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.
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
