Heat is an unavoidable by-product of any cutting or machining operation. Think about it: you’re creating friction on a piece of material with a fast-moving piece of harder material in order to forcibly separate pieces of the original material from its existing shape & size. No matter what, something’s going to get hot: the work piece, the tooling, or (almost always) both. If you don’t do something about it, your parts can become damaged, your tooling can become dull and brittle, and productivity will suffer.
There are ways to alleviate the problem…you can slow the speed of your tooling, but that’s hardly practical, and only marginally effective. You can use liquid cooling…in fact, you may have to if the particulars of the operation require the lubrication you can only get from a cutting oil or liquid coolant. But those can be messy, expensive, and the time you spend maintaining the coolant could certainly be spent better elsewhere…like, on machining your products!
The Cold Gun uses compressed air to produce a stream of clean, cold air at 50°F (28°C) below supply air temperature.
They use Vortex Tube technology…no moving parts to wear out.
Cold flow and temperature are preset to optimize cooling capability, and are non-adjustable to prevent freeze-up during use.
Eliminates the expense of both the purchase & disposal of cutting fluids.
Removes the potential for health problems associated with breathing mist & vapors, and the safety issue of slipping on a wet floor.
Cold Gun Aircoolant System selection is easy & straightforward…we offer a standard, and a High Power version to meet your specific needs.
We also offer Single & Dual Point Hose Kits, to further meet the needs of your application. Right now, you don’t have to decide up front…order a Cold Gun Aircoolant System with a Single Point Hose Kit before December 31, 2018, and we’ll throw in the Dual Point Hose Kit for free.
If you’d like to find out more about how Cold Gun Aircoolant Systems can improve your machining or cutting operations, give me a call.
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There are many theories regarding the dynamics of a vortex tube and how it works. Many a graduate student has studied them as part of their research requirements.
The Vortex Tube was invented by accident in 1928, by George Ranque, a French physics student. He was performing experiments on on a vortex-type pump that he had developed and noticed that warm air exhausted from one end and cold air from the other! Ranque quickly stopped work on the pump, and started a company to take advantage of the commercial possibilities for this odd little device that produced both hot and cold air, using only compressed air, with no moving parts. The company was not successful, and the vortex tube was forgotten until 1945 when Rudolph Hilsch, a German physicist, published a widely read paper on the device.
A vortex tube uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of the two air streams is adjustable with a valve built into the hot air exhaust. Temperatures as low as -50°F (-46°C) and as high as 260°F (127°C) are possible.
Here is one widely accepted explanation of the physics and the phenomenon of the vortex tube.
Compressed air is supplied to vortex tube and passes through nozzles that are tangent to to an internal counterbore (1). As the air passes through it is set into a spiraling vortex motion (2) at up to 1,000,000 rpm. The spinning stream of air flows down the hot tube in the form of a spinning shell, like a tornado (in red). The control valve (4) at the end allows some of the warmed air to escape (6) and what does not escape reverses direction and heads back down the tube as a second vortex (in blue) inside of the low pressure area of the larger warm air vortex. The inner vortex loses heat and exits the through the other end of as cold air (5).
It is thought that that both the hot and cold air streams rotate in the same direction at the same angular velocity, even though they are travelling in opposite directions. A particle of air in the inner stream completes one rotation in the same amount of time that an air particle in the outer stream. The principle of conservation of angular momentum would say that the rotational speed of the inner inner vortex should increase because the angular momentum of a rotating particle (L) is equal to the radius of rotation (r) times its mass (m) times its velocity (v). L = r•m•v. When an air particle moves from the outer stream to the inner stream, both its radius (r) and velocity (v) decrease, resulting in a lower angular momentum. To maintain an energy balance for the system, the energy that is lost from the inner stream is taken in by the outer stream as heat. Therefore, the outer vortex becomes warm and the inner vortex is cooled.
If you have questions about Vortex Tubes, or would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.
Vortex Tube Generators are the internal component that controls the volume of air entering the Vortex Tube and ultimately the volume of cool/cold air produced.
EXAIR manufactures three sizes of Vortex Tubes, small, medium & large. Each size can produce a range of cooling power that can be changed by installing a different generator that will change the volume output capability of that Vortex Tube. The generators for small size vortex tubes can operate at 2, 4 or 8 SCFM (maximum cooling power of 550 BTU/HR), generators for the medium size at 10, 15, 25, 30, or 40 SCFM (maximum cooling power of 2,800 BTU/HR) and the generators for the large size operate at 50, 75, 100 or 150 SCFM (maximum cooling power of 10,200 BTU/HR). The Vortex Tube is sold with one generator installed.
The generators are marked with a number and a letter. The number indicates the capacity (SCFM of air consumption) and the letter indicates the type of operation (“R” for maximum refrigeration or “C” for maximum cold temperature). The maximum refrigeration (“R”) works best when the majority of the inlet air is exhausted out the cold end of the Vortex Tube. They work most efficiently with smaller temperature drops and larger volume of flow than the other generators. The maximum cold generators (“C”) can produce temperatures below 0°F, and work best when the minority of the inlet air is exhausted out the cold end of the Vortex Tube. The volume of cold air produced is less but you will experience greater temperature drops.
If a different cooling capacity is desired, other generators are available by either purchasing them individually or by purchasing one of the (3) highly versatile Vortex Tube Cooling Kits designated as the 3908 (small), 3930 (medium) or 3998 (large). The Kits include the Vortex Tube, Filter Separator, Vinyl Tubing, Tubing Adapter, Tube Clamps, Cold End Muffler (Optional Hot End Muffler Available) and Both “R” & “C” Generators.
If you would like to discuss Vortex Tubes, their Generators, or any of EXAIR’s safe, quiet & efficient compressed air products, I would enjoy hearing from you…give me a call.
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).
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)
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.
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.
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.
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.
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.
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
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.)
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)
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%.
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.
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.