Introduction

To determine the highest possible percentage of mass of steam that condenses at the turbine exit and leaves the turbine as a liquid, we need to analyze the thermodynamic processes involved in the turbine.

Given Data:
- Inlet temperature (T1) = 400°C
- Inlet pressure (P1) = 5 MPa
- Outlet pressure (P2) = 20 kPa

Analysis

The steam turbine operates on the principle of converting the energy of high-pressure steam into mechanical work. The steam enters the turbine at a high temperature and pressure and exits at a lower pressure. During this process, some of the steam may condense and leave the turbine as a liquid.

Process 1: Isentropic Expansion

The steam enters the turbine and undergoes an isentropic (reversible adiabatic) expansion. This process is assumed to be ideal, meaning there are no losses due to friction or heat transfer. The isentropic expansion can be represented by the following equation:

h2s = h1 - (h1 - h2),

where h2s is the specific enthalpy of the steam at the exit assuming isentropic expansion, h1 is the specific enthalpy at the inlet, and h2 is the specific enthalpy at the actual exit.

Process 2: Condensation

After the isentropic expansion, the steam may condense at the turbine exit due to the decrease in pressure. The extent of condensation depends on the saturation properties of the steam at the exit pressure. If the steam is superheated initially, it will first undergo partial condensation to reach the saturation state.

Process 3: Isenthalpic Expansion

If condensation occurs, the remaining steam will undergo an isenthalpic expansion to reach the exit pressure of 20 kPa. This process is assumed to be reversible and adiabatic.

Calculations

To determine the highest possible percentage of mass that condenses at the turbine exit, we need to compare the specific enthalpies at the actual exit (h2) and the saturation state at 20 kPa (hf2).

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The highest possible percentage of mass that condenses can be calculated using the equation:

Percentage of mass condensed = (h1 - h2) / (h1 - hf2) * 100%

Conclusion

By analyzing the thermodynamic processes involved in the turbine, we can determine the highest possible percentage of mass of steam that condenses at the turbine exit and leaves the turbine as a liquid. The calculations involve comparing the specific enthalpies at the actual exit and the saturation state at the exit pressure. The percentage of mass condensed can be calculated using the equation mentioned above.