A manufacturer of automotive power transmission shafts was experiencing frequent failure of high pressure plastic rollers on their spin tester. There are four rollers in a 90° array that center the shaft during spin testing. They exert a pressure of around 1,500psi onto the shaft while it’s rotating at 1,000rpm. This generates enough heat to actually melt the rubber coating on rollers, which means stopping testing (which holds up production) while they change out the rollers. Just for it to start all over again.
Thing was, they wanted to mount the Adjustable Spot Coolers where they could have access to the Temperature Control Valve, but the cold air Hose Kit wouldn’t reach the shaft. So they got a couple of extra sections of the cold air hose…they needed one section of the ‘main’ (shown circled in blue, below) to reach into the test rig’s shroud, and two sections of the ‘branch’ (circled in green) to reach to each roller.
Now, adding too much hose length will start to put line loss on the cold air flow, and it will pick up heat from the environment. But if you just need that extra foot of hose to get the job done, this generally works just fine. The extra foot or so they’ve added (5″ to the main and 6″ to each branch) has solved their problem…they haven’t had to replace a roller since the Adjustable Spot Cooler Systems were installed.
Throughout my tenure with EXAIR there are may days where I have tested different operating pressure, volumetric flow rates, back pressures, lengths of discharge tubing, generator compression, and even some new inquiries with cold air distribution all on a vortex tube. These all spawn from great conversations with existing customers or potential customers on different ways to apply and applications for vortex tubes.
Many of the conversations start in the same spot… How exactly does this vortex tube work, and how do I get the most out of it? Well, the answer is never the same as every application has some variation. I like to start with a good idea of the area, temperatures, and features of exactly what we are trying to cool down. The next step is learning how fast this needs to be done. That all helps determine whether we are going to be looking at a small, medium, or large vortex tube and which cooling capacity to choose. After determining these factors the explanation on how to adjust the vortex tube to meet the needs of the application begins.
This video below is a great example of how a vortex tube is adjusted and what the effects of the cold fraction have and just how easy it is to adjust. This adjustment combined with varying the air pressure gives great versatility within a single vortex tube.
The table below showcases the test points that we have cataloged for performance values. As the video illustrates, by adjusting the cold fraction lower, meaning less volumetric flow of air is coming out of the cold side and more is exhausting out the hot side, the colder the temperature gets.
This chart helps to determine the best case scenario of performance for the vortex tube. Then the discussion leads to delivery of the cold or hot air onto the target. That is where the material covered in these two blogs, Blog 1, Blog 2 comes into play and we get to start using some math. (Yes I realize the blogs are from 2016, the good news is the math hasn’t changed and Thermodynamics hasn’t either.) This then leads to a final decision on which model of vortex tube will best suit the application or maybe if a different products such as a Super Air Amplifier (See Tyler Daniel’s Air Amplifier Cooling Video here.)is all that is needed.
Where this all boils down to is, if you have any questions on how to apply a vortex tube or other spot cooling product, please contact us. When we get to discuss applications that get extremely detailed it makes us appreciate all the testing and experience we have gained over the years. Also, it helps to build on those experiences because no two applications are exactly the same.
EXAIRVortex 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.
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.
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.
The flow from the cold side of the Vortex Tubeis characterized in two different ways. First, we characterize the air by ΔT (temperature drop) from the starting compressed air temperature. With a supply pressure of 100 PSIG, the drop in temperature can range from 54° to 123° Fahrenheit. Second, we characterize the flow of air in Standard Cubic Feet per Minute. The different models of vortex tube are design to provide a range of flows and temperature.
When facing this list you have numerous choices that can be daunting. My priorities for selecting a Vortex Tube for a customer are twofold. First, you need the Vortex Tube that will work in your application. Second, I want to choose the model with the least amount of compressed air in order to solve their problem with the least amount of air possible. The smallest Vortex Tube is a model 3202. It also utilizes the least amount of compressed air, 2 SCFM. At 100 PSIG and an 80 percent cold fraction, it will produce a cold flow of 1.6 SCFM at 54° F below your compressed air temperature. If your compressed air temperature is starting at 70° F, your cold temperature will 16° F. All of the Vortex Tubes will be able produce this same temperature drop, but depending on which Vortex Tube you use will determine the volume of flow produced at that temperature.
1.6 SCFM of flow 54° F below compressed air temperature will take 135 BTU/HR away from a small 100°F box, which is enough energy to cool a needle, a small sensor, or a tiny camera, but what if you have a bigger area you need to cool. Then you need to use a Vortex Tube that will produce more flow. The 3202, 3204, and 3208 will all produce air at the same temperature, but the 3204 and 3208 will produce more volume of cold air. With the same parameters as above (100 PSIG of inlet pressure and 80 percent cold fraction) the 3204 will produce 3.2 SCFM of cold air and cool 275 BTU/Hr. out of a 100° F environment. The 3208 will produce 6.4 SCFM of cold air and cool 550 BTU/Hr. These larger Vortex Tubes could be used to cool a closed circuit camera in a hot environment or a small drill bit where coolant is prohibited or undesired. From here our product continue to produce more volume of flow and we can go up to our largest Vortex Tube, 3299 which will use 150 SCFM of compressed and cool up to 10,200 BTU/HR.
What if you have an application where you don’t need more air but 16°F isn’t cold enough? Then you can adjust your cold fraction. Adjusting the cold fraction will allow you to increase the temperature drop. Opening the brass hot valve, will lower the cold fraction. As more air is allowed to escape out of the hot end of the Vortex Tube, the temperature and the flow rate of the cold flow decrease. If you need to cool below a 50% cold fraction we recommend the 3400 series Vortex Tubes. At 100 PSIG this would occur when you need more than 100° F temperature drop.