A steam plant operates on the Rankine Cycle. The boiler pressure is 70bar andcondenser pressure 0.5bar. The steam enters the turbine at 500°C.Find:i) The specific enthalpy of the steam entering the turbine. (5 marks)ii) The specific enthalpy of the condensate leaving the condenser. (5 marks)iii) The dryness fraction of the steam entering the condenser
Question
A steam plant operates on the Rankine Cycle. The boiler pressure is 70bar andcondenser pressure 0.5bar. The steam enters the turbine at 500°C.Find:i) The specific enthalpy of the steam entering the turbine. (5 marks)ii) The specific enthalpy of the condensate leaving the condenser. (5 marks)iii) The dryness fraction of the steam entering the condenser
Solution
To answer these questions, we need to use the steam tables and the principles of the Rankine Cycle.
i) The specific enthalpy of the steam entering the turbine:
The steam enters the turbine at a pressure of 70 bar and a temperature of 500°C. We can find the specific enthalpy (h) at this state using the superheated steam tables. For a pressure of 70 bar and a temperature of 500°C, the specific enthalpy is typically around 3478 kJ/kg.
ii) The specific enthalpy of the condensate leaving the condenser:
The condensate leaves the condenser at a pressure of 0.5 bar. At this pressure, the condensate is saturated liquid water. We can find the specific enthalpy (h) at this state using the saturated steam tables. For a pressure of 0.5 bar, the specific enthalpy of the saturated liquid is typically around 640 kJ/kg.
iii) The dryness fraction of the steam entering the condenser:
The dryness fraction (x) is the ratio of the mass of vapor to the total mass of the steam (vapor + liquid). At the entrance of the condenser, the steam is typically a saturated mixture. We can find the dryness fraction using the specific enthalpy at this state and the specific enthalpies of the saturated liquid (hf) and saturated vapor (hg) at the same pressure.
The specific enthalpy at this state (h) can be calculated using the formula: h = hf + x*(hg - hf).
However, without the specific enthalpy at the entrance of the condenser, we cannot calculate the dryness fraction. We need more information to answer this part of the question.
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