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Physics 161:
Physics of Energy and the Environment
Prof. Raghuveer Parthasarathy
Fall 2008
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
November 4, 2008
R. Parthasarathy
University of Oregon
Fall 2008
Lecture 10: Announcements• Vote: Don’t forget!
• Reading: Wolfson, Chapter 5
• Problem Set 5: (posted on‐line later today)– Due NEXT Thursday, November 13, 5pm.
• Midterm:
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
We *have not* finished grading the midterm, but are on track to finish by Wednesday. I therefore can't comment much today, but I'll certainly discuss it at length in class on Thursday. Sorry to keep you in suspense. For now, all I'll say from our preliminary work is that some people did well; some did poorly; and many results surprise me. I'll be trying to learn from all this how to structure the rest of the course.
R. Parthasarathy
University of Oregon
Fall 2008
Advice• One comment now:
• Be sure to study your lecture slides / notes. (I’m sure many of you do this; it’s clear that many do not!)
• “Study” does not mean “glance at while doing other things,” but rather “read carefully within a day or two of class; annotate; ask yourself whether you could explainmaterial to others.”
• If you don’t understand: ASK. This is your responsibility. If you don’t ask, I have two options:– assume you understand the material
– assume you’re too lazy to care
– (None of the above? How would I know?)
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Advice
• Does the following look familiar?
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Hydroelectric powerPhysics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
• ΔEgrav=ΔEkinetic=ΔEelectric
• Power = ΔEgrav / t = Mgh/t = (M/t)gh
Rate of mass flow (e.g. in kg/s). Could write ΔM / Δt
Consider a h = 100 meter dam, and perfect conversion of energy.
What mass flow rate would give 1 kW of electrical power generation?
R. Parthasarathy
University of Oregon
Fall 2008
Hydroelectric powerPhysics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
• Power = (M/t)gh
• 1000 W = (M/t) (9.8 m/s2) 100 m
• 1000 W = (M/t) (10 m/s2) 100 m
• 1000 W = (M/t) 1000 m2/s2.
• (M/t) = 1 kg/s
• Units? Consistently SI, so must be kg/s; or could express W in terms of kg, m, s.
≈ 10 m/s2
R. Parthasarathy
University of Oregon
Fall 2008
Advice
• Exact slides from lecture 5!
• Exceptionally similar to a midterm problem!
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Advice
Procedure:
A. Review notes
B. Do I understand this?
Yes: Good.
No: Ask for help. (Or study with classmates)
C. Solve similar problem on exam.
D. “But I can’t solve the problem.”
Are you sure your answer to B is correct?
(More Thursday)
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Last Lecture• ≈ 85% of our energy comes from Fossil Fuels• Fossil Fuels: Hydrocarbons (molecules composed of carbon and hydrogen) formed from the decomposition of organisms long ago
• Long ago = hundreds of millions of years – i.e. long accumulation of stored chemical energy
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Fossil fuels• Fossil fuels
– Coal
– Oil and Natural Gas
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Petroleum• Petroleum: Oil and Natural Gas
• Ancient marine life → ocean floor sediments. Pressure, temperature → rock + organic liquids and gases
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
PetroleumPetroleum: these liquids and gases, though often used to refer to liquid onlyR. Parthasarathy
University of Oregon
Fall 2008
Petroleum• Petroleum in many sedimentary rocks: typically useless
• Accumulates in porous rock, trapped by impermeable rock
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Petroleum
• In these rare geological structures, useful reservoirs of petroleum. (Useful = economically feasible)
• How to find these deposits? – Not easy!
– Reflections of sound waves, for example
– Only 1 in 10 exploratory drillings strike oil
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
PetroleumHistory: First oil well• 1859, Titusville Pennsylvania
• “Colonel” Edwin Drake
• Many active oil seeps in the area
• Many wells had previously struck oil. The problem: they didn’t want oil, they wanted water!
• Drake’s well: 69 feet.
• Oil → kerosene
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
PetroleumPetroleum: What is it?• A mixture of hydrocarbons
• The gas part: natural gas– mostly methane, CH4 (the simplest, lightest hydrocarbon) [Remember]
– [Draw: CH4]
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
carbon
hydrogen
from “World of Molecules”
Size 4 × 10‐10 m
R. Parthasarathy
University of Oregon
Fall 2008
PetroleumPetroleum: What is it?• A mixture of hydrocarbons
• The gas part: natural gas
• The liquid part: crude oil– various components (and impurities: sulfur, oxygen) must be separated to generate useful products: refining
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Petroleum Products
Note: higher molecular weight→ higher boiling point
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Roofing, pavingResidue in boilerHighPitch and tar
CandlesMelts at 52‐5720 and upParaffin (wax)
LubricationSemisolid18 and upGreases
LubricationAbove 35016 to 20Lubricating oil
Furnace OilUp to 37515 to 18Fuel oil
Stove, diesel, jet fuel175 to 27512 to 16Kerosene
Motor fuel30 to 2005 to 12Gasoline
Solvent; dry cleaning30 to 905 to 7Petroleum ether
Gaseous fuel‐164 to 301 to 5Gas
Typical usesBoiling point (°C)# CarbonsFraction
R. Parthasarathy
University of Oregon
Fall 2008
Gasoline• In gasoline
– e.g....
