Chapter 7, Problem 7.2E

The exergy change of a system can be negative, but the exergy destruction cannot.

Apply exergy balance to closed systems and control volumes.

Define the exergy destruction, which is the wasted work potential during a process as a result of irreversibilities.

If heating from saturated liquid to saturated vapor would occur at 100°C (373.15 K), evaluate the exergy transfers accompanying heat transfer and work, each in kJ/kg. Ans. 484, 0.

The exergy transfer to a steady-flow system is equal to the exergy transfer from it plus the exergy destruction within the system.

Answer the following true or false. Explain. (a) A process that violates the second law of thermodynamics violates the first law of thermidynamics. (b) When a net amount of work is done on a closed system undergoing an internally reversible process, a net heat transfer of energy from the system also occurs. (c) One corollary of the second law of thermodynamics states that the change in entropy of a closed system must be greater than zero or equal to zero. (d) A closed system can experience an increase in entropy only when irreversibilities are present within the system during the process. (e) Entropy is produced in every internally reversible process of a closed system. (f) In an adiabatic and internally reversible process of  a closed system, the entropy remains constant. (g) The energy of an isolated system must remain constant, but the entropy can only decrease.

Using image below Evaluate the exergy X1 of the initial state 1 and answer the following question: • Is the useful work in the process 1 → 2 → DS smaller, equal, or greater than exergy X1? • Discuss your result

A domestic water heater holds 189 L of water at 60°C, 1 atm. Determine the exergy of the hot water, in kJ. To what elevation, in m, would a 1000-kg mass have to be raised from zero elevation for its exergy to equal that of the hot water? Let T0 = 298 K, p0 = 1 atm, g = 9.81 m/s2 .

EXPLAIN THE THE DECREASE OF EXERGY PRINCIPLE AND EXERGY DESTRUCTION.