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recitation7 - Recitation 7 Solution Problem-1 Known...

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Recitation 7 Solution October 22, 2004 Problem-1 Known Nitrogen, from p 1 , T 1 expands to p 2 , turbine efficiency is given. Find final temperature. Schematic and given data Assumptions 1. Ideal gas model. 2. No kinetic and potential energy changes Analysis η t = h 1 - h 2 h 1 - h 2 s (1) From T 1 = 443 . 15 K , look up in the ideal gas properties table fro Nitrogen (table-A23) and get ¯ h 1 = 12904 kJ/kmol, ¯ s 0 1 = 203 . 071 kJ/kmolK . ¯ s 0 2 s = ¯ s 0 1 + ¯ R ln p 2 p 1 = 191 . 972 kJ/kmolK (2) From ¯ s 0 2 s ,look up in the table-A23 and get ¯ h 2 s = 9976 . 58 kJ/kmol . So ¯ h 1 - ¯ h 2 = η t × ( ¯ h 1 - ¯ h 2 s ) = 3232 . 27 kJ/kmol. (3) 1
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Thus ¯ h 2 = 10671 . 73 kJ/kmol and look up in the table-A23 to get T 2 = 366 . 87 K = 93 . 72 C. Problem-2 Known Steam enters at p 1 , T 1 and exits at p 2 , T 2 . Find work done, final temperature if isentropic and η t . Schematic and given data T 1 p1 p2 s 2s 2 Figure 1: Isentropic process Assumptions 1. No kinetic and potential energy changes Analysis a) From the given p 1 , T 1 , p 2 , T 2 , look up in the superheated vapor table(A-4) find h 1 = 3787 . 2 kJ/kg, (4) s 1 = 8 . 1290
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