EXERCISE 1 CHAPTER 12

QUESTION 1 1. 0.22 kg of a saturated vapor is converted to a saturated liquid by being cooled in a weighted piston-cylinder device maintained at 350 kPa. During the phase conversion, the system volume decreases by 0.04 m3; 250 kJ of heat are removed; and the temperature remains fixed at -10°C. Estimate the boiling point temperature of this substance when its pressure is 420 kPa. 350 kPa -10°C 0.22 kg sat. vapor

Using the finite difference approximation, Solving for T2, 350 kPa -10°C 0.22 kg sat. vapor

QUESTION 2 2. Determine the change in the enthalpy of air, in kJ/kg, as it undergoes a change of state from 100 kPa and 20°C to 600 kPa and 300°C using the equation of state P(v-a) = RT where a = 0.01 m3/kg, and compare the result to the value obtained by using the ideal gas equation of state.

2. Determine the change in the enthalpy of air, in kJ/kg, as it undergoes a change of state from 100 kPa and 20°C to 600 kPa and 300°C using the equation of state P(v-a) = RT where a = 0.01 m3/kg, and compare the result to the value obtained by using the ideal gas equation of state. Solving the equation of state for v, Differentiating the equation, For enthalpy change,

Integrating ; For ideal gas,

QUESTION 3 3. Methane is compressed adiabatically by a steady-flow compressor from 0.8 MPa and -10°C to 6 MPa and 175°C at a rate of 0.2 kg/s. Using the generalized charts, determine the required power input to the compressor. 6 MPa 175°C Ẇ CH4 ṁ = 0.2 kg/s 0.8 MPa -10°C

6 MPa 175°C Ẇ CH4 ṁ = 0.2 kg/s 0.8 MPa -10°C