EML3100 Exam #2.1 - Fall 1996

1. Work done on a system is
(a) negative
(b) positive

2. Heat transferred to a system is

(a) negative
(b) positive

3. For a compression process where the pressure is varied such that pV is held constant; what is the work in going from state 1 to state 2 in terms of p1, V1, p2, and V2?

4. For which processes is (p2V2 - p1V1)/(1 - n) a valid expression for the WORK?

Several different processes shown on p-V plots -- select one

5. All of the following statements about work done on or by a gas are true EXCEPT:

(a) The differential of work is exact.
(b) Work is transitory in nature.
(c) Work is zero for a constant volume process.
(d) Work is a path-function.
(e) Work is the area under a curve on a p-V plane.

For problems 6 and 7,

¥ Specify the tables and equations used.
¥ Properly identify all values taken from tables.
¥ Remember to include units.

6. What is the specific internal energy of the ideal gas Oxygen (O2) at 600 K (in kJ/kg ) ?

7. A 3 kg iron horseshoe is heated from 27oC to 500oC.

Assuming no change in the kinetic energy, potential energy, and volume for the horseshoe,
What is the heat transfer for this process (in kJ)?

8. A new high-power turbine is being used by the City of Tallahassee.
400oC superheated water vapor enters at an elevation of 50 m (relative to the outlet pipe) with pressure 5 bars and velocity 1000 m/s. The inlet pipe has a cross-sectional area of 200 cm2.
Saturated liquid water exits the turbine at 100 kPa with a velocity of 20 m/s.

(a) Draw a schematic of this device. Write your assumptions.
(b) Write the pertinent info for each inlet and outlet flow. Be sure to list tables used.
(c) What is the mass flow rate of water entering the turbine?
(d) What is the power input/output for this turbine (in kW)?
Show all work, and specify tables used!

9. Last week an new ideal gas, Petersonium (Pe), was discovered. It has an atomic mass of 15 and the constant volume specific heat varies with temperature as follows:

Cv = ( 0.06T - 3 ) kJ/kgK,     T (in K)
10 kg of Petersonium, initially at 327oC and 5 bars is expanded in a polytropic process with n = 1.2 to a final pressure of 1 bar.
(a) Draw a picture of the initial and final states, and write the given information under each.
(b) What is the initial specific volume?
(c) What is the final specific volume?
(d) What is the final temperature?
(e) Find the work for this process (in kJ).
(f) Find the change in internal energy for this process (in kJ).
(g) Find the heat transfer for this process (in kJ).
Show all work, and specify tables used!

BONUS: 2 kg of R-12 initially at 1.4 bars occupies 3.042 m3. The R-12 is expanded against a piston attached to a linear spring to 2.0 bars and triple the initial volume.

If the cross sectional area of the piston is 0.2 m2,
What is the spring constant (ksp) in kN/m?