Magnetohydrodynamic converter

Last updated

A magnetohydrodynamic converter (MHD converter) is an electromagnetic machine with no moving parts involving magnetohydrodynamics, the study of the kinetics of electrically conductive fluids (liquid or ionized gas) in the presence of electromagnetic fields. Such converters act on the fluid using the Lorentz force to operate in two possible ways: either as an electric generator called an MHD generator, extracting energy from a fluid in motion; or as an electric motor called an MHD accelerator or magnetohydrodynamic drive, putting a fluid in motion by injecting energy. MHD converters are indeed reversible, like many electromagnetic devices. [1]

Contents

Michael Faraday first attempted to test a MHD converter in 1832. MHD converters involving plasmas were highly studied in the 1960s and 1970s, with many government funding and dedicated international conferences. One major conceptual application was the use of MHD converters on the hot exhaust gas in a coal fired power plant, where it could extract some of the energy with very high efficiency, and then pass it into a conventional steam turbine. The research almost stopped after it was considered the electrothermal instability would severely limit the efficiency of such converters when intense magnetic fields are used, [2] although solutions may exist. [3] [4] [5] [6]

Crossed-field magnetohydrodynamic converters (linear Faraday type with segmented electrodes). A: MHD generator. B: MHD accelerator. MHD converters (generator and accelerator).svg
Crossed-field magnetohydrodynamic converters (linear Faraday type with segmented electrodes). A: MHD generator. B: MHD accelerator.


Crossed-field magnetohydrodynamic converters

(linear Faraday type with segmented electrodes)

A: MHD generator. B: MHD accelerator.

MHD power generation

A magnetohydrodynamic generator is an MHD converter that transforms the kinetic energy of an electrically conductive fluid, in motion with respect to a steady magnetic field, into electricity. MHD power generation has been tested extensively in the 1960s with liquid metals and plasmas as working fluids. [7]

Basically, a plasma is hurtling down within a channel whose walls are fitted with electrodes. Electromagnets create a uniform transverse magnetic field within the cavity of the channel. The Lorentz force then acts upon the trajectory of the incoming electrons and positive ions, separating the opposite charge carriers according to their sign. As negative and positive charges are spatially separated within the chamber, an electric potential difference can be retrieved across the electrodes. While work is extracted from the kinetic energy of the incoming high-velocity plasma, the fluid slows down during the process.

MHD propulsion

A magnetohydrodynamic accelerator is an MHD converter that imparts motion to an electrically conductive fluid initially at rest, using cross electric current and magnetic field both applied within the fluid. MHD propulsion has been mostly tested with models of ships and submarines in seawater. [8] [9] Studies are also ongoing since the early 1960s about aerospace applications of MHD to aircraft propulsion and flow control to enable hypersonic flight: action on the boundary layer to prevent laminar flow from becoming turbulent, shock wave mitigation or cancellation for thermal control and reduction of the wave drag and form drag, inlet flow control and airflow velocity reduction with an MHD generator section ahead of a scramjet or turbojet to extend their regimes at higher Mach numbers, combined to an MHD accelerator in the exhaust nozzle fed by the MHD generator through a bypass system. Research on various designs are also conducted on electromagnetic plasma propulsion for space exploration. [10] [11] [12] [13]

In an MHD accelerator, the Lorentz force accelerates all charge carriers in the same direction whatever their sign, as well as neutral atoms and molecules of the fluid through collisions. The fluid is ejected toward the rear and as a reaction, the vehicle accelerates forward.

See also

Related Research Articles

<span class="mw-page-title-main">Ion thruster</span> Spacecraft engine that generates thrust by generating a jet of ions

An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. An ion thruster creates a cloud of positive ions from a neutral gas by ionizing it to extract some electrons from its atoms. The ions are then accelerated using electricity to create thrust. Ion thrusters are categorized as either electrostatic or electromagnetic.

<span class="mw-page-title-main">Magnetohydrodynamics</span> Model of electrically conducting fluids

Magnetohydrodynamics is a model of electrically conducting fluids that treats all interpenetrating particle species together as a single continuous medium. It is primarily concerned with the low-frequency, large-scale, magnetic behavior in plasmas and liquid metals and has applications in numerous fields including geophysics, astrophysics, and engineering.

<span class="mw-page-title-main">Electric generator</span> Device that converts other energy to electrical energy

In electricity generation, a generator is a device that converts motion-based power or fuel-based power into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas turbines, water turbines, internal combustion engines, wind turbines and even hand cranks. The first electromagnetic generator, the Faraday disk, was invented in 1831 by British scientist Michael Faraday. Generators provide nearly all the power for electrical grids.

