Chapter 7, Problem 7.24CU

Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x, = 0.5 undergo the two different processes 7.33 described below. In each case, the mixture is brought from the initial state to a saturated vapor state, while the volume remains constant. For each process, determine the change in exergy of the water, the net amounts of exergy transfer by work and heat, and the amount of exergy destruction, each in kJ. Let To = 300 K, Po =1 bar, and ignore the effects of motion and gravity. Comment on the difference between the exergy destruction values. a. The process is brought about adiabatically by stirring the mixture with a paddle wheel. Answer b. The process is brought about by heat transfer from a thermal reservoir at 610 K. The temperature of the water at the location where the heat transfer occurs is 610 K Answer

At a pressure of 1 bar, a temperature of 17 °C and a mass flow of 0.3 kg/s, air enters a stable insulated compressor and exits at 3 bar, 147 °C. Determine the power required by the compressor and the exergy destruction in kW. Express the exergy disappearance as a percentage according to the power required by the compressor. Changes in kinetic and potential energy will be neglected. dead state; T0=17 °C, P0=1 bar

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 relative to the reference environment for its exergy to equal that of the hot water? Let To = 298 K, po = 1 atm, g = 9.81 m/s².

Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x1= 0.3 undergo the two different processes described below. In each case, the mixture is brought from the initial state to a saturated vapor state, while the volume remains constant. For each process, determine the change in exergy of the water, the net amounts of exergy transfer by work and heat, and the amount of exergy destruction, each in kJ. Let To = 300K, po 1 bar, and ignore the effects of motion and gravity. Comment on the difference between the exergy destruction values. a. The process is brought about adiabatically by stirring the mixture with a paddle wheel.

Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x1= 0.3 undergo the two different processes described below. In each case, the mixture is brought from the initial state to a saturated vapor state, while the volume remains constant. For each process, determine the change in exergy of the water, the net amounts of exergy transfer by work and heat, and the amount of exergy destruction, each in kJ. Let To = 300K, po 1 bar, and ignore the effects of motion and gravity. Comment on the difference between the exergy destruction values. a. The process is brought about adiabatically by stirring the mixture with a paddle wheel. b. The process is brought about by heat transfer from a thermal reservoir at 610 K. The temperature of the water at the location where the heat transfer occurs is 610 K.

The water vapor enters a throttling valve with a mass flow rate of 2.7 kg/s, a temperature of 280 °C and a pressure of 30 bar, and undergoes a throttling process up to 20 bar. Determine the flow exergy and exergy extinction at the inlet and outlet of the throttling valve in kW. dead state; T0=25° C, P0=1 atm

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.

A mole of an ideal, diatomic gas undergoes isothermal, reversible expansion from 1.0 dm 3 to 10.0 dm 3 at 100 oC. If the same gas undergoes irreversible expansion against a constant pressure of 1.00 bar, which of the following quantities would change? A. Internal Energy B. Enthalpy C. Free Energy D. Entropy

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