Direct energy conversion devices convert one form of energy directly into another through a single process. For example, a solar cell directly converts sunlight (optical electromagnetic radiation) into electricity. Geothermal energy is not a direct energy conversion device because it does not directly convert one form of energy into another - heat energy from geothermal sources must first be converted into mechanical energy and then into electricity. Direct energy conversion devices avoid the limitations of the Carnot cycle by directly converting one form of energy into another without intermediate steps.

1. UNIT-IV

2. DIRECT ENERGY CONVERSION
• Energy conversion devices convert between electrical, magnetic,
kinetic, potential, optical, chemical, nuclear, and other forms of
energy.
• Energy conversion processes occur naturally. For example,
energy is converted from optical electromagnetic radiation to
heat when sunlight warms a house, and energy is converted from
potential energy to kinetic energy when a leaf falls from a tree.
• Alternatively, energy conversion devices are designed and
manufactured by a wide range of scientists and engineers.

3. • A direct energy conversion device converts one form of energy to
another through a single process.
• For example, a solar cell is a direct energy conversion device that
converts optical electromagnetic radiation to electricity.
DIRECT ENERGY CONVERSION

4. • Which is not the direct energy conversion device
• Explanation: Geothermal energy is not available everywhere because
it not converts directly into one form to other form.
 There are two methods of conversion: direct, when heat energy is
converted directly into electricity and indirect, when heat energy is
converted into mechanical energy first and afterwards into electricity.
 For indirect method, first heat energy is converted to mechanical
energy.

5. NEED FOR DIRECT ENERGY CONVERSION

11. LIMITATIONS OF CARNOT CYCLE
• (a) It is difficult to compress a wet vapour isentroprically to the saturated state
as required by the process (4-1).
• (b) It is difficult to control the quality of the condensate coming out of the
condenser so that the state ‘4’ is exactly obtained.
• (c) The efficiency of the Carnot cycle is correctly attached by the temperature
T1 at which heat is transferred to the working fluid. Since the temperature of
steam is only 374oC, therefore, if the cycle is to be operated in the wet region,
the maximum possible temperature is severely limited.
• (d) Isentropic compression of a vapour requires more work due to its high
specific volume thereby reducing the work ratio.
• (e) Isothermal heat addition after the saturated vapour line is very difficult to
achieve as it involves heat addition at the same time expansion of steam.

14. THERMO ELECTRIC POWER
GENERATION (PEG)

16. SEEBECK EFFECT
• The Seebeck effect is a phenomenon in which a temperature
difference between two dissimilar electrical conductors or
semiconductors produces a voltage difference between the two
substances.
• If the pair is connected through an electrical circuit, direct current
(DC) flows through that circuit.

18. Peltier effect
• The Peltier effect is the phenomenon that a potential difference
applied across a thermocouple causes a temperature difference
between the junctions of the different materials in the thermocouple.
• This effect is the opposite of the Seebeck effect (named after the scientist
who discovered it in 1821).

21. JOULE EFFECT
• Joule heating is the physical effect by which the pass of current through
an electrical conductor produces thermal energy.
• This thermal energy is then evidenced through a rise in the conductor
material temperature, thus the term “heating”.