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201 Lecture 11

# 201 Lecture 11 - Energy Considerations and Fuels 1 A Energy...

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Energy Considerations and Fuels A. Energy and Units Primer Energy and energy units 1. Energy expressed as a finite quantity § Joule (J) = SI unit of energy = (force)(distance) = (1 N)(1 m) § British Thermal Unit (Btu) = English unit of energy § 1 Btu is the energy required to raise the temperature of 1 lbm of water 1° F @ 68° F § Basic energy quantity in English system? § 1000 J = 1 kJ; 1 Btu = 1.055 kJ BSE 201 Lecture 11 1

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Energy Considerations and Fuels A. Energy Primer Energy and energy units 2. Energy expressed as a rate § Rate of energy is the same as power=energy per unit time § 1 Watt = 1 Joule/sec 1 kW = 1000 Joules/sec § 1 horsepower (hp) = 550 ft-lbf/sec = 0.7068 Btu/sec § Conversion: 1 hp = 745.7 W = 0.74570 kW § Example: a typical car currently 200 hp. In Europe, this would be a 150 kW engine BSE 201 Lecture 11 2
Corvette ZR1 BSE 201 Lecture 11 3 2012 Corvette ZR1: 638 hp = 475.8 kW! 0 – 60 mph in 3.4 seconds top speed is 205 mph

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Energy Considerations and Fuels A. Energy Primer Energy and energy units 3. Energy rate vs. finite quantity § Electrical power: since kW are a rate, then your electrical bill needs to be a finite quantity : § (energy)/(time)*[time] = finite quantity (energy) § So, the rate of 1 kW for 1 hour = 1 kW-h § Your electric meter keeps track of this automatically § Currently: 1 kW-h ≈ \$ 0.065 in PNW § In Connecticut, 1 kW-h ≈ \$0.20! BSE 201 Lecture 11 4
Energy Considerations and Fuels A. Energy Primer Energy and energy units 4. Mass vs. force quantities: MASS ≠ WEIGHT! § kg = basic mass unit in SI system; 1 Newton (N) = force unit in SI § lbm = basic mass unit in English system § lbf = “pounds force” = basic force unit in English system BSE 201 Lecture 11 5 F = ma g c g c

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