For an ideal regenerative Rankine cycle, as shown in the figure below, which one of the following options is the correct representation of temperature-entropy (T-s) diagram?
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Remember that an ideal pump and an ideal turbine are both isentropic, so those two legs must be vertical on the T-s diagram.
Look at the flow sketch first: water leaves the condenser at 1, gets pushed to higher pressure by the pump at 2, is warmed further by steam bled from the turbine until it reaches 3, is boiled and heated fully at 4, and expands through the turbine down to 5 before returning to the condenser. Two of these five steps are meant to be frictionless and reversible: the pump (1 to 2) and the turbine (4 to 5). On a temperature versus entropy plot, a reversible pump or turbine shows up as a straight vertical line because entropy cannot change during that step.
Option A: shows 1 to 2 as a vertical rise and 4 to 5 as a vertical drop, with the regeneration step 2 to 3 clearly slanting up toward the liquid side of the dome before the boiler section 3 to 4 runs nearly flat across the top. This is exactly the shape an ideal regenerative cycle should have.
Option B: has state 5 sitting far to the right of the dome, at a spot that does not line up with a wet, low quality mixture entering the condenser, so the bottom of the cycle looks wrong.
Option C: crowds 2, 3, and 4 onto what looks like one continuous slanted line instead of a distinct vertical pump step followed by a separate feedwater heating step, hiding the regeneration effect the question is testing.
Option D: gives the pump line 1 to 2 a clear slant instead of a vertical rise, which is only correct for a real, irreversible pump, not the ideal one this question describes.
Since the ideal cycle needs both the pump and turbine legs to stand vertical while still showing a separate heating step from 2 to 3, option A is the one that fits.
