I am pretty rusty in Thermodynamics, and I have spent time reading my old texts, but no luck to find a classical text-book solution:

What will the resulting fluid properties be if, 1200kg/h SH steam at 0.8 bar(a) and 340 deg. C is allowed to flow into a exhuast steam duct kept at 0.8 bar(a), 93.5 deg. C (saturated temperature) by means of exhausting to the  vacuum pump unit and the condenser.

Will the SH steam 'flash', cool down to 93.5 deg. C? Will the duct heatup to 340 deg. C.

I am unable to formulate the thermodynamic equations. Any help/ hints greatly appreciated.
 
This condition is encountered during the turbine startup heating.

Your condenser circ water must remove enough heat to condense the incoming steam.  If the condenser load increases such that there is not enough surface area or circ water flow to remove all the heat, the pressure in the condenser will increase.  This should not be the case if all you are considering is small flow from warm up of piping/components.

The exhaust steam appears to be rather hot for warmup.  The steam will cool/condense as the components are warmed.

Drains from the turbine are usually designed for high temperature.  Typically, the turbine manufacturer will not close drain valves(Safety Valves) until it is certain that no condensing will occur within the the turbine casing.  In other words, you will have steam flowing through the drain valves before they are closed and you must design the drain system to handle this steam.  Because steam turbines are generally inefficient at low throttle flows and low loads, temperatures at the drains can approach the inlet steam temperature.

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