上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 18 Chapter 5 Mass and Energy Analysis of Control Volume Analysis Spring,3/30/2018 Prof.,Dr.Yonghua HUANG 强 月n http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日
Engineering Thermodynamics I Lecture 18 Spring, 3/30/2018 Prof., Dr. Yonghua HUANG Chapter 5 Mass and Energy Analysis of Control Volume Analysis http://cc.sjtu.edu.cn/G2S/site/thermo.html
Typical CV system applications/examples ④ Several devices of interest in engineering ·Nozzle ●Diffuser ●Turbine Compressor Single device 。Pump ●Heat exchanger combination 。Throttling device (system integration) 上游气通大粤 March 31,2018 2 SHANGHAI JLAO TONG UNIVERSITY
March 31, 2018 2 Typical CV system applications/examples Several devices of interest in engineering • Nozzle • Diffuser • Turbine • Compressor • Pump • Heat exchanger • Throttling device Single device (system integration) combination
Nozzle and Diffuser V2>V1 P2P1 A↑ Practical application Diffuser:velocity in the direction of flow Diffuser 上游充通大 March 31,2018 3 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 3 Nozzle and Diffuser Nozzle: velocity ↑ in the direction of flow Diffuser: velocity ↓ in the direction of flow Cross-sectional area (A) varying A ↓ A ↑ Practical application
Work for nozzles and diffusers (1,1,1: -a,-成*(a+曾+）-a+ dt V2>V1 V2P1 2 Nozzle Diffuser W W W The only work is flow work at the inlet and outlet of the CV. drops out 上游通大学 March 31,2018 4 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 4 Work for nozzles and diffusers W W W The only work is flow work at the inlet and outlet of the CV. Wcv drops out (1,1,1):
Steady state of nozzle or diffuser dt SS 0 m-ri dt d 2 832 inlet exit △PE negligible V2>V1 m +--(心，) Nozzle Relatively much smaller 上游充通大 March 31,2018 5 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 5 Steady state of nozzle or diffuser SS inlet exit ∆PE negligible Relatively much smaller Qcv
Example 18.1 m =2 kg/s Known: Insulation ·SS Heat transfer negligible Steam P2 15 bar △PE→0 P1=40 bar V2=665m/s T1=400C V1=10m/s Determine: Control volume ·Area A2,inm2 boundary Converging-diverging nozzle Assumptions: 1.The control volume shown on the accompanying figure is at steady state. 2.Heat transfer is negligible and 3.The change in potential energy from inlet to exit can be neglected. 上游通大学 March 31,2018 6 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 6 Example 18.1 Steam Converging-diverging nozzle Known: • SS • Heat transfer negligible • ∆PE0 Determine: • Area A2 , in m2 Assumptions: 1. The control volume shown on the accompanying figure is at steady state. 2. Heat transfer is negligible and 3. The change in potential energy from inlet to exit can be neglected
Solution Thermodynamic diagram (T-v): T T1=400C m=2 kg/s Insulation p=40 bar P2=15 bar P1=40 bar V2=665m/s T1=400C V1=10m/s p=15 bar Control volume boundary Volume flow rate A2=?→A2= Mass flow rate,give V2r、Velocity,.given V ?→state2 property p2,given Two independent intensive properties determine the state -->h2,Energy Eq. 上游充通大 March 31,2018 7 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 7 Solution Thermodynamic diagram (T-v): A2=? 2 2 2 2 2 A V V V mv Volume flow rate Velocity, given Mass flow rate, given ? state 2 property Two independent intensive properties determine the state p2 , given h2 , Energy Eq
Solution cont. m=2 kg/s Insulation P2=15 bar SS,nozzle,neglect Q V2=665m/s P1=40 bar T1=400C V1 =10 m/s Control volume boundary 0=在-E+(a+ 1+ h,+2 (82 0=-创（心，）户 lia -Table A-6(water steam 3213.6kJkg [ors（) 1kJ 2 =3213.6-221.1=2992.5kJ/kg P2=15bar Table A-6(water steam ---------≥v2=0.1627m3/kg What about A1？ h2=2992.5k/kg_i (2kgs)0.1627m/kg) =4.89×104m2 665m/s 上游充通大 March 31,2018 8 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 8 Solution cont. SS, nozzle, neglect Q = Table A-6 (water steam) p2= 15bar h2 =2992.5 kJ/kg Table A-6 (water steam) What about A1 ?
Turbine shaft W Gas/liquid Applications: ·vapor power plants, gas power plants, 。 Aircraft engine, Hydraulic power plant Stationary bladesL Rotating blades dam Water level. Higher p;superheated steam/gas>turbine lower pe 、7 Water flow- W Water level 上游充通大学 March 31,2018 9 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 9 Turbine shaft W Gas/liquid Applications: • vapor power plants, • gas power plants, • Aircraft engine, • Hydraulic power plant Higher pi superheated steam/gas turbine lower pe W dam
Example 18.2 Known: Steam Q=?个 Assumption: m1=4600kg/h ·SS P1=60 bar △PE→0 T1=400C V1=10m/s Wey=1000 kW Determine: 2 Rate of heat transfer,in kW P2 =0.1 bar x2=0.9(90%) V2=50m/s T T1=400C p=60 bar Schematic? p=0.1 bar 上游充通大学 March 31,2018 10 SHANGHAI JIAO TONG UNIVERSITY
March 31, 2018 10 Example 18.2 Assumption: • SS • ∆PE0 Determine: • Rate of heat transfer, in kW Steam Q=? Known: Schematic?