Which combination of the following statements is correct The incorporation of reheater in a steam power plant: P: always increases the thermal efficiency of the plant. Q: always increases the dryness fraction of steam at condenser inlet. R:  always increases the mean temperature of heat addition. S:  always increases the specific work output.?

Option 2 : Q and S

Concept:

In the reheat cycle, the total expansion of steam from the boiler to condenser pressure is carried out in more than one stage with reheating of steam in between the stages.

The main advantage of the reheat cycle is that it increases the dryness fractions of steam at condenser inlet thus making it possible to use higher boiler pressure. It also increases the net-work output thus decreasing the mass flow rate of steam required for the same power output. 

By reheating it's not sure that efficiency will increase, it may decrease also depending on the mean temperature of heat addition.

Also, the mean temperature of heat addition doesn't always increase. It depends on the pressure in the reheater and entry pressure. 

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