Serial port

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Serial_port

A male D-subminiature connector used for a serial port on an IBM PC compatible computer along with the serial port symbol

On computers, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.

While interfaces such as Ethernet, FireWire, and USB also send data as a serial stream, the term serial port usually denotes hardware compliant with RS-232 or a related standard, such as RS-485 or RS-422.

Modern consumer personal computers (PCs) have largely replaced serial ports with higher-speed standards, primarily USB. However, serial ports are still frequently used in applications demanding simple, low-speed interfaces, such as industrial automation systems, scientific instruments, point of sale systems and some industrial and consumer products.

Server computers may use a serial port as a control console for diagnostics, while networking hardware (such as routers and switches) commonly use serial console ports for configuration, diagnostics, and emergency maintenance access. To interface with these and other devices, USB-to-serial converters can quickly and easily add a serial port to a modern PC.

Hardware

Modern devices use an integrated circuit called a UART to implement a serial port. This IC converts characters to and from asynchronous serial form, implementing the timing and framing of data specified by the serial protocol in hardware. The IBM PC implements its serial ports, when present, with one or more UARTs.

Very low-cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the bit banging technique. These early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS-232.

Before large-scale integration (LSI) made UARTs common, serial ports were commonly used in mainframes and minicomputers, which would have multiple small-scale integrated circuits to implement shift registers, logic gates, counters, and all the other logic needed. As PCs evolved serial ports were included in the Super I/O chip and then in the chipset.

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  An IBM PC serial card with a 25-pin connector (obsolete 8-bit ISA card)

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  A PCI Express ×1 card with one serial port

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  A four-port serial (RS-232) PCI Express ×1 expansion card with an octopus cable that breaks the card's DC-37 connector into four standard DE-9 connectors

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  A converter from USB to an RS-232 compatible serial port—more than a physical transition, it requires a driver in the host system software and a built-in processor to emulate the functions of the IBM XT compatible serial port hardware.

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  UART to USB adapter

DTE and DCE

The individual signals on a serial port are unidirectional and when connecting two devices, the outputs of one device must be connected to the inputs of the other. Devices are divided into two categories: data terminal equipment (DTE) and data circuit-terminating equipment (DCE). A line that is an output on a DTE device is an input on a DCE device and vice versa, so a DCE device can be connected to a DTE device with a straight wired cable, in which each pin on one end goes to the same numbered pin on the other end.

Conventionally, computers and terminals are DTE, while peripherals such as modems are DCE. If it is necessary to connect two DTE (or DCE) devices together, a cable with reversed TX and RX lines, known as a cross-over, roll-over or null modem cable must be used.

Gender

Generally, serial port connectors are gendered, only allowing connectors to mate with a connector of the opposite gender. With D-subminiature connectors, the male connectors have protruding pins, and female connectors have corresponding round sockets. Either type of connector can be mounted on equipment or a panel; or terminate a cable.

Connectors mounted on DTE are likely to be male, and those mounted on DCE are likely to be female (with the cable connectors being the opposite). However, this is far from universal; for instance, most serial printers have a female DB25 connector, but they are DTEs. In this circumstance, the appropriately gendered connectors on the cable or a gender changer can be used to correct the mismatch.

Connectors

The only connector specified in the original RS-232 standard was the 25-pin D-subminiature, however, many other connectors have been used to save money or save on physical space, among other reasons. In particular, since many devices do not use all of the 20 signals that are defined by the standard, connectors with fewer pins are often used. While specific examples follow, countless other connectors have been used for RS-232 connections.

The 9-pin DE-9 connector has been used by most IBM-compatible PCs since the Serial/Parallel Adapter option for the PC-AT, where the 9-pin connector allowed a serial and parallel port to fit on the same card. This connector has been standardized for RS-232 as TIA-574.

Some miniaturized electronics, particularly graphing calculators and hand-held amateur and two-way radio equipment, have serial ports using a phone connector, usually the smaller 2.5 or 3.5 mm connectors and the most basic 3-wire interface—transmit, receive and ground.

A Cisco rollover cable using the 8P8C Yost standard

8P8C connectors are also used in many devices. The EIA/TIA-561 standard defines a pinout using this connector, while the rollover cable (or Yost standard) is commonly used on Unix computers and network devices, such as equipment from Cisco Systems.

Pair of female Mini DIN-8 connectors used for RS-422 serial ports on a Macintosh LC computer

Many models of Macintosh favor the related RS-422 standard, mostly using circular mini-DIN connectors. The Macintosh included a standard set of two ports for connection to a printer and a modem, but some PowerBook laptops had only one combined port to save space.

10P10C connectors can be found on some devices.

Another common connector is a 10 × 2 pin header common on motherboards and add-in cards which is usually converted via a ribbon cable to the more standard 9-pin DE-9 connector (and frequently mounted on a free slot plate or other part of the housing).

Pinouts

The following table lists commonly used RS-232 signals and pin assignments:

Signal			Direction		Connector pin
Name	V.24 circuit	Abbreviation	DTE	DCE	DB-25	DE-9 (TIA-574)	MMJ	8P8C ("RJ45")					10P10C ("RJ50")
								EIA/TIA-561	Yost (DTE)	Yost (DCE)	Cyclades	Digi (ALTPIN option)	National Instruments	Cyclades	Digi
Transmitted Data	103	TxD	Out	In	2	3	2	6	6	3	3	4	8	4	5
Received Data	104	RxD	In	Out	3	2	5	5	3	6	6	5	9	7	6
Data Terminal Ready	108/2	DTR	Out	In	20	4	1	3	7	2	2	8	7	3	9
Data Carrier Detect	109	DCD	In	Out	8	1	—	2	2	7	7	1	10	8	10
Data Set Ready	107	DSR	In	Out	6	6	6	1		—	8	—	5	9	2
Ring Indicator	125	RI	In	Out	22	9	—		—	—	—	—	2	10	1
Request To Send	105	RTS	Out	In	4	7	—	8	8	1	1	2	4	2	3
Clear To Send	106	CTS	In	Out	5	8	—	7	1	8	5	7	3	6	8
Signal Ground	102	G	Common		7	5	3, 4	4	4, 5	4, 5	4	6	6	5	7
Protective Ground	101	PG	Common		1	—	—	—	—	—	—	3	—	1	4

Signal Ground is a common return for the other connections; it appears on two pins in the Yost standard but is the same signal. The DB-25 connector includes a second Protective Ground on pin 1, which is intended to be connected by each device to its own frame ground or similar. Connecting Protective Ground to Signal Ground is a common practice but not recommended.

Note that EIA/TIA 561 combines DSR and RI, and the Yost standard combines DSR and DCD.

Hardware abstraction

Operating systems usually create symbolic names for the serial ports of a computer, rather than requiring programs to refer to them by hardware address.

