This set of Power Plant Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Reheating of Steam “.
1. Why Reheating of steam is used?
a) to increase efficiency
b) to increase work output
c) to increase Turbine Inlet Temperature
d) to reduce amount of fuel used
Explanation : Work output = work done by turbine – work done by compressor
2. Reheating of steam
a) decreases steam rate
b) increases steam rate
c) no effect on steam rate
d) none of the mentioned
Explanation : Since work output increases the steam rate decreases.
3. Efficiency of cycle will increase due to Reheating if
a) mean temperature of heat addition in boiler is higher than in reheat process
b) mean temperature of heat addition in boiler is lower than in reheat process
c) it will increase without any conditions
d) it will not increase
Explanation : Efficiency = work output / heat supplied, heat supplied is less in this condition only.
4. Why don’t we use more than two reheats?
a) not economical
b) increased mechanical stresses
c) net efficiency is decreased
d) all of the mentioned
Explanation : The mechanical stresses increases in much higher proportion than the pressure pressure because of the prevailing high temperature.
5. The cycle efficiency in a single reheat plant is influenced by
a) pressure at tubine inlet
b) pressure at which steam is reheated
c) temperature at which steam is reheated
d) temperature at tubine inlet
Explanation : The cycle efficiency is a function of the ratio of reheat to initial pressure.
6. The optimum reheat pressure for the most of the modern power plants is ___________ of the initial steam pressure
Explanation : In this range of reheat pressure efficiency is maximum.
7. What is the effect of reheat on steam quality?
c) does not change
d) depends on several parameters
Explanation : Because this steam is undergoing expansion two times.
8. What should be the dryness fraction at the time of exhaust?
Explanation : For modern turbines the admissible dryness fraction of exhaust steam (at the turbine exit) should be not less than x = 0.86 to 0.88.
9. Reheat is preferred for the plants having efficiency greater than
Explanation : For producing power less than this reheat will not be economical.
10. Which one of the following is an advantage of reheat cycle
a) the size of the Low pressure (LP) turbine blades is reduced because specific volume is reduced by 7 to 8%
b) the reheating reduce 4 to 5% fuel consumption with a corresponding reduction in the fuel handling
c) lower steam pressures and temperatures and less costly materials can be used to obtain the required thermal performance
d) all of the mentioned
Explanation : Reheat increases work output.
Sanfoundry Global Education & Learning Series – Power Plant Engineering.
To practice all areas of Power Plant Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.