1. Refrigerant R-134a and air streams enter a steady state heat exchanger. The R-134a stream enters with a pressure of 4.1 bar and a temperature of 0°C, and exits at a pressure of 4.0 bar and a temperature of 20°C. At the inlet, the air stream has a volumetric flow rate of 40 m3/s, the temperature of the air stream is 50°C, and the pressure is 1.01 bar. The air stream exits with a temperature of 20°C and a pressure of 0.99 bar.
(a) Calculate the mass flow rate of R-134a in kg/s.
2. Water and ammonia streams flow through a steady state heat exchanger. The water stream enters the heat exchanger with a velocity of 40 m/s, a temperature of 200°C, and a pressure of 15 bar through a pipe with a diameter of 0.1 m. The water stream leaves as a saturated liquid-vapor mixture with a quality of 0.2. Before entering the heat exchanger, the ammonia stream flows through a throttling valve. At the inlet of the throttling valve the ammonia pressure and temperature are 12 bar and 28°C. At the exit the pressure of the ammonia stream has dropped to 4 bar. The stream then enters the heat exchanger and exits with a temperature of 60°C. The pressure drop across the heat exchanger is negligible for both the ammonia and water streams. Neglect heat transfer to the surroundings.
(a) Determine the mass flow rate of the water stream in kg/s.
(b) Determine the mass flow rate of the ammonia stream in kg/s.
(c) Determine the state of the ammonia after the throttling process. If the ammonia is a saturated liquid-vapor mixture, calculate the quality x2.
3. One pound of nitrogen as an ideal gas expands isothermally at 70oF from a volume of 1 ft3 to a volume of 2 ft3. During this process there is heat transfer to the gas from a single reservoir (the surrounding atmosphere) and the gas does work. Evaluate the work and heat transfer for the process, in Btu. Is this process a violation of the Kelvin-Planck statement of the second law of thermodynamics? Explain why or why not.