Three power plants have been suggested that operate at these efficiencies.
|
Plant
|
Power Plant Efficiency (%)
|
|
I
|
81
|
|
II
|
66
|
|
III
|
41
|
a. Determine the overall efficiency of each plant (not the maximum theoretical efficiency) using the other efficiencies given in Table
b. Categorize the factors that affect the efficiency.
c. Discuss the practical limits that govern such efficiencies. Which plant could be most likely to be built? If plant III only costs half of plant I or II to operate, which could be most likely to be built?
Answer:
a. For each plant, the overall efficiency = the efficiency of (power plant) x (boiler) x (turbine) x (electrical generator) x (power transmission). The overall efficiencies are:
Plant 1: 46.7%; Plant II: 38.1%; Plant III: 23.7%.
b. The main factors affecting the efficiency are the several steps of energy transformation: the combustion of the fuel and boiling of the water (potential to kinetic), the turning of the turbine (kinetic to mechanical), and the operation of the machine (mechanical to electrical).
c. The second law of thermodynamics states the efficiencies of each step. Heat will never completely be converted into work. With both the operating costs of Plant and efficiency I being twice that of Plant III, either of these would be equally likely to be prepared. One may be preferred if there were other factors such as initial construction costs or environmental impacts.