Why does the Rankine cycle require the condensation of water before reheating?

[fred2028]

In a Rankine cycle such as a steam power plant, why does the liquid (water) have be condensed before being reheated first? Isn't the Q just extracted during the condensation stage, wasted into a nearby reservoir, and then re-added in the boiler? Could this water not be fed straight to the boiler, and because it is at a higher temperature than fully condensed water, would require less W to heat it?

 

[SteamKing]

When the working fluid (water, or steam more precisely) exits the turbine, it is still in a gaseous state. The function of the condenser is to perform the phase change of the steam back into liquid water. Liquid water takes less power to pump back into the boiler than steam does.

 

[njardus]

What SteamKing said seems like a good answer, I'd just like to add one thing: Pumps like to work in either a fully liquid or fully gaseous regime. This is why the condenser completely condenses the working fluid. If the working fluid were to have some gaseous component to it, you run the risk of cavitation occurring in your pump, which will kill the pump rather quickly.

 

[fred2028]

When the working fluid (water, or steam more precisely) exits the turbine, it is still in a gaseous state. The function of the condenser is to perform the phase change of the steam back into liquid water. Liquid water takes less power to pump back into the boiler than steam does.

Thanks, so in this case, the pumping would require more power than the amount of power the condenser and boiler would save?

What SteamKing said seems like a good answer, I'd just like to add one thing: Pumps like to work in either a fully liquid or fully gaseous regime. This is why the condenser completely condenses the working fluid. If the working fluid were to have some gaseous component to it, you run the risk of cavitation occurring in your pump, which will kill the pump rather quickly.

Thanks for the reply!