Chemical Thermodynamics

10. A stream turbine receives 25 kg/s of steam at 5.0 MPa and 500°C, and the steam exits at 150 kPa. The turbine is adiabatic. Plot the power produced, the entropy generation rate for isentropic efficiencies varying between 0.4 and 1.0. [MO3, MO4, MO5, M07]

4.14 WP Figure P4.14 provides steady-state data for water vapor flowing through a piping configuration. At each exit, the volumetric flow rate, pressure, and temperature are equal. Determine the mass flow rate at the inlet and exits, each in kg/s.

1. Consider an ordinary vapor compression cycle with a condenser at 40°C, an evaporator at -20°C, and R134a as the working fluid. The compressor is 75.% efficient. For each kg of R134a circulated, determine the amount of cooling, the heat rejected, the work, and the COP.

2. Draw the cycle from problem 1 on (a) a temperature-entropy diagram and (b) a pressure-enthalpy diagram. For each diagram, include a curve for the phase envelope, labels for each step, and an additional cycle in which the compressor is 60.% efficient.

3. Carbon monoxide is compressed reversibly and adiabatically in a piston-cylinder from 1.0 bar and 75°C to 47 bar. a. Use the Peng-Robinson equation of state to determine the amount of work performed on the gas. b. How much work would be required for an ideal gas? c. Explain the reasons for the differences between (a) and (b) based on interactions between the gas molecules.

4. For an exact differential, the second derivative of the function (P in this case) is independent of the order of differentiation. Is the proposed function for an equation of state possible? That is, is P an exact differential? Note: Parameters a, b, and c are non-zero constants. Explain.

7. A fixed-volume container at 45°C contains 5 mol hexane liquid and 0.1 mol hexane vapor in equilibrium. An additional 0.2 mol of hexane vapor are added, while keeping the temperature constant. What happens to the pressure and the amount of liquid and vapor in the container? Why?

7. Nitrogen in laboratory settings can be supplied from liquid nitrogen tanks. These tanks contain mostly liquid N₂ by mass, but one of the ports on the tank is connected to the "headspace", i.e. the region above the liquid. When the port to the headspace is opened, cold nitrogen vapor flows out of the tank. a. If the tank is well-insulated, how will the pressure and temperature inside the tank change as the nitrogen is used up? (It would commonly take days or weeks to use all the nitrogen.) Explain. b. How will they change if the tank is very poorly insulated? Explain.

8. Plot the phase envelope for propane on a P-V diagram by using the equation of state (EOS) spreadsheet to determine saturation pressures.

A pump brings in 20.0 kg/s of liquid water feed at 1.92 bar and 50 °C. The exit pressure from this pump is 7.05 bar. The pump (being real, not reversible) has an isentropic efficiency of 82%. What is the actual work input (in kW) required to run this pump, assuming the specific volume of the water remains constant at 0.001012 m³/kg?