Why does the steam turbine exhaust port keep vacuum?

The reason why the exhaust port of the steam turbine is kept in vacuum is because according to the principles of Rankine cycle and Carnot cycle, if steam wants to do work in the steam turbine as much as possible, its enthalpy drop should be as high as possible, while the exhaust port of the steam turbine is vacuum, which can make the steam at the exhaust port of the steam turbine in a negative pressure state, where the steam enthalpy is very low, which can make the steam of the same quality in the steam turbine do work to the maximum extent.

Carnot cycle was put forward by French engineer Nicolas Leonard sadi carnot in 1824 to analyze the working process of heat engines. Carnot cycle includes four steps: isothermal heat absorption, adiabatic expansion, isothermal heat release and adiabatic compression. That is, the ideal gas isothermally absorbs heat from state 1(P 1, V 1, T 1) to state 2(P2, V2, T2), then adiabatically expands from state 2 to state 3(P3, V3, T3), and then isothermally releases heat from state 3 to state 4(P4). This cycle consisting of two isothermal processes and two adiabatic processes is called Carnot cycle.