The Power Producing Cycles

Power Producing Cycles

are the fundamental processes by which heat energy

is converted into mechanical work.

Carnot Cycle

→ theoretical maximum efficiency, benchmark for comparison.

Rankine Cycle

→ used in steam power plants.

Otto Cycle

gasoline engines.

Diesel Cycle

→ diesel engines.

Brayton Cycle

→ jet engines and gas turbines.

Carnot cycle

is the most efficient thermodynamic cycle.

Isothermal Expansion

Process 1 - 2 carnot cycle

Isentropic Expansion

Process 2 - 3 carnot cycle

Isothermal Compression

Process 3 - 4 carnot cycle

Isentropic Compression

Process 4 - 1 in carnot cycle

Thermal Efficiency(e)

defined as the fraction of the heat supplied to a thermodynamic cycle that is converted into work.

Rankine cycle

describes the process by which heat engines (such as

steam turbines and reciprocating steam engines) extract mechanical work from a

fluid as it circulates between a heat source (boiler) and a heat sink (condenser).

Rankine Cycle

is the practical engineering counterpart of the Carnot cycle, adapted to real power

plants where water undergoes phase changes.

isentropic expansion in the engine, s = C

rankine cycle process 1-2

constant pressure rejection of heat in the condenser, p = C

rankine cycle process 2-3

adiabatic pumping, s = C

rankine cycle process 3-4(b)

constant pressure addition of heat in the steam generator, p = C

rankine cycle process 4(b)-1

Thermal Efficiency, η

efficiency gauges the extent to which the energy input to the working fluid passing through the boiler is converted to the net work output

Back Work Ratio, bwr

Defined as the ratio of the pump work input to the work developed by the turbine.

Approximate Pump Work

The state of feed water leaving the pump is that of a compressed liquid. Very

often, compressed liquid specific table properties are not available, hence, the

properties of a compressed liquid are not easily obtainable. Therefore, the exact

pump work is difficult to determine.

steam rate, msr

is the mass of steam used to perform a unit work or the mass flow

rate of steam consumed to produce a unit of power. For good design, a lower value is desired.