First Class - · PDF filePatrick Lynch - Mr. Lynch or Patrick - not yet a doctor/professor (April) Syllabus -online - Same book used in ME 400 Use 6th edition of book -5th has wrong

Patrick Lynch - Mr. Lynch or Patrick - not yet a doctor/professor (April)Syllabus - online

Same book used in ME 400-

Use 6th edition of book - 5th has wrong questions

Office hours: Tuesday 4-5 in 1220 MEL, Thursday 3-5 in 336 MEBThermodynamics: how universe works with energy transferSterling engine: heat to workWeekly HMWK - due fridays - do it NEATLY, with computer generated plotsQuizzes on Fridays - every 2 weeks - bring text and calculatorMidterms (2) in class

First ClassWednesday, January 20, 2010

10:55

Notes Page 1

Control mass□

No mass exchange□

Ex: gas in cylinder□

Closed system

No mass transfer (mT) or heat transfer (HT)□

Isolated system (subset of closed system)

Control volume□

Mass can be exchanged□

Ex: pumps, turbines, people (food/air in, CO2/waste out)□

Open system

Systems are separated from surroundings by boundaries

boundaries can move

Selection of boundaries effects type of system

Systems - ignore everything else in universe-

What do we actually study?

Need to do lasers, chemical kinetics …

Microscopic view: Could use individual molecular behaviour, with quantum mechanics, statistics and total description (done in ME 404)

-

Macroscopic view (we will use it): overall behaviour -

Set of properties is a state

Properties: macroscopic characteristics (ex: variables in pV=nRT)-

This change is called a process (a series of states in a system)

Change states: T, n, V: want P to go to 2P-

Cycle: a series of states that repeat themselves and come back to where they were (like cupstacking cycle)

-

Describing systems

The capacity to produce an effect

Translational energy

Rotational

Potential

Adding energy but not going into motion□

Internal energy

In bonds□

Chemical energy

Total energy = E = Ekinetic+Epotential +IE

Energy-

Properties

Correspondence principle: limit of microscopic into macroscopic

These 3 are energy related to motion - in each they are related to the mass

Lecture 1Wednesday, January 20, 2010

11:17

Notes Page 2

HMWK 1 on website (5 problems) - due Friday

Must be in a specific format --

Given-Find-Solution format, then box answer at end-

Graphs: use computer generated ones (can sketch too, but must have the computer one)

-

Homework format

Problems are in American units

Units are Joules (Internal energy is same as IE is same as U)

All depend on mass

KE and PE depend on motion

Energy: E = (KE)+(PE)+(IE)-

Sense of hotness/coldness

With thermometer (mercury/alcohol) - kindergarten way□

Thermocouple - higher temperatures, dissimilar metals - puts out changes in voltage (ME 360)

□

Pyrometry - uses radiation to determine what temperature is (ME 522)□

Measure

Intensive property

Temperature is a unit that tells us if there will be a change when two "blocks" at different "hotnesses" are brought together

Temperature-

Properties:

Intensive property: not dependent on massExtensive property: dependent on massSpecific property: an extensive property divided by mass

Lower case means it is the intensive property of the extensive property.

Bar means molar - this is molecular specific energyThese all have the same temperature

If A is in thermal equilibrium with B and B is in thermal equilibrium with C then A is in thermal equilibrium with C.

Zeroeth law of thermodynamics:

0 C is freezing point of pure water at 1 atm

100 C is boiling point of pure water at 1 atm

Celsius:-

F=1.8C+32

Farenheit scale-

Tabsolute zero = -273.15 C

Tabsolute=C+273.15

It is the Kelvin scale

Absolute scale-

Temperature Scales:

X degrees FahrenheitY degrees CelsiusZ Kelvin (no degrees)

Fahrenheit scale goes to Rankine for absolutes

Extensive property

Specific property: specific volume

Volume-

Mass and volume are easy to measure, so see a lot

Density in liquids (and sometimes solids) is often normalized to density of pure water

Specific gravity: ratio of density to density of water (Hg has specific gravity of 13.6 - more in tables in text)

Start with definition from Physics 211

Pressure-

PropertiesFriday, January 22, 2010

10:56

Notes Page 3

1 Newton is about the weight of an apple□

Units: base is Pascal, 1 Pa=1Nm-2 - extremely small unit

1 bar = 105 Pa

1 MPa = 106 Pa

English units: lbfin2=psi => 14.5 psi~= 1 bar

Often accepted to assume 1 atm ~= 1 bar = 0.1 Mpa

Alternate unit, 1 atm = 1.013 bar□

Pgage=Pabs-Patm◊

This can be negative:◊

Pvacuum=Patm-Pabsolute=-Pgage◊

Difference in pressure from atmospheric is called gage pressure:

Pressure measurements not easy to make on absolute scale - usually done as a difference, often from atmospheric pressure

□

Atmospheric air pressure: 1.013 bar, 101300 Pa (at sea level)

Gives the funny units of pressure: 1" water, 1"HG, 1 mm = 1 Torr□

1 Torr = 33.416 Pa□

Important application: liquid volume

Notes Page 4

Pure substance: has one chemical composition: ex: CO2, H2O, N2, O2 - air and gasoline and vodka are not pure substancesPhase: a quantity of matter that is homogeneous both chemically and physically EX: water (H2O) as solid, liquid and gas (we primarily deal with liquids and gases)

