The video below is one that I have explained to customers countless times over my tenure here at EXAIR. Vortex Tubes are most efficient when discharging the cold and hot air streams into atmospheric conditions. This video is my attempt to showcase just how much it will affect your performance when a restriction on the discharge cannot be avoided.
If you would like to discuss Vortex Tubes and their feasibility in your application, feel free to contact an Application Engineer today!
EXAIR has been manufacturing Intelligent Compressed Air Products since 1983. They are engineered with the highest of quality, efficiency, safety, and effectiveness in mind. Since compressed air is the utility for operation, the performance limitations can be defined by its supply. With EXAIR products and pneumatic equipment, you will need a way to transfer the compressed air from the source to the point-of-use. There are three main ways; pipes, hoses and tubes.
One of the largest systematic problems with compressed air systems is pressure drop. If too large a pressure loss occurs, pneumatic equipment will not have enough power to operate effectively and efficiently. The amount of pressure drop is based on restrictions, obstructions, and piping. When air is forced into small areas, it will cause a high velocity. The high velocity will create turbulent air flow which increases the pressure loss. A restrictive type of pressure drop can be found in different forms, like small diameter pipes or tubing; or restrictive fittings like quick disconnects and needle valves, and undersized filters, regulators and valves.
Why did I bring this up? Pressure drop… Pressure Drop is a waste of energy, and it reduces the ability of your compressed air system to do work. To cut waste, we need to reduce pressure drop. If we look at the equation for pressure drop, we can find the factors that play an important role. Equation 1 shows an equation for pressure drop.
Equation 1:
From Equation 1, differential pressure is controlled by the flow of compressed air, the length of the pipe, the diameter of the pipe, and the inlet pressure. As you can see, the pressure drop is inversely affected by the inner diameter to the fifth power. So, if the inner diameter of the pipe is twice as small, the pressure drop will increase by 25, or 32 times.
It is very important to know the inner diameter of the supply lines to your pneumatic devices. As an example, a model 110006 6” Super Air Knife will need a 3/8″ black, schedule 40 pipe that has an I.D. of 0.493″ (12.5 mm). We use this pipe to flow 21 SCFM of compressed air at 100 PSIG through 50 feet of pipe. What would be the pressure drop? With Equation 1, we get a pressure drop of 1.28 * (21 SCFM/60) ^1.85 * 50 feet / ((0.493″)^5 * 100 PSIG) = 3.15 PSID. Thus, you started with 100 PSIG, and at the end of the 50 ft. pipe, you will only have (100 PSI – 3.15 PSI) = 96.85 PSIG to use.
Let’s look at a 3/8” hose and a 3/8” tube. The 3/8” hose has an inner diameter of 0.375” (9.5 mm), and the 3/8” tube has an inner diameter of 0.25” (6.4 mm). In keeping the same variables except for the diameter, we can calculate the pressure drop with the above equation. 3/8″ hose = 1.28 * (21 SCFM/60) ^1.85 * 50 feet / ((0.0.375″)^5 * 100 PSIG) = 12.4 PSID. 3/8″ tube = 1.28 * (21 SCFM/60) ^1.85 * 50 feet / ((0.25″)^5 * 100 PSIG) = 94 PSID.
As you can see, the 3/8” hose has a pressure drop 3.94 times higher than the 3/8″ NPT pipe. Also, the 3/8″ tube has a pressure drop 7.6 times higher than the hose.
Diameters: 3/8″ Pipe vs. 3/8″ tube
At EXAIR, we want to make sure that our customers are able to get the most from our products. To do this, we need to properly size the compressed air lines. Within our installation sheets for our Super Air Knives, we recommend the in-feed pipe sizes for each air knife at different lengths. (You will have to sign in to the website to download). We also have an excerpt about replacing schedule 40 pipe with a compressed air hose. We state; “If compressed air hose is used, always go one size larger than the recommended pipe size due to the smaller I.D. of hose”. Here is the reason. The 1/4” NPT Schedule 40 pipe has an inner diameter of 0.364” (9.2mm). Since the 3/8” compressed air hose has an inner diameter of 0.375” (9.5mm), the diameter will not create any additional pressure drop. Some industrial facilities like to use compressed air tubing instead of hoses. This is fine as long as the inner diameters match appropriately with the recommended pipe in the installation sheets. Then you can reduce waste from pressure drops and get the most from your EXAIR as well as all other pneumatic products.
With the diameter playing such a significant role in creating or mitigating pressure drop, it is very important to understand the type of connections to your pneumatic devices; i.e. hoses, pipes, or tubes. In most cases, this could be the reason for the under performance of your pneumatic products, as well as wasting money through operation of your compressed air system. If you would like to discuss further the ways to save energy and reduce pressure drops, an Application Engineer at EXAIR will be happy to help you.
