Question #187477

An ideal reheat turbine with one stage of reheat receives steam at 8.0 MPa,

480°C. Reheat pressure is 0.83 MPa and exhaust pressure is 0.007MPa. The

work is 1559 KJ/kg and the thermal efficiency is 41.05%. Find the

temperature of steam leaving the reheater.

Expert's answer

Given work = 1559 KJ/kg

η_{h} = 41.05%

When, steam is stable at P₁ = 8 MPa, T_{1} = 480°C

h_{1} = 3319.6 KJ/kg; S = 6.6613 KJ/kg.K at P_{2} = 0.83 Mpa.

S_{g2} = 6.625 KJ/kg.K

S_{1} = S_{2} = S_{g2}

Entry to reheater in Saturated vapour:

T_{2} = 170.5°C

h₂ = h_{21g} = 27689 kJ/kg.

(h_{1} - h_{6}) + (h_{2} - h_{3}) = 3747.807

(3349.6-170.626) + (h_{3} - 2768.9) = 3797.807

h_{3} = 3387.773 kJ/kg.

let c_{p1v} = 2.1 kJ/kg.K

h_{3} = 3387.733 kJ/kg.K

From Superheated steam tables corresponding to h_{3} = 3387.733 kJ/kg.K, and

P_{3} = 0.83Mpa

T_{3} = 454°C

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