Recall that a state is a series of properties that define a system

Gibb's was the first PhD in America (Yale 1863)-

Number of degrees of freedom = number of compounds - number of phases + 2-

We can't prove until last week of class-

Degrees of freedom: # of variables that can change independently-

Usually written as: F = C - P +2-

C = 1, P = 1, F = 1-1+2=2

This means that if we know two properties the third will be defined

Example: water vapor-

C =1, P=2, F= 1-2+2=1

Therefore if you have one property the other two will be defined

Example: ice water-

C=1, P=3, F = 1-3+2=0

All of them are known at this point

Example: triple point-

Example-

Gibb's Phase Rule

Supercritical fluid: cannot tell the difference between vapor and liquid

If melting line has a negative slope the species expands on freezingIf melting line has a positive slope the species contracts on freezing

Isotherms: constant temperature lines

Isobars: lines of constant pressure on T-V diagram

More Properties: Description of P,V,T systemsMonday, January 25, 2010

10:58

Notes Page 5

Isobars: lines of constant pressure on T-V diagram

2-phase region also known as vapor dome

Points on diagram are states-

If you change something, that is a process - a line on the diagram-

Diagrams:

Process 1-2: compression with pV = constant from p1=1 bar, V1 = 1.0m^3, to V2 = 0.2m^3

Process 2-3: constant pressure expansion to V3=1.0m^3

Process3-1: constant volume

Problem 1: A gas contained within a piston-cylinder assembly undergoes three processes in series.-

Examples:

The critical point is an isobar inflection point

Problem 2: A closed system consisting of 5 kg of gas undergoes a process during which the relationship between pressure and specific volume is pv1.3=constant. The process begins with p1=1 bar and v1 =0.2m^3/kg and ends with p2 = 0.25 bar. Determine the final volume in m^3 and plot the process on a PV graph.

Notes Page 6

DiagramsMonday, January 25, 2010

18:42

Notes Page 7

Notes Page 8

Notes Page 9

Notes Page 10

Notes Page 11

Notes Page 12

Notes Page 13

Notes Page 14

Notes Page 15

Notes Page 16

Only part of homework that needs to be on computer is graphs

dw=F.ds=Fcos(phi)ds-

Work is force times distance-

Work:

Differential notation because (1) they apply at very small changes and (2) they are then path dependent

W=J/shP=745WPS (german horsepower) = 736W

Units of Power

Electric work

Thermodynamic definition of work: Energy exchange equivalent to lifting a weight - requires organized motion of boundaries of a system

System: gas inside the room

Work going into system is negative (done on system)

-

Work going out of system is positive (done by system)

-

Sign notation:

Heat: Energy exchange from a system at one temperature to a system with a lower temperature (note: not equivalent to the lifting of a mass)

-

Heat:

ProcessesWednesday, January 27, 201010:56

Notes Page 17

Heat transfer is microscopic changes in molecular motion - disorganizedAll heating up will never make the cold one move away

(more detail in ME 320)-

Conduction-

Convection-

Radiation-

Three forms of heat transfer

Heat is not shown on pV diagram

Units: Joules, Bru, calories (4.184 Joules, 1 calorie is the heat needed to raise 1g of water from 14.5 to 15.5 C)

Add heat to a system, positive-

Pull heat out then negative-

Sign convention:

Heat transfer by two objects in contact with each other-

Conduction

Heat transfer by bulk movement of a fluid-

Convection

Heat transfer that doesn't depend on anything between the two bodies - can happen in a vacuum -

Strong temperature dependence (difference thereof)-

Everything radiates (presuming it's above 0K)-

Radiation

Work Heat

Organized motion of system boundaries Disorganized molecular motion

W: extensivew: intensive

Q: extensiveq: extensive

Many modes 3 modes

Can see on diagram Not explicit on P-v diagram

Sign: +ve if extracted, -ve if provided Sign: +ve if provideded, -ve if extracted

Summary:

Note: for radiation must use Kelvin, as have T4 (could use rankine, but uncommon -just needs to be absolute)

Notes Page 18

Path dependent Path dependent

Notes Page 19

Work (W) Heat (Q)

Organized motion of system boundaries Disorganized molecular motion

W: extensive (J)w: intensive (J/kg or J/kmol)

Q: extensive (J)q: intensive (J/kg or J/kmol)

Many modes: all of form Only three modes:conduction, convection, radiation

Can see explicitly on P-v diagram Does not appear explicitly on P-v diagram.

Sign: (+) extracted from the system (expansion)

(-) provided to the system (contraction)

Sign: (+) provided to the system(-) extracted from the system

Path dependent Path dependent

Heat always flows from hot to cold

Pick a direction when solving equations, if Q comes out positive the heat transfer direction is correct - sign accordingly, positive if provided to system, negative if extracted from system

Work-Heat comparisonFriday, January 29, 201011:01

Notes Page 20

1st quiz next week in class - 15-20 minutes, will cover HMWKS 1 and 2

Axiom: The amount of work produced in a closed cycle is the same as the amount of heat provided to that cycle.

