Vortex-Formed Chimney
From the inside, an AVE will look like a large circular, open-roof structure with a vortex firmly anchored at its center. Figure 2 shows how a natural draft cooling tower could be altered to create a controlled vortex. Warm air enters the area within a cylindrical wall, called the arena, via tangential entry ducts, giving the air a swirl and producing a vortex. An AVE with a diameter of 200 meters (m) and a height of 50 m to 100 m would produce a rising air column (the vortex) with a diameter of 30 m extending up to 15 km into the atmosphere. The mechanical energy is produced in peripheral turbo-generators generating 200 MW of electrical power for an AVE that is the size referenced above. Wet or dry heat exchangers similar to those used in cooling towers are used to heat the air.
2. Harvesting a whirlwind. Atmospheric vortex engine plan and side views. Source: AVEtec Energy Corp.
The AVE has the same thermodynamic basis as the solar chimney. A solar chimney consists of a tall vertical tube surrounded by a solar energy collector. The 200-m-tall Manzanares prototype solar chimney built in Spain in the 1980s operated successfully for seven years and had an electrical output of 50 kW. The work of buoyancy was transferred to a vertical axis turbine located at the base of the chimney. The draft at the bottom of a natural draft chimney is proportional to the difference in temperature between the rising warm air and the surrounding ambient air and to the height of the chimney.
In the AVE, the wall of the physical chimney is replaced by the centrifugal force produced by the vortex, and the solar collector is replaced by natural or waste heat. Not constrained by the physical limitations of a chimney, the vortex diameter adjusts itself until the radial pressure differential is in equilibrium with the centrifugal force produced by the spinning vortex. The vortex transmits the draft produced by the warm buoyant air above to the turbines below. The vortex chimney goes up with the rising air and is continuously replaced from the bottom. In essence, the chimney and the rising air column are one.
The vortex is also self-sustaining. Should the vortex be broken up by a gust, the lower half of the vortex would reestablish itself with new warm spinning air from below, and the upper half of the vortex would fill from the bottom with high-level cool air and die off.
The maximum efficiency of the solar chimney is 1.5% because of chimney height limitations; the efficiency of the AVE could be up to 30% because a vortex chimney can extend up to 15 km into the atmosphere.
An AVE using waste heat should self-start. Steam injection could be used to help start the AVE using natural heat sources. Once the vortex is established, the pressure difference between the surrounding ambient air and the reduced pressure at the base of the vortex becomes the driving force to spin the turbines. The airflow is controlled with dampers located either upstream of the heat exchangers or within the tangential entry ducts. An annular roof with a central circular opening forces the air entering the arena to converge, thereby forming a vortex with a diameter somewhat smaller than the roof opening.
Figure 3 shows a small vortex produced in a pilot plant. The 0.4-m-diameter vortex extended up to 15 m in the free atmosphere above the 3-m-high plastic cylinder. The deflectors were located in a 1-m-high by 4-m-diameter base unit located under the plastic cylinder. Four 20-kW propane heaters were used to warm the air 20C above ambient; the vortex was made visible with smoke emitters.
3. Twisted energy. Photo of a vortex produced with a small physical model. Source: AVEtec Energy Corp.
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