Question

Determine the power output from a steam turbine if it receives steam at 40 bar, 350°C, and the steam leaving the turbine is at 15 bar, 200°C. The steam mass flow rate is 0.5 kg/s.

Answer 1

To determine the power output from a steam turbine, we can use the following equation:

Power = Mass flow rate × Specific enthalpy change

First, we need to calculate the specific enthalpy change of the steam. The specific enthalpy is the amount of energy per unit mass of the substance.

Step 1: Find the specific enthalpy at the turbine inlet (h1) and outlet (h2).
We can use steam tables or steam property calculators to obtain these values.

For steam at 40 bar and 350°C (turbine inlet):
From the steam tables, the specific enthalpy at these conditions is approximately h1 = 3217 kJ/kg.

For steam at 15 bar and 200°C (turbine outlet):
From the steam tables, the specific enthalpy at these conditions is approximately h2 = 2786 kJ/kg.

Step 2: Calculate the specific enthalpy change (∆h).
∆h = h2 - h1
∆h = 2786 kJ/kg - 3217 kJ/kg
∆h = -431 kJ/kg (Note: The negative sign indicates a decrease in enthalpy)

Step 3: Calculate the power output.
Power = Mass flow rate × ∆h
Power = 0.5 kg/s × (-431 kJ/kg)
Power = -215.5 kW (Note: The negative sign indicates power extraction from the steam)

Therefore, the power output from the steam turbine is approximately 215.5 kW.