March 13, 2009 - This is now a heat machine 23Latm our 17...

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March 13, 2009
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This is now a heat machine 23Latm our 17 used to return piston at colder temperature 23-17 = 6 = extra work available to turn a wheel. Summary draw in heat at hot temperature and it does work T constant so no ΔE Total work divides into useful work and heat returned to surroundings (waste heat of power plant fame) when compressed at lower T ( T c )
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Main equation Work done/heat absorbed at T h = w/q h = (T h –T c )/T h For T h = 400K and T c = 300K w/q h = (400 -300)/400 = ¼ 0.25 of all the heat converted to useful work (anther name – free energy)
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2 = ¼ (1000) = 250J Remainder 750 J is waste heat. If pull in 1000J of heat at T h = 400
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Greater fraction turned to work if T h is higher Steam engine water vapor 400K surroundings 300K ¼ of energy used Diesel T h =500K w/q h = (500-3)/500 = 200/500 = 0.4
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Extreme case solar energy T h = T sun = 6000 • T earth = 300K w/q h = (6000 – 300)/6000 = 57/60 = 0.95 of solar energy received could potentially be turned into work
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Use T h = 300K (room temperature) T c = 270K 0C,
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