Rankine Cycle

The Rankine cycle generates about 80% of all electric power used in the world at this point, a remarkable percentage. Many different sources of energy are used to operate Rankine cycles on, it is not simply one engine and one application. It is a heat engine because it uses heat and thermodynamics to move a working fluid through a closed loop. We will go through the system and talk about how it works much more in depth throughout this page.


http://montaraventures.com/energy/wp-content/uploads/2008/05/rankine-cycle-diagram.jpg



Observe the diagram above. A working fluid is contained in a closed loop of piping. A pump is used to move the fluid through the pipe where it is then heated. The heat adds energy to the system and causes the working fluid to change phases. Now this high energy fluid in a gaseous state turns a turbine, turning that energy from heat into mechanical energy. After this process heat is removed from the working fluid using a heat transfer device, much like the radiator in your car, which causes the working fluid to return to its initial phase, generally the liquid phase. At this point the cycle simply repeats itself.

From a first law of thermodynamics analyses of this system we can say that:


The idea here is to minimize W(in) and Q(out), and maximize Q(in) therefore maximizing W(out).

As previously stated, Rankine cycles produce about 80% of our electric power and is the exact cycle used in just about every power plant you visit today, whether its coal, geothermal, patroleum, just about all of them. Coal produces most of our electricity today because it is readily available and produce a lot of heat when burned. Coal power plants have a theoretical Carnot efficiency of about 63%, which is very high, and in reality are about 42% efficient, which is still very high. This is due to the high temperatures of coal being burned.


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