Unix-like operating systems usually label the serial port devices /dev/tty*. TTY is a common trademark-free abbreviation for teletype, a device commonly attached to early computers' serial ports, and * represents a string identifying the specific port; the syntax of that string depends on the operating system and the device. On Linux, 8250/16550 UART hardware serial ports are named /dev/ttyS*, USB adapters appear as /dev/ttyUSB* and various types of virtual serial ports do not necessarily have names starting with tty.

The DOS and Windows environments refer to serial ports as COM ports: COM1, COM2,..etc.

Common applications for serial ports

This list includes some of the more common devices that are connected to the serial port on a PC. Some of these such as modems and serial mice are falling into disuse while others are readily available. Serial ports are very common on most types of microcontroller, where they can be used to communicate with a PC or other serial devices.

• Dial-up modems
• Configuration and management of networking equipment such as routers, switches, firewalls, load balancers
• GPS receivers (typically NMEA 0183 at 4,800 bit/s)
• Bar code scanners and other point of sale devices
• LED and LCD text displays
• Satellite phones, low-speed satellite modems and other satellite based transceiver devices
• Flat-panel displays to control screen functions by external computer, other AV components or remotes
• Test and measuring equipment such as digital multimeters and weighing systems
• Updating firmware on various consumer devices
• CNC controllers
• Uninterruptible power supply management and status reporting
• Stenography or Stenotype machines
• Software debuggers that run on a second computer
• Console or debugger interface to microprocessor development or evaluation boards
• Industrial field buses
• Printers
• Computer terminal, teletype
• Networking (Macintosh AppleTalk using RS-422 at 230.4 kbit/s)
• Serial mouse

Since the control signals for a serial port can be driven by any digital signal, some applications used the control lines of a serial port to monitor external devices, without exchanging serial data. A common commercial application of this principle was for some models of uninterruptible power supply which used the control lines to signal loss of power, low battery, and other status information. At least some Morse code training software used a code key connected to the serial port to simulate actual code use; the status bits of the serial port could be sampled very rapidly and at predictable times, making it possible for the software to decipher Morse code.

Serial computer mice, certain interface converters and other parasite powered devices would draw their operating current or signalling voltages from the received data or control signals to better conform to the bipolar standard voltages without a source of dual, or any, local supply rails. 

Settings

Common serial port speeds

Bit rate (bit/s)	Time per bit (μs)	Windows predefined serial port speed	Common applications
75	13333.3	Yes
110	9090.9	Yes	Bell 101 modem
134.5	7434.9	Yes
150	6666.6	Yes
300	3333.3	Yes	Bell 103 modem or V.21 modem
600	1666.7	Yes
1,200	833.3	Yes	Bell 202, Bell 212A, or V.22 modem
1,800	555.6	Yes
2,400	416.7	Yes	V.22bis modem
4,800	208.3	Yes	V.27ter modem
7,200	138.9	Yes
9,600	104.2	Yes	V.32 modem
14,400	69.4	Yes	V.32bis modem
19,200	52.1	Yes
31,250	32	No	MIDI port
38,400	26.0	Yes
56,000	17.9	Yes	V.90/V.92 modem
57,600	17.4	Yes	V.32bis modem with V.42bis compression
76,800	13.0	No	BACnet MS/TP networks
115,200	8.68	Yes	V.34 modem with V.42bis compression, low cost serial V.90/V.92 modem with V.42bis or V.44 compression
128,000	7.81	Yes	Basic Rate Interface ISDN terminal adapter
230,400	4.34	No	LocalTalk, high end serial V.90/V.92 modem with V.42bis or V.44 compression
250,000	4.0	No	DMX512, stage lighting and effects network
256,000	3.91	Yes

Serial standards provide for many different operating speeds as well as adjustments to the protocol to account for different operating conditions. The most well-known options are speed, number of data bits per character, parity, and number of stop bits per character.

In modern serial ports using a UART integrated circuit, all these settings can be software-controlled. Hardware from the 1980s and earlier may require setting switches or jumpers on a circuit board.

The configuration for serial ports designed to be connected to a PC has become a de facto standard, usually stated as 9600/8-N-1.

Speed

Serial ports use two-level (binary) signaling, so the data rate in bits per second is equal to the symbol rate in baud. The total speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate. For example, with 8-N-1 character framing, only 80% of the bits are available for data; for every eight bits of data, two more framing bits are sent.

A standard series of rates is based on multiples of the rates for electromechanical teleprinters; some serial ports allow many arbitrary rates to be selected, but the speeds on both sides of the connection must match for data to be received correctly. Bit rates commonly supported include 75, 110, 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 bit/s. Many of these standard modem baud rates are multiples of either 0.9 kbps (e.g., 19200, 38400, 76800) or 1.2 kbps (e.g., 57600, 115200). Crystal oscillators with a frequency of 1.843200 MHz are sold specifically for this purpose. This is 16 times the fastest bit rate, and the serial port circuit can easily divide this down to lower frequencies as required.

The capability to set a bit rate does not imply that a working connection will result. Not all bit rates are possible with all serial ports. Some special-purpose protocols such as MIDI for musical instrument control, use serial data rates other than the teleprinter standards. Some serial port implementations can automatically choose a bit rate by observing what a connected device is sending and synchronizing to it.

Data bits

The number of data bits in each character can be 5 (for Baudot code), 6 (rarely used), 7 (for true ASCII), 8 (for most kinds of data, as this size matches the size of a byte), or 9 (rarely used). 8 data bits are almost universally used in newer applications. 5 or 7 bits generally only make sense with older equipment such as teleprinters.

Most serial communications designs send the data bits within each byte least significant bit first. Also possible, but rarely used, is most significant bit first; this was used, for example, by the IBM 2741 printing terminal. The order of bits is not usually configurable within the serial port interface but is defined by the host system. To communicate with systems that require a different bit ordering than the local default, local software can re-order the bits within each byte just before sending and just after receiving.

Parity

Main article: Parity bit

Parity is a method of detecting errors in transmission. When parity is used with a serial port, an extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. Correct parity does not necessarily indicate absence of corruption as a corrupted transmission with an even number of errors will pass the parity check. A single parity bit does not allow implementation of error correction on each character, and communication protocols working over serial data links will typically have higher-level mechanisms to ensure data validity and request retransmission of data that has been incorrectly received.

The parity bit in each character can be set to one of the following:

• None (N) means that no parity bit is sent and the transmission is shortened.
• Odd (O) means that the parity bit is set so that the number of 1 bits is odd.
• Even (E) means that the parity bit is set so that the number of 1 bits is even.
• Mark (M) parity means that the parity bit is always set to the mark signal condition (1 bit value).
• Space (S) parity always sends the parity bit in the space signal condition (0 bit value).

Aside from uncommon applications that use the last bit (usually the 9th) for some form of addressing or special signaling, mark or space parity is uncommon, as it adds no error detection information.

Odd parity is more useful than even parity since it ensures that at least one state transition occurs in each character, which makes it more reliable at detecting errors like those that could be caused by serial port speed mismatches. The most common parity setting, however, is none, with error detection handled by a communication protocol.

