MEEN 315, SECTION 503 PRINCIPLES OF THERMODYNAMICS Spring 2013 Homework #8 DUE March 26, 2013 N.B.: The enhancement lectures “Example_Closed System Work Process” and “Example_Closed System First Law” may be helpful on this homework. They are located on the elearning website LecturesEnhancement LecturesExample_Closed System Work Process and Example_Closed System First Law, respectively. 1. A piston / cylinder, shown below, has 2 lbm of R-134a at state 1 with 200 F, 90 psia, and is then brought to saturated vapor (state 2) by cooling while the piston is locked with a pin. Now, the piston is balanced with an additional constant force and the pin is removed (piston does not move and cylinder pressure does not change as pin is removed because of the balancing force). The cooling continues to state 3, where the R-134a is saturated liquid. Show the processes in a P-V diagram and find the work in each of the two steps, i.e. Process 1-2 and Process 2-3, and the total heat transfer. 2. A piston / cylinder assembly contains 1 kg of liquid water at 20°C and 300 kPa, as shown below. There is a linear spring mounted on the piston such that when the water is heated the pressure reaches 3 MPa with a volume of 0.1 m3. a) Find the final temperature. b) Plot the process in a P-v diagram. c) Find the work transfer in the process. d) Find the heat transfer in the process. e) Find the change in entropy of the water.3. Nitrogen gas is expanded in a polytropic process with n = 1.35 from 2 MPa and 1200 K to 120 kPa in a piston-cylinder device. How much work is produced during this process, in kJ/kg, what is the final temperature, and what is the change in entropy of the nitrogen gas? 4. Air is contained in a cylinder device fitted with a piston-cylinder (see below). The piston initially rests on a set of stops, and a pressure of 300 kPa is required to move the piston. Initially, the air is at 100 kPa and 27°C and occupies a volume of 0.4 m3. Determine the amount of heat transferred to the air, in kJ, while increasing the temperature to 1200 K. 5. Two 10-ft3 adiabatic tanks are connected by a valve (see below). Initially, one tank contains water at 450 psia with quality of 0.1. The second tank contains water at 15 psia with quality of 0.75. The valve is now opened, allowing the water vapor from the high-pressure tank to move to the low-pressure tank until both tanks are at the same thermodynamic state. Calculate the two independent properties you would use to “fix” the final thermodynamic state. Determine the final mass in each tank. This is an irreversible process; explain why. What is one thing you could have done to this process to at least decrease its