Tag: cooling tubes

The Legend of Rudolf Hilsch

Published on by jasonkirbyLeave a comment

It is thought that Georges Ranque, a French inventor, inadvertently discovered a key principle while developing early prototypes during the German occupation of France. These prototypes later attracted the interest of Rudolf Hilsch, a German physicist who was working on low-temperature refrigeration systems for military applications. Although Hilsch improved upon Ranque’s original design, he found that it did not surpass conventional refrigeration methods in achieving lower temperatures. Ultimately, the device became known as the Hilsch tube.

The Hilsch tube was constructed using a pair of modified nuts along with several other components. The horizontal section of the T-shaped fitting contains a specially machined element that fits tightly within the arm, featuring a spiral cross-section on the inside that differs from its external shape. At the spiral’s “step,” a small opening connects to the T’s leg, allowing air to enter through the leg and exit via this opening, creating a spiraling flow. The “hot” pipe measures approximately 14 inches in length with a half-inch internal diameter, and its far end is fitted with a stopcock to control the system’s pressure. In contrast, the “cold” pipe is about four inches long, also with a half-inch internal diameter, and its end that connects to the spiral piece includes a washer with a central hole of roughly a quarter of an inch in diameter. Various washers with different hole sizes can be utilized to adjust the system’s performance.

EXAIR’s Vortex Tube operates by channeling compressed air into a tube where it flows through nozzles positioned tangentially to an internal counter-bore. This innovative nozzle design induces the air to rotate in a vortex at speeds reaching up to 1,000,000 RPM. As the air spins, it makes a 90° turn, allowing a valve at one end to release some of the heated air. The remaining air continues down the tube, losing heat in the process, and ultimately exits through the opposite end as cold air.

Both streams in a Vortex Tube rotate in the same direction and at the same angular velocity, which would typically suggest that the rotational speed of the inner vortex should increase due to the conservation of angular momentum. However, this is not observed in practice. A useful analogy can be drawn from Olympic Figure Skating: when a skater extends her arms, her spinning slows down, but as she pulls them in, her rotational speed increases significantly. In the case of the Vortex Tube, the inner vortex maintains a constant speed because it has lost angular momentum. This loss manifests as heat, which is expelled from the hot side of the tube. Consequently, the inner vortex cools down, allowing the cooled air to be channeled for various industrial applications.

How the EXAIR Cabinet Cooler System Works

The theory behind the Vortex Tube is applied to standard Vortex Tubes and a range of other products designed with specific features tailored to your needs. EXAIR offers a variety of solutions, including Cabinet Coolers, Cold Guns, Adjustable Spot Coolers, Mini Coolers, and Vortex Tubes, all of which function based on this fundamental principle.

If you have questions about Rudolf Hilsch, or anything regarding EXAIR and our products, please do not hesitate to reach out.

Jason Kirby
Application Engineer
Email: jasonkirby@exair.com
Twitter: @EXAIR_jk

Utilizing EXAIR Accessories

Published on by jasonkirbyLeave a comment
Accessories

At EXAIR, we take great pride in our Intelligent Compressed Air Products, which are renowned for their efficiency and minimal maintenance requirements, thanks to their design featuring few or no moving parts. While we often highlight these advantages, we also do not want to overlook the importance of the accompanying accessories that enhance our products’ performance. These accessories play a crucial role in ensuring our compressed air solutions maintain their low maintenance and reduced noise levels, further solidifying their compliance with OSHA safety standards.

Compressed air filters and regulators are among the most essential accessories we offer, and we highly recommend their use with all our products, as well as with other brands. The Filter Separator effectively eliminates water, dirt, and rust from your compressed air system, while the 5-micron filter element prevents contaminants from clogging or damaging connected equipment. For more precise and additional filtration, an Oil Removal Filter should be installed downstream of the Filter Separator; it utilizes a 0.03-micron element to remove oil and solid particles. Our Pressure Regulators allow you to set the desired operating pressure, and we advise maintaining the minimum pressure necessary for optimal performance. This not only conserves air but also fine-tunes the efficiency of EXAIR products in various applications.

Good engineering practice calls for point of use filtration and moisture removal, such as that provided by EXAIR Filter Separators.
The Thermostat’s leads (left) are spliced into the Solenoid Valve’s ‘hot’ lead (bottom right), which essentially acts as the automatic temperature controlled ‘on/off’ switch for the Cabinet Cooler System. NEMA 4/4X versions include mounting hardware (top right).

