Plasma (Part-VII)- Converting Plasma Into Electricity

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Technology That Converts High Velocity Plasma into Electricity: Magneto-Hydrodynamic Converter

Here comes the seventh and last part of the blog on plasma. Those who have missed the sixth part can read it from Here. It will help to connect with this last part of the blog which provides a detail discussion on technology which enables conversion of high velocity plasma into electricity. How does High Velocity Plasma converts into electricity through the help of Magneto-Hydrodynamic converter? To know all these explore this blog. In words of Michael Faraday:

 

"It is right that we should stand by and act on our principles; but not right to hold them in obstinate blindness, or retain them when proved to be erroneous".

Introducing Magneto-Hydrodynamic Converter

In the year 1960, the concept of  magneto-hydrodynamic (MHD) converters was used in order to bring MHD power conversion to market with commercial power plants of a new kind, converting the kinetic energy of a high velocity plasma into electricity with no moving parts at a high efficiency.  Research was also conducted in the field of supersonic and hypersonic aerodynamics to study plasma interaction with magnetic fields to eventually achieve passive and even active flow control around vehicles or projectiles, in order to soften and mitigate shock waves, lower thermal transfer and reduce drag. In the year 1832, Michael Faraday  attempted the first time to test an MHD converter. MHD converters involving plasma were highly studied in the 1960s and 1970s, with many government funding and dedicated international conferences. The research almost stopped after it was considered the electro-thermal instability would severely limit the efficiency of such converters when intense magnetic fields are used, although solutions may exist. Such ionized gases used in "plasma technology" ("technological" or "engineered" plasma) are usually weakly ionized gases in the sense that only a tiny fraction of the gas molecules are ionized. These kinds of weakly ionized gases are also non-thermal "cold" plasmas. In the presence of magnetic fields, the study of such magnetized non-thermal weakly ionized gases involves resistive magneto-hydrodynamics with low magnetic Reynolds number, a challenging field of plasma physics where calculations require dyadic tensors in a 7-dimensional phase space. 

How does the Generation of MHD Power Occurs?

A magneto-hydrodynamic 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 plasma as working fluids. 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 magneto-hydrodynamic 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. 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 to become 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. 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.