discussion: 3.1 For (a) Is it possible for exergy to be negative? Discuss. (b) Consider an evacuated space with volume V as the system. Eval- uate its exergy and discuss. (c) Is it possible for the specific physical exergy ePH associated with a stream of matter to be negative? Discuss.

Determine the exergy, in Btu, of one pound mass of: a) saturated liquid Refrigerant 134a at -5°F b) saturated vapor Refrigerant 134a at 140°F c) Refrigerant 134a at 60°F, 20lbf/in.2 d) Refrigerant 134a at 60°F, 10lbf/in.2 In each case, consider a fixed mass at rest and zero elevation relative to an exergy refernce environment for which To=60°F, Po=15 lbf/in.2

Define the entropy of a pure substance is determined from the tables (like other properties).

For a thermodynamic process, when delta Hsys > 0, and delta Ssys < 0, the process is (spontaneous at all temperatures, non-spontaneous at all temperatures or spontaneous only at high temperatures).

answer 92 and 93

5. Consider the two processes A and B shown in the pV diagram that take a gas from an initial state to a final state. Which process requires you to perform less work? Initial 12. final (a) A. (b)) (c) Both require exactly the same work.

7.66 Referring to the discussion of Sec. Z.6.2 as required, evaluate the exergetic efficiency for each of the following cases, assuming steady-state operation with negligible effects of heat transfer with the surroundings: a. Turbine: Wer 1200 hp, e 250 Btu//lb, eg = 15 Btu/lb, m 240 lb/min. b. Compressor: Wev/m=-105 kJ /kg, e = 5 kJ/kg, eg = 90 kJ/kg, m 2 kg /s. c. Counterflow heat exchanger: mh = 3 kg/s, me 10 kg /s, ef = 2100 kJ/kg, e = 300 kJ/kg, É = 3.4 MW 10 lb /s, m3 15 b /s, en = 1000 Btu/Ib, eg = 50 Btu/Ib, eg = 400 Btu/lb d. Direct contact heat exchanger: m1