Archimedes' screw#Reverse action

A hydrodynamic screw is a hydropower machine, ie an industrial plant for energy conversion of water power into electricity.

Principle, one can refer to a hydrodynamic screw as energetic reversal of the Archimedean screw. This water runs can be used (up to about ten feet ) for energy ( amount of water per snail to ten cubic meters per second ), which have to overcome a slight difference in height. The largest plants built move in eight cubic meters per second and six meter drop height. The worm, which is comparable with a huge screw that is oblique, directed water flow downward, introduced at a weir. The water then treated while it is moving down in a chamber between the threads that screw into a rotary motion. To keep the friction and momentum losses in energy conversion low, the screw rotates relatively slowly (20 to 60 revolutions per minute). After translation by a gear, an electric generator is driven at a higher speed.

For measurements of Lashofer et al. (2011 ) to 14 existing plants in Germany, Austria and South Tyrol were plant efficiencies of more than 75 % measured. The average of all plants at different loadings was 69 %. The plant efficiency includes the product of the efficiencies of screw, bearing, gear, generator and own consumption. So he describes how much is being implemented by the energy of the water in available power. In laboratory tests at the University of Agricultural Sciences (BOKU ) were purchased from Lashofer et. al (2013 ) Worm efficiencies (including storage) determined. In partial load efficiencies were more than 90 % reached ( at about 40 % of the admission value ). Typical efficiencies ranged between 75 and 85 %.

Benefits

The advantage of water power auger is in good tolerability of flow rate variations (from 0.1 cubic meters per second), Treibgutverträglichkeit and fish- friendly water delivery. Unlike turbines for river power plants ranging from a small height difference between the two water levels. The civil engineering works are less complex and therefore less expensive. There are no fine computing facilities needed. Compared to the waterwheel, a better efficiency can be achieved. Lashofer et al. could (2013 ) measure of efficiency to over 90% in hydraulic laboratory BOKU Vienna. Depending on the slope coefficient and diameter ratio and velocity profile can be assumed that an average turbine efficiencies between 80 and 90 %.

Disadvantages

In comparison to the screw pump, the reversal of the flow direction of the water leads to some initially surprising effects. Most striking is the beating noise. It occurs when the upper flow of a shovel release an inflow. The water accelerates and shoots out on the opposite side. This always happens in the same place and was Kantert in the " Practical Guide screw pump " as " shot point " (English " shot point" ) referred. The load is so high that in older hydropower screw mechanical damage and corrosion occurred after about two years. In addition, similar to a dynamic pressure screw the water in the downstream region behind each blade falls back. Also, the accelerated expiration of the last worm gear causes rhythmic noise.

There are different approaches to curb the noise. Modifications of the blade ends, a larger number of gears (it also improves the efficiency ), only one-sided fastening of the lower bearing etc. Many modifications brought little improvement. For example, the diameter of the outlet blades has been reduced to a hydrodynamic screw in the city of Munich. However, the most effective is the complete enclosure, which can be especially near residential areas can hardly be avoided and increases investment costs. So it was in the aforementioned plant in Munich.

Dissemination

Already in 1819, the French engineer Claude Louis Marie Henri Navier expressed the idea to operate the screw as a kind of water wheel. Presumably he has observed what happens when you let go of a water-filled screw pump. The forces can destroy a conventional screw pump, which is why they are usually equipped with backstops (hydropower screw with brake). The first hydrodynamic screw has been manufactured by a Czech manufacturer, tested from 1995 to 1997 at the Technical University of Prague Prof. Dr. Brada and then used by the friends of wind and water power Ostalb eV. It has been running since 1997 in Upper Schlägweidmühle an der Eger in Bopfingen -Aufhausen with 4 kW generator power. Special feature is the ability to change the mounting angle.

In 2001, the first two commercial plants were put into operation. The Röder mill with 7.5 kW at the Franconian Saale in Diebach in mutton castle and a plant with 18.5 kW at the Nethe in Hoexter - Godelheim.

By mid-2013 the world can be expected in operation and about the same number in preparation of more than 250 plants. As the technology has proven very large systems are now mostly built and many are in the range of 140 to 200 kW.

One of the largest hydroelectric power screw is in the Austrian Kindberg.

Further hydrodynamic screws are:

• Bavarian Kiefersfelden: drop height 3.8 m, hydropower screw diameter 3.0 m, length 9.0 m, since 2005
• In Molini di Tures
• In the Swiss Hirschthal
• In the Upper Styrian village Niklas
• In Lower Austria Lunz am See
• In Freiburg im Breisgau on the Dreisamstadion (since 2008)
• In Lobenhausen at the Jagst, Since 2013

The city was built in 2006 in Munich Bach stage operates on the principle of hydrodynamic screw. Since 2012, a hydrodynamic screw covers on the river Diemel the power needs of a brewery in Warburg.

Fish compatibility

There are already some independent reports and reports on fish compatibility ( Schmalz, 2010 and 2011 ) speak of a high compatibility. However, some species of fish and also ages can be affected by poor maintenance or inadequate production. In Münsterland Krechting ( roadstead ) a hydrodynamic screw is operated by the local municipal utility, where the effects of hydrodynamic screws on the fish fauna and possible optimizations to improve the conservation of fish are examined by auger power plants.

History

Originally described by Archimedes screw pump as the water elevation, it was used in modern times again in the polder drainage. In combination with a windmill, the screw pump water over the dikes raised.

Perhaps the oldest description of a hydrodynamic screw in the patent literature is by William Mörscher.

In 1991, the Water lifting screws engineer Karl- August Radlík filed for the invention of the hydrodynamic screw for a patent. This was granted in 1992 and sold in 2001 to a German manufacturer of screw pumps. However, a patent dispute with a competitor could not be won.