Clockwise positive workAnticlockwise negative work

Note: unlike Q and W, Q-W does not depend on the path taken, but just on the initial and final states = energy

As in E0=0, then ΔES0=Es-E0=ES-

Can have a reference state of energy

Is dV all that really matters for work?

Balance of heat and workFriday, January 29, 2010

10:59

Notes Page 21

H=U+PV (J)-

H=u+Pv (J/kg)-

Therefore: u=h-pv-

Enthalpy: accommodates the fact that changes in pressure are important

Notes Page 22

In class quiz on Friday - open book, need calculator - chapters 1/2 and a bit of 3

dQ=dW+dU-

dW=pdV, thus dQ=pdV+dU-

Enthalpy, H=U+pV-

dQ=dH-VdP, -VdP is technical work-

First law of thermodynamics:

dq=du+pdV=du

dq=du - additions of heat go directly into internal energy changes

The internal energy changes with Temperature

ΔV=0, constant volume-

a

Note: may also see in per mole forms, (dH)p=ncp(dT)p

Δp=0, constant pressure-

Solids and liquids: cp and cV are approximately constants, and are approximately the same

Substance Specific heat (J/kgK)

Aluminium 900

Steel 480

Copper 385

Water 4180 = 1kcal/kgK

□

Examples (pg850 in text)

Gases,

cp and cV are functions of T and p-

Special cases:

Addition of heat under constant pressure situations go directly to changes in enthalpy.

First law continuedMonday, February 01, 201010:59

Notes Page 23

d

dq=du+pdv => dq=cvdT+pdVdq=dh-vdp => dq=cpdT-vdp

When cp and cv are only dependent on temperature the first law becomes:

Notes Page 24

Notes Page 25

Make sure to do computer generated graphs on homework

Concepts: identifying governing equations, assessing work term, heat term, change in internal energy term…

-

Quiz Friday in class - open book, closed notes, bring calculator

pV=nRT, R is universal gas constant, R=8314 J.kmol-1K-1, can also use mass based unitsi.Equation of state: p,V,T1.

All ideal gasses have this property (converse is false)i.For ideal gasii.

cv and cp (and consequently U and h) are only functions of T2.

Ideal gas is an assumption we often use

Helium (sunny gas)

Neon (new gas)

Ar (slow gas)

Kr (hidden gas)

Xe (foreign gas)

Inert gases (noble gases)-

O2,N2, CO, CO2

Components of air-

In principle gases not close to vaporization (not always true though)-

Gaseous fuels: CH4 (methane), C2H2 (ethyne, but better called acetylene), C2H4 (ethene, better ethylene), C3H8 (propane)

-

Note: not water - it is not an ideal gas - will use steam tables-

What gases are ideal?

Ideal GasWednesday, February 03, 2010

10:58

Notes Page 26

Must use close points to match slope well (eg don't use 650K and 750K)

-

Can do 2D as well, values at T and P can be averaged

-

Caveats:

Notes Page 27

HMWK 3 ready - plots/sketches… must be computer generatedQuiz is 15 minutes

Isopleth, Isochore-

Constant volume process:

Isobar-

Constant pressure process

Isothermal process-

Constant temperature process:

Consequences of Ideal gas approximationFriday, February 05, 2010

10:53

Notes Page 28

No heat transfer-

Adiabatic process

On Monday we will discuss polytropic process, PVn=constant

Notes Page 29

1lbf = 32.2 lb.ft.s-2-

'lb' is same as 'lbm'-

Torr is mm Hg-

Units: will be on website - a description thereof

pVn=constant-

Polytropic process

Constant V-

Constant p-

Constant T-

Adiabatic - constant pV, dQ=0-

Generalized Polytropic -

Consequences of ideal gas assumption

n=0

Isobaric (constant p)-

n=1

Isothermal (constant T)-

n=gamma

Adiabatic (no ΔQ)-

n=infinity

Isochoric (constant V)-

All cases we have gone over are special cases of polytropic process

Units, Quiz, Polytropic ProcessMonday, February 08, 2010

10:54

Notes Page 30

3.75 not on homework anymore

Example: 10g of air at 250kPa, 300 C Piston has a mass of 75 kg, d=0.1mAtmosphere is 20 C and 100 kPa

What is the total heat transfer?a.What is T when the piston detaches from the stops?b.

Cylinder cools to room temperature

2 processesWednesday, February 10, 201011:00

Notes Page 31

Notes Page 32

Pv=RTIsotherms: P=1/v*constant

IG EOS:Non-Ideal Gases:

In this upper region have ideal gas behaviour, that is T>>TC

ΔU? ΔH?How to deal with other properties?

