Steam Power Plant Reheat Efficiency Calculation

AI Thread Summary
The discussion centers on calculating the reheat efficiency of a steam power plant, focusing on the enthalpy values and efficiency formulas. The user initially struggled with determining the heat added (Qa) and net work (Wnet), leading to an efficiency calculation of 0.3752. Confusion arose regarding the enthalpy values, particularly h3, which was thought to be incorrect. After receiving guidance on using steam tables and correcting a schematic diagram, the user successfully recalculated the values. The conversation highlights the importance of accurate diagrams and the use of steam tables in thermal efficiency calculations.
Sent
Messages
7
Reaction score
0

Homework Statement


vuKJEna.png


Homework Equations


Heat added, Qa (This I'm not sure how since the steam passed through a reheater before it enters the HPT. That is what I understand based on the problem above)
Work Net, Wnet
Efficiency, Wnet/Qa
Heat Rate, WP/EP (Not sure if that is the correct formula)

The Attempt at a Solution


First I made a T-S Diagram
w4NX6Ax.jpg


Based on the diagram above, I got all these enthalpy values.
OZzSVlg.png

h1 = h @ 3 MPa & 370C
h2 = h @ 0.7 MPa & s1
h3 = h @ 0.7 MPa & 500C
h4 = hf4 +x hfg4 (All values, 0.007 MPa)
where x = (s4 - sf4)/sfg4
h5 = hf @ 0.007 MPa
h6 = vf5 (P6-P5)
WP1 = h6-h5
ha = h @ 3 MPa and 500C

The WNet that I got is, 1485.491
For the Qa = (ha-h6) + (h3-h2) = 3959.022

Eff = .3752

Was not able to solve Heat Rate.

-------------
I can't seem to understand how the answers shown in the problem was got. Please enlighten me. Thanks in advance!
 
Physics news on Phys.org
It looks to me like h3 is wrong. It should be equal to h2 plus the heat given up by the high pressure stream between 500 C and 370 C. So, it should be about 3100 J/kg.
 
  • Like
Likes Sent
Thank you for your reply.
Should I get the heat given up by using this formula?
Q=mcT
 
Sent said:
Thank you for your reply.
Should I get the heat given up by using this formula?
Q=mcT
Sure. Or you can get it from the steam tables as the ##\Delta h##. Both should give about the same answer.
 
  • Like
Likes Sent
Chestermiller said:
Sure. Or you can get it from the steam tables as the ##\Delta h##. Both should give about the same answer.
Hello,

We was informed that the label in the schematic diagram that was given to us was wrong. I adjusted my TS diagram based on the correction and tried to solve it again. Thankfully I got the answers now.

Thank you very much for your replies.
 
Back
Top