# Mass and energy analysis of control Volumes (thermodynamics)

1. Jun 9, 2013

### RevanKnight

1. The problem statement, all variables and given/known data

1) A cylinder with an initial volume of 1.5 m3 initially contains water 1 MPa and 200 ° C (condition 1). Container is cooled at constant temperature until the volume is 42% of the initial volume (state 2). The constant temperature process is followed by a constant volume process that ends with a cylinder pressure of 40 bar (state 3). a) Determine the pressure, in bars, and the enthalpy, in kJ / kg, in state 2. b) Determine the temperature in ° Celsius, and the enthalpy at state 3. c) Draw the two processes in a P-v diagram.

2. A cubic meter of water at 10.0 MPa and 400 ° C is found inside a rigid tank. The fluid is cooled until its temperature reaches 320 ° C. Determine the final pressure in bars, and heat transfer in kilojoules if the fluid is a) a real gas and b) an ideal gas, in both cases using tabulated data. c) Calculate the percentage of error made in determining the heat transfer when using the ideal gas model.

3. One kilogram of saturated steam at 0.6 MPa dried in a cylinder with piston. The system receives 250 kJ of heat, and performs certain amount of work to electric current circulating 1.6 ampere through a resistor in the fluid for an hour and a half (1.5 h). If the final temperature of water is 500 ° C and the process is at constant pressure. Draw the complete system and enter the addresses (work and heat). Determine: a) The required voltage, in volts, giving the current stack. Neglect the energy stored in the resistor, b) piston work c) The electrical work.

2. The attempt at a solution
about first problem : How I can calculate the final pressure of the fluid and this water vapor is not an ideal gas?
about second problem: problem talk about real gas concept and ideal gas concept , I'm really confused and do not know how start.
about third:I know I have to start with the final data, finding the values ​​of enthalpy and specific volume. And I have to finish writing the energy balance equation. The system does not seem to affect the potential or kinetic energy. I need help to solve it.

2. Jun 10, 2013

### Staff: Mentor

Hi RevanKnight. Welcome to Physics Forums.

In your thermo course, have they covered how to used the steam tables yet? Without being able to use the steam tables, these are much more complicated problems.

Chet