cairo 2nd petrol lecture 7
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2nd year Petrol dept.2011-2012
Mechanical EngineeringThermodynamics
Lecture (7) Gas Power Cycles
Lecturer : Dr. Esmail Bialy
Background
1- Ideal Gas Relation
2- 1st Law of Thermodynamics (Closed Systems)
Ideal Gas Relation
Forms
1- PV=mRT
Pressure Volume mass Gas Const. Temperature
(kPa) (m3) (kg) (kJ/kg.K) (K)
Forms
2- Pv=RT
Pressure Specific Volume Gas Const. Temperature
(kPa) (m3/kg) (kJ/kg.K) (K)
Forms
3- PV=nRuT
Pressure Volume no. of Universal Temperature
kmoles Gas Const. (kPa) (m3) (kmole) (kJ/kmole.K)
(K)تاني عايزينها مش
Specific Heats
Specific Heats
Specific Heats
γγ
Specific HeatsFrom 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
Note: 1-For Ideal GasesΔ h= CpΔT
Δu = Cv ΔT
2- For SteamΔ h= h2-h1
Δu = u2-u1 from steam tables
1st Law of Thermodynamics(Closed Systems)
(Revision)
Note!!!rp, r, rc
rp: Pressure ratio (Brayton Cycle)r: Compression ratio (Otto & Diesel Cycles)rc: Cutoff ratio ( Diesel Cycle)
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.
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