Steam Cycle Flashcards
Understanding the Steam Cycle
What are the four phases of the basic steam cycle?
Generation, Expansion, Condensation, Feed.
Explain the purpose of the boiler in the generation phase of the conventional steam cycle.
The boiler heats water to produce steam. In conventional systems, fuel is burned to produce heat, which is transferred to the water, causing it to boil and form steam.
Why is superheated steam preferred in the steam cycle?
Superheated steam minimizes erosion, minimizes corrosion, and maximizes temperature difference, improving Carnot efficiency.
What is the primary difference between the generation phase in conventional and nuclear steam plants?
In conventional plants, a boiler produces steam, while in nuclear plants, a reactor generates thermal energy, which is then transferred to water in a steam generator.
What is Carnot efficiency, and how is it calculated?
Carnot efficiency is a measure of the maximum possible efficiency of a heat engine operating between two temperatures, calculated as (Tsource – Tsink)/Tsource.
Describe the process by which steam is generated in a nuclear steam plant.
Fission in the reactor core transforms nuclear energy into thermal energy, which is then transferred to water in the steam generator, producing steam.
What role do moisture separators play in the nuclear steam cycle?
Moisture separators remove moisture from the steam to ensure it is dry before it enters the turbines.
In the expansion phase, how is thermal energy converted into mechanical energy?
Thermal energy in the steam is converted to mechanical energy in the turbines via nozzles and blades, which turn the rotor and shaft.
Why does the pressure of steam drop as it passes through the turbine during the expansion phase?
The pressure drops because the energy in the steam is converted into mechanical work, reducing its pressure.
How does the main condenser function in the condensation phase?
The main condenser condenses steam into water using seawater in a cross-flow shell-and-tube heat exchanger.
Why is a vacuum maintained in the main condenser?
A vacuum is maintained to ease steam recovery by “pulling” the steam into the condenser and to extract more work from the turbines due to a larger pressure differential.
What is the purpose of the hotwell in the main condenser?
The hotwell acts as a holding area for condensate water at 80-100°F, which is the lowest temperature in the cycle.
Explain the role of the deaerating feed tank (DFT) in the feed phase.
The DFT preheats feed water, removes dissolved oxygen to minimize corrosion, and serves as a storage and surge volume.
What is represented by a T-s diagram in the context of the steam cycle?
A T-s (Temperature-Entropy) diagram represents the states of water within each region of the steam cycle, showing the phase transformations and energy changes.
Why is it important to remove dissolved oxygen from the feed water in the feed phase?
Removing dissolved oxygen is crucial to minimize corrosion of the system components.
