Exam 1 Cheat sheet Complete Solution
USA Energy Use
• 38% of energy goes to transportation
• almost all transportation energy comes from
... [Show More] petroleum
• Gasoline is most used – gas and diesel make up 86% of energy used in trans.
• Industrial energy use – Boiler Fuel- generate steam or hot water; Process heat- raise temp. of products in manufacturing process; Electricity - for lighting, running motos etc
• Chemical industry uses the most energy, petroleum refining second most- metal industry uses the least
• Most energy in commercial sector goes to space heating, then lighting next
• Electricity and natural gas are most common energy sources in commercial
• Most home energy goes to space heating, then lighting and appliances
• Biggest factor in home heating and cooling is weather
• HDD- heating degree days – energy used to heat homes
• CDD- cooling degree days- energy used to cool homes
• R value measures insulating property of material (resistance to heat flow)
• Increase R value by adding more thickness or changing material
• Natural Gas used the most for home heating – Easy clean up (no ash), pipe lined to home
• Geothermal heat pump exchange heat with earth
• Refrigerators consume 5% of energy at home- move heat from inside (low temp) to outside (high temp) called “heat movers”
o How it works: Compressor – compresses refrigerant gas which raises its pressure and temperature; heat exchange pipes (outside) expansion valve - moves refrigerant from high pressure to low pressure; heat exchange pipes (inside); refrigerant- liquid that evaporates to create cold temp
o Lighting – used as one fourth of home energy; Incandescent light – two connections and a coil gets hot producing light; Halogen light bulb- uses halogen gas that makes it bright and give off lots of heat – used for security, display lighting, sports events; fluorescent light bulbs- electrons flow through the tube, excite mercury and give off UV radiation – very efficient
Energy Accounting
• Most manufacturing and food businesses involve adding value to raw materials – involves energy like cooking and processing which can cause unapparent energy cost
Global Energy Use
• Most of global energy use is petroleum, coal, then natural gas
Doubling Time = .7/rate of change
Energy Efficiency
• Efficiency = (Useful Energy Output)/(Total Energy Input)
• Laws of thermodynamics (reiterated from 9/8/14)
o Conservation of Energy
Energy can neither be created nor destroyed; it can only be transformed from one form into another
o Energy moves from high temperatures to low
In any conversion of energy from one form to another there is always a decrease in the amount of useful energy
The least useful form of energy is low temperature heat
• Electric things are very efficient; incandescent light bulbs are not – on exams
• System Efficiency
o The efficiency of a system is equal to the product of efficiencies of the individual devices (sub systems)
o No energy conversion device is 100% efficient, so the useful energy form the system is guaranteed to be less than the energy required to make it run
Energy Transformations
• Conduction -Items must be touching for conduction- Liquids and solids
• Radiation- Sense energy even though not touching
• Convection -Heat in air travels to cooler air and warms the air up
Thermodynamics- The study of heat energy Weather; Air conditioners; Jet engines, auto engines; Home heating
Energy vs. Power-Energy is the amount “the ability to do work” - Power is the rate or speed of the energy flow
• Power- Rate at which work is done, the rate of the energy flow
o 550 ft-lbs/sec=1 horsepower; One joule per second=Watt
• Getting anything done takes work or energy; Energy/work is released when things come undone
• Mostly this released energy is random and undirected – heat
• Efficiency of space heater – electricity 24%; fuel oil 53%; natural gas 70%
Nuclear Energy – e=mc^2
• Fission – break apart large nucleus: Fusion – Combining two small nuclei
Energy quality Ranking
1. Electricity 2. Mechanical 3. Chemical 4. Heat
Kinetic Energy
• Energy that is possessed by a body due to its motion
o 38% of energy Americans used in 2011 was for transportation
• Energy is definded as “capacity to do work”
o Work = force x displacement
Heat energy
o Kinetic energy of random motion of molecules of a substance
o Temperature is a measure of motion
o Easier to obtain heat than to produce work
o Heat flows from a body at higher temp to a body at lower temp.
• BTU – British Thermal Unit is the amount of energy required to raise temperature of 1 pound of water by one degree Fahrenheit
o Small; ex: a match
• calorie – the amount of heat energy needed to raise the temperature of 1 gram of water by 1 degree Celsius
o 1 kilo calorie (kcal) = 1000 cal = 1 food Calorie
Work and Heat
• Heat can be converted to Work or mechanical energy
• Work can be converted to heat energy
Chemical Energy
• Energy that is stored in chemical bonds that hold molecules together
o Hand warmers
Nuclear Energy
• Energy locked in the nucleus of atom and is released by destruction of mass, also called mass energy
o E=mc^2 [Show Less]