venerdì 15 giugno 2012

Magnetohydrodynamics

Volevo condividere la notizia di martedì 12 giugno apparsa su renewable energy magazine:


""Rensselaer Polytechnic Institute has announced the signing of an exclusive license agreement with Concentrating Solar Power Utility, Inc. for a breakthrough solar power technology utilising magnetohydrodynamics (MHD). This science fiction sounding technology uses superconducting magnets to strip electrons from high energy plasma jets, and generate power with no moving parts. [..] MHD is derived from Magneto- meaning magnetic field, hydro- meaning liquid, and dynamics- meaning movement. MHD generates electricity directly from a body of very hot moving gas without any mechanical moving parts. Solar energy, concentrated by mirrors or lens can create this superheated gas; magnetohydrodynamics works by using superconducting magnets to extract electricity from the superheated gas. In a sense, MHD replaces the wires used in conventional electrical generators with ionised gas.
“Solar MHD power generation represents a breakthrough in CSP technology. It is a new, more efficient way of generating electricity by utilising higher temperatures. It is more efficient for this reason and the fact that MHD utilises no moving parts except for the flow of the ionised gas through a magnetic field. This is accomplished through breakthroughs in heat pipe technology, microchannel cooling and permanent super conductive magnets, heliostats and materials,” Thomas P. Kay, founder of Concentrating Solar Power Utility, explained to Renewable Energy Magazine recently. Much of the technology behind this system has already been patented by Kay and two Rensselaer Polytechnic Institute professors, Douglas B Chrisey and Yoav Peles. Some of their joint work was, in turn, based on earlier MHD patents held by Kay himself.
“In developing this technology, the use of the extremely large superconducting permanent magnets will improve efficiency, and this is even more so when combined with the micro-channel cooling process developed by Professor Peles,” explains Chrisey. [..] ""

Da concentrating solarpower utility si legge:
""[..] Magneto- Hydro- Dynamics (MHD) is derived from Magneto- meaning magnetic field, Hydro- meaning liquid , and Dynamics- meaning movement. MHD generates electricity directly from a body of very hot moving gas without any mechanical moving parts. Magnetohydrodynamics works by using magnets to extract electricity from superheated charged gas. In a sense MHD replaces the wires used in conventional electrical generators with Ionized gas. The basic principle of MHD power generation, is the same as that of conventional power generation. Namely that “a conductor moving across the magnetic field induces an electrical potential perpendicular to both the magnetic field and the direction of the conductor movements Faraday’s law of electromagnetic induction. However, in the MHD process, the metallic conductor of the conventional generator is replaced by a gaseous conductor, called “plasma”. The principle of MHD generation was discovered by Faraday when an electric conductor moves across a magnetic field, a emf. Is induced in it, which produced an electric current. This is the principle of the conventional generator also, where the conductors consists of copper strips. 
In MHD generator the solid conductors are replaced by a gaseous conductor; i.e. an ionized gas "plasma". [..] ""













Invito ad esplorare il sito concentrating solarpower utility , tra cui ho letto quanto segue:
""The surface temperature of the sun is about 6000° K. Theoretically this is the highest temperature achievable at the focal point of a concentrating mirror. On the ground this is not possible since a part of the solar spectrum is absorbed by the earth's atmosphere. However, that is not true in space or on the moon. Yet, to use such extremely high temperatures is impractical and also not necessary. Presently it is believed that temperatures between 2500° K and 3000° K would be sufficient to operate a MHD device. For photo-ionization to occur, the energy of the ionizing radiation has to be equal to or greater than the ionization energy of the atom to be ionized. In the case of cesium, this would be about 3 eV. Optical radiation of this energy has a wavelength of 200 nm (2000 Angstrom) or shorter. Radiation having wavelengths shorter than 200 nm is absorbed by the earth's atmosphere. Therefore, in space or on the moon, this energy could be used to augment the ionization of a MHD device. The absorption of a photon by an atom and subsequent ejection of an electron is almost instantaneous (on the order of 10−8 seconds). This means the photo-ionization could be created right between the electrodes in the duct. The working fluid is practically standing still during such a time span. Fortunately, for the inverse reaction (recombination) to occur, a 3-body collision is needed. This could be a collision between a helium atom, a cesium ion, and an electron. (The wall of the duct can also act as the third particle). Consequently, the number of recombination events can be adjusted by the gas pressure. [..]
The solar radiation is concentrated by multi-aperture optics on to a tungsten housing. [..] Inside the tungsten housing is the high-pressure part of the working fluid. Initially helium seeded with 2% cesium is considered as the working fluid. Inside the tungsten housing the working fluid will reach the static design pressure and temperature. The static pressure will force the working fluid through a nozzle, which converts some of the pressure to kinetic energy (pressure is potential energy density).
In the MHD duct some, but not all, of the kinetic energy is converted into electrical energy. Any remaining kinetic energy of the gas stream is converted in the gas turbine into mechanical (kinetic) energy. The Roots blower returns the working fluid to the tungsten housing. The gas turbine and the Roots blower have a common shaft. Alternatively, the Roots blower, or any other type of pump used in place of the Roots blower, can be driven independently of the turbine, such as electrically.
The rotation of the gas turbine by the working fluid can be used to drive an electrical generator. The gas turbine could be a Bryton cycle engine including a compressor, a combustor, and a turbine, the compressor and turbine being on the same shaft. The electrical energy created by the generator is available to supplement the electrical energy generated by the flow of working fluid through the MHD duct. Alternatively, the magnetic field and electrodes in the MHD duct could be eliminated, and the working fluid used to drive the turbine which in turn drives the electrical generator so as to create electrical energy. In series, following the gas turbine, could be a Bryton cycle engine followed by a Stirling cycle engine. [..]
Before the working fluid is allowed to enter the Roots blower it is detoured to cooling panels and a cesium recovery system. The heat still remaining in the working fluid after passing through the gas turbine is waste heat and needs to be cooled away. However the waste heat can be used further for, e.g., room heating. The cesium is returned as a liquid to the tungsten housing.
[..]  The speed of movement may be augmented by varying the dimensions of the accordian folds and/or the honeycombs cells. Increased speed will result in an increase in the electrical output of the MHD device. Speed of movement of the working fluid can also be increased by shaping the outer walls of the MHD duct to produce convection currents, which further increase working fluid temperature. The increased temperature contributes to spinning of the plasma which might cause it to reach supersonic speeds.
The heat pipe used inside the MHD duct may be made of a ceramic or other non-magnetic, high-temperature-resistant material. The unit comprising a heat pipe within the MHD duct may be thought of as a closed unit solid state MHD cell.
It is possible that the MHD cell could be heated by energy sources other than the sun, such as geothermal, natural gas, nuclear, chemical reaction, or any other suitable source of energy capable of providing sufficient heat to the heat pipe. ""

2 commenti:

Tom Kay ha detto...

http://concentratingsolarpowerutility.com/

Marco ha detto...

Mr Tom Kay,
Thanks for reporting my blog address on your homepage.
I have just written a few posts scheduled into one, so the information that I can give is better.

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