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Unformatted text preview: 7-39An insulated rigid tank contains a saturated liquid-vapor mixture of water at a specified pressure. An electric heater inside is turned on and kept on until all the liquid vaporized. The entropy change of the water during this process is to be determined. AnalysisFrom the steam tables (Tables A-4 through A-6) ( )( )( )( )KkJ/kg6.8649vaporsat.KkJ/kg2.81680562.625.3028.1/kgm0.42430.0011.69410.250.00125.kPa1002121131111⋅==⋅=+=+==-+=+===ssxssxxPfgffgfvvvvvThen the entropy change of the steam becomes ( )kJ/K8.10=⋅-=-=KkJ/kg)2.81686.8649)(kg2(12ssmSΔ7-64Steam expands in an adiabatic turbine. Steam leaves the turbine at two different pressures. The process is to be sketched on a T-sdiagram and the work done by the steam per unit mass of the steam at the inlet are to be determined. Assumptions1 The kinetic and potential energy changes are negligible. Analysis (b) From the steam tables (Tables A-4 through A-6), 831.kJ/kg6.2179kPa10kJ/kg3.2921MPa1KkJ/kg8826.6kJ/kg1.3423MPa6C0053313321221111=======⋅===°=sssxhssPhssPshPTA mass balance on the control volume gives 321mmm&&&+=where 13129.1.mmmm&&&&==We take the turbine as the system, which is a control volume. The energy balance for this steady-flow system can be expressed in the rate form as 3121out,113322out,11outin9.1.hmhmWhmhmhmWhmEEss&&&&&&&&&&++=++==or kJ/kg3.1169)6.2179)(9.()3.2921)(1.(1.34220.127.116.11.321out,32out,1=--=--=++=hhhwhhwhssThe actual work output per unit mass of steam at the inlet is kJ/kg993.9===)kJ/kg3.1169)(85.(out,outsTwwηWeH2O 2 kg 100 kPa Turbine P1 = 6 MPa T1= 500°C P3= 10 kPa P2= 1 MPa 0.01.12.23.18.104.22.168.78.89.911.0100200300400500600700s [k J /k g -K ]T [°C]6 0 0 0 k P a1 0 0 0 k P a1 0 k P aSteamIAP W S1237-93Air is compressed in a piston-cylinder device in a reversible and adiabatic manner. The final temperature and the work are to be determined for the cases of constant and variable specific heats. the work are to be determined for the cases of constant and variable specific heats....
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This note was uploaded on 01/25/2010 for the course ME 55806 taught by Professor Chen during the Spring '10 term at Berkeley.
- Spring '10