Judah Levine, 3070L12 1http://physics.colorado.edu/phys3070http://physics.colorado.edu/phys3070Judah LevineJudah LevineJILA SJILA [email protected]@colorado.edu303 492303 492--7785 (27785 (2--7785)7785)M,F 11M,F 11--Noon, W 1Noon, W 1--3 pm3 pmalso by appointmentalso by appointmentJudah Levine, 3070L12 2Special Special ““officeoffice””hourshoursTuesday, Starting at about 5:30 pmUMC, opposite Baby Doe’sJudah Levine, 3070L12 3CAPA 4 #1CAPA 4 #1An inventor claims to have developed a wonderful new heat engine that operates with a relatively cool (and therefore nonpolluting) flame at 150 degrees Celsius, and discharges waste heat to the environment at 20 C. His promotional literature advertises that 45 percent of the fuel energy is converted into useful work. Calculate the maximum efficiency that can be expected for such an engine. (If your answer is 45 percent, enter .45) (Is he scamming you or not?)Judah Levine, 3070L12 4CAPA 4 #1CAPA 4 #1307.0693.14232931129320273423150273=−=−=−==+==+=HLLHTTefficiencyKTKTJudah Levine, 3070L12 5CAPA 4 #2CAPA 4 #2The Valmont Power station has a 150 MW coal fired heat engine generating electricity for Boulder. The high temperature furnace is at around 900 degree F, the cooling pond might be around 50 F. What is the Carnot efficiency (i.e. the BEST possible efficiency the plant could possibly have for generatingelectricity?) (If your answer is 45 percent, enter .45)Judah Levine, 3070L12 6CAPA 4 #2CAPA 4 #2First, convert 900 F to K:KCKCFC2.7552732.4822732.4828.1329008.132=+=+==−=−=KCKCFC28327310273108.132508.132=+=+==−=−=Convert 50 F to K:625.02.75528311 =−=−=HLTTeJudah Levine, 3070L12 7CAPA 4 #3CAPA 4 #3The plant, in reality, has an efficiency only half of what you just calculated (due to friction, losses, etc) Given that the power OUTPUT is 150 MW, how much coal (in tons) do they have to burn every day? (Note: the efficiency is not .5, it's 0.5 times the answer to the previous part) (Please do not enter units. If the answer is 2 tons, enter 2.) (Use the energy equivalent for coal given in the front flyfleaf of your text)Judah Levine, 3070L12 8CAPA 4 #3CAPA 4 #3daytonsjouletondayjouledayhrhrjouleWWeffoutputinputeff14751081.211015.41241min60min1sec60sec108.479108.479313.010150313.0625.05.01013666=××××××××=×===×=Judah Levine, 3070L12 9CAPA 4 #4CAPA 4 #4A single train car might carry about 90 tons of coal. Given your answer to the previous question, how many train cars/day arrive at the Valmont power plant? (Does your answer seem reasonable?)daycarstonscardaytons174.169011475 ==×Judah Levine, 3070L12 10External combustion enginesExternal combustion enginesQQHeat is added to gas outside of the Heat is added to gas outside of the cylindercylinderQQHot, high pressure gas enters engine, Hot, high pressure gas enters engine, does work against piston or against fan does work against piston or against fan bladesbladesQQCooler, lower pressure gas is exhaustCooler, lower pressure gas is exhaustQQWater/Steam is very favorable systemWater/Steam is very favorable system––Lots of energy at given temperatureLots of energy at given temperatureJudah Levine, 3070L12 11“Original recipe” Steam EngineCamValveBoilerJudah Levine, 3070L12 12Steam EngineExhaustSecondcylinderhereValveBoilerJudah Levine, 3070L12 13Diameterof the bladesincreases aspressure dropsSteam inputLarge exhaustducts tominimize backpressureExhaustJudah Levine, 3070L12 14Gas turbine engineGas turbine engineQQRelative of a jet engineRelative of a jet engineQQFuel burned at the input to the turbineFuel burned at the input to the turbineQQHot gas exhaust drives turbine bladesHot gas exhaust drives turbine blades––Serious corrosion and materials problemsSerious corrosion and materials problemsJudah Levine, 3070L12 15Internal combustion engineInternal combustion engineQQFuel is burned inside the cylinderFuel is burned inside the cylinder––Rapid increase in pressure and Rapid increase in pressure and temperature exerts force on pistontemperature exerts force on pistonQQSmaller for comparable output powerSmaller for comparable output powerQQConflicting requirements hard to satisfy Conflicting requirements hard to satisfy in a single cylinderin a single cylinderJudah Levine, 3070L12 16The Otto cycle engine The Otto cycle engine --11AirPistonConnecting rodFlywheel/crankshaftGasIntake strokeAir/gasdrawn inFlywheelDrives pistonJudah Levine, 3070L12 17The Otto cycle engine The Otto cycle engine --11AirPistonConnecting rodFlywheel/crankshaftInjectorIntake strokeAir/gasdrawn inFlywheelDrives pistonJudah Levine, 3070L12 18The Otto cycle engine The Otto cycle engine --22AirPistonConnecting rodFlywheel/crankshaftGasCompressionstrokeAir/gasheatedFlywheelDrives pistonJudah Levine, 3070L12 19The Otto cycle engine The Otto cycle engine --33AirPistonConnecting rodFlywheel/crankshaftGasPowerstrokeAir/gasexplodesPistonDrives flywheelTHJudah Levine, 3070L12 20The Otto cycle engine The Otto cycle engine --44AirPistonConnecting rodFlywheel/crankshaftGasExhaust gasesExhaust Forced outFlywheelDrives pistonCompressionRatioJudah Levine, 3070L12 21WhatWhat’’s wrong with the Otto cycle?s wrong with the Otto cycle?QQPower stroke is 1 stroke out of 4Power stroke is 1 stroke out of 4––1 power stroke for 2 revolutions1 power stroke for 2 revolutionsQQFlywheel drives piston for the other 3Flywheel drives piston for the other 3QQStored flywheel energy ~ (rpm)Stored flywheel energy ~ (rpm)22QQEngine cannot run at low rpmEngine cannot run at low rpm––Minimum about 600 rpmMinimum about 600 rpmJudah Levine, 3070L12 22WhatWhat’’s wrong with the Otto cycle?s wrong with the Otto cycle?QQEfficiency is about 25%Efficiency is about 25%--30%30%––Exhaust gases are HOT and corrosiveExhaust gases are HOT and corrosive––Engine cooled with water (or air)Engine cooled with water (or air)••Some cogeneration recoverySome cogeneration recoveryJudah Levine, 3070L12 23WhatWhat’’s wrong with the Otto cycle?s wrong with the Otto cycle?QQIncreasing efficiency pushes towards Increasing efficiency pushes towards higher compression ratios and higher compression ratios and combustion temperaturescombustion temperatures––Increases NIncreases N22O, NO, NOO, NO, NO22, HNO, HNO33……––Makes preMakes pre--ignition problem worseignition problem worseJudah Levine, 3070L12 24The Diesel cycle engine The Diesel
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