TK2103 5 Siklus Mesin Panas

Summary

This video lecture on thermodynamics in chemical engineering focuses on the Rankine cycle, using a coal-fired power plant (PLTU) as a real-world example. It explains the process flow, including the expansion of steam in the turbine, condensation, pumping, and reheating in the boiler. The lecturer demonstrates how to calculate the thermal efficiency of the Rankine cycle, both for ideal and realistic systems with efficiency losses in the turbine and pump. A practical example is provided to compute steam mass flow rates and net work, offering valuable insights for students studying thermodynamic cycles.

Takeaways

• 😀 The Rankine cycle is a key thermodynamic cycle used in power plants, such as coal-fired power plants, to generate electricity.
• 😀 In a typical Rankine cycle, the four main components are the turbine, condenser, pump, and boiler.
• 😀 The turbine expands high-pressure steam from the boiler to generate work, while the condenser cools the steam to a saturated liquid.
• 😀 The pump increases the pressure of the saturated liquid from the condenser, which is then sent back to the boiler for reheating.
• 😀 Thermal efficiency can be calculated based on the work produced by the turbine and the heat input to the boiler.
• 😀 The ideal Rankine cycle assumes 100% efficiency, but in real systems, efficiency losses occur due to non-ideal components like the turbine and pump.
• 😀 In practical scenarios, turbine efficiency is often less than 100%, affecting the overall cycle efficiency.
• 😀 A typical example of a real-world Rankine cycle involves a steam temperature of 500°C and a pressure of 8600 kPa for the turbine input.
• 😀 The Rankine cycle efficiency is calculated by comparing the net work produced by the system to the heat input to the boiler.
• 😀 By adjusting the efficiency of components like the turbine and pump, the overall thermal efficiency of the system can be impacted, leading to lower performance in real-world scenarios.
• 😀 To calculate the mass flow rate of steam required for a specific power output, the net work per kilogram of steam is used, factoring in system efficiencies.

Q & A

What is the main topic of the video lecture?

The main topic of the video lecture is the Rankine cycle, which is explained in the context of thermodynamics for chemical engineering, particularly its application in coal-fired power plants (PLTU).

What are the four key components of the Rankine cycle discussed in the video?

The four key components of the Rankine cycle discussed in the video are the turbine, condenser, pump, and boiler.

How does the coal-fired power plant generate electricity using the Rankine cycle?

In the Rankine cycle of a coal-fired power plant, coal is burned to generate heat that turns water into steam in the boiler. The steam expands in the turbine to produce mechanical energy, which is then converted into electricity. The steam is then cooled and condensed in the condenser, before being pumped back into the boiler for the cycle to continue.

What is the difference between the ideal and real Rankine cycle in the context of turbine and pump efficiency?

In the ideal Rankine cycle, it is assumed that the turbine and pump operate with 100% efficiency, meaning all energy is converted into useful work. In the real Rankine cycle, the turbine and pump have efficiencies lower than 100% (in this case, 75%), meaning some energy is lost in the form of heat or friction.

How is the thermal efficiency of the Rankine cycle calculated?

Thermal efficiency of the Rankine cycle is calculated by dividing the net work output (work produced by the turbine minus the work consumed by the pump) by the heat input, which is the heat energy added to the system through the boiler.

What is the effect of increasing pressure and temperature on the efficiency of the Rankine cycle?

Increasing the pressure and temperature of the steam in the Rankine cycle increases its efficiency. Higher temperature and pressure mean more work can be extracted from the steam, resulting in a higher thermal efficiency for the power plant.

What role does the condenser play in the Rankine cycle?

The condenser's role in the Rankine cycle is to cool and condense the steam back into water after it has passed through the turbine. The steam loses heat to the surroundings, and the condensed water is then pumped back into the boiler for the cycle to continue.

How is the work done by the turbine in the Rankine cycle calculated?

The work done by the turbine in the Rankine cycle is calculated by finding the difference in enthalpy (heat content) between the steam entering the turbine and the steam leaving the turbine. The formula is the enthalpy at the inlet minus the enthalpy at the outlet.

Why is the pump in the Rankine cycle only effective for incompressible fluids like water?

The pump in the Rankine cycle is effective for incompressible fluids like water because it relies on the fluid’s constant volume (incompressibility). This ensures that when the pump applies pressure, the volume doesn't change significantly, allowing the pump to efficiently raise the pressure of the liquid without causing cavitation.

How does the efficiency of the turbine affect the overall thermal efficiency of the Rankine cycle?

The efficiency of the turbine directly affects the overall thermal efficiency of the Rankine cycle because it determines how much of the thermal energy is converted into mechanical work. A less efficient turbine will waste more energy as heat, reducing the amount of work produced and lowering the overall efficiency of the cycle.