EML3100 - Exam #2.2 from Fall 1997

1. ₁W₂ = [integral evaluated from state 1 to state 2 of] pdV is a valid expression for the work for processes where, (circle one)

(a) P is constant

(b) pV is constant

(c) pVⁿ is constant, n not equal to 1

(d) the pressure is applied by a linear spring

(e) all of the above

(f) none of the above

For questions 2 & 3 refer to the p-v plot shown to the right, (process shown was a process where states 1 and 2 are connected by a straight line. v₁ > v₂, and P₁ > P₂)

2. For the process shown,

(a) work is done by the system

(b) work is done on the system

(c) none of the above

3. For the process shown,

(a) the work is negative

(b) the work is positive

(c) the work is equal to zero

(d) none of the above

4. The heat transfer for an adiabatic process is

(a) negative

(b) positive

(c) equal to zero

(d) none of the above

5. The work for an isochoric process is

(a) negative

(b) positive

(c) equal to zero

(d) none of the above

6. What is the change in potential energy (in kJ) for a 10 kg object that is raised 57 m (meters)?

7. Assuming ideal gas behavior, what is the change in specific enthalpy (in kJ/kg) when Nitrogen is heated from 27^oC, 2 bars, to a final state of 347^oC, 5 bars?

8. 5 kg of R-12 is contained in a closed piston cylinder assembly. Initially the R-12 is at 4^oC, with a quality of 40%. The R-12 is heated in a isothermal process to saturated vapor. The R-12 is then expanded in a polytropic process, with exponent n=0.80, to a final pressure of 2.0 bars.

(a) Draw a picture of each state, and write the given information under each.

(b) Sketch this process on a p-u plot. (be sure to label each state.)

(c) initial specific volume.

(d) initial specific internal energy (in kJ/kg).

(e) specific volume at state 2.

(f) specific internal energy at state 2 (in kJ/kg).

(g) final specific volume.

(h) final specific internal energy (in kJ/kg).

(i) total work for this process (in kJ).

(j) total heat transfer for this process (in kJ).

9. An adiabatic gas turbine expands air at 35 bars, 447^oC to 4 bars, 127^oC. The volumetric flow rate at the exit is 2 m³/s, and the outlet pipe cross-sectional area is 0.036 m². The inlet pipe area is 0.07 m².

(a) Show that it is valid to assume ideal gas behavior for the air for this system.

(b) Draw a schematic of this device. Write your assumptions.

(c) Write the pertinent info or each inlet and outlet flow. Be sure to list tables used.

(d) specific volume of the air entering the turbine (in m³/kg).

(e) specific volume of the air exiting the turbine (in m³/kg).

(f) mass flow rate for this system.

(g) velocity of the air entering the turbine.

(h) velocity of the air exiting the turbine.

(i) power input/output for this turbine (in kW).

BONUS:

(I) Write at least 5 sentences about something you saw at the Tallahassee Power Plant Open House.

OR

(II) A new ideal gas has been discovered with the following characteristics:

Name Floridium

Symbol FL

Atomic Mass 14.7

Constant Pressure Specific Heat C_po = ( 0.14T - 2 ) , T (in K)