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Thermodynamics - Chapter 6: Thermodynamic cycles - Ngo Thanh An

•Introduction

Classification of thermodynamic cycle:

•Power / refrigeration cycle

•Gas / vapor cycle

•Closed / open cycle

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Nội dung text: Thermodynamics - Chapter 6: Thermodynamic cycles - Ngo Thanh An

  1. Chapter 6 – Thermodynamic cycles Classification of thermodynamic cycle: • Power / refrigeration cycle • Gas / vapor cycle • Closed / open cycle
  2. Chapter 6 – Thermodynamic cycles Carnot cycle Gas cycle Stirling cycle Rankine Vapor cycle cycle
  3. Chapter 6 – Thermodynamic cycles Brayton cycle Ideal Diesel cycle Ideal Otto cycle
  4. Chapter 6 – Thermodynamic cycles Diagrams for a Carnot Cycle 1 – 2 isothermal expansion (in contact with TH) 2 – 3 isentropic expansion to TC 3 – 4 isothermal compression (in contact with TC) 4 – 1 isentropic compression to TH
  5. Chapter 6 – Thermodynamic cycles W = Q1 - Q2 Q Since dS = then Q= TdS T SS W= Q − Q =24 T dS − T dS 1 2 SS 1 2 13 WQQTTSS=1 − 2 =( 1 − 2 )( 2 − 1 ) W (TTSST−− )( ) Efficiency:  =  =1 2 2 1 =1 − 2 Q1 TSST1() 2− 1 1 • Observation #1: The efficiency increases as T1 increases (higher quality heat) and T2 (typically the ambient temperature) decreases. • Observation #2: Since T2 can never be zero, the efficiency can never be 1. • Observation #3: Stirling engines operation approximates a Carnot Cycle.
  6. Chapter 6 – Thermodynamic cycles • Vapor power cycle: the one in which the working fluid is alternatively vaporized and condensed. • Steam is the most common working fluid used in vapor power cycles because of its many desirable characteristics, such as low cost, availability, and high enthalpy of vaporization.
  7. Chapter 6 – Thermodynamic cycles Ideal cycle for vapor power cycles, consists of the following four processes: • 1-2 Isentropic compression in a pump • 2-3 Constant pressure heat addition in a boiler • 3-4 Isentropic expansion in a turbine • 4-1 Constant pressure heat rejection in a condenser
  8. Chapter 6 – Thermodynamic cycles Pump (q = 0) w pump ,in = h2 − h1 w pump ,in = v (P2 − P1 ) h = h and v  v = v 1 f @ P1 1 f @ P1 Boiler (w = 0): qin = h3 − h2 Turbine (q = 0) wturb,out = h3 − h4 Condenser (w = 0): qout = h4 − h1
  9. Chapter 6 – Thermodynamic cycles
  10. Chapter 6 – Thermodynamic cycles
  11. Chapter 6 – Thermodynamic cycles
  12. Chapter 6 – Thermodynamic cycles