To allow detection of messages damaged by line noise, electromechanical teleprinters were arranged to print a special character when received data contained a parity error.

Stop bits

Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronize with the character stream. Electronic devices usually use one stop bit. If slow electromechanical teleprinters are used, one-and-one half or two stop bits may be required.

Conventional notation

The data/parity/stop (D/P/S) conventional notation specifies the framing of a serial connection. The most common usage on microcomputers is 8/N/1 (8N1). This specifies 8 data bits, no parity, 1 stop bit. In this notation, the parity bit is not included in the data bits. 7/E/1 (7E1) means that an even parity bit is added to the 7 data bits for a total of 8 bits between the start and stop bits.

Flow control

Flow control is used in circumstances where a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a handshaking method. There are hardware and software handshaking methods.

Hardware handshaking is done with extra signals, often the RS-232 RTS/CTS or DTR/DSR signal circuits. RTS and CTS are used to control data flow, signaling, for instance, when a buffer is almost full. Per the RS-232 standard and its successors, DTR and DSR are used to signal that equipment is present and powered up so are usually asserted at all times. However, non-standard implementations exist, for example, printers that use DTR as flow control.

Software handshaking is done for example with ASCII control characters XON/XOFF to control the flow of data. The XON and XOFF characters are sent by the receiver to the sender to control when the sender will send data, that is, these characters go in the opposite direction to the data being sent. The system starts in the sending allowed state. When the receiver's buffers approach capacity, the receiver sends the XOFF character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an XON character to tell the sender to resume transmission. It is an example of in-band signaling, where control information is sent over the same channel as its data.

The advantage of hardware handshaking is that it can be extremely fast, it works independently of imposed meaning such as ASCII on the transferred data and it is stateless. Its disadvantage is that it requires more hardware and cabling, and both ends of the connection must support the hardware handshaking protocol used.

The advantage of software handshaking is that it can be done with absent or incompatible hardware handshaking circuits and cabling. The disadvantage, common to all in-band control signaling, is that it introduces complexities in ensuring that control messages get through even when data messages are blocked, and data can never be mistaken for control signals. The former is normally dealt with by the operating system or device driver; the latter normally by ensuring that control codes are escaped (such as in the Kermit protocol) or omitted by design (such as in ANSI terminal control).

If no handshaking is employed, an overrun receiver might simply fail to receive data from the transmitter. Approaches for preventing this include reducing the speed of the connection so that the receiver can always keep up, increasing the size of buffers so it can keep up averaged over a longer time, using delays after time-consuming operations (e.g. in termcap) or employing a mechanism to resend data which has not been received correctly (e.g. TCP).

School

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/School

First primary school in Nigeria, built in 1845

A school is an educational institution designed to provide learning spaces and learning environments for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is sometimes compulsory. In these systems, students progress through a series of schools. The names for these schools vary by country (discussed in the Regional terms section below) but generally include primary school for young children and secondary school for teenagers who have completed primary education. An institution where higher education is taught is commonly called a university college or university.

In addition to these core schools, students in a given country may also attend schools before and after primary (elementary in the U.S.) and secondary (middle school in the U.S.) education. Kindergarten or preschool provide some schooling to very young children (typically ages 3–5). University, vocational school, college or seminary may be available after secondary school. A school may be dedicated to one particular field, such as a school of economics or dance. Alternative schools may provide nontraditional curriculum and methods.

Non-government schools, also known as private schools, may be required when the government does not supply adequate or specific educational needs. Other private schools can also be religious, such as Christian schools, gurukula (Hindu schools), madrasa (Arabic schools), hawzas (Shi'i Muslim schools), yeshivas (Jewish schools), and others; or schools that have a higher standard of education or seek to foster other personal achievements. Schools for adults include institutions of corporate training, military education and training and business schools.

Critics of school often accuse the school system of failing to adequately prepare students for their future lives, of encouraging certain temperaments while inhibiting others, of prescribing students exactly what to do, how, when, where and with whom, which would suppress creativity, and of using extrinsic measures such as grades and homework, which would inhibit children's natural curiosity and desire to learn.

In homeschooling and distance education, teaching and learning take place independent from the institution of school or in a virtual school outside a traditional school building, respectively. Schools are organized in several different organizational models, including departmental, small learning communities, academies, integrated, and schools-within-a-school.

Etymology

The word school derives from Greek σχολή (scholē), originally meaning "leisure" and also "that in which leisure is employed", but later "a group to whom lectures were given, school".

History and development

See also: History of education

Plato's academy, mosaic from Pompeii

The concept of grouping students together in a centralized location for learning has existed since Classical antiquity. Formal schools have existed at least since ancient Greece (see Academy), ancient Rome (see Education in Ancient Rome) ancient India (see Gurukul), and ancient China (see History of education in China). The Byzantine Empire had an established schooling system beginning at the primary level. According to Traditions and Encounters, the founding of the primary education system began in 425 AD and "... military personnel usually had at least a primary education ...". The sometimes efficient and often large government of the Empire meant that educated citizens were a must. Although Byzantium lost much of the grandeur of Roman culture and extravagance in the process of surviving, the Empire emphasized efficiency in its war manuals. The Byzantine education system continued until the empire's collapse in 1453 AD.

In Western Europe, a considerable number of cathedral schools were founded during the Early Middle Ages in order to teach future clergy and administrators, with the oldest still existing, and continuously operated, cathedral schools being The King's School, Canterbury (established 597 CE), King's School, Rochester (established 604 CE), St Peter's School, York (established 627 CE) and Thetford Grammar School (established 631 CE). Beginning in the 5th century CE, monastic schools were also established throughout Western Europe, teaching religious and secular subjects.

Mental calculations. In the school of S. Rachinsky by Nikolay Bogdanov-Belsky. Russia, 1895.

In Europe, universities emerged during the 12th century; here, scholasticism was an important tool, and the academicians were called schoolmen. During the Middle Ages and much of the Early Modern period, the main purpose of schools (as opposed to universities) was to teach the Latin language. This led to the term grammar school, which in the United States informally refers to a primary school, but in the United Kingdom means a school that selects entrants based on ability or aptitude. The school curriculum has gradually broadened to include literacy in the vernacular language and technical, artistic, scientific, and practical subjects.

Obligatory school attendance became common in parts of Europe during the 18th century. In Denmark-Norway, this was introduced as early as in 1739–1741, the primary end being to increase the literacy of the almue, i.e., the "regular people". Many of the earlier public schools in the United States and elsewhere were one-room schools where a single teacher taught seven grades of boys and girls in the same classroom. Beginning in the 1920s, one-room schools were consolidated into multiple classroom facilities with transportation increasingly provided by kid hacks and school buses.

