rankine - Units Engines/motors in hp Gasoline in gallons...

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1 Units Engines/motors in hp Gasoline in gallons Oil in Barrels (By international agreement a barrel of petroleum equals 42 U. S. gallons) Natural gas in therms or decatherms – 1 therm = 100,000 Btu (about 10 cf) – 1 decatherm = 1 ccf or 1 MMBTU Electricity in kWh – But Watt was English!!!
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2 Carnot Cycle Revisited Requires constant temperature heat addition (how do you do this?) Not practical But, we could do constant pressure heat addition – And when water is boiling, this means constant temperature!
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3 Idealized Rankine cycle We study the Rankine cycle because it is a theoretical cycle which can be closely approximated in practice William Rankine (1820-1872) – Scottish Professor Manual of the Steam Engine and Other Prime Movers (1859)
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4 William Rankine In 1855, Rankine was appointed Chair of Civil Engineering and Mechanics at the University of Glasgow which enjoyed no notable reputation in education. But Rankine changed that. – He instituted a degree program in engineering and a Bachelors of Science degree. – He stressed the importance of combining practice and theory in teaching. – He wrote many of the textbooks used at the time.
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5 Steam engines worked! As thermodynamics developed, how to optimize the use of steam was deduced Idealized Rankine cycle ¾ Simple steam power plant 1-2 reversible adiabatic pumping 2-3 constant pressure heating 3-4 reversible adiabatic expansion 4-1 constant pressure cooling • Water does not have to be the working fluid It is cheap Ammonia is common (Kalina cycle) – Use of freon or other chemicals – called generally “Organic Rankine Cycles”
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6 Pump Powered From Turbine Output Heat Input From Furnace Boiler Pump Steam Turbine Condenser (When cycle is closed) 1 2 3 4 Heat Output To Atmosphere Idealized rankine cycle
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7 Idealized Rankine cycle s T 1 2 s 3 4s P= c o n s t high P =const low
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8 Cycle equations h q h w h q P v h w out turbine in pump Δ = Δ = Δ = Δ = Δ = Energy transfers across components are straightforward Efficiency of the cycle is boiler pump turbine in net cycle h h h q w Δ Δ Δ = = η
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9 What Makes a Rankine Cycle Different than a Carnot Cycle?
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10 Open cycles You do not need to recover steam – Reciprocating steam engines routinely discharged steam – Railroads had to put water towers around the circuit – Discharged steam eventually condenses back to liquid (rain or dew) and flows to a river where it is reused in power plant Acts like a Rankine cycle with atmospheric low pressure side
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11 Example – Open Rankine Cycle Given: – 1) inlet to pump 70 ° F, 1 atm – 2) Pressure after the pump = 200 psia – 3) Saturated steam into the turbine – 4) atmospheric pressure at turbine exit – 5) ideal components – 6) Flow rate = 60 lbm/min Wanted: Cycle efficiency Start by fixing all of the states:
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12 Pump Inlet conditions – In our case, at 1 atm, boiling would be at 212 ºF So at 70 ºF we are VERY subcooled
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13 Pump Inlet conditions
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This note was uploaded on 09/30/2011 for the course MECH 486 taught by Professor Zho during the Spring '11 term at Rutgers.

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rankine - Units Engines/motors in hp Gasoline in gallons...

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