University of Victoria, Department of Mechanical Engineering
MECH 240 Thermodynamics
© 2021-24 Henning Struchtrup
Assignment 10
posted: 22.11.2024
due: 29.11.2024
For all questions provide p-v- and T-s-diagrams (relative to saturation lines) and schematics!
10.1 Geothermal Steam Power Plant
In the Larderello (Italy) steam power plant, steam at 5 𝑏𝑏𝑏𝑏𝑏𝑏, 220℃ is produced by geothermal heating.
Assume that the processes in the plant follow the basic Rankine cycle with reversible turbine and
reversible pump. The condenser temperature is 40℃.
Determine the enthalpies at the corner points and the thermal efficiency. Discuss its value as compared
to standard steam power plants, which operate at higher pressures and temperatures.
10.2 Reheat Rankine Cycle
A vapor power plant with reheat works according to the following cycle
1 – 2 Adiabatic pumping of saturated liquid water at 𝑇𝑇1 = 30℃ to 𝑇𝑇2 = 35℃, 𝑝𝑝2 = 125 𝑏𝑏𝑏𝑏𝑏𝑏
2 – 3 Isobaric heating, evaporation and superheating to 𝑇𝑇3 = 550℃
3 – 4 Adiabatic expansion in high pressure turbine to 𝑝𝑝4 = 6 𝑏𝑏𝑏𝑏𝑏𝑏, isentropic efficiency 𝜂𝜂𝑇𝑇 = 0.9
4 – 5 Isobaric reheat to 𝑇𝑇5 = 𝑇𝑇3
5 – 6 Adiabatic expansion in the low pressure turbine to saturated vapor at condenser pressure
6 – 1 Isobaric condenser
a) Make a table with the enthalpies and other interesting properties of all relevant points.
b) Determine the isentropic efficiencies of pump and low pressure turbine.
c) Determine net work, heat input and thermal efficiency of the cycle.
d) For power output of 240 𝑀𝑀𝑀𝑀, determine the mass flow, and the volume flows at the turbine exits.
e) The boiler temperature is 𝑇𝑇𝐵𝐵 = 600℃ and the environment is at 𝑇𝑇0 = 20℃. Determine the entropy
generation and associated work loss for the boiler (heat and reheat). Also, determine the overall work
loss from comparing to a Carnot engine operating between 𝑇𝑇𝐵𝐵 and 𝑇𝑇0 , and compare to boiler loss.
10.3 Vapor refrigeration cycle
On a hot summer day, with outside air temperature of 36℃, the air-conditioning system of a car must
remove 14 𝑘𝑘𝑘𝑘 of heat to keep the car's interior at a comfortable temperature of 18℃. The air
conditioning system runs on the standard vapor refrigeration cycle (R134a) with the following
characteristics: Evaporator temperature is 4℃ and compressor inlet state is saturated vapor; condenser
pressure is 1.2𝑀𝑀𝑀𝑀𝑀𝑀, and condenser exit temperature is 40℃; the isentropic efficiency of the compressor
is 𝜂𝜂𝐶𝐶 = 0.85.
a) Make a table with the values of pressure, temperature and enthalpy at the corner points.
b) Determine the COP of the cycle and compare to that of the corresponding Carnot cycle.
c) Determine the mass flow of cooling fluid, and the power required to drive the system.
d) The air-conditioning draws outside air and cools it to 18℃. Determine the volume flow of air entering
the car.
© 2021-24 Henning Struchtrup