Islam was another culture that developed a school system in the modern sense of the word. Emphasis was put on knowledge, which required a systematic way of teaching and spreading knowledge and purpose-built structures. At first, mosques combined religious performance and learning activities. However, by the 9th century, the madrassa was introduced, a school that was built independently from the mosque, such as al-Qarawiyyin, founded in 859 CE. They were also the first to make the Madrassa system a public domain under Caliph's control.

Under the Ottomans, the towns of Bursa and Edirne became the main centers of learning. The Ottoman system of Külliye, a building complex containing a mosque, a hospital, madrassa, and public kitchen and dining areas, revolutionized the education system, making learning accessible to a broader public through its free meals, health care, and sometimes free accommodation.

Regional terms

The term school varies by country, as do the names of the various levels of education within the country.

United Kingdom and Commonwealth of Nations

In the United Kingdom, the term school refers primarily to pre-university institutions, and these can, for the most part, be divided into pre-schools or nursery schools, primary schools (sometimes further divided into infant school and junior school), and secondary schools. Various types of secondary schools in England and Wales include grammar schools, comprehensives, secondary moderns, and city academies. While they may have different names in Scotland, there is only one type of secondary school. However, they may be funded either by the state or independently funded. Scotland's school performance is monitored by Her Majesty's Inspectorate of Education. Ofsted reports on performance in England and Estyn reports on performance in Wales.

In the United Kingdom, most schools are publicly funded and known as state schools or maintained schools in which tuition is provided for free. There are also private schools or private schools that charge fees. Some of the most selective and expensive private schools are known as public schools, a usage that can be confusing to speakers of North American English. In North American usage, a public school is publicly funded or run.

In much of the Commonwealth of Nations, including Australia, New Zealand, India, Pakistan, Bangladesh, Sri Lanka, South Africa, Kenya, and Tanzania, the term school refers primarily to pre-university institutions.

India

Loyola School, Chennai, India – run by the Catholic Diocese of Madras. Christian missionaries played a pivotal role in establishing modern schools in India.

In ancient India, schools were in the form of Gurukuls. Gurukuls were traditional Hindu residential learning schools, typically the teacher's house or a monastery. Schools today are commonly known by the Sanskrit terms Vidyashram, Vidyalayam, Vidya Mandir, Vidya Bhavan in India. In southern languages, it is known as Pallikoodam or PaadaSaalai. During the Mughal rule, Madrasahs were introduced in India to educate the children of Muslim parents. British records show that indigenous education was widespread in the 18th century, with a school for every temple, mosque, or village in most regions. The subjects taught included Reading, Writing, Arithmetic, Theology, Law, Astronomy, Metaphysics, Ethics, Medical Science, and Religion.

A school building in Kannur, India

Under British rule, Christian missionaries from England, the United States, and other countries established missionary and boarding schools in India. Later as these schools gained popularity, more were started, and some gained prestige. These schools marked the beginning of modern schooling in India. The syllabus and calendar they followed became the benchmark for schools in modern India. Today most schools follow the missionary school model for tutoring, subject/syllabus, and governance, with minor changes.

Schools in India range from large campuses with thousands of students and hefty fees to schools where children are taught under a tree with a small / no campus and are free of cost. There are various boards of schools in India, namely Central Board for Secondary Education (CBSE), Council for the Indian School Certificate Examinations (CISCE), Madrasa Boards of various states, Matriculation Boards of various states, State Boards of various boards, Anglo Indian Board, among others. Today's typical syllabus includes language(s), mathematics, science – physics, chemistry, biology, geography, history, general knowledge, and information technology/computer science. Extracurricular activities include physical education/sports and cultural activities like music, choreography, painting, and theatre/drama.

Europe

Albert Bettannier's 1887 painting La Tache noire depicts a child being taught about the "lost" province of Alsace-Lorraine in the aftermath of the Franco-Prussian War – an example of how European schools were often used in order to inoculate Nationalism in their pupils.

In much of continental Europe, the term school usually applies to primary education, with primary schools that last between four and nine years, depending on the country. It also applies to secondary education, with secondary schools often divided between Gymnasiums and vocational schools, which again, depending on country and type of school, educate students for between three and six years. In Germany, students graduating from Grundschule are not allowed to progress into a vocational school directly. Instead, they are supposed to proceed to one of Germany's general education schools such as Gesamtschule, Hauptschule, Realschule or Gymnasium. When they leave that school, which usually happens at age 15–19, they may proceed to a vocational school. The term school is rarely used for tertiary education, except for some upper or high schools (German: Hochschule), which describe colleges and universities.

In Eastern Europe modern schools (after World War II), of both primary and secondary educations, often are combined. In contrast, secondary education might be split into accomplished or not. The schools are classified as middle schools of general education. For the technical purposes, they include "degrees" of the education they provide out of three available: the first – primary, the second – unaccomplished secondary, and the third – accomplished secondary. Usually, the first two degrees of education (eight years) are always included. In contrast, the last one (two years) permits the students to pursue vocational or specialized educations.

North America and the United States

One-room school in 1935, Alabama

In North America, the term school can refer to any educational institution at any level and covers all of the following: preschool (for toddlers), kindergarten, elementary school, middle school (also called intermediate school or junior high school, depending on specific age groups and geographic region), high school (or in some cases senior high school), college, university, and graduate school.

In the United States, school performance through high school is monitored by each state's department of education. Charter schools are publicly funded elementary or secondary schools that have been freed from some of the rules, regulations, and statutes that apply to other public schools. The terms grammar school and grade school are sometimes used to refer to a primary school due to British colonial legacies. In addition, there are tax-funded magnet schools which offer different programs and instruction not available in traditional schools.

Africa

In West Africa, "school" can also refer to "bush" schools, Quranic schools, or apprenticeships. These schools include formal and informal learning.

Bush schools are training camps that pass down cultural skills, traditions, and knowledge to their students. Bush schools are semi-similar to traditional western schools because they are separated from the larger community. These schools are located in forests outside of the towns and villages, and the space used is solely for these schools. Once the students have arrived in the forest, they cannot leave until their training is complete. Visitors are prohibited from these areas.

Instead of being separated by age, Bush schools are separated by gender. Women and girls cannot enter the boys' bush school territory and vice versa. Boys receive training in cultural crafts, fighting, hunting, and community laws among other subjects. Girls are trained in their own version of the boys' bush school. They practice domestic affairs such as cooking, childcare, and being a good wife. Their training is focused on how to be a proper woman by societal standards.

A madrasah in the Gambia

Qur'anic schools are the principal way of teaching the Quran and knowledge of the Islamic faith. These schools also fostered literacy and writing during the time of colonization. Today, the emphasis is on the different levels of reading, memorizing, and reciting the Quran. Attending a Qur'anic school is how children become recognized members of the Islamic faith. Children often attend state schools and a Qur'anic school.

In Mozambique, specifically, there are two kinds of Qur'anic schools. They are the tariqa based and the Wahhabi-based schools. What makes these schools different is who controls them. Tariqa schools are controlled at the local level. In contrast, the Wahhabi are controlled by the Islamic Council. Within the Qur'anic school system, there are levels of education. They range from a basic level of understanding, called chuo and kioni in local languages, to the most advanced, which is called ilimu.