Compressibility, Z = Pv/(RT)Compressibility is the difference from ideal gasZ=1 for Ideal GasZ is a function of how far or close you are from the critical pointReduced pressure: PR=P/PC

Reduced temperature: Tr=T/TC

Compressibility:

Tr>>1, T>>TC-

Pr<<1, P<<PC-

To be an ideal gas:

Only relates P,v,T - doesn't mention ΔU or Δh-

Can't deal with the two phase region-

Compressibility is not the whole story -

Must rely on tabulated values

Use interpolation, pressures 6kPa to 320 barFor each P, lowest T is saturated temperatureFor each row have v,u,h,sBelow saturated temperature must go to compressed liquid tables

Find v, v=1.112e-3 m3.kg-1, therefore 180 C in the tableIf given pho is 900 kg.m-3

, p=20 bar, find T

EX: Start as superheated water vapor (vapor hotter than saturated temperature) - tables on page 821 (A-4)

Tables for this too, table A-2, can look up with either T or P2 phase region:

P and T are not the only inputs, also have phase

BRING TEXT ON FRIDAY

Book has water, refrigerant 134A, ammonia, propane

Non Ideal gasesWednesday, February 10, 2010

11:16

Notes Page 33

Q=W+UEasy: take the whole box

-W1=W2=Q2=-Q1, Q1=W1, therefore ΔU is zeroHard: choose the two parts separately, W1=-W2, ΔU2=U2-U1, W2=Q2, Q1=-Q2,

3.122: could identify system in two ways

For a given P there is a Tsaturated, if T>Tsat then vapor, if T<Tsat then compressed liquidFor a given T, then if P>Psat then liquid, then P<Psat in vapor

Properties in compressed liquid/superheated vapor

=100 bar

Tsaturated is the lowest in saturated vapor table, and highest in compressed liquid

At Tsat and Psat-

Gibb's Phase rule: F=C-P+2-

Also kind of sets v: the properties of the liquid are set and the properties of the gas are set

In this region there is a mixture of saturated vapor and saturated liquid

New property: quality x=mvapor/(mvapor+mliquid)

F=1-2+2=1, so only 1 dof in two phase region - if you choose a T that sets P -

What happens in 2 phase region?

This allows properties to change continuously in the two phase region

Sudden expansion of a non ideal gas1.Example:

2 phase regionFriday, February 12, 201010:58

Notes Page 34

Sudden expansion of a non ideal gas1.

Isochoric heating and cooling of a real gas1.

Find mass and T and P after partition bursts

Notes Page 35

Notes Page 36

Quiz FridayProbably keep a copy of homework

2 phase region-

x=mvapor/mtotal=mvapor/(mvapor+mliquid)-

Quality: the extent to which a substance vaporizes-

x=0 saturated liquid

x=1 saturated vapor

Can be anywhere in between

(Psat,Tsat),-

Given v, u find T, P and x - most difficult case, requires iteration

If in 2 phase region probably need quality to find anything (unless can be calculated)

If state is 'saturated vapor' or 'saturated liquid' then use x - just use the values in the column

Finding properties in 2 phase region-

v=xvgas+(1-x)vliquid

Cancel vliquid since it is essentially 0 (vg>>vf), then x=v/vg

Good approximation far from critical point

Approximate way□

h=xhg+(1-x)hf

h=xhg+hf-xhf

x=(h-hf)/(hg-hf)

This is because hg-hf=hfg, and is in the table as well - in between the saturated liquid and saturated vapor values

◊

This is easiest to do with enthalpy (but can be done with any property)

A more rigorous way□

T=200 C, therefore 852.45=>2793.2 is 2 phase, so this is 2 phase, so P=15.54 bar

h=hf+hfgx, 1730 kJ/kg =852 kJ/kg +x 1941 kJ/kg, therefore x=45%

v=xvg+(1-x)vf= 0.45 * 0.1274 m^3/kg+0.55*0.0115 m^3/kg= 0.058 m^3/kg

Example: T=200 C, h=1730 kJ/kg. Find P, x, v if saturated□

Find quality

Interpolation-

Quality:

5 basic steam table cases online

This is very important for quiz

QualityMonday, February 15, 2010

10:58

Notes Page 37

So far we've studied processes in a control mass system. It is much more useful to study scenarios in open systems - control volumes.

Mass flow rate is conserved-

Mass balance:

Energy is extensive-

Change in energy in a control volume-

Energy balance

All heat sourcesAll work sourcesEnergy flowing in and out of cv (control volume)

Need to separate work terms

1st law analysis of a control volumeMonday, February 15, 2010

11:17

Notes Page 38

CV cannot move1.No accumulation terms and dWcv/dt and dQcv/dt are constant2.

Two things:-

Steady state operation-

Steady State flow processes Passive system = no work done

Wednesday will do passive systems

Notes Page 39

Friday HMWK due + quiz - BRING BOOK, can use1st test is next Friday

Primarily chapter 3-

Inclusive-

Quiz Friday:

Open systems/control volumes

Open SystemsWednesday, February 17, 2010

10:58

Notes Page 40

Notes Page 41

Notes Page 42

Notes Page 43

Many of these - engines, pumps - we will do compressors and turbines-

Recall control mass:-

Active devices: consume or produce work

Put names on assignments (your name) Test next Friday: everything through today - won't test system integrationWill put some problems upMust bring book

Driving force is mass flow rate => does work, turbine-

Can force water with a pump/compressor-

Add power (work) to increase the pressure of a fluid-

Schematic:-

Special case: fluids of constant density (liquid) - called a pump-

Compressor:

Remove work to decrease the pressure of fluid-

Schematic:-

Turbine

Of both turbines/compressors-

Ideally adiabatic devices, but in reality there is heat transfer - still good assumption-

Analysis:

