Hw6 assig - hw6 PDF

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MAE 11 Fall 2018 HW #6 Due: Friday, November 9 (beginning of class at 12:00p) Requirements: • Include T − s diagrams for all problems (except H6.5).

H6.1 Refrigerant 134a at 2.8 bar and 60◦ C is compressed to a final pressure of 14 bar in an internally reversible isothermal process. Determine: a. sketch cycle on both p − v and T − s diagrams b. the work and heat transfer [kJ/kg] c. repeat a. and b. using air as the working fluid and assume ideal gas behavior H6.2 Air in a piston cylinder assembly undergoes a Carnot power cycle. Heat is added at temperature T1 = 1400K and rejected at T3 = 350K. At the beginning and end of the heat rejection process, the pressures are p3 = 100 kPa and p4 = 500 kPa, respectively. Assume the air behaves as an ideal gas with variable specific heats. Determine: a. pressures [kPa] at beginning and end of the isothermal heat addition process (p1 , p2 ) b. heat transfer and work [kJ/kg] for each process c. thermal efficiency H6.3 Refrigerant 134a undergoes a Carnot heat pump cycle. Isothermal heat addition occurs at p1 = p2 = 1 bar. During the isothermal heat rejection process, the refrigerant changes from saturated vapor (state 3) to saturated liquid (state 4) at 40◦ C. Determine: a. coefficient of performance of cycle b. heat addition, heat rejection [kJ/kg] c. net work input of cycle [kJ/kg] H6.4 Two kilograms of air, initially at 100 kPa and 27◦ C, are contained in an insulated piston-cylinder assembly. The air is compressed to 700 kPa. Consider air as an ideal gas with constant specific heats. Determine: a. minimum possible work [kJ] required to compress air (clearly justify your result, that it is the minimum possible) b. if the actual work is 25% greater, the final temperature of the air [◦ C] and the entropy produced during the process [kJ/K] c. show both processes on T − s diagram H6.5 Recall problem H3.8 in HW3. Determine the amount of entropy produced within the tank [kJ/K]....