Sample_Problems_3

# Sample_Problems_3 - Engi2800 Engineering Thermodynamics I...

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Sample Problems #3 (Chapter 4) Ismet Ugursal, J.M. Chuang Dalhousie University Dept. of Mechanical Engineering September 27, 2009 Engi2800 Engineering Thermodynamics I

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Problems (Textbook 7 th Ed.) Questions Page Topics 4.58 118 4.61 118 4.101 121 Rate of Work 4.118 122 Review Problems Polytropic Process Boundary Work: Multistep Process
Prob. 4.58 Polytropic Process Consider a piston cylinder with 0.5 kg of R-134a as saturated vapor at . It is now compressed to a pressure of 500 kPa in a polytropic process with . Find the final volume and temperature, and determine the work done during the process. Solution: Take CV as the R-134a which is a control mass. Process: until State 1: From Table B.5.1 ( see slide #4 ) State 2: ( P , process) From B.5.2, for given : it is superheated vapor at Process gives , which is integrated for the work term, Eq.(4.5), p. 95 m 2 = m 1 = m ( T; x ) P = Cv ¡ 1 : 5 1 W 2 = Z PdV = m 1 ¡ 1 : 5 £ ( P 2 v 2 ¡ P 1 v 1 ) n = 1 : 5 ( P; v ) P = 500 kPa = ¡ 7 : 07 kJ ¡ 10 o C v 2 = v 1 ( P 1 =P 2 ) 1 = 1 : 5 = 0 : 09921 £ (201 : 7 = 500) 2 = 3 = 0 : 05416 m 3 = kg ( see slide #5 ) Pv 1 : 5 = constant v 1 = 0 : 09921 m 3 = kg ; P = P sat = 201 : 7 kPa = ¡ 4 kg £ (500

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