In Nigeria, the term school broadly covers daycares, nursery schools, primary schools, secondary schools and tertiary institutions. Primary and secondary schools are either privately funded by religious institutions and corporate organisations or government-funded. Government-funded schools are commonly referred to as public schools. Students spend six years in primary school, three years in junior secondary school, and three years in senior secondary school. The first nine years of formal schooling is compulsory under the Universal Basic Education Program (UBEC). Tertiary institutions include public and private universities, polytechnics, and colleges of education. Universities can be funded by the federal government, state governments, religious institutions, or individuals and organisations.

Ownership and operation

Many schools are owned or funded by states. Private schools operate independently from the government. Private schools usually rely on fees from families whose children attend the school for funding; however, sometimes such schools also receive government support (for example, through School vouchers). Many private schools are affiliated with a particular religion; these are known as parochial schools.

Components of most schools

See also: Learning environment and Learning space

A school entrance building in Australia

Schools are organized spaces purposed for teaching and learning. The classrooms where teachers teach and students learn are of central importance. Classrooms may be specialized for certain subjects, such as laboratory classrooms for science education and workshops for industrial arts education.

Typical schools have many other rooms and areas, which may include:

• Cafeteria (Commons), dining hall or canteen where students eat lunch and often breakfast and snacks.
• Athletic field, playground, gym, or track place where students participating in sports or physical education practice
• Schoolyards, all-purpose playfields typically in elementary schools, often made of concrete.
• Auditorium or hall where student theatrical and musical productions can be staged and where all-school events such as assemblies are held
• Office where the administrative work of the school is done
• Library where students ask librarians reference questions, check out books and magazines, and often use computers
• Computer labs where computer-based work is done and the internet accessed
• Cultural activities where the students uphold their cultural practice through activities like games, dance, and music

Education facilities in low-income countries

In low-income countries, only 32% of primary, 43% of lower secondary and 52% of upper secondary schools have access to electricity. This affects access to the internet, which is just 37% in upper secondary schools in low-income countries, as compared to 59% in those in middle-income countries and 93% in those in high-income countries.

Access to basic water, sanitation and hygiene is also far from universal. Among upper secondary schools, only 53% in low-income countries and 84% in middle-income countries have access to basic drinking water. Access to water and sanitation is universal in high-income countries.

Security

Main article: School security

To curtail violence, some schools have added CCTV surveillance cameras. This is especially common in schools with gang activity or violence.

The safety of staff and students is increasingly becoming an issue for school communities, an issue most schools are addressing through improved security. Some have also taken measures such as installing metal detectors or video surveillance. Others have even taken measures such as having the children swipe identification cards as they board the school bus. These plans have included door numbering to aid public safety response for some schools.

Other security concerns faced by schools include bomb threats, gangs, and vandalism. In recognition of these threats, the United Nations Sustainable Development Goal 4 advocates for upgrading education facilities to provide a safe, non-violent learning environment.

Health services

Main article: School health services

School health services are services from medical, teaching and other professionals applied in or out of school to improve the health and well-being of children and, in some cases, whole families. These services have been developed in different ways around the globe. However, the fundamentals are constant: the early detection, correction, prevention, or amelioration of disease, disability, and abuse from which school-aged children can suffer.

Online schools and classes

Main article: Virtual school

Some schools offer remote access to their classes over the internet. Online schools also can provide support to traditional schools, as in the case of the School Net Namibia. Some online classes also provide experience in a class. When people take them, they have already been introduced to the subject and know what to expect. Classes provide high school/college credit, allowing students to take the classes at their own pace. Many online classes cost money to take, but some are offered free.

Online class in Greece, October 2021. Online classes have been very common during the early 2020s, due to the mass closures of schools as a result of the Covid pandemic.

Internet-based distance learning programs are offered widely through many universities. Instructors teach through online activities and assignments. Online classes are taught the same as in-person, with the same curriculum. The instructor offers the syllabus with their fixed requirements like any other class. Students can virtually turn their assignments in to their instructors according to deadlines. This being through via email or on the course webpage. This allows students to work at their own pace yet meet the correct deadlines. Students taking an online class have more flexibility in their schedules to take their classes at a time that works best.

Conflicts with taking an online class may include not being face to face with the instructor when learning or being in an environment with other students. Online classes can also make understanding the content challenging, especially when unable to get in quick contact with the instructor. Online students have the advantage of using other online sources with assignments or exams for that specific class. Online classes also have the advantage of students not needing to leave their house for a morning class or worrying about their attendance for that class. Students can work at their own pace to learn and achieve within that curriculum.

The convenience of learning at home has been an attraction point for enrolling online. Students can attend class anywhere a computer can go – at home, in a library, or while traveling internationally. Online school classes are designed to fit a student's needs while allowing students to continue working and tending to their other obligations. Online school education is divided into three subcategories: Online Elementary School, Online Middle School, Online High school.

Stress

See also: Cram school

As a profession, teaching has levels of work-related stress (WRS) that are among the highest of any profession in some countries, such as the United Kingdom and the United States. The degree of this problem is becoming increasingly recognized and support systems are being put into place.

Stress sometimes affects students more severely than teachers, up to the point where the students are prescribed stress medication. This stress is claimed to be related to standardized testing, and the pressure on students to score above average.

According to a 2008 mental health study by the Associated Press and mtvU, eight in 10 U.S. college students said they had sometimes or frequently experienced stress in their daily lives. This was an increase of 20% from a survey five years previously. Thirty-four percent had felt depressed at some point in the past three months, 13 percent had been diagnosed with a mental health condition such as an anxiety disorder or depression, and 9 percent had seriously considered suicide.

Discipline towards students

Main article: School discipline

The activity of carrying out the flag ceremony at Indonesian schools every Monday morning, With the aim of educating discipline and a sense of national spirit

Schools and their teachers have always been under pressure – for instance, pressure to cover the curriculum, perform well compared to other schools, and avoid the stigma of being "soft" or "spoiling" toward students. Forms of discipline, such as control over when students may speak, and normalized behaviour, such as raising a hand to speak, are imposed in the name of greater efficiency. Practitioners of critical pedagogy maintain that such disciplinary measures have no positive effect on student learning. Indeed, some argue that disciplinary practices detract from learning, saying that they undermine students' dignity and sense of self-worth – the latter occupying a more primary role in students' hierarchy of needs.

Magnetohydrodynamic generator

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator 

A magnetohydrodynamic generator (MHD generator) is a magnetohydrodynamic converter that transforms thermal energy and kinetic energy directly into electricity. An MHD generator, like a conventional generator, relies on moving a conductor through a magnetic field to generate electric current. The MHD generator uses hot conductive ionized gas (a plasma) as the moving conductor. The mechanical dynamo, in contrast, uses the motion of mechanical devices to accomplish this.