– heptane C7H16 [draw]
– octane C8H18 [draw]
– nonane C9H20 [draw]
– decane C10H22 [draw]
• (Greater octane / heptane ratio → less “knocking” in engines)
• Energy content ≈ 50 MJ / kg [Energy released from chemical bonds (chemical energy)}
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
carbon hydrogen
R. Parthasarathy
University of Oregon
Fall 2008
Petroleum Products
Petroleum isn’t just for burning
≈ 7% (in “Other”) →lubricants, roadmaking, petrochemical feedstocks
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Petrochemical Feedstocks•→ Plastics! (& countless medicines, paints, food ingredients, and other chemicals)
• Why? Organic chemistry: Carbon
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Poly‐methyl‐methacrylate, i.e. “acrylic glass,” “plexiglass”
A polymer: chainlike, repeating molecule
[Draw]
A future view of petroleum use... “Did they actually burn such valuable stuff?”
R. Parthasarathy
University of Oregon
Fall 2008
Petroleum Products
Note: higher molecular weight→ higher boiling point
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Roofing, pavingResidue in boilerHighPitch and tar
CandlesMelts at 52‐5720 and upParaffin (wax)
LubricationSemisolid18 and upGreases
LubricationAbove 35016 to 20Lubricating oil
Furnace OilUp to 37515 to 18Fuel oil
Stove, diesel, jet fuel175 to 27512 to 16Kerosene
Motor fuel30 to 2005 to 12Gasoline
Solvent; dry cleaning30 to 905 to 7Petroleum ether
Gaseous fuel‐164 to 301 to 5Gas
Typical usesBoiling point (°C)# CarbonsFraction
R. Parthasarathy
University of Oregon
Fall 2008
Distillation• How do we separate these components of crude oil? (Note the different boiling points) [Ask]
• Fractional distillation– vaporize crude oil (> 400 °C)– vapor goes to a tower with a temperature gradient (T changes with height)
– vapors condense at various points along the tower, depending on their boiling point
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Distillation• Fractional distillation
– vaporize crude oil (> 400 °C)– tower with a temperature gradient
– vapors condense at various points along the tower, depending on their boiling point
• In the diagram, does T increase or decrease going from bottom to top along the tower?
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
A. increase
B. decreaseenergyinst.org.uk
R. Parthasarathy
University of Oregon
Fall 2008
Distillation• In the diagram, does T increase or decrease going from bottom to top?
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
A. increase
B. decrease
Cool a bit: heavy hydrocarbons become liquid; drawn off
Cool more: next lighter hydrocarbons...
Cool more: ... kerosene... gasoline ...
Lightest molecules remain gas even at coolest temperatures, at top
energyinst.org.uk
R. Parthasarathy
University of Oregon
Fall 2008
Distillation• (Pictures)
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
energyinst.org.uk
Distillation unit, CorytonRefinery, UKOil Refinery near Rodeo, SF Bay
area, California, USA – QT Luong
R. Parthasarathy
University of Oregon
Fall 2008
Coal• Coal: From decaying plant matter, on land, 100’s of millions of years ago.
• Acidic swamps. Ferns, etc. decay (anaerobic, without O2); compressed into layers → peat.
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
cut peat, Scotland. (photo: U. Wyoming)
R. Parthasarathy
University of Oregon
Fall 2008
Coal• Coal: From decaying plant matter, on land, 100’s of millions of years ago.
• Acidic swamps. Ferns, etc. decay (anaerobic, without O2); compressed into layers → peat.
• Geology: Buried further. Slowly...– Temperature, pressure
– Most oxygen, hydrogen leaves
– A black solid: Coal
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Coal• Coal: Trapped chemical energy from long‐dead plants
• Mostly carbon
• Many varieties, grades– e.g. anthracite, ≈ 80% carbon
– e.g. bituminous, ≈ 50% carbon– the rest is oxygen, hydrogen, sulfur, ...
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
(an example of a chemical structure of coal. Each vertex is a C. [Wikipedia: Karol Glab])R. Parthasarathy
University of Oregon
Fall 2008
ReviewWhat is this a structure of?
A. methane
B. hexane
C. octane
D. coal
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
CH
HH H
R. Parthasarathy
University of Oregon
Fall 2008
ReviewWhat is this a structure of?
A. methane
B. hexane
C. octane
D. coal
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
CH
HH HC
H
HCH
HCH
HCH
HCH
HR. Parthasarathy
University of Oregon
Fall 2008
Carbon• Carbon forms four chemical bonds
– bond: a pair of shared electrons that “connect”atomic nuclei
– some bonds are “double bonds,” indicated by double lines [none shown so far]
• 4 bonds at each C (shown: hexane)– some C‐C
– some C‐H
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
CH
HH HC
H
HCH
HCH
HCH
HCH
H
R. Parthasarathy
University of Oregon
Fall 2008
ReviewArrange methane, hexane, and decane by hydrogen‐to‐carbon ratio. (Can you do this without counting atoms?)
