Power Generation, Thermal Cycles, its Thermal Efficiency
Laws of thermodynamics Thermo-dynamical processes Fluid properties and phases Carnot and Rankin cycles Cycle efficiency and optimisation Subcritical
Laws of thermodynamics
- Thermo-dynamical processes
- Fluid properties and phases
- Carnot and Rankin cycles
- Cycle efficiency and optimisation
- Subcritical, supercritical and ultra-supercritical plants
Laws of thermodynamics
1st law of Thermo-dynamics
Law of conservation of energy
The flow of energy into and out of a process must be fully accounted for; Energy cannot be created or destroyed. Total mass entering Into the system is equal to the total mass going system.
2nd law of thermodynamics
also known as “ Kalvin-Plank Statement “
States “It is impossible for any device which operates on a cycle to receive heat from a single reservoir and produce the net amount of work.”
A heat engine must exchange heat with low- temperature sink as well as the high-temperature reservoir to keep operating.
1st law of thermo-dynamics places no restriction on the direction of energy flow.
2nd law of thermodynamics states that processes proceed in a certain direction.
A process cannot occur unless both laws of thermodynamics are satisfied.
Reversible: Any process that can proceed from state 1 to state 2 and then can be made to proceed in reverse back to state 1.
Isothermal: A process where the temperature of the fluid does not change.
Adiabatic: A process where there is no heat added or removed.
Entropy: A measure of the disorder of a system (dS = dQ/T)
Isentropic: A reversible, adiabatic process where the entropy remains constant.
Polytropic: A process that follows the relationship:
Where: P is Pressure
v is the specific volume
n is the ratio of specific heats, (cp/cv)
Fluid Properties & Phases
Any two properties of a fluid or gas can be used to define the state of a fluid or gas. At the saturated state of a fluid, only one property is required to determine it states.
Pressure Internal Energy
Specific Volume Entropy
Any two independent properties define the thermodynamic state.
Press and temp usually define energy level.
Energy level referred to as enthalpy.
Steam properties are usually presented in steam tables. The tables facilitate the ease of finding the property and increase the accuracy.
The steam tables show properties of water for :
•The saturated phase
•The superheated and sub-cooled phases
Basic Rankine Steam-Power Cycle
Four Basic Components
1-2 Water at low pressure has pressure increased by feed water pump to state 2. Work (Wa) is added to the cycle.
2-3 Heat (Qa) is added in the boiler to form superheated vapor.
3-4 Vapor expands in the turbine, producing useful work (Wr).
4 1 Vapor is condensed in the condenser and flows back to the pump (Qr).