MHD generators are different from traditional electric generators in that they operate without moving parts (e.g. no turbine) to limit the upper temperature. They therefore have the highest known theoretical thermodynamic efficiency of any electrical generation method. MHD has been extensively developed as a topping cycle to increase the efficiency of electric generation, especially when burning coal or natural gas. The hot exhaust gas from an MHD generator can heat the boilers of a steam power plant, increasing overall efficiency.

Practical MHD generators have been developed for fossil fuels, but these were overtaken by less expensive combined cycles in which the exhaust of a gas turbine or molten carbonate fuel cell heats steam to power a steam turbine.

MHD dynamos are the complement of MHD accelerators, which have been applied to pump liquid metals, seawater and plasmas.

Natural MHD dynamos are an active area of research in plasma physics and are of great interest to the geophysics and astrophysics communities, since the magnetic fields of the Earth and Sun are produced by these natural dynamos.

Principle

The Lorentz Force Law describes the effects of a charged particle moving in a constant magnetic field. The simplest form of this law is given by the vector equation.

${\displaystyle \mathbf{F}=Q(\mathbf{v}\times \mathbf{B})}$

where

• F is the force acting on the particle.
• Q is the charge of the particle,
• v is the velocity of the particle, and
• B is the magnetic field.

The vector F is perpendicular to both v and B according to the right hand rule.

Power generation

Typically, for a large power station to approach the operational efficiency of computer models, steps must be taken to increase the electrical conductivity of the conductive substance. The heating of a gas to its plasma state or the addition of other easily ionizable substances like the salts of alkali metals can accomplish this increase. In practice, a number of issues must be considered in the implementation of an MHD generator: generator efficiency, economics, and toxic byproducts. These issues are affected by the choice of one of the three MHD generator designs: the Faraday generator, the Hall generator, and the disc generator.

Faraday generator

The Faraday generator is named for Michael Faraday's experiments on moving charged particles in the Thames river.

A simple Faraday generator would consist of a wedge-shaped pipe or tube of some non-conductive material. When an electrically conductive fluid flows through the tube, in the presence of a significant perpendicular magnetic field, a voltage is induced in the fluid, which can be drawn off as electrical power by placing the electrodes on the sides at 90 degree angles to the magnetic field.

There are limitations on the density and type of field used. The amount of power that can be extracted is proportional to the cross sectional area of the tube and the speed of the conductive flow. The conductive substance is also cooled and slowed by this process. MHD generators typically reduce the temperature of the conductive substance from plasma temperatures to just over 1000 °C.

The main practical problem of a Faraday generator is that differential voltages and currents in the fluid short through the electrodes on the sides of the duct. The most powerful waste is from the Hall effect current. This makes the Faraday duct very inefficient. Most further refinements of MHD generators have tried to solve this problem. The optimal magnetic field on duct-shaped MHD generators is a sort of saddle shape. To get this field, a large generator requires an extremely powerful magnet. Many research groups have tried to adapt superconducting magnets to this purpose, with varying success. (For references, please see the discussion of generator efficiency, below.)

Hall generator

Diagram of a Hall MHD generator showing current flows

The typical solution, historically, has been to use the Hall effect to create a current that flows with the fluid. (See illustration.) This design has arrays of short, segmented electrodes on the sides of the duct. The first and last electrodes in the duct power the load. Each other electrode is shorted to an electrode on the opposite side of the duct. These shorts of the Faraday current induce a powerful magnetic field within the fluid, but in a chord of a circle at right angles to the Faraday current. This secondary, induced field makes current flow in a rainbow shape between the first and last electrodes.

Losses are less than a Faraday generator, and voltages are higher because there is less shorting of the final induced current.

However, this design has problems because the speed of the material flow requires the middle electrodes to be offset to "catch" the Faraday currents. As the load varies, the fluid flow speed varies, misaligning the Faraday current with its intended electrodes, and making the generator's efficiency very sensitive to its load.

Disc generator

Diagram of a disk MHD generator showing current flows

The third and, currently, the most efficient design is the Hall effect disc generator. This design currently holds the efficiency and energy density records for MHD generation. A disc generator has fluid flowing between the center of a disc, and a duct wrapped around the edge. (The ducts are not shown.) The magnetic excitation field is made by a pair of circular Helmholtz coils above and below the disk. (The coils are not shown.)

The Faraday currents flow in a perfect dead short around the periphery of the disk.

The Hall effect currents flow between ring electrodes near the center duct and ring electrodes near the periphery duct.

The wide flat gas flow reduced the distance, hence the resistance of the moving fluid. This increases efficiency.

Another significant advantage of this design is that the magnets are more efficient. First, they cause simple parallel field lines. Second, because the fluid is processed in a disk, the magnet can be closer to the fluid, and in this magnetic geometry, magnetic field strengths increase as the 7th power of distance. Finally, the generator is compact for its power, so the magnet is also smaller. The resulting magnet uses a much smaller percentage of the generated power.

Generator efficiency

The efficiency of the direct energy conversion in MHD power generation increases with the magnetic field strength and the plasma conductivity, which depends directly on the plasma temperature, and more precisely on the electron temperature. As very hot plasmas can only be used in pulsed MHD generators (for example using shock tubes) due to the fast thermal material erosion, it was envisaged to use nonthermal plasmas as working fluids in steady MHD generators, where only free electrons are heated a lot (10,000–20,000 kelvins) while the main gas (neutral atoms and ions) remains at a much lower temperature, typically 2500 kelvins. The goal was to preserve the materials of the generator (walls and electrodes) while improving the limited conductivity of such poor conductors to the same level as a plasma in thermodynamic equilibrium; i.e. completely heated to more than 10,000 kelvins, a temperature that no material could stand.

But Evgeny Velikhov first discovered theoretically in 1962 and experimentally in 1963 that an ionization instability, later called the Velikhov instability or electrothermal instability, quickly arises in any MHD converter using magnetized nonthermal plasmas with hot electrons, when a critical Hall parameter is reached, hence depending on the degree of ionization and the magnetic field. Such an instability greatly degrades the performance of nonequilibrium MHD generators. The prospects about this technology, which initially predicted awesome efficiencies, crippled MHD programs all over the world as no solution to mitigate the instability was found at that time.

Consequently, without implementing solutions to master the electrothermal instability, practical MHD generators had to limit the Hall parameter or use moderately heated thermal plasmas instead of cold plasmas with hot electrons, which severely lowers efficiency.

As of 1994, the 22% efficiency record for closed-cycle disc MHD generators was held by Tokyo Technical Institute. The peak enthalpy extraction in these experiments reached 30.2%. Typical open-cycle Hall & duct coal MHD generators are lower, near 17%. These efficiencies make MHD unattractive, by itself, for utility power generation, since conventional Rankine cycle power plants easily reach 40%.

However, the exhaust of an MHD generator burning fossil fuel is almost as hot as a flame. By routing its exhaust gases into a heat exchanger for a turbine Brayton cycle or steam generator Rankine cycle, MHD can convert fossil fuels into electricity with an estimated efficiency up to 60 percent, compared to the 40 percent of a typical coal plant.