TurbinesFriday, February 19, 2010

10:58

Notes Page 44

Notes Page 45

Format similar to quizzes, conceptual based questions and then problems

Hard way: ΔQ=ΔW+ΔU - can then use coupling (but difficult) - solve for x from Q=m(u2-u1)+mP(v2-v1) => use x eqns

-

Medium way (book): collect terms Q=m(u2+Pv2)-m(u1+Pv1)=m(h2-h1), h2=h1+Q/,=465kJ/kg, therefore in 2 phase therefore T=41 C, get that x=0.85 (piston is ΔV/A)

-

Easy way (class): notice constant pressure, dQ=dH-Vdp, dp=0, dQ=dH-

Identifying systems on quiz

Enthalpy is for no pressure change systemsConstant volume: Q=ΔU+pdVConstant pressure: Q=ΔH-Vdp

Test/QuizMonday, February 22, 2010

10:59

Notes Page 46

Online problems for review - solutions on Wednesday evening

Exam informationMonday, February 22, 201011:00

Notes Page 47

Notes Page 48

Compressor Turbine

hout>hin hout<hin

Pout>Pin Pout<Pin

Power plant has 4 components

Even if we know P4 we cannot yet fully determine state 4 because we cannot yet solve for adiabatic expansion of non-ideal gas. For now will also be given that state 4 is a saturated vapor and state 1 is a saturated liquid and state 2 is close to a saturated liquid.

More active systems - power plantMonday, February 22, 201011:21

Notes Page 49

Notes Page 50

Test Friday - need book, strict time limit - at 11:50 no more writingWill have more office hours tomorrow

Power plant has 4 components

Figure 8.1 in text

Pump increases pressureBoiler creates steamExtract work from turbine to make work

There is a separate condenser loop here tooLow pressure, high enthalpy steam goes into condenser

Back to pump

Integrating of control volume systems:

Important ObservationsWednesday, February 24, 201011:00

Notes Page 51

Notes Page 52

Transient analysis: terms change with timeWe use a special case - uniform state, also called a uniform flow process

Can't move, can't expand (Not a balloon)i.A rigid box is an exampleii.

Control volume is fixed1.

Change in properties is allowed, but has to be uniform - must assume you fill the entire box2.

If there's a moving stream (to fill a box) it does not change. But if you fill something up, it changes.

i.

Example: filling a boxii.

Constant state in areas of flow3.

Assumptions:

Filling a box-

Example:

Final internal energy is streams enthalpy

If ufinal=hinitial, then, T=0 reference state-

Cv(Tf-Ti)=cp(Ti-0)-

Tf=Ticp/cv=kTi-

Ideal Gasses:

Transient analysisWednesday, February 24, 2010

11:27

Notes Page 53

Friday, 12 March will meet in 160 English BuildingAlso will have Quiz 3 then

Exams back on Friday likely

Hot water will not get even hotter in a room temperature roomBalloon will not blow up by itselfBook will not fall upwards1st law: conserve energy

Predicts direction of a process-

Determine theoretical limits of engineering systems-

2nd law of thermodynamics

EX: rivers, lakes, oceans, atmosphere-

Thermal reservoir: special hypothetical body that always remains the same temperature even though is added or removed by heat transfer

Clausius statement: It is impossible to construct a device that operates in a cycle and produces no other effect other than the heat transfer of heat from a lower temperature body to a higher temperature body.

-

Kelvin-Planck statement: It is impossible to construct a thermodynamic cycle to produce work only interacting with a single thermal reservoir.

-

This restricts efficiency to less than 100%

2nd law of thermodynamics statements

Doesn't work

Perpetual motion machine-

Examples

Also, only one thermal reservoir.

2nd law: Spontaneous processesMonday, March 01, 201010:58

Notes Page 54

Could put balloon back together after popping it-

There are no reversible processes (at least not real ones)-

Reversible process: process that can be reversed without leaving any trace on its surrouundings

Friction1.Heat transfer through a finite temperature difference2.

Break a partition in a box, gas spreads, cannot go back to have gas in only halfi.Unrestrained expansion of a gas or liquid3.

Spontaneous mixing4.Spontaneous chemical reactions5.Electric current flow through a resistance6.Magnetism or polarization with hysteresis 7.Inelastic deformation8.

Irreversabilities

Power cycle

Refrigeration cycle

Efficiency cannot be one

Restrict our efficiency -

Effect of irreversibilities

Easy to analyze-

Serve as an idealized model to which we compare real cycles-

Carnot cycle - highest maximum efficiency of every cycle we know of

Can define the Kelvin temperature scale

By combining 4 reversible processes, we can make a reversible cycle and come up with maximum theoretical efficiency.

-

Why discuss reversible processes?

Notes Page 55

It is reversible

1 to 2 Adiabatic compression - very fast

2 to 3 Isothermal expansion, ΔT=0 - very slow

3 to 4 Adiabatic expansion - very fast

4 to 1 Isothermal compression - ΔT=0 - very slow

Efficiency of an irreversible heat engine is always less than the efficiency of a reversible one operating between the same two reservoirs.

-

Efficiencies of all reversible heat engines operating between the same two reservoirs are the same.

-

The Carnot corollaries

Efficiency is independent of the working fluid, type of cycle, or type of reversible engine, since the two reservoirs are characterized by temperature.

