Cairo 2nd Petrol Lecture 7
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This document provides lecture notes on gas power cycles from a mechanical engineering course. It covers the ideal gas relation, specific heats of gases, and the first law of thermodynamics as they relate to closed systems. Formulas are presented for the ideal gas law in various forms, as well as specific heat capacities for air. The notes also define important terms used in analyzing thermodynamic cycles, such as pressure ratio, compression ratio, and cutoff ratio. An example problem is included to demonstrate calculating maximum pressure, net specific work, and thermal efficiency for a diesel engine cycle.
Cairo 2nd Petrol Lecture 7
- 1. Mechanical Engineering Thermodynamics 2nd year Petrol dept. 2011-2012 Lecture (7) Gas Power Cycles Lecturer : Dr. Esmail Bialy
- 2. Background 1- Ideal Gas Relation 2- 1st Law of Thermodynamics (Closed Systems)
- 4. Forms 1- PV=mRT Pressure Volume mass Gas Const. Temperature (kPa) (m3) (kg) (kJ/kg.K) (K)
- 5. Forms 2- Pv=RT Pressure Specific Volume Gas Const. Temperature (kPa) (m3/kg) (kJ/kg.K) (K)
- 6. Forms 3- PV=nRuT Pressure Volume no. of Universal Temperature kmoles Gas Const. (kPa) (m3) (kmole) (kJ/kmole.K) (K)
- 9. Specific Heats γ γ
- 10. Specific Heats From the last two relations, we can drive another two relations Cp=γR/(γ-1) For Air= 1.0035 kJ/kg.K Cv=R/(γ-1) For Air= 0.716 kJ/kg.K
- 11. Note: 1-For Ideal Gases Δ h= CpΔT Δu = Cv ΔT 2- For Steam Δ h= h2-h1 Δu = u2-u1 from steam tables
- 12. 1st Law of Thermodynamics (Closed Systems) (Revision)
- 21. Note!!! rp, r, rc rp: Pressure ratio (Brayton Cycle) r: Compression ratio (Otto & Diesel Cycles) rc: Cutoff ratio ( Diesel Cycle)
- 22. Example (5-10): A Diesel engine has a compression ratio of 20:1 with an inlet state of 95 kPa, 290 K, and volume 0.5 L. The maximum cycle temperature is 1800 K. find the maximum pressure, the net specific work, and the thermal efficiency.