Chapter 7, Problem 7.22CU

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

Determin the exergy, in kJ, of the contents of a 1.5 m3 storage tank, if the tank is filled with: a) air as an ideal gas at 440°C and 0.70 bar b) water vapor at 440°C and 0.70 bar Ignore the effects of motion and gravity and let To = 22°C and Po=1 bar.

7.58 Figure PZ.58 shows a gas turbine power plant using air as the working fluid. The accompanying table gives steady-state operating data. Air can be modeled as an ideal gas. Stray heat transfer and the effects of motion and gravity can be ignored Let To 290 K, po = 100 kPa. Determine, each in kJ per kg of air flowing, (a) the net power developed, (b) the net exergy increase of the air passing through the heat exchanger, (eg- e), and (c) a full exergy accounting based on the exergy supplied to the plant found in part (b). Comment. State p(kPa) T(K) h(kJ/kg) s° (kJ/kg K) 1100 290 290.16 1.6680 500 505 508.17 2 2.2297 3 500 875 904.99 2.8170 4 100 635 643.93 2.4688 a o is the variable appearing in Eq. 6.20a and Table A-22. Heat exchanger Compressor Turbine FIGURE P7.58

7.5 Equal molar amounts of carbon monoxide and neon are maintained at the same temperature and pressure. Which has the greater value for exergy relative to the same reference environment? Assume the ideal gas model with constant c, for each gas. There are no significant effects of motion and gravity.

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.

Which of the following descriptions about entropy is/are true? 1. It is positive for an isolated system 2. It is zero for a reversible process 3. It is negative for an irreversible process A. 1 and 3 only B. 1 and 2 only C. 2 and 3 only D. All, 1, 2 and 3

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 .

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…