Chapter 8, Problem 8.8P

78 kg of water vapor is found as saturated vapor at 650 kPa pressure in a cube-shaped container with a fixed volume. The cube lost heat and its pressure dropped to 325 kPa. Since the environmental conditions are 100 kPa 25 ºC, find the exergy change of the steam in the first and the last state, the exergy change in the steam, the exergy destruction and the second-law efficiency for this process change.

EXPLAIN THE THE DECREASE OF EXERGY PRINCIPLE AND EXERGY DESTRUCTION.

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

Consider a heat transfer process of the steady form that occurs along a plain wall. While the inner room temperature was kept at 25 °C, the outdoor environment temperature was measured to be 2 °C. If the heat transfer at this plain wall in an hour is 3,528 kJ, determine the.total exergy destruction per unit time (the rate), which occurs during this heat transfer process, a) use the total entropy generation to find the rate of the total exergy destruction in the room (i.e.., use the entropy balance), b) use the exergy balance to find the rate of the total exergy destruction in the room

A heat exchanger enters a mass flow of 100 / b / s of water at 30psia and 100 ° F and exits at 200 ° F. The heat supplied to the water stream comes from a stream of hot air that enters at 1000R and 45psia and exits at 680R. Considering that the ambient temperature is 520R. Determine: Ans: a) The exergy variation of the water current. b) The exergy variation of the air stream. c) The total irreversibility of the heat exchange process d) The exergy efficiency of the heat exchanger

How reversible process differs from irreversible process?

A system undergoes a refrigeration cycle while receiving Qc by heat transfer at temperature Tc and discharging energy Qu by heat transfer at a higher temperature TH. There are no other heat transfers. (a) Using energy and exergy balances, show that the net work input to the cycle cannot be zero. (b) Show that the coefficient of performance of the cycle can be expressed as: Tc TH – TeA'¯ T(Qn – Q). B = where E, is the exergy destruction and To is the temperature of the exergy reference environment. (c) Using the result of part (b), obtain an expression for the maximum theoretical value for the coefficient of performance.

In a cycle what always happens when an ideal process is replaced by a real process The efficiency decreases. The internal energies decrease. The mass flow rate increases. The enthalpies decrease. The enthalpies increase.

4 An air nozzle has an efficiency of .90 and is adiabatic. air enters at p1=200 kPa, T1=1300 K with negligible velocity. air exits at p2=130 kPa. use dead state variables of T0=293 k and P0= 100 kPa and a variable heat capacity. what is t2 and the rate of exergy destruction?