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As a result, entropy production does not necessarily cause the entropy of the system to increase. In fact the entropy or disorder in a system can spontaneously decrease, such as an aircraft gas turbine engine cooling down after shutdown, or like water in a cup left outside in sub-freezing winter temperatures.
Here S is the entropy of the system; T k is the temperature at which the heat enters the system at heat flow rate ˙; ˙ = ˙ = ˙ represents the entropy flow into the system at position k, due to matter flowing into the system (˙, ˙ are the molar flow rate and mass flow rate and S mk and s k are the molar entropy (i.e. entropy per unit ...
In terms of energy flow, the movement from a magnetically aligned state requires energy from the thermal motion of the molecules, converting thermal energy into magnetic energy. [24] Yet, according to the second law of thermodynamics , because no heat can enter or leave the container, due to its adiabatic insulation, the system should exhibit ...
It is in this sense that entropy is a measure of the energy in a system that cannot be used to do work. An irreversible process degrades the performance of a thermodynamic system, designed to do work or produce cooling, and results in entropy production. The entropy generation during a reversible process is zero. Thus entropy production is a ...
Entropy is one of the few quantities in the physical sciences that require a particular direction for time, sometimes called an arrow of time. As one goes "forward" in time, the second law of thermodynamics says, the entropy of an isolated system can increase, but not decrease. Thus, entropy measurement is a way of distinguishing the past from ...
In a stationary state, the production of entropy inside a thermodynamic system with constant external parameters is minimal and constant. If the system is not in a stationary state, then it will change until the entropy production rate, or, in other words, the dissipative function of the system, takes the smallest value.
In contrast, if the process is irreversible, entropy is produced within the system; consequently, in order to maintain constant entropy within the system, energy must be simultaneously removed from the system as heat. For reversible processes, an isentropic transformation is carried out by thermally "insulating" the system from its surroundings.
The term "entropy" has been in use from early in the history of classical thermodynamics, and with the development of statistical thermodynamics and quantum theory, entropy changes have been described in terms of the mixing or "spreading" of the total energy of each constituent of a system over its particular quantized energy levels.