A. all are the same
B. decane > hexane > methane
C. hexane > methane > decane
D. methane > hexane > decane
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
ReviewArrange methane, hexane, and decane by hydrogen‐to‐carbon ratio. (Can you do this without counting atoms?)
A. all are the same
B. decane > hexane > methane
C. hexane > methane > decane
D. methane > hexane > decane
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
4H / 1C 14H / 6C – certainly < 4!
All C’s except ends have 2 H per C. Longer → ratio approaches 2
> Coal (lots of C)
R. Parthasarathy
University of Oregon
Fall 2008
Burning
• Why is the relative amount of H vs. C important?
• Let’s see what it means to burn a fuel... (i.e. combustion)
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Burning• Burning: a chemical reaction
• Burning methane:CH4 + 2 O2 → CO2 + 2 H2O + Energy
• Meaning:
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
1 methane molecule
Combines with 2 oxygen molecules (each O2 has two oxygen atoms)
... to form...
one carbon dioxide (CO2) moleculeand 2 water molecules
and release energy*
* 55 MJ per kg of methane
R. Parthasarathy
University of Oregon
Fall 2008
Burning• Burning: a chemical reaction
• Burning methane:CH4 + 2 O2 → CO2 + 2 H2O + Energy
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
and release energy*Note:
• Total energy is conserved – same on both “sides”
• Left side (before burning): more chemical energy
• Right side: Chemical energy “released,” i.e. can be converted into other forms (typically thermal)
* 55 MJ per kg of methane
R. Parthasarathy
University of Oregon
Fall 2008
Burning• Burning: a chemical reaction
• Burning methane:CH4 + 2 O2 → CO2 + 2 H2O + Energy
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Note:
• Chemical elements are conserved (except in nuclear reactions)
• So 1 C atom on left side means there must be 1 C on the right side. Also: 4 O atoms on left, 4 O on right; etc.
• If you’re unaware that molecules are made of atoms, that H2O is 2 H and 1 O, please don’t tell me.
R. Parthasarathy
University of Oregon
Fall 2008
Burning• Burning: a chemical reaction
• Burning methane:CH4 + 2 O2 → CO2 + 2 H2O + Energy
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Note:
• Chemical elements are conserved (except in nuclear reactions)
• Necessarily: 1 methane molecule → 1 CO2 molecule
R. Parthasarathy
University of Oregon
Fall 2008
Burning octane• Burning octane:
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O + Energy• Equivalent to
C8H18 + 12.5 O2 → 8 CO2 + 9 H2O + Energy,but non‐integers are usually frowned upon
• Note # atoms of each element are balanced on each side of the equation
• 1 octane molecule → 8 CO2 molecules
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
and release energy*
* 48 MJ per kg of octane
R. Parthasarathy
University of Oregon
Fall 2008
Burning• In general:
hydrocarbon + # O2 → # CO2 + # H2O + Energy# = various numbers, to balance the equation
• CO2, H2O, and energy are the products!
• CO2: The major greenhouse gas; → climate change
• H2O: mostly harmless
• Energy: What want. Energy from breaking C‐C and C‐H chemical bonds (& forming C‐O and H‐O bonds)
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Burning• In general:
hydrocarbon + # O2 → # CO2 + # H2O + Energy# = various numbers, to balance the equation
• CO2, H2O, and energy are the products!
• All the carbon from the hydrocarbon → CO2
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
So: you should be able to figure out the following:
R. Parthasarathy
University of Oregon
Fall 2008
Carbon emissions
Arrange methane, hexane, and coal by carbon dioxide emission per molecule burned, starting with the most emission (i.e. > means “more CO2
emission than...”)
A. all are the same
B. coal > hexane > methane
C. hexane > methane > decane
D. methane > hexane > coal
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Carbon emissions
Arrange methane, hexane, and coal by carbon dioxide emission per molecule burned
A. all are the same
B. coal > hexane > methane
C. hexane > methane > decane
D. methane > hexane > coal
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Coal: lots of C per molecule; Methane: only one (→ 1 CO2)R. Parthasarathy
University of Oregon
Fall 2008
Carbon emissions
Arrange oil, natural gas, and coal by carbon dioxide emission per molecule burned, starting with the most emission (i.e. > means “more CO2
emission than...”
A. all are the same
B. oil > coal > natural gas
C. coal > oil > natural gas
D. natural gas > oil > coal
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008
Carbon emissionsCO2 is the major greenhouse gas (will discuss more later). I.e. it’s bad!
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
Natural gas emits less CO2 than other fossil fuels.
Should examine per unit of energy, rather than per molecule; trend still holds (Fig.)
Unfortunately, there’s lots of coal...
R. Parthasarathy
University of Oregon
Fall 2008
Burning• In general:
hydrocarbon + # O2 → # CO2 + # H2O + Energy# = various numbers, to balance the equation
• CO2, H2O, and energy are the products!
• A key point: CO2 is an unavoidable product of fossil fuel combustion! If there’s combustion, there’s CO2 emission!
Physics 161:Physics of Energy and Environment R. Parthasarathy Fall 2008
R. Parthasarathy
University of Oregon
Fall 2008