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How to Find the Efficiency of a Steam Turbine

The steam turbine was invented by Sir Charles Parsons in 1884 and consists of a mechanical machine capable of extracting thermal energy from high pressure steam.

There are many applications of steam turbines including trains (used in the 1800s and early 1900s), power stations and steamboats. One of the most important figures of merit in steam turbines is the efficiency; it is defined to be the ratio of energy extracted to the amount of energy put in.

Things You'll Need

Calculator

Instructions

- 1
  Write down the equation for efficiency of a steam turbine. The isentropic (constant entropy) efficiency (n) is defined as being:
  
  n = (h_HP - h_LP) / (h_HP - h_LPisen)
  
  h_HP is defined as being the specific enthalpy of the steam at the turbine inlet
  
  h_LP is defined as being the specific enthalpy of the steam at the turbine outlet
  
  LPisen is defined as being the specific enthalpy of the steam at exhaust pressure after the steam has expanded from the high pressure conditions.
  
  Enthalpy is a measure of the total energy of the system.
- 2
  Plug the values into the equation for efficiency. For example, if the specific enthalpy of the steam at the turbine inlet is 10 kilo-Joules, specific enthalpy of the steam at the turbine outlet is 6 kilo-Joules, and the specific enthalpy of the steam at exhaust pressure after the steam has expanded is 4 kilo-Joules, then the equation becomes:
  
  n = (h_HP - h_LP) / (h_HP - h_LPisen) = (10000 - 6000) / 10000 - 4000)
- 3
  Type the numbers into a calculator to generate the efficiency. Following the example, the efficiency is 0.66 (66 percent).

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