Tornado in a Can

Tornado in a Can – forces behind the grinding and drying process

In 1980s a Texan wheat farmer, named Frank Polifka, was following the annual tornados that rolled over his fields and home areas. By watching the torrent power of the nature he got an idea to tame the violent tornado forces for something usual, to work for him in his farm.

Polifka started a research and development work for the challenge. After 15 years of studies, building of prototypes and assembling of pilot installations, he asked for a patent (2002) for a new innovation. He gave it a business name Windhexe; as a nickname he called it as Tornado in a Can.

The patent rights were bought by another Group, GreenShift, which further tests and distributes the Tornado Generator under GS-Cleantech. The first commercial plant was built in 2006 in Joplin, Missiouri (Tornado Generator).

In 2003 the patent (sub)rights were also obtained by a North-Swedish company Airginder. The following photos have been taken during a study tour into Airgrinder company in Skelleftea, on 1 March 2006.

Photo 1. Tornado dryer, model 1, in Airgrinder AB

What happens to the biomass in the Tornado Dryer? What are the forces behind the drying process?

The whirl of the artificial tornado is generated by an electric blower (middle photo right corner down). It accelerates the air into supersonic speed and blows it into the upper part of a cone-like cyclone that is upside down. Inside the cone the air starts to rotate at high angle velocity. At the same time the whole air mass starts moving downwards. At the bottom of the cone part of the moving air is redirected into the centre of the whirl. Opposite air mass movement, upwards the cone axel is created. Inner whirl has opposite rotating direction to the outer whirl. The typical double whirl of a tornado emerges.

The principle behind the Tornado Dryer is an application of the so called Hilsch Vortex Tube. The theory for the tube was invented by James Clerk Maxwell in 1800s. It is known in the literature of physics as Maxwell’s Demon.

In 1867, Maxwell presented a thought experiment in which, (i) a wall separates two compartments filled with gas, (ii) a little demon sits by a tiny trapdoor in the wall, (iii) it looks at oncoming gas molecules, (iv) and depending on their speeds it opens or closes the trapdoor. Slow molecules are directed to the right, slow molecules to the left.

The object of the game is to eventually collect all the molecules faster than average on to the right side, and the slower ones on to the left side compartment. Since temperature in an enclosure is related to the average kinetic energy of the particles contained in it, the right side compartment should start to warm up and the left side chamber to cool down.

Maxwell thus postulated theoretically that a known volume or magnitude of air, at a known temperature, can be artificially divided into hot and cold parts.

For 50 years Maxwell’s Demon was considered to be just a play of thought, until a French student of physics George Ranque invented (1928) a practical application for it. He managed to build an air pump that with a help of T-shaped assembly of pipe could divide a room temperature air stream into potions of hot and cold air. George Ranque applied for a patent for his invention. He, however, did not manage to development it into successful commercial application. The invention was forgotten for another 15 years.

It became possible to commercialize George Ranque’s invention only when a strong theory behind the phenomenon was developed. This was done by a German physicist Rudolf Hilsch in 1945. Since then the invention has been called Hilsch tube, Rangue Vortex Tube, Ranque-Hilsch Tube or just Vortex Tube. It has led into commercial applications, like Exair.

Tornado Dryer, Tornado Generator or Airgrinder is an astonishing new application of the Hilsch Tube. Frank Polifka found the idea to bring a third component to the Vortex Tube (the other two are the cyclone chamber and the air). He threw the third component into the eye of the torrent whirl. This happens in natural tornados, too. In both cases the third particle crashes into pieces.

Besides crashing the fed material the artificial tornado revealed another phenomenon. The third particle also dries up. It happens without a substantial rise in the temperature which is the case with thermal driers.

As the whirl in the Tornado Dryer has a high angular velocity, about one million rounds per minute, strong forces affect the grinding. At its best, the grinded and dried material turns into solid fluid, and runs like sand in the hourglass (photos below).

Photos 4-6: Mr. Erik Backlund (Airgrinder AB) demonstrates biomasses that have been dried and ground with Tornado Generator; dryed and ground wood (phtos 4 and 5 to the left), dryed and ground bark (right).