(a) Explanation Write the reduced Equation for energy and mass balance. h 2 = h 1 − W ˙ c v m ˙ (I) Here, mass flow rate is m ˙ , power developed is W ˙ c v , enthalpy at state 1 is h 1 and the enthalpy at state 2 is h 2 . Write the expression for dryness fraction at state 2. x 2 = ( h 2 − h f 2 ) ( h g 2 − h f 2 ) (II) Here, dryness fraction at state 2 is x 2 , enthalpy at point 2 is h 2 , enthalpy of saturated liquid at point 2 is h f 2 and the enthalpy of superheated liquid at state 2 is h g 2 . Write the expression for dryness fraction at point 2s. x 2 s = s 2 s − s f 2 s g − s f 2 . (III) Here, dryness fraction at point 2s is x 2 s , entropy at point 2s is s 2 s , entropy of saturated liquid at point 2 is s f 2 and the entropy of superheated liquid at state 2 is s g 2 . Write the expression for enthalpy at point 2s. h 2 s = h f 2 + x 2 s ( h g 2 − h f 2 ) (IV) Here, enthalpy at point 2s is h 2 s , enthalpy of saturated liquid at state 2 is h f 2 and the enthalpy of superheated liquid at the state 2 is h g 2 . Write the expression for isentropic efficiency of the turbine. η t = h 1 − h 2 h 1 − h 2 s (V) Here, enthalpy at point 2s is h 2 s and isentropic efficiency is η t . Conclusion: The figure below shows the T-s diagram. Figure-(1) Refer to Table A-4, “Properties of saturated water vapor” to obtain the value of h 1 as 3658.4 kJ / kg and s 1 as 7.1677 kJ / kg ⋅ K . Substitute 3658.4 kJ / kg for h 1 , 2626 kW for W ˙ c v and 2 kg / s for m ˙ in Equation (I). h 2 = 3658.4 kJ / kg − 2626 kW 2 kg / s = 3658.4 kJ / kg − 2626 kW ( 1 kJ / s 1 kW ) 2 kg / s = 3658.4 kJ / kg − 1313 kJ / kg = 2345.4 kJ / kg Refer to Table A-3, “Properties of Saturated Water (Liquid–Vapor): Pressure Table” at 0.1 bar to obtain the value of h f 2 as 191.83 kJ / kg , 2584.63 kJ / kg for h g 2 . Substitute 191.83 kJ / kg for h f 2 , 2584.63 kJ / kg for h g 2 and 2345 (b) To determine The rate of entropy production.

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ISBN: 2818440116926

Author: MORAN

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Entropy

In physics, entropy means the amount of disorder or the degree of randomness associated with a thermodynamic system. The system is not self-organized when the entropy of the system is high. For instance, when a system is at an elevated temperature, its m…

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Chapter 6.13, Problem 143P

(a)

To determine

The isentropic turbine efficiency.

(b)

To determine

The rate of entropy production.

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Chapter 6.13, Problem 142P

Chapter 6.13, Problem 144P

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