direct energy conversion

6. CARNOT CYCLE FOR DEC SYSTEM
 Almost all DEC system, except fuel cells and nuclear DEC
systems, follow Carnot principle in its working.
 The Carnot cycle has greater efficiency possible of an engine
based on the assumption of the absence of friction
 No conduction of heat between different parts of the engine at
different temperatures.

7. The Carnot Cycle
• Idealized thermodynamic cycle consisting of four reversible processes (any
substance):
 Reversible isothermal expansion (1-2, TH=constant)
 Reversible adiabatic expansion (2-3, Q=0, THTL)
 Reversible isothermal compression (3-4, TL=constant)
 Reversible adiabatic compression (4-1, Q=0, TLTH)
1-2 2-3 3-4 4-1

9. The Carnot Cycle
Work done by gas = PdV, area under the
process curve 1-2-3.
1
2
3
3
2
1
Work done on gas = PdV, area under the
process curve 3-4-1
subtract
Net work
1
2
3
4
dV>0 from 1-2-3
PdV>0
Since dV<0
PdV<0

10. The Carnot Principles
• The efficiency of an irreversible heat engine is always less than the efficiency of a
reversible one operating between the same two reservoirs. hth, irrev < hth, rev
• The efficiencies of all reversible heat engines operating between the same two
reservoirs are the same. (hth, rev)A= (hth, rev)B
• Both Can be demonstrated using the second law (K-P statement and C-statement).
Therefore, the Carnot heat engine defines the maximum efficiency any practical heat
engine can reach up to.
• Thermal efficiency hth=Wnet/QH=1-(QL/QH)=f(TL,TH) and it can be shown that hth=1-
(QL/QH)=1-(TL/TH). This is called the Carnot efficiency.
• For a typical steam power plant operating between TH=800 K (boiler) and TL=300
K(cooling tower), the maximum achievable efficiency is 62.5%.

16. THERMO ELECTRIC POWER GENERATION

38. THERMO IONIC POWER GENERATION

39. THERMO IONOC POWER GENERATION
• Thermionic power converter, also called thermionic generator, thermionic
power generator, or thermoelectric engine, any of a class of devices that
convert heat directly into electricity using thermionic emission rather than
first changing it to some other form of energy.
• Thermionic power converter has two electrodes.
• One of these is raised to a sufficiently high temperature to become a
thermionic electron emitter, or “hot plate.”
• The other electrode, called a collector because it receives the emitted
electrons, is operated at a significantly lower temperature.
• The space between the electrodes is sometimes a vacuum but is normally
filled with a vapour or gas at low pressure.

40. PRINCIPLES OF THERMO IONIC
GENERATION
 Thermionic power converter can be viewed as an
electronic diode that converts heat to electrical energy via
thermionic emission.
 It can also be regarded in terms of thermodynamics as a heat
engine that utilizes an electron-rich gas as its working fluid

41. PHOTOVOLTAIC SYSTEM

42. PHOTOVOLTAIC SYSTEM