Termodinamika : Siklus Rankine 2

Summary

This video script explains the thermal efficiency calculation of a Steam Power Plant (PLTU) based on the Rankine cycle. It outlines the processes involved, from water being pumped into the boiler at high pressure to steam expansion in the turbine and condensation in the condenser. The script describes the necessary steps to calculate thermal efficiency, including the calculation of work done by the pump and turbine, the heat input to the boiler, and the use of steam tables to find enthalpy values. The result of the calculation yields a thermal efficiency of 32.28%, showcasing the efficiency of the system.

Takeaways

• 😀 The thermal efficiency of a PLTU system can be calculated using the formula: thermal efficiency = Wnet / Qin.
• 😀 The system operates based on the Rankine cycle, where water is pumped from the condenser to the boiler.
• 😀 The pumping process between points 1 and 2 is adiabatic (no heat exchange), with pressure increasing to 4 MPa.
• 😀 The steam exiting the boiler at 500°C is superheated and follows a constant pressure line in the T-s diagram.
• 😀 The turbine expands the steam isentropically (constant entropy), reducing pressure to 50 kPa.
• 😀 The condenser returns the steam to liquid state, and the process repeats from point 1.
• 😀 The work required by the pump is calculated as Wpump_in = h2 - h1, where h1 is the enthalpy at the condenser outlet.
• 😀 The enthalpy values are calculated using steam tables or a steam calculator app to find properties like HF, V1, and specific volume.
• 😀 The heat input to the boiler (Qin) is calculated as Q_in = h3 - h2, where h3 is the enthalpy at the boiler outlet (500°C, 4 MPa).
• 😀 The work output from the turbine (Wout) is calculated as Wout = h3 - h4, where h4 is the enthalpy after expansion to 50 kPa.
• 😀 The overall thermal efficiency of the PLTU system is approximately 32.28%, calculated by comparing the net work produced with the heat input.

Q & A

What is the system described in the transcript?

The system discussed is a thermal power plant (PLTU) operating based on the Rankine cycle, specifically focusing on calculating the thermal efficiency of the system.

How does the water in the system move through the various stages?

Water is pumped from the condenser to the boiler, where it is pressurized. The water then transforms into steam at 500°C before being expanded in the turbine and eventually condensed back into liquid water.

What is the significance of the point 1 in the system?

Point 1 represents the state where water enters the pump as saturated liquid at a pressure of 50 kPa. It marks the beginning of the process where water is pressurized before entering the boiler.

What does the term 'isentropic expansion' mean in this context?

Isentropic expansion refers to a process in which the entropy of the steam remains constant. In the transcript, the steam undergoes an isentropic expansion in the turbine from point 3 to point 4.

How is the thermal efficiency of the PLTU calculated?

The thermal efficiency is calculated as the ratio of net work (Wnet) to the heat input (Qin), where Wnet is the difference between the work done by the turbine and the work required by the pump, and Qin is the heat added in the boiler.

What is the formula used to calculate the work required by the pump?

The work required by the pump (W_in) is calculated using the formula: W_in = v * (P2 - P1), where v is the specific volume of the water, P2 is the pressure at the pump exit, and P1 is the pressure at the pump inlet.

How do you determine the enthalpy at each point in the system?

Enthalpy values (H1, H2, H3, H4) at each point are determined using steam tables or software tools like Steam Tab or a steam calculator app, based on the pressure and temperature conditions at those points.

What is the enthalpy at point 1, and how is it calculated?

The enthalpy at point 1 (H1) is calculated using the steam tables for a saturated liquid at a pressure of 50 kPa, which gives a value of 340.542 kJ/kg.

How is the heat added in the boiler (Qin) calculated?

The heat added in the boiler (Qin) is the difference between the enthalpy at point 3 (H3) and point 2 (H2), where H3 is the enthalpy at 500°C and 4 MPa, and H2 is the enthalpy after the pump, calculated earlier.

What is the final thermal efficiency of the system, and how is it calculated?

The final thermal efficiency of the system is 32.28%, calculated by subtracting the work required by the pump from the work produced by the turbine, and dividing that by the heat input to the boiler, then converting the result to a percentage.