Efficiency of Carnot engine

This function can only be satisfied if the function has the form

The Carnot Cycle (or engine)Wednesday, March 03, 201010:58

Notes Page 56

This function can only be satisfied if the function has the form

Must use absolute temperature scale here

Have a diesel cycle operating between TH=2000K and TL=300K.Examples:

Example 2: Find thermal efficiency and amount of heat rejected

Example 3:

Find an expression for the efficiency for a single power cycle operating between T H and TC in terms of the efficiencies of the two cycles here.

Notes Page 57

85+ very good:75+ good understanding50-75 average

Problem mine Out of

1 16 16

2 9 9

3 10 10

4 6 10

5 17 25

6 24 30

total 16+9+10+6+17+24=82 16+9+10+10+25+30=100

My:

4. don't use ΔU, but use ΔH5b. Don't overcomplicate - just do graphically5d. Just use Q=U-W and tables6. read the table correctly

ExamFriday, March 05, 2010

11:02

Notes Page 58

The direction that processes go - if they only go one way, they are irreversible -

Just because something satisfies the first law doesn't mean it can happen:-

Heat flows from hot to cold, not the other way□

Heat transfer through a finite temperature difference

Bursting of a diaphragm □

Unrestrained expansion

But p2<p1, gas/liquid always flows towards lower pressure□

Throttling valve, where Δh=0

Examples-

Irreversibility:

Cycle that has no irreversibilities-

The best such cycle-

No heat transfer => no irreversibility -

dT=0, isothermal heating, no finite temperature difference for heat transfer, so no irreversibility-

Efficiency of Carnot cycle - maximum efficiency-

Only dependent on temperature

Only works for Carnot cycles

-

Carnot cycle

Works when heat is added or removed reversibly, infitesimly small amounts at a time

Arbitrary cycle:

Based on geometry, one can break a reversible cycle into Carnot parts as long as the cycle is also reversible.

ReviewFriday, March 05, 2010

11:12

Notes Page 59

These are numerically integrated and tabulated

Easy to calculateFor an ideal gas?

Entropy is not just a function of T, but also has a log dependence on v. (unlike u, h, c p, cv.

Only puts the part of entropy that depends on temperature, but not the part on specific volume or pressure.

-

's0' is called absolute entropy and is only based on T.-

Table A-22 has ideal gas entropies.

Notes Page 60

HMWK due Friday 16:45 in mailbox - 158 MEBClass Friday cancelledQuiz is take-home, will get it on Wednesday - due same time

Related to disorganized heat transfer and not work: EntropyEntropy:

Calculated and tabulated using first law

Example:-

Entropy and irreversible processes:

Disorganized energy transferMonday, March 08, 201010:59

Notes Page 61

Notes Page 62

Saturated liquid line on left, saturated vapor on right.Has a vapor dome - CP at top

Carnot cycle

Specific entropy

Temperature

2 adiabatic and reversible expansions/compressions2 isothermal heatings/coolings Carnot cycle appears as a BOX on the diagram

Carnot cycle

Notice:

Reversible heat is area under T-S curveFor a cycle, Q=W

Just as pV diagram did - but easier to calculate here for Carnot cycle

So, for a cycle work is area under curve too

Power producingQrev>0,W>0

Clockwise:

Refrigeration cycleQrev<0, W<0 - consumed work

Anticlockwise:

T-S diagram also has enthalpy, pressure, volume, and quality - can calculate internal energy from those -has everything necessary to solve a problem

Very important Topic: TS diagramMonday, March 08, 201011:32

Notes Page 63

Put HMWK in mailbox - 158 MEB, 16:45, as well as take home quiz

Carnot cycle appears as a squareArea under curve gives us Heat (which, in a cycle, gives us Work)Has almost everything

Constant temperature

Isothermal process-

Constant pressure

Isobaric process-

Constant volume processes

Isochoric process-

Different processes on the diagram:

Processes on T-S diagramWednesday, March 10, 2010

10:58

Notes Page 64

Constant enthalpy, decreasing pressure

Much easier on TS diagram

Isenthalpic throttling (Joule-Thompson throttling)-

NOTE: if something is both adiabatic and reversible then it is isentropic

Isentropic expansion/compression-

Also important for passive devices - heat was mass flow rate times change in enthalpy - chart with enthalpy as an axis! - mollier diagram-

Notes Page 65

Mollier: German Changes in enthalpy very important - so this is a useful diagram.Shows relatively high enthalpies/entropies - vapour regionsThere is a vapour dome - but peak is NOT critical point - whole thing is saturated vapour lineIsobars/isotherms parallel in 2-phase region, isochors are NOT

Isotherms-

Isobaric-

Isochor-

Isenthropic throttling-

Active devices (turbine / compressor)

Isentropic expansion/compression-

Processes:

Enthalpy/Entropy diagram (Mollier Diagram)Monday, March 15, 2010

10:58

Notes Page 66

d-

Notes Page 67

HMWK 7: state 2 is a saturated vapour not liquid

Tables1.T-s diagram2.h-s diagram3.

