Abstract :
The
electricity requirements of the world including India
When an
electrical conductor is moved so as to cut lines of magnetic induction, charged
particles in the conductor experience a force in a direction mutually
perpendicular to the B field and to the velocity of the conductor. The negative
charges tend to move in one direction, and the positive charges in the opposite
direction. This induced electric field, or motional emf, provides the basis for
converting mechanical energy into electrical energy. In conventional steam power plants, the heat
released by the fuel is converted into rotational mechanical energy by means of
a thermo cycle and the mechanical energy is then used to drive the electric
generator.
Thus two
stages of energy conversion are involved in which the heat to mechanical energy
conversion has inherently very low efficiency. Also, the rotating machine has
its associated losses and maintenance problems. In MHD generation, electrical
energy is directly generated from hot combustion gases produced by the
combustion of fuel without moving parts. The conventional electrical machines
are basically electro mechanical converters while an MHD generator is heat
engine operating on a turbine cycle and transforming the internal energy of gas
directly into electrical energy.
PRINCIPLE
OF WORKING OF AN MHD GENERATOR
The basic
principle of MHD is just similar to dynamo except that the solid conductor of
high electrical conductivity is replaced by a gas with comparatively low value
of electrical conductivity. If the gas is heated to high temperature it gets
converted into plasma and plasma is conductor of electricity.
HOW AN MHD
GENERATOR WORKS?
In an MHD
generator, electrically conducting gas at a very high temperature is passed at
high velocity through a strong magnetic field at right angles to the direction
of flow, there by generating electrical
energy. The electrical energy is then collected from stationary
electrodes placed on the opposite sides of the channel. The current
so obtained is direct current which can be converted
into ac by an inverter. Ionized gas can be produced by heating it to a high temperature. On heating of a gas, the outer electrons escape out from
its atoms or molecules.
The particles acquire an electric charge and the gases passes into
the state of plasma. However to achieve thermal ionization
of products of combustion of fossil fuels or inert gases extremely high temperatures
are necessary. Air becomes highly ionized at temperatures of 5,0000 to
6,0000C. To have a reasonable value of electrical conductivity of gases at
temperatures around 2,000 to 3,000 K by reasonable ionization, the gases are
seeded with additives of easily ionizing materials (Alkali metals) such as Cesium
or Potassium. The induced current are
collected by suitably placed electrodes and simplest system would carry direct
current to the external load.
Download :
Download :