A mass of 8 kg of helium undergoes a process from an initial state of 3.9 m³/kg and 15°C to a final state of 0.5 m³/kg and 80°C. Assuming the surroundings to be at 25°C and 100 kPa, determine the increase in the useful work potential of the helium during this process. The gas constant of helium is 2.0769 kJ/kg-K. Use the table containing the ideal-gas specific heats of various common gases. The increase in the useful work potential is kJ.

A 0.08-m rigid tank initially contains saturated water vapor at 180 °C. The tank is connected by a valve to a supply line that carries steam at 1400 kPa and 400 °C. Now the valve is opened, and steam is allowed to enter the tank. Heat transfer takes place with the surroundings such that the temperature in the tank remains constant at 180 °C at all times. The valve is closed when it is observed that one-third of the volume of the tank is occupied by liquid water. Find (a) the amount of steam that has entered the tank, and (b) the amount of heat transfer. 1400 kPa Steam 400°C Saturated vapor Qout V=0.08 m T, = 180°C

The volume of 1 kg of helium in a piston-cylinder device is initially 5 m³. Now helium is compressed to 2.5 m³ while its pressure is maintained constant at 130 kPa. Determine the initial and final temperatures of helium as well as the work required to compress it, in kJ. The gas constant of helium is R=2.0769 kJ/kg-K. The initial temperature of helium is 311.39 K. The final temperature of helium is 125.18 ► K. The work required to compress helium is 390 kJ.