Chapter 7, Problem 7.45CU

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

Determine the specific exergy of saturated water vapor at 137 °C, where To = 313K, Po = 101.3kPa. Assume the velocity and elevation is zero with reference to the environment. You must use following tables to solve this problem. (answer to 2 decimal) Saturated water temperature table Sat Liq. Temp., Sat Liq. Sat Liq. Sat Liq. vf uf hf sf °C m3/kg kJ/kg kJ/kg kJ/kg.K 30 0.001004 125.73 125.74 0.4368 35 0.001006 146.63 146.64 0.5051 40 0.001008 167.53 167.53 0.5724 45 0.00101 188.43 188.44 0.6386 Saturated water temperature table Temp., Sat. Vap. Sat. Vap. Sat. Vap. Sat. Vap. hg kJ/kg vg ug sg °C m3/kg kJ/kg kJ/kg.K 125 0.7508 2534.5 2713.5 7.0745 126 0.7358 2535.5 2714.8 7.0649 127 0.7208 2536.5 2716.1 7.0553 128 0.7058 2537.5 2717.4 7.0457 129 0.6908 2538.5 2718.7 7.0361 130 0.6758 2539.5 2720.0 7.0265 131 0.6608 2540.5 2721.4 7.0169 132 0.6458 2541.4 2722.7 7.0073 133 0.6308 2542.4 2724.0 6.9977 134 0.6158 2543.4 2725.3 6.9881 6.9785 135 0.6008 2544.4 2726.6 136 0.5858 2545.4 2727.9…

Exergy of a Flow Stream: Flow (or Stream) Exergy.

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.

At steady state, an electric pump motor develops power along its output shaft of 0.7 hp whiledrawing 6 amps at 100 V. The outer surface of the motor is at 150°F. Let T = 40°F.Determine:(b) the exergy flow with input power, exergy flow with output power, magnitude of exergy flowwith heat transfer leaving the motor, and exergy destruction, all in Btu/h.

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 .

At steady state, an electric pump motor develops power along its output shaft of 0.7 hp whiledrawing 6 amps at 100 V. The outer surface of the motor is at 150°F. Let T = 40°F.Determine: (a) the magnitude of the rate of heat transfer leaving the motor, in Btu/h.(b) the exergy flow with input power, exergy flow with output power, magnitude of exergy flowwith heat transfer leaving the motor, and exergy destruction, all in Btu/h.

Thermodynamics. 1) For a closed system, as the exergy reference environment temperature ___________, the exergy destruction rate decreases 2) Which of the following statements does not describe the exergy reference environment? It is large in extent. It has a uniform temperature. It is incompressible. It has a uniform pressure.   3) Air within a piston–cylinder assembly undergoes an expansion process from an initial volume of 0.5 m3 to 1 m3. The dead state pressure is 100 kPa. If the work associated with the process is 60 kJ, determine the exergy transfer accompanying work, in kJ.

EXERGY TRANSFER BY HEAT, WORK, AND MASS