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Old Dec 8th 2015, 04:12 PM   #1
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Closed feedwater heater problem

Hello,

I've got to solve a thermodynamic problem for my university classes.
Here's the text of the problem:

In a regenerative Rankine cycl, the closed feedwater heater with pump as shown in the figure is arranged so that the water at state 5 is mixed with the water at state 2 to form a feedwater which is a saturated liquid at 1,4 MPa. Feedwater enters this heater at 175degC and 1,4 MPa with a flow rate of 1 kg/s. Bleed steam is taken from the turbine at 1MPa and 200degC, and enters the pump as saturated liquid at 1 MPa. Determine the mass flow rate of bleed steam required to operate this unit.

I have evaluated the energy balance equation and drawn the T-s diagram.
Energy balance: yh3 + (1-y)h1 = (1-y)h2 + yh4
where h3 is the enthalpy of the bleed steam before entering the closed FWH, h1 is the enthalpy of the feedwater before closed FWH, h2 stands for the feedwater after the fwh and h4 for bleed steam after fwh.

After the fwh bleed steam becomes saturated liquid and goes through a pump that rises its pressure to 1,4 MPa from 1 MPa.

The task would be easy if I knew the condenser pressure, but I don't know anything but this little part of the whole system.

After the mixing chamber described on the beggining of the task, the feedwater goes to the boiler (most probably), as saturated liquid. This is unusual as the water before the boiler is most common compressed liquid. Here the point where it starts being heated lays on the saturation line.

I have no idea how to solve it. Can you help?
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Old Dec 9th 2015, 10:55 AM   #2
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Picture = 10,000 words.

BillyBlacc, Hi...

I assume the Rankine Cycle has only one Open Heater (right?). Do you have a schematic showing the arrangement of the equipment? What
text is it?

Jim
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Old Dec 9th 2015, 11:11 AM   #3
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Heater and mixing chamber actually

I'm uploading the diagram with all the equations evaluated and the sheet with the task text.
Attached Thumbnails
Closed feedwater heater problem-zadania-terma.jpg   Closed feedwater heater problem-wykres.jpeg  
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Old Dec 10th 2015, 12:58 PM   #4
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Anyone got any idea?
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