was sure that we could meet the requirements for proper cooling. 

To determine the correct size, I had to look at the temperature drop and the flow requirement.  The temperature had to decrease from the 125oF (52oC) incoming compressed air to at least 77oF (25oC).  This would equate to a 48oF (27oC) temperature drop.  The other requirement was the amount of air flow, 3.2 SCFM (90 SLPM).  With the chart below, I see that we are able to get a 52oF (29oC) temperature drop at a 70% Cold Fraction and 40 PSIG (2.8 bar) inlet pressure.  EXAIR Vortex Tubes are very adjustable to get different outlet temperatures by changing the inlet pressure and the Cold Fraction.  The Cold Fraction (CF) is the amount of air that will be coming out the cold end.  With a 70% CF, that means that the adjusting screw on the hot end of the Vortex Tube is turned to allow 70% of the incoming compressed air to go out the cold end.  So, with that information, we can size to the correct model. 

In comparing the above information to the catalog data at 100 PSIG (6.9 bar), we have to consider the difference in absolute pressures.  With an atmospheric pressure of 14.5 PSIG (1 bar), the equation looks like this:

Qv = (Qc / CF) * (Pc + 14.5 PSIA) / (Ps + 14.5 PSIA)

Qv – Catalog Vortex Tube flow (SCFM)

Qc – Cold Air Flow (SCFM)

CF – Cold Fraction

Pc – Catalog Pressure – 100 PSIG

Ps – Supply Pressure – PSIG (Chart above)

From this equation, we can solve for the required Vortex Tube: 

                Qv = (3.2 SCFM / 0.7) * (100 + 14.5 PSIA) / (40 + 14.5 PSIA) = 9.6 SCFM. 

In looking at the catalog data, I recommended our model HT3210 Vortex Tube which uses 10 SCFM of compressed air at 100 PSIG.  The HT prefix is for our High Temperature models for use in temperatures in the range of 125oF to 200oF (52oC to 93oC).  So, after installing, the Vortex Tube was able to supply 73oF (23oC) air at a flow of 3.3 SCFM (94 SLPM); keeping the UV scanner reading correctly and accurately. 

Sometimes compressed air by itself is not enough to “cool” your instruments.  The EXAIR Vortex Tubes can reduce the temperature of your compressed air to very cold temperatures.  If you believe that your measuring equipment is being affected by elevated temperatures like the company above, you can contact an Application Engineer at EXAIR to find the correct solution for you. 

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

Choosing Max Refrigeration Or Max Cold Temp Vortex Tubes

Vortex Tubes have been studied for over 90 years. These “phenoms of physics” and the theory behind them have been discussed on this blog before. But, when it comes to the practical use of a Vortex Tube it is good to discuss how to correctly select the model that may be needed in your application. The reason being, there are different flow rates and an option for maximum refrigeration or maximum cold temperature.

The tendency is to say, well I need to cool this down as far as possible so I need the coldest air possible, give me the maximum cold temperature. More times than not, the maximum cold temperature model is not the best solution for your application because maximum cooling power and maximum cold temperature are not the same thing.  A maximum cold temperature Vortex Tube is best for spot cooling processes that require greater than 80F temperature drop covering a small area – spot cooling at its finest. Theis very cold air is delivered in a low volume. A maximum cooling power Vortex Tube is the best mix of cold temperature and volume of flow. This cold air (50F-80F temperature drop) is delivered at higher volumes which has the ability to remove more heat from certain processes. If you do not know which is bets for your application, follow these next steps. 

The first step, is to call, chat, or email an Application Engineer so that we can best outfit your application and describe the implementation of the Vortex Tube or spot cooling product for you. You may also want to try and take some initial readings of temperatures. In a perfect world you would be able to supply all of the following information to us, but recognizing how imperfect it all is…some of this information could go a long way toward a solution. The temperatures that would help to determine how much cooling is going to be needed are listed below:

Part temperature:
Part dimensions:
Part material:
Ambient environment temperature:
Compressed air temperature:
Compressed air line size:
Amount of time desired to cool the part:
Lastly desired temperature:

With these bits of information, we can use standard cooling equations to determine what temperature of cold air stream and volume of air is needed in order to produce the cooling and your desired outcome. To give an idea of some of the math we have used, check out this handy educational video of how Newton’s law of cooling was used to calculate the amount of time it takes to cool down a room temp beverage in an ice cold refrigerator. 

If you would like to discuss a cooling application, heating application, or any point of use compressed air application, contact an Application Engineer today.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

1 – ThinkWellVids – Newton’s Law of Cooling – Feb. 27, 2014 – retrieved from https://www.youtube.com/watch?v=y8X7AoK0-PA

Convective Heat Transfer: How Do We Use It?