This Vortex Tube was not operating properly when initially connected to compressed air
One of the fun parts of Application Engineering at EXAIR is explaining the operation of Vortex Tubes to our customers. Sometimes they’re described as a “reverse tornado” inside of a tube, spinning a pressurized airstream and converting it into a hot and cold flow. Other times we describe it through the generation of two vortices with differing diameters, and the difference in diameters results in one vortex shedding energy in the form of heat.
But, no matter the way we explain their operation, we always stress the importance of proper compressed air plumbing. If the compressed air piping/hoses/connections are not properly sized, performance problems can arise. (This is true for any compressed air driven device.)
This fundamental came to light when working with one of our customers recently. They were using a medium sized Vortex Tube to provide spot cooling in an enclosed space, but were not seeing the flow and temperature drop they knew to be possible with an EXAIR Vortex Tube. And, after looking at installation photos of the application, the root cause was quickly spotted.
The red arrow in the bottom right corner of this image shows the beginnings of a reduction in compressed air supply.
I noticed what looked to be a very small hose connected to the inlet of the Vortex Tube in the image above.
In this additional image, the small compressed air line is in full view. This was the root cause for performance problems in this application.
After further inspection of another photo, the small diameter tube was in full view. This small hose serves as a restriction to compressed air flow, which in turn limits both flow and operating pressure of the downstream devices. What that meant for this application, was poor performance from the Vortex Tube, all stemming from this reduction in piping size.
When looking to find the root cause of a performance issue with a compressed air driven unit, things aren’t always as easy as they were with this application. A visual inspection is always a good idea, but if everything looks correct, here is a list of troubleshooting steps to consider:
Check for quick-disconnects in the plumbing system. Quick-disconnects are great from an operator’s perspective, but they can wreak havoc on compressed air flows due to small inside diameters and air volume restriction.
Determine the operating pressure at the device. This is imperative. In order to make proper decisions to correct the performance concern, good information is required. Knowing what is happening at the device is crucial for proper understanding. There may be 100 PSIG at the main compressed air line, but only 60 PSIG at the device due to plumbing problems. A pressure gauge at the inlet of the compressed air product can provide this information.
Check that the compressed air system has enough volume to properly supply the device. A compressed air driven unit without the correct volume of compressed air is just as bad as having a lack of pressure.
Check for leaks. The US Department of Energy estimates that 20-30% of compressor output in industrial facilities is lost as leaks. If your system and devices aren’t operating as they’re supposed to, check for leaks. They may be contributing to the poor performance. (Don’t know where your leaks are coming from? Use our Ultrasonic Leak Detector!)
Fortunately for this customer, after improving the size of this tubing performance was on par with our published specifications and this customer was back in operation. If you have a question about how to improve the utilization of the compressed air devices in your application, contact an EXAIR Application Engineer.
Quick disconnect pneumatic fittings have been a staple in any manufacturing facility I have ever visited in my 10+ years as part of the manufacturing world. The fact is, they have been around for a lot longer than 10 years. The style we see most often is the 1/4″ Quick Disconnect Fitting, and we are typically troubleshooting a lack of air volume problem because they are not sized properly for the application. These can be found in any industrial supply companies catalog, your local hardware stores, and even auto parts stores. Quick Disconnects are even sold with certain EXAIR Industrial Housekeeping products, the key being they are properly sized.
Properly sizing the quick disconnect is a critical step in the process of deciding how to lay out your piping system as well as how to ensure products operate at optimal performance. As you can see in the picture above, the two quick disconnects on the left are both larger quick disconnects as well as larger NPT thread sizes. The two on the right are smaller and probably a bit more common to see. Also notice the thread sizes on each, these are also manufactured in many other NPT thread options. The through hole on the quick disconnects is decided by the size of the QD, not the thread size on the other end. The example I am illustrating is comparing the 3/8 NPT and 1/4 NPT quick disconnects: Even though you can have 3/8 NPT threads, your throat diameter of the QD is still restricted to .195″ I.D., the same as the 1/4 NPT. This can be a large restriction on a product with a 3/8 NPT thread size.
The Inner Diameters of the Quick Disconnects
Also to be noted is that all QD’s of the same size are not made equally, tests have shown that you can lose as much as 20 psi through a quick disconnect and up to 40 psi when not properly matched with the female QD. This leads to the next step which is to ensure that you are not purchasing a QD on appearance. MAke sure to choose the QD designed to permit the amount of air you need to operate your point of use product without a volume or pressure loss.
These two points are reasons why quick disconnects can diminish your point of use compressed air product performance. If you have questions on which size to use with your EXAIR product or need help determining why your point of use product is not performing how you would like, contact us.
