#Workdone by engine vs heat exhausted generator

For this type of power plant, the maximum (ideal) efficiency will be: In a modern coal-fired power plant, the temperature of high-pressure steam (T hot) would be about 400☌ (673K) and T cold, the cooling tower water temperature, would be about 20☌ (293K).

T H is the absolute temperature (Kelvins) of the hot reservoir.

T C is the absolute temperature (Kelvins) of the cold reservoir,.

is the efficiency of the Carnot cycle, i.e., it is the ratio = W/Q H of the work done by the engine to the heat energy entering the system from the hot reservoir.

The formula for this maximum efficiency is:

The efficiencies of all reversible engines ( Carnot heat engines) operating between the same constant temperature reservoirs are the same, regardless of the working substance employed or the operation details.

No engine can be more efficient than a reversible engine ( Carnot heat engine) operating between the same high-temperature and low-temperature reservoirs.

In short, this principle states that the efficiency of a thermodynamic cycle depends solely on the difference between the hot and cold temperature reservoirs. In 1824, a French engineer and physicist, Nicolas Léonard Sadi Carnot, advanced the study of the second law by forming a principle (also called Carnot’s rule) that specifies limits on the maximum efficiency any heat engine can obtain. In modern nuclear power plants, the overall thermodynamic efficiency is about one-third (33%), so 3000 MWth of thermal power from the fission reaction is needed to generate 1000 MWe of electrical power. Steam generators, steam turbines, condensers, and feedwater pumps constitute a heat engine subject to the efficiency limitations imposed by the second law of thermodynamics.

#Workdone by engine vs heat exhausted generator

Many heat engines operate cyclically, adding energy in the form of heat in one part of the cycle and using that energy to do useful work in another part of the cycle.įor example, as is typical in all conventional thermal power plants, the heat is used to generate steam which drives a steam turbine connected to a generator that produces electricity.

The Rankine cycle closely describes the processes in steam-operated heat engines commonly found in most thermal power plants. In general, a heat engine is a device that converts chemical energy to heat or thermal energy and then to mechanical energy or electrical energy.

A heat engine must be used to convert thermal energy into another form of energy. Therefore these energy sources are so-called “ primary energy sources” that must be converted to the secondary energy source, so-called energy carriers ( electrical energy, etc.). But the burning of fossil fuels generates only thermal energy. At present, fossil fuel is still the world’s predominant energy source. But most of our energy comes from burning fossil fuels (coal, oil, and gas) and nuclear reactions. Sometimes, mechanical energy is directly available, for example, wind power and hydropower. For example, electricity is particularly useful since it has very low entropy (is highly ordered) and can be converted into other forms of energy very efficiently. It is closely associated with the concept of entropy. But to get work from thermal energy is more difficult. In general, it is easy to produce thermal energy by doing work, for example, by any frictional process. One of the most wonderful properties of the universe is that energy can be transformed from one type to another and transferred from one object to another. Sometimes it is like the “currency” for performing work. Energy is generally defined as the potential to do work or produce heat. About 70-75% is rejected as waste heat without being converted into useful work, i.e., work delivered to wheels.Įnergy sources have always played a very important role in the development of human society. For example, automotive engines are heat engines that can consume primary energy sources.Īll conventional thermal power plants are heat engines subject to the efficiency limitations imposed by the second law of thermodynamics.Ī typical gasoline automotive engine operates at around 25% to 30% of thermal efficiency.