Exergy change of a system

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Uppercase X is used to represent absolute exergy.

Lowercase Phi (Greek alphabet) is used to represent exergy per unit mass.

<-- where the properties of the specified state of the mass are e, v, s, and the properties of the state of the environment are e0, P0, v0, T0, s0. The internal, kinetic and gravitational potential energies have been absorbed into the e terms.

<-- note that the "initial state" in this case is the same as the "specified state" of the "mass" from the definition of exergy, so no change is required. Also note that the environmental pressure and temperature remain in the equation.

<-- where the properties of the initial state are e1, v1, s1, the properties of the final state are e2, v2, s2, and the environmental pressure and temperature is P0 and T0 respectively.

<-- Flow exergy per unit mass is represented by lowercase Psi (Greek alphabet)

Writing this per unit mass:

Recall that the total energy, e, of a system is comprised of internal, kinetic and gravitational potential energies. Therefore, the total exergy of a closed system (per unit mass) can be written:

So, to find the change in exergy of a closed system when it undergoes a process from an initial state to a final state, simply use the final state of the process instead of the state of the environment in the equation above. The result is:

Change in exergy of a flow

The total exergy of a flow is given by:

The change in exergy of a flow is given by: