ASSIGNMENT 2

CHE 221

1. Steam is continuously expanded from a pressure of 25 bars and 300°C to 1 bar through a

Joule-Thomson expansion valve. Calculate me final temperature and the entropy generated

per kilogram of steam using

a. The ideal gas law

b. The van der Waals equation of state

c. The Peng-Robinson equation of state

d. The steam tables

2. Ammonia is to be isothermally compressed in a specially designed flow turbine from 1 bar

and 1000C to 50 bars. If the compression is done reversibly, compute the heat and work flows

needed per mole of ammonia if

a. Ammonia obeys the principle of corresponding states

b. Ammonia satisfies the Clausius equation of state P (V - b) = RT with b = 3.730 * 10-2

m3/kmol.

c. Ammonia obeys the Peng-Robinson equation of state.

3. One hundred cubic meters of carbon dioxide initially at 150°C and 50 bars is to be

isothermally compressed in a frictionless piston and cylinder device to a final pressure

of 300 bar. Calculate

i. The volume of the compressed gas

ii. The work done to compress the gas

iii. The heat flow on compression

Assuming carbon dioxide

a. Is an ideal gas

b. Obeys the principle of corresponding states

c. Obeys the Peng-Robinson equation of state

4. A 0.7-m3 tank containing helium at 15 bars and 22°C will be used to supply 4.5 moles per

minute of helium at atmospheric pressure using a controlled adiabatic throttling valve.

a. If the tank is well insulated, what will be the pressure in the tank and the temperature of the

gas stream leaving the throttling valve at any later time t?

b. If the tank is isothermal, what will be the pressure in the tank as a function of time?

You may assume helium to be an ideal gas with CP* = 22 J/ (mol K), and that there is no heat

transfer between the tank and the gas.

5. a. Steam at 35 bars and 600 K enters a throttling valve that reduces the steam pressure to 7

bars. Assuming there is no heat loss from the valve, what is the exit temperature of the steam

and its change in entropy?

b. If air (assumed to be an ideal gas with CP* = 29.3 J/(mol K) entered the valve at 35 bar and

600 K and left at 7 bar, what would be its exit temperature and entropy change?

6. Joe Unidel claims to have invented a steady-state now device in which the inlet is steam at

300C and 5 bar, the outlet is saturated steam at 100°C and 1 bar, the device is adiabatic and

produces approximately 388 kJ per kilogram of steam passed through the device. Should we

believe his claim?

7. Consider an ideal dual-loop heat-powered refrigeration cycle using R-12 as the working

fluid, as shown in Figure below. Saturated vapor at 105°C leaves the boiler and expands in

the turbine to the condenser pressure. Saturated vapor at −15°C leaves the evaporator and is

compressed to the condenser pressure. The ratio of the flows through the two loops is such

that the turbine produces just enough power to drive the compressor. The two exiting streams

mix together and enter the condenser. Saturated liquid leaving the condenser at 45°C is then

separated into two streams in the necessary proportions. Determine the ratio of mass flow rate

through the power loop to that through the refrigeration loop. Find also the performance of

the cycle, in terms of the ratio

8. Steam enters the turbine of a power plant at 5 MPa and 400°C, and exhausts to the

condenser at 10 kPa. The turbine produces a power output of 20 000 kW with an isentropic

efficiency of 85%. What is the mass flow rate of steam around the cycle and the rate of heat

rejection in the condenser? Find the thermal efficiency of the power plant.

9. Steam flows steadily through an adiabatic turbine. The inlet conditions of the steam are 10

MPa, 450°C, and 80 m/s, and the exit conditions are 10 kPa, 92 % quality, and 50 m/s. The

mass flow rate of the steam is 12 kg/s. Determine (a) the power output, and (b) the turbine

inlet area.

[1] 3-5-6-7 is the Power

loop.

[2] 3-4-1-2 is the

refrigeration loop

[3] In between 3-5

there’s a pump.

[4] In between 3-4

there’s an

expansion valve

10. Steam expands in a two-stage adiabatic turbine from a specified state to another state.

Some steam is extracted at the end of the first stage. The power output of the turbine is to be

determined.