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Thermodynamics - Rankine Cycle - Superheated Steam
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Thermodynamics - Rankine Cycle - Superheated Steam
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Jose Alfonso F. FabeBSME 2 – Thermodynamics 2
Level 4: Rankine Cycle
b.) Ideal Rankine Cycle with boiler producing superheated steam.
A steam powerplant operates on an ideal Rankine cycle between the pressure limits of 4.6 MPa
and 0.4 MPa. The temperature of the steam at the turbine inlet is 450℃, and the mass flow rate
𝑘𝑔
of the steam through the cycle is 25 . Find the steam rate, turbine work, pump work, total heat
𝑠
added to the cycle, total heat rejected by the condenser, power output of the cycle, net heat, and
thermal efficiency.
Solution:
Schematic Diagram:
T-s Diagram:
, At State 1:
𝑝1 = 4.6𝑀𝑃𝑎
𝑡1 = 450℃
From table 2.
𝑡𝑠𝑎𝑡 @ 4.6𝑀𝑃𝑎 = 258.83℃
Since, 𝑡1 > 𝑡𝑠𝑎𝑡 , then, it is in superheated steam state.
From table 3.
𝑘𝐽
ℎ1 = 3,321.9
𝑘𝑔
𝑘𝐽
𝑠1 = 6.8630
𝑘𝑔 ∙ 𝐾
At State 2:
𝑝2 = 0.4𝑀𝑃𝑎
𝑘𝐽
𝑠2 = 𝑠1 = 6.8630
𝑘𝑔 ∙ 𝐾
From table 2 @ 0.4 MPa
𝑘𝐽
𝑠𝑓 = 1.7799
𝑘𝑔 ∙ 𝐾
𝑘𝐽
𝑠𝑔 = 6.8959
𝑘𝑔 ∙ 𝐾
𝑠𝑓 < 𝑠2 < 𝑠𝑔 , then, it is in wet steam state.
Solve for the quality, 𝑥2;
𝑠2 = 𝑠𝑓 + 𝑥2 𝑠𝑓𝑔
𝑠2 − 𝑠𝑓
𝑥2 =
𝑠𝑓𝑔
𝑘𝐽 𝑘𝐽
6.8630 − 1.7766
𝑘𝑔 ∙ 𝐾 𝑘𝑔 ∙ 𝐾
𝑥2 =
𝑘𝐽 𝑘𝐽
6.8959 − 1.7766
𝑘𝑔 ∙ 𝐾 𝑘𝑔 ∙ 𝐾
𝑥2 = 0.9936 𝑜𝑟 99.36%
Solving for the enthalpy in state 2, ℎ2;
𝑘𝐽 𝑘𝐽
ℎ2 = ℎ𝑓 + 𝑥2 ℎ𝑓𝑔 ; ℎ𝑓 = 604.74 𝑘𝑔 & ℎ𝑓𝑔 = 2,133.8 𝑘𝑔
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