Serie A brev nr 26

Magazine Overview

Title: BREVCIRKELN
Issue: 26
Volume: SERIE A
Date: 1947

This issue of Brevcirkeln features an in-depth article titled "DR. HILSCH'S VORTEXRÖR" (Dr. Hilsch's Vortex Tube), detailing a remarkable scientific apparatus.

Dr. Hilsch's Vortex Tube

The article begins by referencing an article in the February 1947 issue of "The Review of Scientific Instruments" by Dr. R. Hilsch, titled "The Use of Expansion of Gases in a Centrifugal Field as a Cooling Process." This seemingly technical title hides details of a revolutionary construction that appears almost magical in its function.

Background and Discovery

Following World War II, American scientists scoured Germany for secret projects and constructions of technical and scientific value to the American industry and science. Among these, they discovered the "Hilsch's Wirbelrohr" (Hilsch's Vortex Tube). This device consists of three thin-walled metal tubes joined in a 'T' shape. Compressed air is introduced through one end of the tube, resulting in one stream of air becoming hot and the other cold. The construction has no moving parts, and its effect is entirely dependent on the internal design of the tubes.

The Principle and its Explanation

Numerous explanations have been proposed for the principle behind this seemingly simple device, including theories about the separation of slow and fast gas molecules. However, Dr. Hilsch's article clarifies that the explanation is relatively straightforward.

Dr. Hilsch is not the sole inventor of the apparatus; he has further developed it. The article credits the pioneering work to the Frenchman M.G. Ranque, whose construction was published in the French journal "Journal de Physique et de Radiologie" in 1933. Nevertheless, Dr. Hilsch has created a cleverly constructed apparatus that is likely to have significant technical importance in the near future. The apparatus can be called a "Virvelrör" (Vortex Tube), a name that almost describes what happens inside the tubes.

As illustrated by the sketches, the Vortex Tube is a T-shaped metal tube. Compressed air is forced into one arm. Of the two remaining arms, one becomes hot and the other cold. Nothing more, seemingly.

Dr. Hilsch's own statements about the Vortex Tube give the impression that even he, who detailed its development, is surprised by its functionality. It is based on a fundamental scientific principle: the fewer moving parts a machine has, the higher its efficiency. The transformer is cited as the best example, with no moving parts and an efficiency of nearly 99%.

Dr. Hilsch's Description

Dr. Hilsch states: "A demonstration of a Vortex Tube is simply astonishing. With the correct physical dimensions of the tube, one can easily produce a temperature of +200°C in the left tube and -50°C in the right tube, starting with compressed air at +20°C and a few atmospheres of overpressure."

Dr. Hilsch appears impressed that such a trivial construction can achieve such a remarkable effect.

How it Works

In essence, compressed air enters a metal tube through a tangentially connected nozzle. This results in a gas flow (air) within the tube, creating a turbulent yet screw-like motion that spirals through the tube via two open ends. This rotating air stream generates an area of increased pressure near the inner wall of the tube and an area of reduced pressure along the tube's axis. If the opening at one end of the tube is restricted by a diaphragm with a precisely regulated aperture, allowing only air from the axial region to escape, and the opposite end's opening is regulated, the temperature of the air exiting the diaphragm-restricted end drops, while the temperature of the air exiting the regulated end rises.

Simplicity and Potential

The Vortex Tube's function is so simple that it is surprising it wasn't discovered earlier. The article suggests that studies of air currents in aerodynamics, rocket propulsion, and jet engines should have provided the necessary knowledge for such a device long ago. However, it is unclear where Frenchman Ranque got his idea.

In his initial experiments, Hilsch used a tube made of nickel silver, which has relatively poor thermal conductivity, to prevent heat transfer between the tube ends. Perhaps other metals with even lower thermal conductivity would be preferable. It might also be possible to manufacture the tube from a non-metallic material or a combination of materials. Further experiments could lead to improvements.

It is known that Vortex Tubes with small dimensions have low efficiency, meaning a significant portion of the energy in the compressed air is lost. However, in a large-dimensioned Vortex Tube, say 30 to 50 centimeters in diameter instead of a few centimeters, the efficiency would be considerable.

Hilsch states that it is unlikely the Vortex Tube will compete with conventional cooling machinery due to its dimensions and efficiency. However, in cases where large-scale cooling is required, such as in mine shafts, it could be very valuable due to its simple construction.

Hilsch also mentions that he continues to experiment with the Vortex Tube. It is also known that several very large companies in the USA are interested and are undoubtedly conducting their own research.

Given the Vortex Tube's incredibly simple construction, it should be possible for practically anyone with access to simple tools to build and operate it. However, the aforementioned limitations might mean it is not of immediate practical value. Building one would be interesting, if only to test the practical realization of a theoretical idea.

Optimists have considered using the Vortex Tube for heating and cooling in homes. Although this idea may not seem immediately feasible, it is certainly a possibility worth considering.

Recurring Themes and Editorial Stance

The article highlights scientific innovation and the potential of simple yet effective technological solutions. The editorial stance appears to be one of fascination with the Vortex Tube's principle and its potential, while acknowledging its current limitations and the ongoing research and development in the field. There is an emphasis on the elegance of a device with no moving parts achieving significant results, drawing parallels to other efficient technologies like transformers.