<span class="mw-page-title-main">Magnetohydrodynamic drive</span> Vehicle propulsion using electromagnetic fields

A magnetohydrodynamic drive or MHD accelerator is a method for propelling vehicles using only electric and magnetic fields with no moving parts, accelerating an electrically conductive propellant with magnetohydrodynamics. The fluid is directed to the rear and as a reaction, the vehicle accelerates forward.

<span class="mw-page-title-main">Lightcraft</span> Aerospace craft utilizing beam-powered propulsion

The Lightcraft is a space- or air-vehicle driven by beam-powered propulsion, the energy source powering the craft being external. It was conceptualized by aerospace engineering professor Leik Myrabo at Rensselaer Polytechnic Institute in 1976, who developed the concept further with working prototypes, funded in the 1980s by the Strategic Defense Initiative organization, and the decade after by the Advanced Concept Division of the US Air Force AFRL, NASA's MFSC and the Lawrence Livermore National Laboratory.

A thermionic converter consists of a hot electrode which thermionically emits electrons over a potential energy barrier to a cooler electrode, producing a useful electric power output. Caesium vapor is used to optimize the electrode work functions and provide an ion supply to neutralize the electron space charge.

A magnetohydrodynamic 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 as the moving conductor. The mechanical dynamo, in contrast, uses the motion of mechanical devices to accomplish this.

<span class="mw-page-title-main">Field-reversed configuration</span> Magnetic confinement fusion reactor

A field-reversed configuration (FRC) is a type of plasma device studied as a means of producing nuclear fusion. It confines a plasma on closed magnetic field lines without a central penetration. In an FRC, the plasma has the form of a self-stable torus, similar to a smoke ring.

<span class="mw-page-title-main">Magnetic pressure</span> Energy density associated with a magnetic field

In physics, magnetic pressure is an energy density associated with a magnetic field. In SI units, the energy density of a magnetic field with strength can be expressed as

<span class="mw-page-title-main">Plasma propulsion engine</span> Type of electric propulsion

A plasma propulsion engine is a type of electric propulsion that generates thrust from a quasi-neutral plasma. This is in contrast with ion thruster engines, which generate thrust through extracting an ion current from the plasma source, which is then accelerated to high velocities using grids/anodes. These exist in many forms. However, in the scientific literature, the term "plasma thruster" sometimes encompasses thrusters usually designated as "ion engines".

<span class="mw-page-title-main">Pinch (plasma physics)</span> Compression of an electrically conducting filament by magnetic forces

A pinch is the compression of an electrically conducting filament by magnetic forces, or a device that does such. The conductor is usually a plasma, but could also be a solid or liquid metal. Pinches were the first type of device used for experiments in controlled nuclear fusion power.

<span class="mw-page-title-main">Spacecraft electric propulsion</span> Type of space propulsion using electrostatic and electromagnetic fields for acceleration

Spacecraft electric propulsion is a type of spacecraft propulsion technique that uses electrostatic or electromagnetic fields to accelerate mass to high speed and thus generate thrust to modify the velocity of a spacecraft in orbit. The propulsion system is controlled by power electronics.

The magnetic field oscillating amplified thruster is a versatile electrothermodynamic system, which is able to accelerate nearly every electrically charged gaseous medium to extremely high velocities, thereby generating a high energetic plasma jet in the exhaust and also electrical conductive fluids in general.

<span class="mw-page-title-main">Evgeny Velikhov</span> Russian physicist

Evgeny Pavlovich Velikhov is a physicist and scientific leader in the Russian Federation. His scientific interests include plasma physics, lasers, controlled nuclear fusion, power engineering, and magnetohydrodynamics. He is the author of over 1500 scientific publications and a number of inventions and discoveries.

<span class="mw-page-title-main">Ayaks</span>

The Ayaks is a hypersonic waverider aircraft program started in the Soviet Union and currently under development by the Hypersonic Systems Research Institute (HSRI) of Leninets Holding Company in Saint Petersburg, Russia.

The electrothermal instability is a magnetohydrodynamic (MHD) instability appearing in magnetized non-thermal plasmas used in MHD converters. It was first theoretically discovered in 1962 and experimentally measured into a MHD generator in 1963 by Evgeny Velikhov.

"This paper shows that it is possible to assert sufficiently specifically that the ionization instability is the number one problem for the utilization of a plasma with hot electrons."

