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THERMODYNAMICS - CASE STUDY

    Introduction


Problem Description
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Neon, working at a steam power plant, received a call from a worker who reported that the moisture content at the exit of the turbine was exceeding its allowed value range. In order to improve this situation, Neon decides that a reheat process should be added to the cycle. The moisture content at the exit of the turbine and the net work output from the cycle need to be determined to make sure the cycle will run well.

What is known:

  • Steam enters the high-pressure turbine at 16 MPa and 600oC
  • The pressure in the condenser is 10 kPa.
  • The moisture content of the steam at the exit of the low-pressure turbine is not allowed to exceed 10.0 percent.
     
    Question




 
  • Determine the pressure at which the steam should be reheated if the steam is reheated to the inlet temperature of the high-pressure turbine.
  • Determine the net work output and thermal efficiency of the cycle after adding the reheat process.
   
    Approach



Schematic of the Reheat Rankine Cycle

 
  • The reheat pressure can be determined from the requirement that the stream expands isentropically in the low-pressure turbine. That is, the entropies at the inlet and the exit of the low-pressure turbine are the same.
  • Use the water tables to determine the enthalpy at each state.
  • The net work output equals the difference between the total turbine works from the high-pressure and low-pressure turbines and the pump work.