Question

What is the effect of involving Reheat and Regenerative cycle individually on cycle efficiency in the same sequence?

• A. High, High
• B. Low, Low
• C. High, Low
• D. Low, High

Hint:

Reheat primarily improves work output and reduces moisture content in the low-pressure turbine stages, with a modest impact on efficiency alone. Regeneration significantly improves efficiency by reducing heat input through feedwater preheating.

Answer 1

The Correct Option is D

Step 1: Understand the effect of the Reheat cycle on efficiency.
The reheat cycle involves expanding the steam in a high-pressure turbine, then returning it to the boiler for reheating before expanding it further in a low-pressure turbine. The primary purpose of reheat is to increase the net work output by increasing the average temperature at which heat is added. While reheat increases the net work significantly, the effect on overall cycle efficiency is relatively small, especially when considered in isolation of regeneration. In some cases, the efficiency might slightly decrease without regeneration due to the increased total heat input required. Therefore, the effect of reheat on efficiency alone can be considered relatively low or modest. Step 2: Understand the effect of the Regenerative cycle on efficiency.
The regenerative cycle involves extracting steam from various stages of the turbine and using this steam to preheat the feedwater entering the boiler. This reduces the amount of heat that needs to be added in the boiler to raise the water to the saturation temperature, thus decreasing the total heat input for the same work output. By increasing the average temperature at which heat is added, regeneration significantly improves the thermal efficiency of the cycle. Step 3: Consider the effects individually in the given sequence (Reheat then Regenerative).
The question asks about the effect of involving Reheat individually and then Regenerative individually on cycle efficiency, implying a comparison to a simple Rankine cycle.
Reheat individually: As discussed in Step 1, the impact on efficiency alone is generally low or modest.
Regenerative individually: As discussed in Step 2, the impact on efficiency alone is significantly high.
Step 4: Match the effects with the given options.
The effect of reheat individually on cycle efficiency is relatively "Low," and the effect of regenerative individually on cycle efficiency is "High." Therefore, the sequence of effects is Low, High. This corresponds to option 4. Step 5: Select the correct answer.
The effect of involving Reheat and Regenerative cycle individually on cycle efficiency in the same sequence (compared to a simple Rankine cycle) is Low, High.