Memorize 2

Question 1

Worked Example 3.3: (With Table)

Show that for a polytropic process, the change in
entropy may be expressed as:

Answer 1

( can’t input the answer)

Question 2

Worked Example 3.5: (With Table)

A steam turbine receives steam at 2 MPa and 250°C, and exhausts at 0.1 MPa, 0.85 dry.

a) Neglecting heat losses and changes in ke and Pe, estimate the work output per kg stream.

b) If, when allowance is made for friction, radiation, and leakage losses, the actual work obtained is 80% of the heat estimated in (a), calculate the power output of the turbine when consuming 600 kg of steam per minute

Answer 2

Answer:

539 kJ/kg;
4.31 MW

Question 2

Worked Example 3.11: (With Table)

30 kg/s steam at 3 MPa, 300°C expands isentropically in a turbine to a pressure of 100 kPa. If the heat transfer from the casing to surrounding air represents 1 per cent of the overall change of enthalpy of the steam, calculate the power output of the turbine. Assume exit is 2 m above entry and that initial velocity of steam is 10 m/s whereas exit velocity is 1 m/s.

Answer 2

Answers: W = +19 kW

Question 3

Worked Example 3.14: (With Table)

A reciprocating steam engine cylinder contains 2 kg of steam at a pressure of 30 bar and a temperature of 300°C. The steam expands reversibly to a final pressure of 2 bar, according to the law pv1.2 = c.
Calculate:

a) The final state of the stream
b) The work transfer and
c) The heat transfer in the process

Answer 3

Answers:

0.875;
884 kJ;
-63.4 kJ

Question 4

Worked Example 3.17: (With Table)

3 kg/s of steam enters an adiabatic condenser at a pressure of 100 kPa with dryness fraction 0.80, and the condensate leaves the condenser at a temperature of 30°C. The condenser is cooled by water which enters at a temperature of 5°C and leaves at a temperature of 25°C. Calculate the mass flow rate of cooling water required if all changes in kinetic and potential energy may be neglected. Assume Cp = 4.2 kJ/kg-K, and the enthalpy at 100 kPa and 30°C = 125 kJ/kg

Answer 4

Answer: 75 kg/s

Question 5

Worked Example 3.21: (With Table)

A piston and cylinder mechanism has its piston fixed so that the volume contained is 0.0025 m^3. The mechanism is filled with wet steam at a pressure of 2 bar. The steam is heated until it reaches the critical point. The piston is released and the steam expands adiabatically to a pressure of 2 bar and a volume of 0.5 m^3.
Calculate:

a) The mass of steam in the mechanism,
b) The dryness fraction of the steam after
expansion.

Answer 5

Answer:

0.788 kg;
0.715

Question 6

Worked Example 3.26: (With Table)

A one pass steam generator receives saturated water at 20 bar, and converting it into steam at 400°C. The mass flow rate of steam is 1200 kg/h, calculate the heat transfer in the generator.

Answer 6

Answer: 149.667 kW

Question 6

Worked Example 3.31: (With Table)

Steam at a pressure of 10 bar and dryness fraction of 0.96 expands adiabatically to a pressure of 2 bar according to PV^1.2 = constant. Determine the work done during expansion per unit mass of steam.

Answer 6

Answer: 246 kJ/kg