These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.[6]
The earliest vacuum tubes evolved from incandescent light bulbs, containing a filament sealed in an evacuated glass envelope. When hot, the filament releases electrons into the vacuum, a process called thermionic emission, originally known as the Edison effect. A second electrode, the anode or plate, will attract those electrons if it is at a more positive voltage. The result is a net flow of electrons from the filament to plate. However, electrons cannot flow in the reverse direction because the plate is not heated and does not emit electrons. The filament (cathode) has a dual function: it emits electrons when heated; and, together with the plate, it creates an electric field due to the potential difference between them. Such a tube with only two electrodes is termed a diode, and is used for rectification. Since current can only pass in one direction, such a diode (or rectifier) will convert alternating current (AC) to pulsating DC. Diodes can therefore be used in a DC power supply, as a demodulator of amplitude modulated (AM) radio signals and for similar functions.
Evacuated Tube Transport Technologies Pdf Download
The 19th century saw increasing research with evacuated tubes, such as the Geissler and Crookes tubes. The many scientists and inventors who experimented with such tubes include Thomas Edison, Eugen Goldstein, Nikola Tesla, and Johann Wilhelm Hittorf.[11] With the exception of early light bulbs, such tubes were only used in scientific research or as novelties. The groundwork laid by these scientists and inventors, however, was critical to the development of subsequent vacuum tube technology.
The generic name "[thermionic] valve" used in the UK derives from the unidirectional current flow allowed by the earliest device, the thermionic diode emitting electrons from a heated filament, by analogy with a non-return valve in a water pipe.[67] The US names "vacuum tube", "electron tube", and "thermionic tube" all simply describe a tubular envelope which has been evacuated ("vacuum"), has a heater and controls electron flow.
To prevent gases from compromising the tube's vacuum, modern tubes are constructed with getters, which are usually metals that oxidize quickly, barium being the most common.[79][80] For glass tubes, while the tube envelope is being evacuated, the internal parts except the getter are heated by RF induction heating to evolve any remaining gas from the metal parts. The tube is then sealed and the getter trough or pan, for flash getters, is heated to a high temperature, again by radio frequency induction heating, which causes the getter material to vaporize and react with any residual gas. The vapor is deposited on the inside of the glass envelope, leaving a silver-colored metallic patch that continues to absorb small amounts of gas that may leak into the tube during its working life. Great care is taken with the valve design to ensure this material is not deposited on any of the working electrodes. If a tube develops a serious leak in the envelope, this deposit turns a white color as it reacts with atmospheric oxygen. Large transmitting and specialized tubes often use more exotic getter materials, such as zirconium. Early gettered tubes used phosphorus-based getters, and these tubes are easily identifiable, as the phosphorus leaves a characteristic orange or rainbow deposit on the glass. The use of phosphorus was short-lived and was quickly replaced by the superior barium getters. Unlike the barium getters, the phosphorus did not absorb any further gases once it had fired.
In Switzerland, a national project called Swissmetro was conducted in which a high-speed magnetic levitation (maglev) passenger train system running in an underground vacuum tunnel was supposed to be developed. The concept of Swissmetro was originally proposed by Nieth [1] during the 1970s, a schematic of which is shown in Fig. 1a. Unlike other maglev projects, e.g., the German Transrapid, Japanese JR-Maglev MLX, and Inductrack in the USA, Swissmetro employed the concept of a vacuum tunnel for the purpose of a drag reduction of the train. Preliminary and feasibility studies were undertaken at the Swiss Federal Institute of Technology Lausanne (EPFL), and the project was conducted by EPFL and the company Swissmetro AG from 1994 to 1998, with sponsorship given by the Swiss National Science Foundation [2]. The Swissmetro system features numerous advantages, including a low energy consumption, high speed, low noise, and immunity to weather such as snow and storms. However, mainly owing to the necessity of an immense initial investment for building an underground vacuum tunnel, the project was stopped, and Swissmetro AG was liquidated in 2009. However, after a decade, this transport system has been refocused for development in Switzerland. The next generation of the Swissmetro AG project (SwissMetro-NG) ( -ng.org/) has been recently promoted by the Swiss parliament as a next-generation transportation system for Switzerland as a way to cope with technologies required for a new transport system. Another vacuum transportation project is in process in Switzerland. The EuroTube Foundation ( ) aims to accelerate the breakthroughs in vacuum transportation and to build a 3-km-long vacuum tube to offer European universities and companies a research center in Collombey-Muraz, Canton of Valais, Switzerland. The canton of Valais, the municipality of Collombey-Muraz and the Swiss Federal Railways have already committed themselves by actively supporting the project.
Musk published the Hyperloop Alpha concept for use in the USA [6], the basic idea of which is similar to ETT in that pressurized capsules, or the so-called pods, travel in reduced-pressure tubes. The thrust force was provided by linear induction motors and axial compressors, which differs from ETT. Musk proposed his new transportation system as an alternative to the California high-speed rail ( ), connecting between San Francisco and Los Angeles. Feasibility studies of the Hyperloop concept were also undertaken by NASA with respect to the cost and technical aspects [7,8,9], and the organization provided a high-level evaluation of Hyperloop in terms of its commercial potential, environmental impact, costs, safety issues, and regulatory and policy issues, as well as to identify further research topics related to the technology. Four years after the Hyperloop Alpha paper was published, the first Hyperloop pod competition was held by the private company SpaceX. The Hyperloop pod competition is an engineering contest involving university students from all over the world with the goal to accelerate the development of the Hyperloop concept. The SpaceX Hyperloop test track was constructed in Los Angeles in 2016, which is a subscale model of the Hyperloop system. The track is straight with the length 1.25 km and an outer tube diameter of 1.8 m.
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes.
The use of phase change materials in solar thermal collectors improves their thermal performance significantly. In this paper, a comparative study is conducted systematically between two solar receivers. The first receiver contains paraffin wax, while the other does not. The goal was to find out to which degree paraffin wax can enhance the energy storage and thermal efficiency of evacuated tubes solar collectors. Measurements of water temperature and solar radiation were recorded on a few days during August of 2021. The experimental analysis depended on two stages. The first stage had a flow rate of 7 L/hr, and the second stage had no flow rate. A flow rate of 7 L/hr gave an efficiency of 47.7% of the first receiver with phase-change material, while the second conventional receiver had an efficiency rate of 40.6%. The thermal efficiency of the first receiver during the day at which no flow rate was applied was 41.6%, while the second one had an efficiency rate of 35.2%. The study's significant results indicated that using paraffin wax in solar evacuated tube water-in-glass thermal collectors can enhance their thermal energy storage by about 8.6% and efficiency by about 7%. Moreover, the results revealed that the solar thermal collector containing paraffin wax had an annual cost of 211 USD/year. At the same time, the receiver's yearly fuel cost was 45 USD. Compared to an electrical geyser, the annual cost reached 327 USD, with an annual fuel cost equaled 269 USD. The first receiver's payback period was 5.35 years. 2ff7e9595c
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