Three ways to solve problems:

Can solve for real devices-

In general, devices are not perfect and deviate from perfectly reversible behavior.-

Heat transfer in turbine/compressor

EX: near the wall□

Leaks do not pass through the turbine blades

Friction in the fluid flow

Other irreversibilities (dead cat)

Irreversibilities:-

Example: -

Imperfect devices:

Imperfect devicesWednesday, March 17, 2010

11:02

Notes Page 68

Notes Page 69

6.40, 6.59, 6.85, 6.115, 6.132 - make sketches on print off of T-s diagram

Carnot-like refrigeration cycle on water vapor. There is a turbine to recover some of the compressor work, but neither the compressor nor the turbine is necessarily isentropic (although they are adiabatic)State 3: 530 C and 50 barState 4: 5 barState 1: same temperature as state 4, 50 kPaState 2: 530 CSeveral parts long

Additional Problem

HMWK 8 - look for email:

He will not be here on Wednesday after break - will be acceptable on Monday afterwards so as to go to office hoursQuiz on Monday (1 week after break - see syllabus)

Can still be adiabatic - loss from leaks, friction, general irreversibilities (dead cats)If still adiabatic not isentropic anymore

Actual processes and devices have irreversibilities

Actual ProcessesFriday, March 19, 2010

10:58

Notes Page 70

Because of fluid mechanics, the isentropic efficiency of a turbine is generally greater than that of a compressor.

Notes Page 71

Differential form of entropy

Even in steady state there is generation of entropy with the production term ENTROPY IS NOT CONSERVED

Entropy balance for control volumes (open systems)Friday, March 19, 2010

11:28

Notes Page 72

Notes Page 73

HMWK 8 due on 2 April, but will be accepted until MondayQuiz will be had - will be slightly less involved than the HMWK

Efficiency - irreversibilities reduce efficiencyControl mass

Entropy and the Second LawMonday, March 29, 2010

10:58

Notes Page 74

Notes Page 75

Notes Page 76

Office hours: Friday, 2 April in 336 MEB, 14:00-17:00-

HW8: due 2 or 5 April-

Quiz: 2 April-

Exam: 9 April-

Announcements:

Efficiency of a Carnot cycle-

Change in entrooy-

For a control volume-

Key concepts of 2nd law and entropy analysis

Review of EntropyWednesday, March 31, 2010

10:53

Notes Page 77

Notes Page 78

Notes Page 79

Quiz today

Next Friday - midtermNext Thursday 3-7pm office hours 336 MEBExam will be through chapter 6 - not chapter 7Turn in HMWK Monday in classOffice hours today 2:15 to 5 pm

3 ways: tables, hs diagrams, Ts diagramsSolving problems with real fluids

Electric motor problem

Friday, April 02, 2010

10:58

Notes Page 80

Heat exchangers□

Throttling devices□

Nozzles and Diffusers□

Mixers□

Passive devices (no work)

Turbines□

Compressors□

Pumps□

Active devices (work involved)

System integration (also using entropy considerations to solve these)-

Chapter 4:

Thermal reservoirs-

Clausius (cannot have a system with only result of HT from cold to hot)

Kelvin-Planck (cannot produce work from interacting with one reservoir)

Second law statements-

Causes of irreversibility

Reversible process

Reversible vs. irreversible-

How you make a thermal Carnot cycle (2 adiabats, 2 isotherms)

Maximum efficiency (for any cycle at the two reservoir temperatures)

What this means for real cycles (lower efficiency)

Real substance, ideal gas, ideal gas + const. specific heat

Power, refrigeration, heat pump

Carnot Cycle-

Chapter 5

Two sources (reversible heat transfer and irreversibilities)

Definition of Entropy Change-

Area representation of HT (and when not appropriate)

Carnot cycle on these

Solving processes

T-s and h-s diagrams-

Chapter 6

Will be practice problems online tonight - solutions WednesdayExam on Friday

Exam 2 Key ConceptsMonday, April 05, 201010:59

Notes Page 81

Rankine cycleSteam cycle (today)

Otto (gasoline)DieselBrayton (gas turbines)

Gas cycles (next week)

Inverted Carnot-Rankine cycleRefrigeration

Overview of cycles (Power generating, Refrigeration)

Referred to as Rankine cycle-

Steam cycle

Note: direction of arrow is positive

Power cycle, therefore clockwise on T-s diagram-

QH>QL - heat adding at boiler much higher than heat losing at condenser, makes sense as QH-QL=Wnet

-

Note importance of enthalpy of vaporization - it impedes our ability to go up in temperature (or down) as we must surpass it

-

The amount of work needed to pump a liquid from 3 to 4 is very low - the specific volumes are very low due to high density and Wpump=vΔp, v is small so not much work -incompressible fluid

-

Liquids aren't good for turbines - want it to run with vapor

Greatly increases QH, but does not increase QL, thus

We need superheat - must super heat the steam to gain a lot of work

-

Notes:

CyclesMonday, April 05, 201011:06

Notes Page 82

increasing work and efficiency

How to make better use of QH-

Sketch -

How to improve the efficiency?

Increase the temperature keeping pressure constant1.

Increase pressure in the burner2.

Costly, but can be done-

2a. Put both together - high temperature and pressure - supercritical operation

Lower the condenser pressure3.

Decreases QL, but very difficult to actually do - would necessitate vacuum pressures

Reheat - If too much QH goes unused4.

