{"id":17769,"date":"2018-05-08T12:17:35","date_gmt":"2018-05-08T12:17:35","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=17769"},"modified":"2022-11-15T14:19:31","modified_gmt":"2022-11-15T14:19:31","slug":"rankine-cycle-steam-turbine-cycle","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/thermodynamic-cycles\/rankine-cycle-steam-turbine-cycle\/","title":{"rendered":"Rankine Cycle – Steam Turbine Cycle"},"content":{"rendered":"
<\/div>\n
In general, the Rankine cycle<\/strong> is an idealized thermodynamic cycle of a constant pressure heat engine that converts part of heat into mechanical work. In this cycle, the heat is supplied externally to a closed loop, which usually uses water (in a liquid and vapor phase) as the working fluid.\n

From a thermodynamics point of view, the performance of steam turbines can be derived from the theory of the Rankine cycle.<\/p>\n

In modern nuclear power plants<\/strong><\/a>, the overall thermal efficiency is about one-third <\/strong>(33%), so 3000 MWth<\/strong> of thermal power from the fission reaction is needed to generate 1000 MWe<\/strong> of electrical power.<\/p>\n<\/div><\/div>\n

In 1859, a Scottish engineer, William John Macquorn Rankine,<\/strong> advanced the study of heat engines by publishing the \u201cManual of the Steam Engine and Other Prime Movers<\/em>\u201d. Rankine developed a complete theory of the steam engine<\/strong> and indeed of all heat engines. Together with Rudolf Clausius<\/strong> and William Thomson<\/strong> (Lord Kelvin), he contributed to thermodynamics, particularly focusing on the first of the three thermodynamic laws.<\/p>\n

The Rankine cycle<\/strong> was named after him and describes the performance of steam turbine systems<\/strong>, though the theoretical principle also applies to reciprocating engines such as steam locomotives. The Rankine cycle<\/strong> is an idealized thermodynamic cycle of a constant pressure heat engine that converts part of heat into mechanical work. In this cycle, the heat is supplied externally to a closed loop, which usually uses water (in a liquid and vapor phase) as the working fluid. In contrast to the Brayton cycle<\/a>, the working fluid in the Rankine cycle<\/strong>\u00a0undergo the phase change<\/strong>\u00a0from a liquid to vapor phase and vice versa.<\/p>\n

While many substances could be used as the working fluid in the Rankine cycle (inorganic or even organic), water<\/strong><\/a> is usually the fluid of choice due to its favorable properties, such as its non-toxic and unreactive chemistry, abundance, and low cost, as well as its thermodynamic properties. For example, water<\/strong> has the highest specific heat<\/strong> of any common substance \u2013 \u00a04.19 kJ\/kg K. Moreover it has a very high heat of vaporization<\/strong><\/a>, making it an effective coolant<\/strong> and medium<\/strong> in thermal power plants and other energy industries. In the case of the Rankine cycle, the Ideal Gas Law<\/a> almost cannot be used (steam does not follow pV=nRT). Therefore all important parameters of water and steam are tabulated in so-called \u201cSteam Tables<\/a><\/strong>\u201d.<\/p>\n

One of the major advantages<\/strong> of the Rankine cycle<\/strong> is that the compression<\/strong> process in the pump takes place on a liquid<\/strong>. By condensing the working steam to a liquid (inside a condenser) the pressure at the turbine outlet is lowered and the energy required by the feed pump consumes only 1% to 3% of the turbine output power and these factors contribute to a higher efficiency for the cycle.<\/p><\/div><\/div>

<\/iframe><\/div>\"Rankine<\/a><\/div><\/div>
Today, the Rankine cycle<\/strong> is the fundamental operating cycle of all thermal power plants<\/strong> where an operating fluid is continuously evaporated and condensed. It is the one of most common thermodynamic cycles, <\/strong>because in most of the places in the world the turbine is steam-driven.\n

In contrast to the Carnot cycle, the Rankine cycle does not execute isothermal processes because these must be performed very slowly. In an ideal Rankine cycle, the system executing the cycle undergoes a series of four processes: two isentropic (reversible adiabatic) processes alternated with two isobaric processes.<\/p>\n

Since Carnot\u2019s principle<\/strong><\/a> states that no engine can be more efficient than a reversible engine (a Carnot heat engine<\/strong>) operating between the same high temperature and low-temperature reservoirs, a steam turbine based on the Rankine cycle must have lower efficiency than the Carnot efficiency.<\/p>\n

In modern nuclear power plants<\/strong><\/a>, the overall thermal efficiency is about one-third <\/strong>(33%), so 3000 MWth<\/strong> of thermal power from the fission reaction is needed to generate 1000 MWe<\/strong> of electrical power. Higher efficiencies can be attained by increasing the temperature<\/strong> of the steam<\/a>. But this requires an increase in pressures inside boilers or steam generators<\/a>. However, metallurgical considerations place upper limits on such pressures. In comparison to other energy sources, the thermal efficiency of 33% is not much. But it must be noted that nuclear power plants are much more complex than fossil fuel power plants, and it is much easier to burn fossil fuel than to generate energy from nuclear fuel<\/a>.<\/p><\/div><\/div>

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<\/span>What is Steam Turbine<\/div>
In general, a steam turbine<\/strong> is a rotary heat engine that converts thermal energy<\/strong><\/a> contained in the steam to mechanical energy<\/a> or to electrical energy<\/a>. In its simplest form, a steam turbine consist of:\n