A magnetohydrodynamic generator might also be the first stage of a gas core reactor.

Material and design issues

MHD generators have difficult problems in regard to materials, both for the walls and the electrodes. Materials must not melt or corrode at very high temperatures. Exotic ceramics were developed for this purpose, and must be selected to be compatible with the fuel and ionization seed. The exotic materials and the difficult fabrication methods contribute to the high cost of MHD generators.

Also, MHDs work better with stronger magnetic fields. The most successful magnets have been superconducting, and very close to the channel. A major difficulty was refrigerating these magnets while insulating them from the channel. The problem is worse because the magnets work better when they are closer to the channel. There are also severe risks of damage to the hot, brittle ceramics from differential thermal cracking. The magnets are usually near absolute zero, while the channel is several thousand degrees.

For MHDs, both alumina (Al₂O₃) and magnesium peroxide (MgO₂) were reported to work for the insulating walls. Magnesium peroxide degrades near moisture. Alumina is water-resistant and can be fabricated to be quite strong, so in practice most MHDs have used alumina for the insulating walls.

For the electrodes of clean MHDs (i.e. burning natural gas), one good material was a mix of 80% CeO₂, 18% ZrO₂, and 2% Ta₂O₅.

Coal-burning MHDs have intensely corrosive environments with slag. The slag both protects and corrodes MHD materials. In particular, migration of oxygen through the slag accelerates corrosion of metallic anodes. Nonetheless, very good results have been reported with stainless steel electrodes at 900 K. Another, perhaps superior option is a spinel ceramic, FeAl₂O₄ - Fe₃O₄. The spinel was reported to have electronic conductivity, absence of a resistive reaction layer but with some diffusion of iron into the alumina. The diffusion of iron could be controlled with a thin layer of very dense alumina, and water cooling in both the electrodes and alumina insulators.

Attaching the high temperature electrodes to conventional copper bus bars is also challenging. The usual methods establish a chemical passivation layer, and cool the busbar with water.

Economics

MHD generators have not been employed for large scale mass energy conversion because other techniques with comparable efficiency have a lower lifecycle investment cost. Advances in natural gas turbines achieved similar thermal efficiencies at lower costs, by having the turbine's exhaust drive a Rankine cycle steam plant. To get more electricity from coal, it is cheaper to simply add more low-temperature steam-generating capacity.

A coal-fueled MHD generator is a type of Brayton power cycle, similar to the power cycle of a combustion turbine. However, unlike the combustion turbine, there are no moving mechanical parts; the electrically conducting plasma provides the moving electrical conductor. The side walls and electrodes merely withstand the pressure within, while the anode and cathode conductors collect the electricity that is generated. All Brayton cycles are heat engines. Ideal Brayton cycles also have an ideal efficiency equal to ideal Carnot cycle efficiency. Thus, the potential for high energy efficiency from an MHD generator. All Brayton cycles have higher potential for efficiency the higher the firing temperature. While a combustion turbine is limited in maximum temperature by the strength of its air/water or steam-cooled rotating airfoils; there are no rotating parts in an open-cycle MHD generator. This upper bound in temperature limits the energy efficiency in combustion turbines. The upper bound on Brayton cycle temperature for an MHD generator is not limited, so inherently an MHD generator has a higher potential capability for energy efficiency.

The temperatures at which linear coal-fueled MHD generators can operate are limited by factors that include: (a) the combustion fuel, oxidizer, and oxidizer preheat temperature which limit the maximum temperature of the cycle; (b) the ability to protect the sidewalls and electrodes from melting; (c) the ability to protect the electrodes from electrochemical attack from the hot slag coating the walls combined with the high current or arcs that impinge on the electrodes as they carry off the direct current from the plasma; and (d) by the capability of the electrical insulators between each electrode. Coal-fired MHD plants with oxygen/air and high oxidant preheats would probably provide potassium seeded plasmas of about 4200 °F, 10 atmospheres pressure, and begin expansion at Mach 1.2. These plants would recover MHD exhaust heat for oxidant preheat, and for combined cycle steam generation. With aggressive assumptions, one DOE-funded feasibility study of where the technology could go, 1000 MWe Advanced Coal-Fired MHD/Steam Binary Cycle Power Plant Conceptual Design, published in June 1989, showed that a large coal-fired MHD combined cycle plant could attain a HHV energy efficiency approaching 60 percent—well in excess of other coal-fueled technologies, so the potential for low operating costs exists.

However, no testing at those aggressive conditions or size has yet occurred, and there are no large MHD generators now under test. There is simply an inadequate reliability track record to provide confidence in a commercial coal-fuelled MHD design.

U25B MHD testing in Russia using natural gas as fuel used a superconducting magnet, and had an output of 1.4 megawatts. A coal-fired MHD generator series of tests funded by the U.S. Department of Energy (DOE) in 1992 produced MHD power from a larger superconducting magnet at the Component Development and Integration Facility (CDIF) in Butte, Montana. None of these tests were conducted for long-enough durations to verify the commercial durability of the technology. Neither of the test facilities were in large-enough scale for a commercial unit.

Superconducting magnets are used in the larger MHD generators to eliminate one of the large parasitic losses: the power needed to energize the electromagnet. Superconducting magnets, once charged, consume no power, and can develop intense magnetic fields 4 teslas and higher. The only parasitic load for the magnets are to maintain refrigeration, and to make up the small losses for the non-supercritical connections.

Because of the high temperatures, the non-conducting walls of the channel must be constructed from an exceedingly heat-resistant substance such as yttrium oxide or zirconium dioxide to retard oxidation. Similarly, the electrodes must be both conductive and heat-resistant at high temperatures. The AVCO coal-fueled MHD generator at the CDIF was tested with water-cooled copper electrodes capped with platinum, tungsten, stainless steel, and electrically-conducting ceramics.

Toxic byproducts

MHD reduces overall production of hazardous fossil fuel wastes because it increases plant efficiency. In MHD coal plants, the patented commercial "Econoseed" process developed by the U.S. (see below) recycles potassium ionization seed from the fly ash captured by the stack-gas scrubber. However, this equipment is an additional expense. If molten metal is the armature fluid of an MHD generator, care must be taken with the coolant of the electromagnetics and channel. The alkali metals commonly used as MHD fluids react violently with water. Also, the chemical byproducts of heated, electrified alkali metals and channel ceramics may be poisonous and environmentally persistent.

History

The first practical MHD power research was funded in 1938 in the U.S. by Westinghouse in its Pittsburgh, Pennsylvania laboratories, headed by Hungarian Bela Karlovitz. The initial patent on MHD is by B. Karlovitz, U.S. Patent No. 2,210,918, "Process for the Conversion of Energy", August 13, 1940.

