Question

What are the roles of turbines and cooling towers in cycling (eg Rankine cycle) systems? Support your explanation providing a few pictures of these systems (You can google it or search in your book) and explain how they work.

Answer 1

A fuel is used to produce heat within a boiler, converting water into steam which then expands through a turbine producing useful work and the used steam is again converted to water by condensation(using cooling towers) .The fluid must be cycled through and reused constantly, therefore, water is the most practical fluid for this cycle.

Turbine:
it is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating electrical power when combined with a generator.A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor.

Example:

Cooling tower :
A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature.

Working:

figure-2

Pump: Compression of the fluid to high pressure using a pump (this takes work) (Figure 2: Steps 3 to 4)

Boiler: The compressed fluid is heated to the final temperature (which is at boiling point), therefore, a phase change occurs—from liquid to vapor. (Figure 2: Steps 4 to 1)

Turbine: Expansion of the vapor in the turbine. (Figure 2: Steps 1 to 2)

Condense Condensation of the vapor in the condenser (where the waste heat goes to the final heat sink (the atmosphere or a large body of water (ex. lake or river). (Figure 2: Steps 2 to 3)