We offer specialized accessories designed to enhance the performance of some of our products. For instance, our Line Vacs are complemented by the Line Vac Hose, while our Cabinet Coolers can be paired with Thermostats and Solenoid Valves. Additionally, we recommend Mufflers for optimal use with our Vortex Tubes. When it comes to our Air Knives, we provide several excellent options. The Universal Air Knife Mounting System offers a straightforward and dependable solution for mounting. For applications requiring longer knives or independent control of airflow sections, our Coupling Bracket Kits are ideal. Lastly, our Air Knife Plumbing Kits simplify the plumbing process for Air Knives exceeding 24 inches in length.

For those looking to connect Intelligent Compressed Air Products, we offer a range of compressed air hoses and fittings designed to enhance the convenience of installation. Coiled Hoses are an excellent match for our Safety Air Guns, providing greater mobility during operation. Additionally, our Compressed Air Hoses are frequently utilized with our Industrial Housekeeping products, ensuring that both the drum and dolly have the necessary reach for effective use.

Model 9256 6″ Stay Set Hose

If you are looking for an effective solution to mount or position your Air Nozzles, consider our Magnetic Bases, Stay Set Hoses, and Swivel Fittings, which can be combined to create a comprehensive setup.

If you have questions about our accessories, or anything regarding EXAIR and our products, please do not hesitate to reach out.

Jason Kirby
Application Engineer
Email: jasonkirby@exair.com
Twitter: @EXAIR_jk

Adjustable Spot Cooler – Coarse Adjustments

Published on by John BallLeave a comment

Recently, I had a customer ask me about our Adjustable Spot Cooler and how to change the cold flow and cooling capacity.  In this video, I will demonstrate how to change the generator to accomplish both. Watch below:

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

Controlling Temperature and Flow in a Vortex Tube

Published on by John BallLeave a comment

EXAIR has written many different articles about how Vortex Tubes work and the applications in which they are used.  The idea of making cold air without freon or moving parts is a phenomenon.  This phenomenon is the Vortex Tube.  It 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 with reference to the Cold Fraction.

To give a basic background on the EXAIR Vortex Tubes, we manufacture them in three different body sizes: small, medium, and large.  These sizes can produce a range of cooling capacities, from 135 BTU/hr to 10,200 BTU/hr (34 Kcal/hr to 2,570 Kcal/hr).  The unique design utilizes a generator inside each Vortex Tube.  The generator controls the amount of compressed air that can enter the Vortex Tube as well as initiating the spinning of the air inside.  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 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 side of the Vortex Tube will blow hot air.  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 air 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)

The percentage of inlet air flow that exits the cold end of a vortex tube is known as the Cold Fraction.  As an example, if the Hot Air Exhaust 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 is 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 Inlet Flow (SCFM/SLPM)

EXAIR Vortex Tube Performance Chart

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 the amount of cold air flow becomes less.  You may notice that this chart is independent of the Vortex Tube size.  So, no matter the size of the Vortex Tube that is used, the temperature drop and rise will follow the chart below.

How do you use this chart?  As an example, we can select a model 3240 Vortex Tube.  It will use 40 SCFM (1133 SLPM) of compressed air at 100 PSIG (6.9 Bar).  We can determine the temperature and amount of air that will flow from the cold end and the hot end.  For our scenario, we will set the inlet pressure to 100 PSIG, and adjust the Hot Exhaust Valve to allow for a 60% Cold Fraction.  Let’s say the inlet compressed air temperature is 68oF.  With Equation 2, we can rearrange the values to find the Cold Air Flow, Qc:

Qc = CF * Q

Qc = 0.60 * 40 SCFM = 24 SCFM of cold air flow

The temperature drop shown in the chart above is 86oF.  If the inlet temperature is 68oF, the temperature of the cold air is (68oF – 86oF) = -18oF.  So, at the cold end, we will have 24 SCFM of air at a temperature of -18oF.  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 shown in the chart above is 119oF.  So, with the inlet temperature at 68oF, we get (119oF + 68oF) = 187oF.  So, we have 16 SCFM of air at a temperature of 187oF coming out of the hot end.

With the Cold Fraction and inlet air pressure, you can get specific temperatures for your application.  For cooling and heating capacities, flow and temperature can be used to calculate the correct Vortex Tube size for your application.  If you need help 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