# Energy and Environment Spring 1

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How is exporting in energy expected to change?
It is expected that local exports will become more common, reducing exports from other countries
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What's peak oil?
Peak oil, where oil production reaches maximum before decline, then alternative sources needed
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How has human activity changed CO2 levels? (Keeling curve)
We've increased CO2 in atmosphere from 278 ppm to 403 ppm
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What's work formula?
W= Integral of F dl where F resisting force and dl change in displacement
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What is energy?
Energy is capacity to do work
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How do you convert khw to joules?
To convert kwh to Joules, multiply by time in seconds
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What is consequence of insufficient capacity for energy?
If you don't supply enough capacity for energy, system fails
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What do tera, peta, and exa convert to ? (Magnitudes)
Tera - 10^12 Peta - 10^15 Exa - 10^18
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What is a problem with fossil fuel equivalents?
Fossil fuel equivalent energies approximate and rely on fuel source
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What is concept of internal energy?
Transfer from work to heating always occurs in real machines
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What are formulas for energy to raise temp and rate of energy supply in heat transfer?
Amount of energy to increase temp from T1 to T2 Q(J)= c(T2-T1) where c is thermal capacity. Rate of heat flow dQ/dt (W)= K(T2-T1) where K is thermal conductivity
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What is best thermal capacity for buildings?
U value is thermal capacity for buildings, a lower value is better
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What is first law of thermodynamics?
Energy not created or destroyed, transferred from one body to another or form to another
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What is second law of thermodynamics?
A heat engine which generates mechanical energy will also export heat to a cool surrounding
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What is equation for second law of thermodynamics?
Q (energy supplied)= q(heat lost)+W
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What is concept of energy grade?
Energy can't all be re-used, some energy lost as heat. So energy grade falls with time. Not all energy released in process can be put back in
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What is exergy?
Exergy: maximum extractable work (ie- for chemical batteries nearly 100%) Relies on temp of source and sink (ambient)
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What is exergy equation?
Ex/E = 1-T0/T (T0 ambient temp, T hot temp, E energy flow) As temp of source increases, grade of source and exergy does
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What is energy source?
Energy system accepts energy source and converts to flow of different grade
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what are different types of energy? (Losses between each stage)
Primary energy - raw fuel, secondary energy - refined fuel, gas that runs boiler, delivered energy - sum of all energy that reaches meter, useful energy - energy we receive that can be used - gas to heat to water
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What are different efficiencies?
Delivered efficiency= total delivered/delivered energy input, primary efficiency = delivered energy/primary input, exergy efficiency= exergy delivered/input
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Where is exergy most lost in power plants?
In conventional power plant large exergy loss between combustion and steam
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How do CCGT plants increase efficiency?
Combined cycle gas turbine power plant has gas turbine take exergy away to be used to turn turbine
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What are heat pumps? (Reverse heat engines)
Heat pump takes heat from cold sources and passes somewhere that's hot - fridges
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What is a carnot engine?
Carnot engine takes energy flow to do work with some exergy at heat sink where stuff can still be done with it? Q(1-T0/Th)=q(1-T0/Tc)+W exergy out=exergy in
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What is efficiency of carnot engine?
Eliminating q, efficiency of carnot engine = 1-Tc/Th=W/Q
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How does air conditioning, a heat pump, work?
Air conditioning units take heat from cold room (q), do work on it, and release energy Q at condenscer
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How do air to heat pumps raise energy grade?
Air to heat pump takes heat from air, q, adds exergy with pump, W, to raise energy grade
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What is coefficient of performance equation
Coefficient of performance = Q/W (ratio of heat supplied to power)
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Why are heat pumps better?
Heat pump requires only 13% of heat suplied from work, rest from air, so better than resistive heaters
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What is cogeneration?
Cogeneration: temp of sink is raised, reduces amount of energy that can be output as work but means that lower grade q can be used for heaters, not wasted heat
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## Other cards in this set

### Card 2

What's peak oil?

#### Back

Peak oil, where oil production reaches maximum before decline, then alternative sources needed

### Card 3

#### Front

How has human activity changed CO2 levels? (Keeling curve)

### Card 4

#### Front

What's work formula?

What is energy?