An ionization instability is any one of a category of plasma instabilities which is mediated by electron-impact ionization. In the most general sense, an ionization instability occurs from a feedback effect, when electrons produced by ionization go on to produce still more electrons through ionization in a self-reinforcing way.

<span class="mw-page-title-main">Plasma (physics)</span> State of matter

Plasma is one of four fundamental states of matter, characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars, but also dominating the rarefied intracluster medium and intergalactic medium. Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field.

A plasma railgun is a linear accelerator which, like a projectile railgun, uses two long parallel electrodes to accelerate a "sliding short" armature. However, in a plasma railgun, the armature and ejected projectile consists of plasma, or hot, ionized, gas-like particles, instead of a solid slug of material. Scientific plasma railguns are typically operated in vacuum and not at air pressure. They are of value because they produce muzzle velocities of up to several hundreds of kilometers per second. Because of this, these devices have applications in magnetic confinement fusion (MCF), magneto-inertial fusion (MIF), high energy density physics research (HEDP), laboratory astrophysics, and as a plasma propulsion engine for spacecraft.

Direct energy conversion (DEC) or simply direct conversion converts a charged particle's kinetic energy into a voltage. It is a scheme for power extraction from nuclear fusion.

References

  1. Petit, Jean-Pierre (1983). The Silence Barrier (PDF). The Adventures of Archibald Higgins. Savoir Sans Frontières.
  2. Velikhov, E. P.; Dykhne, A. M.; Shipuk, I. Ya (1965). Ionization instability of a plasma with hot electrons (PDF). 7th International Conference on Ionization Phenomena in Gases. Belgrade, Yugoslavia.
  3. Shapiro, G. I.; Nelson, A. H. (12 April 1978). "Stabilization of ionization instability in a variable electric field". Pis'ma V Zhurnal Tekhnischeskoi Fiziki. 4 (12): 393–396. Bibcode:1978PZhTF...4..393S.
  4. Murakami, T.; Okuno, Y.; Yamasaki, H. (December 2005). "Suppression of ionization instability in a magnetohydrodynamic plasma by coupling with a radio-frequency electromagnetic field" (PDF). Applied Physics Letters. 86 (19): 191502–191502.3. Bibcode:2005ApPhL..86s1502M. doi:10.1063/1.1926410.
  5. Petit, J.-P.; Geffray, J. (June 2009). "Non equilibrium plasma instabilities". Acta Physica Polonica A. 115 (6): 1170–1173. Bibcode:2009AcPPA.115.1170P. doi: 10.12693/aphyspola.115.1170 .
  6. Petit, J.-P.; Doré, J.-C. (2013). "Velikhov electrothermal instability cancellation by a modification of electrical conductivity value in a streamer by magnetic confinement". Acta Polytechnica. 53 (2): 219–222. doi: 10.14311/1765 . hdl: 10467/67041 .
  7. Haines, M. G.; McNab, I. R. (1974). "Magnetohydrodynamic power dynamics" (PDF). Physics in Technology. 5 (4): 278–300. Bibcode:1974PhTec...5..278H. doi:10.1088/0305-4624/5/4/I03.
  8. Dane, Abe (August 1990). "100 mph Jet Ships" (PDF). Popular Mechanics. pp. 60–62. Retrieved 2018-04-04.
  9. Normile, Dennis (November 1992). "Superconductivity goes to sea" (PDF). Popular Science. Bonnier Corporation. pp. 80–85. Retrieved 2018-04-04.
  10. Sherman, A. (January 1963). "Magnetohydrodynamic Propulsion" (PDF). R63SD5 (Report). Air Force Office of Scientific Research.
  11. Carter, A. F.; Weaver, W. R.; Mcfarland, D. R.; Wood, G. P. (December 1971). "Development and initial operating characteristics of the 20 megawatt linear plasma accelerator facility" (PDF). NASA-TN-D-6547 (Report). Langley Research Center: NASA. hdl:2060/19720005094.
  12. Litchford, Ron J.; Lineberry, John T. (May 2008). Magnetohydrodynamic Augmented Propulsion Experiment. Annual Technical Meeting. Yamanakako, Japan: Japan MHD Society. hdl: 2060/20080033025 .
  13. Roy, Subrata; Arnold, David; Lin, Jenshan; Schmidt, Tony; Lind, Rick; et al. (20 December 2011). Air Force Office of Scientific Research; University of Florida (eds.). Demonstration of a Wingless Electromagnetic Air Vehicle (PDF) (Report). Defense Technical Information Center. ASIN   B01IKW9SES. AFRL-OSR-VA-TR-2012-0922. Archived (PDF) from the original on May 17, 2013.

Further reading