RANKINE CYCLE

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The Rankine cycle closely describes the process by which steam-operated heat engines commonly found in thermal power generation plants generate power.

The heat sources used in these power plants are usually nuclear fission or the combustion of fossil fuels such as coal, natural gas, and oil, or concentrated solar power. The higher the temperature, the better.

The efficiency of the Rankine cycle is limited by the high heat of vaporization of the working fluid. Also, unless the pressure and temperature reach super critical levels in the steam boiler, the temperature range the cycle can operate over is quite small: steam turbine entry temperatures are typically around 565 °C and steam condenser temperatures are around 30 °C.

A brief description about the Rankine Cycle

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Who created the

Rankine Cycle?

RANKINE CYCLE

POLYMATH

-is a person whose expertise spans a significant number of different subject areas—such a person is known to draw on complex bodies of knowledge to solve specific problems.

was a scottish mechanical enginewho also contributed in civil engineering, physics and mathematics he was a founding contributor to the science of thermodynamics, particularly focusing on the first law of thermodynamics.

is a model used to predict the performance of a steam turbine system

Rankine developed a complete theory of the steam engine and indeed of all heat engines. His manuals of engineering science and practice were used for many decades after their publication in the 1850s and 1860s. He published several hundred papers and notes on science and engineering topics, from 1840 onwards, and his interests were extremely varied, including, in his youth, botany, music theory and number theory, and, in his mature years, most major branches of science, mathematics and engineering. He was an enthusiastic amateur singer, pianist and cellist who composed his own humorous songs. He was born in Edinburgh and died in Glasgow, a bachelor.

He was called a scottish Polymath

Process 1–2: The working fluid is pumped from low to high pressure. As the fluid is a liquid at this stage, the pump requires little input energy.

The four processes in the Rankine cycle

Variables and Equations

In general, the efficiency of a simple rankine cycle can be written as

Process 4–1: The wet vapour then enters a condenser, where it is condensed at a constant pressure to become a saturated liquid.

Each of the next four equations[1] is derived from the energy and mass balance for a control volume. "ntherm" defines the thermodynamic efficiency of the cycle as the ratio of net power output to heat input. As the work required by the pump is often around 1% of the turbine work output, it can be simplified.

Process 2–3: The high-pressure liquid enters a boiler, where it is heated at constant pressure by an external heat source to become a dry saturated vapour. The input energy required can be easily calculated graphically, using an enthalpy–entropy chart (h–s chart, or Mollier diagram), or numerically, using steam tables.

When dealing with the efficiencies of the turbines and pumps, an adjustment to the work terms must be made:

Process 3–4: The dry saturated vapour expands through a turbine, generating power. This decreases the temperature and pressure of the vapour, and some condensation may occur. The output in this process can be easily calculated using the chart or tables noted above.