Journal of Thermodynamics & Catalysis
Open Access

Applications of Thermodynamic Cycles in Advanced Future Technologies

Frances Arnold^{* *}Correspondence: Frances Arnold, Department of Chemical Engineering, California Institute of Technology (Caltech), Pasadena, USA, Email:

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Thermodynamic cycles are fundamental concepts in the study of energy conversion processes, where an active substance undergoes a series of thermodynamic processes to return to its initial state. These cycles play a crucial role in various engineering applications, especially in power generation and cooling systems. The essential features of a thermodynamic cycle include Closed System, Energy Transfer, State Functions. The working substance remains contained within a closed system, returning to its original state by the end of the cycle. Energy is transferred to and from the system, often in the form of heat (Q) and work (W). The cycle is characterized by changes in state functions, such as internal energy (U), enthalpy (H), and entropy (S), which depend only on the initial and final states, not the path taken.

The Carnot cycle is an idealized thermodynamic cycle that serves as a benchmark for the efficiency of all real heat engines. In isothermal Expansion the working substance (often an ideal gas) absorbs heat from a high-temperature reservoir at a constant temperature, resulting in expansion and work in the environment. In adiabatic expansion: The gas expands more without exchanging heat, causing its temperature to decrease. In isothermal compression the gas is compressed at a constantly low temperature, releasing the heat into a cold reservoir. In adiabatic compression a gas is compressed without heat exchange, which increases its temperature and returns it to its initial state. This cycle illustrates the maximum possible efficiency for any heat engine operating between two temperature reservoirs.

The Rankine cycle is widely used in steam power plants. In isentropic expansion high-pressure steam expands in a turbine, doing work and producing power as its pressure and temperature drop. In isobaric heat addition steam is heated in a boiler at constant pressure, turning water into steam. In isentropic compression low-pressure steam is compressed in a pump, increasing its pressure while maintaining the same entropy. In isobaric heat rejection steam condenses to liquid water in a constant pressure condenser, releasing heat to the environment. The Rankine cycle is essential for converting thermal energy from fuel into mechanical work. The Brayton cycle, also known as the gas turbine cycle, is used in jet engines and gas turbines. In isentropic compression air is compressed in a compressor, increasing its pressure and temperature. In isobaric heat input compressed air is mixed with fuel and ignited in a combustion chamber and absorbs heat at constant pressure. In isentropic expansion gas at high temperature and pressure expands in a turbine, producing work. In isobaric heat release the gas releases heat to the environment and returns to its original state. The Brayton cycle is effective for high power applications, particularly in aviation and power generation.

The Otto cycle is the ideal thermodynamic cycle for gasoline engines. In adiabatic compression the air-fuel mixture is compressed, increasing its temperature and pressure. In isochoric heat input the mixture ignites and combustion takes place at constant volume, which increases the internal energy. In adiabatic expansion the combustion gases expand, do work on the piston and lower its temperature and pressure. In isochoric heat rejection exhaust gases are expelled and heat is removed from the system at constant volume. The effectiveness of the Otto cycle depends on the compression ratio, with higher rates leading to greater efficiency. The Diesel cycle is similar to the Otto cycle, but is used for diesel engines. It includes a higher compression ratio. In adiabatic compression air is compressed to a high pressure, resulting in an increase in temperature. In isochoric heat addition the fuel is injected and ignited at constant pressure, producing a greater increase in energy. In adiabatic expansion the combustion gases expand, doing work on the piston. In isochoric heat rejection the exhaust gases are drawn, with the heat released at constant volume. The Diesel cycle generally achieves higher efficiency than the Otto cycle due to higher compression ratios and a more controlled combustion process.

Thermodynamic cycles are essential for energy production and transportation. Specific areas include power generation, automotive engines, aerospace etc. Rankine and Brayton cycles are widely used in power plants, converting heat from fossil fuels or nuclear sources into electricity. The Otto and Diesel cycles power internal combustion engines, which provide propulsion for vehicles and machinery. Thermodynamic cycles are essential for understanding and optimizing energy conversion processes in various applications. From the idealized Carnot cycle to practical cycles such as Rankine and Brayton, these processes provide information on efficiency, performance and technological advances. As the demand for energy efficiency and sustainable technologies increases, understanding thermodynamic cycles will remain essential for future innovations in energy production and consumption.