Name:______

ENGR 124: Thermodynamics

Test No. 1

Closed Book Portion (25 pts.)

August 6, 2007

______1. (3 pts) Which of the following statements is true regarding a steady flow process?

a.) The mass of the system may change with time

b.) The temperature at any point in the system may not vary with time

c.) The temperature of the fluid moving through the system must be constant

d.) No heat or work interactions may occur

______2. (3 pts) Which of the following is NOT a point function?

a.) Volume

b) Pressure

c.) Internal energy

d.) Work

______3. (3 pts) Which of the following contributes LEAST to smog formation?

a.) Chlorofluorocarbon (CFC) emissions

b) Volatile Organic Compound (VOC) emissions

c.) NOx emissions

d.) Sunlight

______4. (3 pts) Which of the following is NOT true regarding isothermal compression of an ideal gas in a closed system?

  1. Pvk = constant, where k = cv/cp
  2. Mass does not change
  3. Heat must be transferred out of the system
  4. The specific volume of the system must decrease

5. List the four forms of energy that constitute internal energy and describe each form (1.5 pts each, 6 pts total).

1.

2.

3.

4.

6. (7 pts) A saturated mixture (X = 0.60) at 200 kPa is contained in a freely moving piston cylinder device as shown in the figure (State 1). Heat is added to the system until the pressure reaches 400 kPa, at which point the piston rises from the first set of stops (State 2). Heat input continues until the last drop of liquid vaporizes at a pressure reaches 800 kPa (State 3). Carefully, draw this process on a P-v diagram and label the important states 1, 2 and 3.

Name:______

ENGR 124: Thermodynamics

Test No. 1

Open Book/Notes Portion (75 pts.)

August 6, 2007

Note: You may estimate or “eyeball” all property values unless you are explicitly asked to interpolate.

  1. (30 pts.) A freely moving piston cylinder device initially contains 2.5 kg of water with 1.5 kg in the liquid phase. The weight of the piston is such that the pressure inside the cylinder is 800 kPa. Heat is added until the temperature reaches 314.6C.

a. (3 pts.) Determine the initial quality (vapor mass fraction).

b. (3 pts.) Determine the initial temperature.

c. (4 pts.) Determine the internal energy at state 2 in kJ/kg, exactly interpolate the value.

d. (10 pts.) Determine the magnitude and direction of boundary work.

e. (10 pts.) Determine the magnitude and direction heat transfer.

  1. (20 pts) R-134a enters a compressor as saturated vapor at 120 kPa and it exits at 1.2 MPa and 60C. The power input to the compressor is 1.75 kW.
  1. (10 pts) Determine the work input to the compressor in kJ/kg.
  2. (10 pts) Determine the mass flow rate through the compressor.

3. (25 pts) Hot air is used to vaporize water in a heat exchanger as shown in the figure. Water enters at 100 kPa and 80C and exits as saturated vapor (aka steam) at a flow rate of 1 kg/s. The air enters at 2 MPa and 1480 K and exits at 600 K. The velocity of the air through the heat exchanger must be less than 50 m/s.

a. (15 pts) Determine the air mass flow rate.

b. (10 pts) Determine the minimum cross-sectional area of the air inlet (location 3).