An Archimedes screw , also called a water screw , screw pump , or Egyptian screw , [1] is a machine used to transfer water from a lower part of the water to an irrigation ditch . Water is pumped by turning a screw-shaped surface inside a pipe. The Archimedes screw is also used for materials such as powders and grains. In addition, Archimedes screws can produce electricity if they are driven by a flowing fluid rather than lifting fluid ( Archimedes Screw Turbine /Generator). [2] Although usually attributed to Goes to Archimedes, there is some evidence that this tool was used in ancient Egypt long before its time.
History
The screw pump is the oldest positive displacement pump. [1] The first record of a water screw, or screw pump, dates back to Hellenistic Egypt before the 3rd century BC. [1] [4] The Egyptian screw, which was used to lift water from the Nile , was made of tubes wound around a cylinder; As the entire unit rotates, the water is lifted to a higher height within the spiral tube. A later Egyptian screw pump design had a spiral groove cut out of a solid wooden cylinder and then the cylinder was covered with a metal board or sheet that closely covered the surfaces between the grooves. [1]
Some researchers regard it as a tool used to irrigate the Hanging Gardens of Babylon , one of the Seven Wonders of the Ancient World . A cuneiform inscription from the Assyrian king Sennacherib (704–681 BC) interpreted by Stephanie Daly [5] describes water screws in bronze from about 350 years ago. This is in line with the classical writer Strabo , who describes hanging gardens as irrigated by screws.
The screw pump was later brought to Greece from Egypt. [1] It was described by Archimedes , [7] on the occasion of his visit to Egypt , around 234 BC. [8] This tradition only suggests that the instrument was unknown to the Greeks before the Hellenistic period. [7] Archimedes never claimed credit for its invention, but it was given 200 years later by Diodorus , who believed that Archimedes had invented the screw pump in Egypt. [1] Greek and RomanIllustrations of the water screws show them being driven by a human onto the outer casing to turn the entire device into one piece, which would require the casing to be firmly attached to the screw.
German engineer Konrad Kaiser equipped the Archimedes’ screw with a crank mechanism in his Bellifortis (1405). This mechanism quickly replaced the ancient practice of working the pipe by running.
design
Archimedes’ screw consists of a screw (a helical surface around a central cylindrical shaft) inside a hollow pipe. The screw is usually turned by windmills, manual labour, cattle, or modern means such as a motor. As the shaft turns, the bottom end increases the amount of water. This water is then pushed up the tube by rotating the winding until it pours out from the top of the tube.
The contact surface between the screw and the pipe does not need to be completely waterproof, as long as the amount of water with each turn is large compared to the amount of water coming out of each section of the screw per turn. If water from one section seeps into the next lower section, it will be transferred upwards by the next section of the screw.
In some designs, the screw is attached to the casing and they both rotate together, rather than turning the screw within a stationary casing. The screw may be sealed to the casing with pitch resin or other adhesive, or the screw and casing may be cast together as a single piece in the bronze.
The design of the everyday Greek and Roman water screw, in contrast to Sennacherib’s heavy bronze instrument, with its problematic drive chains, has a mighty simplicity. A double or triple helix was built from wooden strips (or sometimes bronze sheets) around a heavy wooden pole. The choppers were built around a cylinder with long, narrow boards fastened to their circumference and waterproofed along the pitch. [6]
Use
Pench was mainly used to transport water in irrigation systems and to drain water in mines or other low-lying areas. It was used to clear land under the sea in the Netherlands and in the construction of polders in other places.
Archimedes screeds are used in sewage treatment plants because they cope well with varying rates of flow and suspended solids. An auger in an ice blower or grain lift is essentially an Archimedes screw. Many variations of the axial flow pump originally had an Archimedes screw.
This principle is also found in pescallators, which are Archimedes’ screws designed to safely lift fish from ponds and transport them to another location. This technique is mainly used in fish hatcheries, where it is desirable to minimize physical handling of fish.
Archimedes’ screw was used in the successful 2001 stabilization of the Leaning Tower of Pisa. Small amounts of subsoil saturated with groundwater were removed from the very bottom of the tower’s north side, and the weight of the tower itself corrected the inclination. Archimedes’ screw is also used in the chocolate fountain.
The Archimedes Screw Turbine (AST) is a novel form of generator for small hydroelectric power plants that can also be implemented in low head sites. [2] The low rotation speed of the AST minimizes the negative impact on aquatic life and fish. [2]
Variants
A screw conveyor is an Archimedes screw contained within a tube and rotated by a motor to move material from one end of the conveyor to the other. It is particularly suitable for transporting granular materials such as plastic granules used in injection molding, and granular granules. It can also be used to transport liquids. Conveyors can be used as rotary feeders or variable rate feeders to deliver a measured rate or quantity of material to a process in industrial control applications.
A variant of the Archimedes screw can also be found in some injection molding machines, die casting machines and plastic extruders, which employ a screw of decreasing pitch to compress and melt the material. It is also used in rotary-screw air compressors. On a large scale, Archimedes’ decreasing pitch screw is used for compaction of waste material.
reverse action
If water is poured into the top of the Archimedes’ screw, it will force the screw to rotate. The rotating shaft can then be used to drive an electric generator. This type of installation has the same benefits as using a screw for pumping: the ability to handle very dirty water and widely varying rates of flow at high efficiency. Settle Hydro and Tors Hydro are two reverse screw micro hydro schemes operating in England. The screw works well as a generator on the low head, commonly found in English rivers including the Thames, providing power to Windsor Castle. [10]
In 2017, the first reverse screw hydropower in the United States opened in Meriden, Connecticut. [11] [12] The Meriden project is built and operated by New England Hydropower, which has a nameplate capacity of 193 kW and a capacity factor of approximately 55% over a 5-year period.
