Rankine cycle explained
Most of the electricity in the world comes from one loop in which water becomes steam and then becomes water again. The Rankine cycle sends that water through a boiler, a turbine, a condenser, and a pump, and the reason the efficiency rises is precisely that change of phase.
The boiler takes in heat, the turbine delivers work, the condenser throws heat away, and the pump lifts the liquid back up. Whether you burn coal, run a reactor, or gather sunlight, the only thing that changes is the heat source, and the loop the water travels stays nearly the same.
On the T-s plane the cycle sits tight against the saturation dome. On a T-s diagram the heat each step trades shows up as the area under its path, the area inside the closed loop is the net heat taken in, and over one turn that area is the net work. When the boiler temperature rises the loop grows, and so does the area, which is the net work.
Net work is what the turbine delivers minus what the pump spends. The pump only presses a liquid, so its work is tiny and almost all of the turbine work remains. A liquid hardly compresses, so pushing water to a high pressure shrinks the volume only a little, whereas pressing a gas would have put a large share of the turbine work back in.
Heating the steam further above the dome raises the average temperature at which heat is added, lifts the efficiency, and leaves the steam drier as it leaves the turbine. A wet exit lets droplets strike the fast blades and wear them down, while keeping the steam dry stops that wear and lets the blades last longer. The place where saturated and superheated part remains.
There are four devices, the efficiency is written η = WnetQH, and water is used because the phase change lets heat move at nearly steady temperature while the pump costs almost nothing. Next come gas cycles with no phase change, Otto and Diesel. A modern steam plant turns about 40% of its heat into electricity, and a combined plant with a gas turbine in front pushes that value past 60%.