上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 29 Chapter 6 The second law of Thermodynamics (Section 6.7-6.11) Spring,2017 强 Prof.,Dr.Yonghua HUANG nna。 http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日
Engineering Thermodynamics I Lecture 29 Spring, 2017 Prof., Dr. Yonghua HUANG Chapter 6 The second law of Thermodynamics (Section 6.7- 6.11) http://cc.sjtu.edu.cn/G2S/site/thermo.html
A cycle exhibits the Carnot efficiency Hot Carnot efficiency of a power cycle: reservoir H Te mmax 1- (Temperatue in Kelvin or Boundary →Weycle=QH-Qc Rankine scale) Cold Carnot cycle,Ericsson cycle, reservoir Stirling cycle,… four internally reversible processes: two adiabatic processes two isothermal processes 3 _TH C 上游充通大 Apr/10,Mon,2017 2 SHANGHAI JIAO TONG UNIVERSITY
Apr/10, Mon, 2017 2 A cycle exhibits the Carnot efficiency Carnot cycle, Ericsson cycle, Stirling cycle, …. Carnot efficiency of a power cycle: four internally reversible processes: two adiabatic processes + two isothermal processes (Temperatue in Kelvin or Rankine scale)
Carnot cycle and processes (1)+(2) Energy source atTH 2 TH=const. (2)→(3) net,out TL=const. uone nsul 个0 3 (4)4一(3) Process 1-2:Reversible Isothermal Expansion (TH). Energy sink s50 at TL Process 2-3:Reversible Adiabatic Expansion(TH>Tc) QL Process 3-4:Reversible Isothermal Compression (T) (1)←(4) Process 4-1:Reversible Adiabatic Compression (Tc>TH) uone nsul T T 上游充通大 Apr/10,Mon,2017 3 SHANGHAI JIAO TONG UNIVERSITY
Apr/10, Mon, 2017 3 Carnot cycle and processes Process 1-2: Reversible Isothermal Expansion (TH ). Process 2-3: Reversible Adiabatic Expansion (THTC ) Process 3-4: Reversible Isothermal Compression (TL ) Process 4-1: Reversible Adiabatic Compression (TCTH )
Reversibility of the processes Process 1-2&3-4:adiabatically reversible (isotropic) Process 2-3 4-1:Heat transfer TH △I vanishingly small→reversible; (1)+(2) 4 Energy source at TH △T→0 Reservoir TH Tc const.>gas Tconst. 上游充通大学 Apr/10,Mon,2017 4 SHANGHAI JLAO TONG UNIVERSITY
Apr/10, Mon, 2017 4 Reversibility of the processes Process 1–2 & 3-4: adiabatically reversible (isotropic) Process 2–3 & 4-1: Heat transfer ∆T vanishingly small reversible; Reservoir TH & TC const. gas T const. ∆T 0
Work on p-v diagram of Carnot cycle Area 1-2-a-b-1:compression work Wcs/m Area 2-3-c-a-2:expansion work WeT/m Area 3-4-d-c-3:expansion work Wes/m Area 4-1-b-d-4:compression work WeT/m “+”0r“”? a d What about the net work of Carnot cycle? How to evaluate the workand heat 上游究通大学 Apr/10,Mon,2017 5 SHANGHAI JIAO TONG UNIVERSITY
Apr/10, Mon, 2017 5 Work on p-v diagram of Carnot cycle Area 1-2-a-b-1: compression work WcS/m Area 2-3-c-a-2: expansion work WeT/m Area 3-4-d-c-3: expansion work WeS/m Area 4-1-b-d-4: compression work WcT/m a b c d What about the net work of Carnot cycle? How to evaluate the workand heat ? “+” or “-” ?