World War II interrupted development. In 1962, the First International Conference on MHD Power was held in Newcastle upon Tyne, UK by Dr. Brian C. Lindley of the International Research and Development Company Ltd. The group set up a steering committee to set up further conferences and disseminate ideas. In 1964, the group set up a second conference in Paris, France, in consultation with the European Nuclear Energy Agency.

Since membership in the ENEA was limited, the group persuaded the International Atomic Energy Agency to sponsor a third conference, in Salzburg, Austria, July 1966. Negotiations at this meeting converted the steering committee into a periodic reporting group, the ILG-MHD (international liaison group, MHD), under the ENEA, and later in 1967, also under the International Atomic Energy Agency. Further research in the 1960s by R. Rosa established the practicality of MHD for fossil-fueled systems.

In the 1960s, AVCO Everett Aeronautical Research began a series of experiments, ending with the Mk. V generator of 1965. This generated 35 MW, but used about 8 MW to drive its magnet. In 1966, the ILG-MHD had its first formal meeting in Paris, France. It began issuing a periodic status report in 1967. This pattern persisted, in this institutional form, up until 1976. Toward the end of the 1960s, interest in MHD declined because nuclear power was becoming more widely available.

In the late 1970s, as interest in nuclear power declined, interest in MHD increased. In 1975, UNESCO became persuaded the MHD might be the most efficient way to utilise world coal reserves, and in 1976, sponsored the ILG-MHD. In 1976, it became clear that no nuclear reactor in the next 25 years would use MHD, so the International Atomic Energy Agency and ENEA (both nuclear agencies) withdrew support from the ILG-MHD, leaving UNESCO as the primary sponsor of the ILG-MHD.

Former Yugoslavia development

Over more than a ten-year span, engineers in former Yugoslavian Institute of Thermal and Nuclear Technology (ITEN), Energoinvest Co., Sarajevo, had built the first experimental Magneto-Hydrodynamic facility power generator in 1989. It was here it was first patented.

U.S. development

In the 1980s, the U.S. Department of Energy began a vigorous multiyear program, culminating in a 1992 50 MW demonstration coal combustor at the Component Development and Integration Facility (CDIF) in Butte, Montana. This program also had significant work at the Coal-Fired-In-Flow-Facility (CFIFF) at University of Tennessee Space Institute.

This program combined four parts:

1. An integrated MHD topping cycle, with channel, electrodes and current control units developed by AVCO, later known as Textron Defence of Boston. This system was a Hall effect duct generator heated by pulverized coal, with a potassium ionisation seed. AVCO had developed the famous Mk. V generator, and had significant experience.
2. An integrated bottoming cycle, developed at the CDIF.
3. A facility to regenerate the ionization seed was developed by TRW. Potassium carbonate is separated from the sulphate in the fly ash from the scrubbers. The carbonate is removed, to regain the potassium.
4. A method to integrate MHD into preexisting coal plants. The Department of Energy commissioned two studies. Westinghouse Electric performed a study based on the Scholtz Plant of Gulf Power in Sneads, Florida. The MHD Development Corporation also produced a study based on the J.E. Corrette Plant of the Montana Power Company of Billings, Montana.

Initial prototypes at the CDIF were operated for short durations, with various coals: Montana Rosebud, and a high-sulphur corrosive coal, Illinois No. 6. A great deal of engineering, chemistry and material science was completed. After final components were developed, operational testing completed with 4,000 hours of continuous operation, 2,000 on Montana Rosebud, 2,000 on Illinois No. 6. The testing ended in 1993.

Japanese development

The Japanese program in the late 1980s concentrated on closed-cycle MHD. The belief was that it would have higher efficiencies, and smaller equipment, especially in the clean, small, economical plant capacities near 100 megawatts (electrical) which are suited to Japanese conditions. Open-cycle coal-powered plants are generally thought to become economical above 200 megawatts.

The first major series of experiments was FUJI-1, a blow-down system powered from a shock tube at the Tokyo Institute of Technology. These experiments extracted up to 30.2% of enthalpy, and achieved power densities near 100 megawatts per cubic meter. This facility was funded by Tokyo Electric Power, other Japanese utilities, and the Department of Education. Some authorities believe this system was a disc generator with a helium and argon carrier gas and potassium ionization seed.

In 1994, there were detailed plans for FUJI-2, a 5 MWe continuous closed-cycle facility, powered by natural gas, to be built using the experience of FUJI-1. The basic MHD design was to be a system with inert gases using a disk generator. The aim was an enthalpy extraction of 30% and an MHD thermal efficiency of 60%. FUJI-2 was to be followed by a retrofit to a 300 MWe natural gas plant.

Australian development

In 1986, Professor Hugo Karl Messerle at The University of Sydney researched coal-fueled MHD. This resulted in a 28 MWe topping facility that was operated outside Sydney. Messerle also wrote one of the most recent reference works (see below), as part of a UNESCO education program.

A detailed obituary for Hugo is located on the Australian Academy of Technological Sciences and Engineering (ATSE) website.

Italian development

The Italian program began in 1989 with a budget of about 20 million $US, and had three main development areas:

1. MHD Modelling.
2. Superconducting magnet development. The goal in 1994 was a prototype 2 m long, storing 66 MJ, for an MHD demonstration 8 m long. The field was to be 5 teslas, with a taper of 0.15 T/m. The geometry was to resemble a saddle shape, with cylindrical and rectangular windings of niobium-titanium copper.
3. Retrofits to natural gas powerplants. One was to be at the Enichem-Anic factor in Ravenna. In this plant, the combustion gases from the MHD would pass to the boiler. The other was a 230 MW (thermal) installation for a power station in Brindisi, that would pass steam to the main power plant.

Chinese development

A joint U.S.-China national programme ended in 1992 by retrofitting the coal-fired No. 3 plant in Asbach. A further eleven-year program was approved in March 1994. This established centres of research in:

1. The Institute of Electrical Engineering in the Chinese Academy of Sciences, Beijing, concerned with MHD generator design.
2. The Shanghai Power Research Institute, concerned with overall system and superconducting magnet research.
3. The Thermoenergy Research Engineering Institute at the Nanjing's Southeast University, concerned with later developments.

The 1994 study proposed a 10 W (electrical, 108 MW thermal) generator with the MHD and bottoming cycle plants connected by steam piping, so either could operate independently.

Russian developments

U-25 scale model

In 1971 the natural-gas fired U-25 plant was completed near Moscow, with a designed capacity of 25 megawatts. By 1974 it delivered 6 megawatts of power. By 1994, Russia had developed and operated the coal-operated facility U-25, at the High-Temperature Institute of the Russian Academy of Science in Moscow. U-25's bottoming plant was actually operated under contract with the Moscow utility, and fed power into Moscow's grid. There was substantial interest in Russia in developing a coal-powered disc generator. In 1986 the first industrial power plant with MHD generator was built, but in 1989 the project was cancelled before MHD launch and this power plant later joined to Ryazan Power Station as a 7th unit with ordinary construction.