Thermodynamics I – Review problems

Dr. H. Assadipour

1. a. Select the T-v diagram if steam at .005 m3/kg is heated to 0.5 m3/kg while maintaining P = 500 kPa.

b. Estimate the enthalpy of steam at 288oC and 2 MPa .

c. Estimate the specific volume of steam at 200 oC and internal energy of 2000 kJ/kg.

d. Saturated water vapor is heated in a rigid vessel from 200 oC to 600 oC. What is the final pressure?

2. a. A nozzle accelerates steam at 4 MPa and 500 oC to 1 MPa and 300 oC.

Calculate the exiting velocity if v1 = 20 m/s.

b. Calculate the mass flow rate at the nozzle exit in part “a” if d1 = 10 cm.

c. Air at 25 oC enters a tube at the rate of 100 kg/min and leaves at 20 oC. Determine the amount of

heat loss.

d. Calculate the power needed to raise the pressure of water at 4 MPa assuming temperature remains

constant. The mass flow rate is 5 kg/s and 0.Q

3. A simple steam power plant operates on 8 kg/s of steam, as shown below.

Neglecting losses in the various components, calculate:

a. The turbine power output.

b. The pump power requirement.

c. The velocity in the pump exit pipe.

d. The heat transfer rate necessary in the boiler

e. The condenser heat transfer rate.

f. The mass flux of cooling water required.

g. The thermal efficiency of the cycle.

4. Steam enters a two-stage adiabatic turbine at 8 MPa and 550 oC, as shown. It expands in the first

stage to a pressure of 2 MPa. Then steam is reheated at constant pressure to 550 oC before it is

expanded in a second stage to a pressure of 200 kPa. The power output of the turbine is 80 MW.

Assuming an isentropic efficiency of 84% for each stage of the turbine,

a. Determine the enthalpy of the exit stream of Stage 1.

b. Find the enthalpy and entropy of the inlet to Stage 2.

c. Determine the required mass flow rate of steam (see hint below).

d. Show the process on a T-s diagram with respect to saturation lines.

Hint: Take the entire two-stage turbine (excluding the reheat system) as the “control volume” and apply

the first law.

5. Two kilograms of steam is contained in a 6-liter tank at 60 oC. If 1000 kJ of heat is added, calculate:

a. Find the final internal energy of the system.

b. Find the final temperature and quality.

c. Calculate the final entropy.