Vortex Tubes have been studied for decades, close to a century. These phenoms of physics and the theory behind them have been discussed on this blog before. Many customers gravitate toward Vortex Tubes when needing parts and processes cooled. The fact of the matter is there is still more to be discussed on how to correctly select the which product may be needed in your application. The reason being, area, temperatures, and air flow volumes play a large role in choosing the best product for cooling. The tendency is to say, well I need to cool this down as far as possible so I need the coldest air possible which leads to the assumption that a Vortex Tube will be the right solution. That isn’t always the best option and we are going to discuss how to best determine which will be needed for your application. The first step, is to call, chat, or email an Application Engineer so that we can learn about your application and assist with the implementation of the Vortex Tube or other cooling product for you. You may also want to try and take some initial readings of temperatures. The temperatures that would help to determine how much cooling is going to be needed are listed below:
  • Part temperature
  • Part dimensions
  • Part material
  • Ambient environment temperature
  • Compressed air temperature
  • Compressed air line size
  • Amount of time desired to cool the part: Lastly desired temperature

With these bits of information, we use cooling equations to help determine what temperature and volume of air will best suit your needs to generate the cooling required. One of the equations we will sometimes use is the Forced or Assisted Convective Heat Transfer. Why do we use convective heat transfer rather than Natural Heat Transfer? Well, the air from EXAIR’s Intelligent Compressed Air Products® is always moving so it is a forced or assisted movement to the surface of the part. Thus, the need for Convective Heat Transfer.
Calculation of convection is shown below: q = hc A dT Where: q = Heat transferred per unit of time. (Watts, BTU/hr) A = Heat transfer area of the surface (m2 , ft2) hc= Convective heat transfer coefficient of the process (W/(m2°C), BTU/(ft2 h °F) dT = Temperature difference between the surface and the bulk fluid (compressed air in this case) (°C, °F)

The convective heat transfer coefficient for air flow is able to be approximated down to hc = 10.45 – v + 10 v1/2

Where: hc = Heat transfer coefficient (kCal/m2 h °C) v = relative speed between the surface of the object and the air (m/s)

This example is limited to velocities and there are different heat transfer methods, so this will give a ballpark calculation that will tell us if we have a shot at a providing a solution.  The chart below is also useful to see the Convective Heat Transfer, it can be a little tricky to read as the units for each axis are just enough to make you think of TRON light cycles. Rather than stare at this and try to find the hidden picture, contact an Application Engineer, we’ve got this figured out. convective_heat_transfer_chart

1 – Convective Heat Transfer Chart
Again, you don’t have to figure any of this out on your own. The first step to approach a cooling application is to reach out to an Application Engineer, we deal with these types of applications and equations regularly and can help you determine what the best approach is going to be.
Brian Farno Application Engineer BrianFarno@EXAIR.com @EXAIR_BF
1 – Engineering ToolBox, (2003). Convective Heat Transfer. [online] Available at: https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html [02/10/2021]

Bifurcation Of Air – The Wonders of Science That Is The Vortex Tube

EXAIR has provided the benefits of vortex tube technology to the industrial world since 1983. Prior to that, French scientist George Ranque wrote about his discovery in 1928 calling it the tube tourbillion. But it wasn’t until German physicist Rudolf Hilsch’s research paper in 1945 on the wirbelrorhr or whirling tube, that the vortex tube entered the minds of commercial engineers. Nearly 60 years later, EXAIR is a leading provider for cooling products utilizing vortex tube technology.

More than 2,000 BTU/hr in the palm of your hand!

EXAIR Vortex Tubes produce a cold air stream down to -50° F and are a low cost, reliable, maintenance-free (there are no moving parts!) solution to a variety of spot cooling applications. These applications span a wide variety of industries and include cooling of electronic controls, soldered parts, machining operations, heat seals, environmental chambers, and gas samples. We’re always finding compelling new cooling opportunities for the vortex tubes.

How a Vortex Tube Works

So how does it produce the cooling stream? Compressed air is plumbed into the side port of the Vortex Tube where it is ejected tangentially into the internal chamber where the generator is located. The air begins flowing around the generator and spinning up to 1 million RPM toward the hot end (right side in the animation above) of the tube, where some hot air escapes through a control valve. Still spinning, the remaining air is forced back through the middle of the outer vortex. Through a process of conservation of angular momentum, the inner stream loses some kinetic energy in the form of HEAT to the outer stream and exits the vortex tube as COLD air on the other side.

The adjustable control valve adjusts what’s known as the cold fraction. Opening the valve reduces the cold air temperature and also the cold airflow volume. One can achieve the maximum refrigeration (an optimum combination of temperature and volume of flow) around an 80% cold fraction. EXAIR publishes performance charts in our catalog and online to help you dial into the right setting for your application, and you can always contact a real, live, Application Engineer to walk you through it.

EXAIR manufactures its vortex tubes of stainless steel for resistance to corrosion and oxidation. They come in small, medium and large sizes that consume from 2 to 150 SCFM and offer from 135 to 10,200 BTU/hr cooling capacity. Each size can generate several different flow rates, dictated by a small but key part called the generator. That generator can be changed out to increase or decrease the flow rate.

While operation and setup of an EXAIR Vortex Tube are easy, its performance will begin to  decrease with back pressure on the cold or hot air exhaust of over 3 PSIG. This is a key  when delivering the cold or hot airflow through tubes or pipes. They must be sized to minimize or eliminate back pressure.

The Vortex Tube is integrated into a variety of EXAIR products for specific applications, like the Adjustable Spot Cooler, the Mini Cooler, the Cold Gun Aircoolant System and our family of Cabinet Cooler Systems.

If you would like to discuss your next cooling application, please contact an Application Engineer directly and let our team lead you to the most efficient solution on the market.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF