EXAMPLE OF ACTUAL RANKINE CYCLE (PART 1)

Summary

This video explains the workings of a Rankine cycle, focusing on the processes in the pump, boiler, turbine, and condenser. It details the flow of liquid through these components, with specific reference to pressure, temperature, and efficiency at each stage. The cycle's thermal efficiency and net power output are calculated using formulas based on the enthalpy and isentropic efficiencies of the pump and turbine. Key values such as pressure, temperature, and enthalpy at various states are derived from standard steam tables, guiding viewers through the essential steps of the Rankine cycle's operation.

Takeaways

• 😀 The script explains the process of the Rankine cycle, including its main components: pump, boiler, turbine, and condenser.
• 😀 The pump takes in a liquid at 10 kPa with a temperature of 38°C and compresses it to 15 MPa and 35°C.
• 😀 The boiler heats the liquid to 600°C while maintaining a pressure of 15 MPa, before sending it to the turbine.
• 😀 The turbine, with an isentropic efficiency of 87%, expands the fluid, reducing the pressure from 15 MPa to 10 kPa.
• 😀 The condenser removes heat from the steam at 10 kPa, completing the cycle.
• 😀 The goal is to determine the thermal efficiency and net power output of the cycle for a mass flow rate of 15 kg/s.
• 😀 Thermal efficiency is calculated using the formula: (Work of turbine - Work of pump) / Heat input.
• 😀 The script emphasizes the importance of using enthalpy values for each state to perform the calculations.
• 😀 A TS (temperature-entropy) diagram is needed to visually represent the cycle and pressure changes.
• 😀 At state 1, the liquid enters the pump as saturated liquid at 10 kPa and 38°C, where the enthalpy is taken from steam tables.
• 😀 The enthalpy at state 2 is calculated using an isentropic assumption for the pump, and efficiency factors are applied to correct for real-world conditions.

Q & A

What is the basic setup of the Rankine cycle explained in the transcript?

The basic setup of the Rankine cycle includes a pump, boiler, turbine, and condenser. The liquid enters the pump at 10 kPa with a temperature of 38°C and is compressed to 15 MPa. It then enters the boiler where heat is added at constant pressure, turning it into steam, which enters the turbine. After expanding in the turbine, the steam enters the condenser where heat is removed before the cycle repeats.

What is the isentropic efficiency of the pump in the cycle?

The isentropic efficiency of the pump is 85%, which means the pump's performance is not ideal, and the actual compression process will require more work than the ideal isentropic process.

What happens to the pressure and temperature of the liquid as it moves through the pump?

As the liquid moves through the pump, its pressure increases from 10 kPa to 15 MPa, and its temperature rises from 38°C to 35°C due to the compression process.

At what conditions does the boiler operate, and what happens to the steam inside it?

The boiler operates at a constant pressure of 15 MPa. Heat is added to the steam, increasing its temperature to 600°C, where it then enters the turbine at this high temperature and pressure.

How does the turbine work, and what is its isentropic efficiency?

The turbine expands the steam from 15 MPa to 10 kPa, doing work in the process. The turbine has an isentropic efficiency of 87%, meaning the actual expansion process is not perfectly isentropic and involves losses compared to an ideal expansion.

What role does the condenser play in the Rankine cycle?

The condenser removes heat from the steam, cooling it down and allowing it to condense back into a liquid. This heat is rejected to the surrounding environment, and the cycle is completed.

How do you calculate the thermal efficiency of the Rankine cycle?

The thermal efficiency of the Rankine cycle is calculated using the formula: (W_turbine - W_pump) / Q_in, where W_turbine is the work done by the turbine, W_pump is the work input to the pump, and Q_in is the heat input to the boiler.

Why is it necessary to find the enthalpy for each state in the cycle?

It is necessary to find the enthalpy at each state to calculate the work and heat transfer throughout the cycle. Enthalpy helps quantify the energy involved in the processes of compression, heating, expansion, and cooling in the Rankine cycle.

What is the specific volume at state 1 of the cycle, and why is it important?

The specific volume at state 1 is 0.0010 m³/kg. This value is important because it is used in calculating the work done by the pump and the specific enthalpy changes during compression.

How is the enthalpy at state 2 (h2s) calculated, and why is it necessary to find this value?

The enthalpy at state 2 (h2s) is calculated using the formula for the pump, which includes the specific volume and the pressures at state 1 and state 2. Finding h2s is necessary to assess the ideal work done by the pump and to determine the isentropic efficiency of the pump.