1) A piston-cylinder device contains air initially at 150kPa, 20oC and 0.5m3. The air is now compressed in a polytropic process to 400kPa and 140oC. Determine the amount of heat transfer and identify if it is the heat loss or gain during this process.
(Hint: you need to solve the value of n the polytropic exponent based on the pressures and volumes at the initial and final states).
2) A closed piston-cylinder device contains 5L of saturated liquid water at a pressure of 150 kPa. Water is stirred and heated by a paddle wheel and a resistor placed in the water.
After the resistor and paddle-wheel are turned on 45 minutes, only one quarter mass of the water remains in liquid phase. During this process, the pressure is kept constant. Given that the paddle wheel work is 400kJ, the heat loss is 50kJ, and the current flows through the resistor is 8A, please determine the voltage of the resistor source.
3) A closed system contains 2kg of air undergoes an isothermal process from 600kPa and 100oC to 80kPa. Determine the internal energy change, the work done and the heat transfer during this process.
4) In a close stationary system, 2 kg of argon is heated from 20oC to 120oC. Determine the amount of heat transfer when this is done during a (i) constant volume process; (ii) a constant pressure process
5) What is the change of internal energy and enthalpy of 4 kg R-134a as it changes from 50oC and 100kPa to 100oC and 300kPa? Does the pressure at the beginning and end of this process have any effect on the results?
6) What is the change of internal energy and enthalpy of 4 kg nitrogen as it changes from 50oC and 100kPa to 100oC and 200kPa? Does the pressure at the beginning and end of this process have any effect on the results?