Notes Page 83

Notes Page 84

Exergy/availability analysis (chapter 7)-

Thermodynamic equilibrium-

Rudimentary combustion-

Novel automotive trends (increasing efficiency/decrease emissions)-

Climate change-

Which topic for extra time teaching (question on exam, Friday, in class):

Office hours 3 to 7 tomorrow

Relatively inefficient cycle

Use superheati.Increase boiler temperature1.

Somewhat lowers QL rejected at condenseri.Increase boiler pressure2.

May have to operate at least partway in a vacuum - not easy but possible

i.Lower the condenser pressure3.

Taking two passes through the boiler - we like the superheated region here

i.

Can do multiple reheatsii.

Reheat4.

Used when running a power plant and use steam for other purposes too

i.Cogeneration5.

Preheat some of the water that enters into the boiler using some of the steam bled off of the turbine

i.

Requires less heat at the boiler1)Heat transfer is occurring at a higher temperature, and this is inherently more efficient

2)

Increases efficiency for two reasonsii.

Regeneration6.

Increase efficiency by:

1 and 2 are limited by the metal used, can operate supercritically (very high T and p)

throttle it and put it back in the condensera.

Use a double condensate pumpi.Overall, reduce the pumping powerii.Pump the condensate liquid up to intermediate pressure, then combine and pump them both up to the boiler

iii.

If you have a liquid coming out of the cogeneration (at high pressure)b.

Two options:

Increasing efficiency of Rankine cycleWednesday, April 07, 2010

10:55

Notes Page 85

Notes Page 86

ExampleWednesday, April 07, 2010

11:27

Notes Page 87

Notes Page 88

Exam problem 1: most answers for automotive trends - so we will do that for the last few daysExams back Wednesday or Friday - are graded already

Similar to other cycles-

Closed Feedwater Heater

Closed Feedwater heater

Rankine cycleMonday, April 12, 2010

10:58

Notes Page 89

IC = Internal Combustion

Reciprocating engines-

Gas turbines-

www.animatedengines.com-

2 types

Spark plug for gasFuel injector for dieselBore: diameter of piston

At top is clearance volume - least amount possible, called top dead centerAt bottom called bottom dead center, that volume is called the displacement volumeDisplacement volume = Area*stroke

Stroke: distance piston travels

Crank angle: measured from top dead center - CAD (crank angle degrees) - degrees from top dead center

Each stroke is half a rotation-

Power stroke is the one where spark plug ignites-

4 stroke engine:

Gasoline air mixture then ignited-

Delivers power at every rotation-

Intake and exhaust at same time-

2 stroke cycle

Intakes air - at top dead center you inject liquid diesel which expands itself-

Diesel engine

Allowed to do so because gasoline is highly volatile - goes to vapor very easily

Otto: control ignition very well as its spark ignition - fast propagation through the cylinder

-

Called "auto-ignition"

Much more difficult to control

Very active area of research

Diesel: not very volatile - inject it and it burns when it's ready -based on appropriate conditions for T,p, oxidizer concentration

-

4 stroke operation - 2 rotations per power cycle-

2 stroke operation - every rotation gives a power cycle-

Fundamental differences between gasoline (Otto cycle) and diesel (diesel cycle):

Not really a thermodynamic cycle-

Has components but not really a cycle - we continuously replenish gasoline/air and release exhaust

-

We can model it as a cycle because of periodically replenishing the air-

Practically (for the purposes of this class) the working medium is almost entirely air-

Even though Mwfuel=170 kg/kmol, and Mwair= 29 kg/kmol, the mass ratio of mfuel/mair

is approximately 1/15□

Therefore we commonly assume working medium is all air□

We also tend to assume it is IG (for the purposes of this classes we assume cp, cv, and γare constant

□

C12H26+37/(2*.21)*(0.21O2+0.79N2)=12CO2+13H2O+37*0.79/0.42*N2

EXAMPLE: dodecane: C12H26 - typical average formula for a diesel-

Thermodynamic Considerations

Constant cp, cv, and γ - referred to as cold air analysis-

P-v diagram can be used-

Our 2 assumptions:

V2: clearance volumeV1-V2: displacement volumeAt V2: top dead centerAt V1: bottom dead center

2 isochors and 2 adiabats-

Rankine cycle had 2 isobars and 2 adiabats-

For a 2 stroke part merely cut off the A->1 part-

A to 1: intake stroke

1 to 2: compression stroke

3 to 4: power stroke

1 to A: exhaust stroke

Strokes:-

Otto Cycle:

At A open inlet valves-

Go from A to 1 by letting in fuel and air mixture into cylinder (assume constant p)

-

At 1 close the intake valve-

Go from 1 to 2 by compressing adiabatically-

At 2 hit the spark plug-

Burn the gas, and it releases the heat isochorically -

Go 3 to 4 by expanding adiabatically-

At 4 open the exhaust valves-

Go 4 to 1 by isochoric-

1 to A is the exhaust stroke-

At A close the exhaust valves and then repeat-

Cycle:

IC EnginesMonday, April 12, 201011:13

Notes Page 90

Knocking: early autoignition of gasoline

If gasoline goes off by itself, that is bad

High compression ratios give us knock-

BUT lead is hazardous to your health

Limit knocking: add lead to the gas, which limits the propensity to burn-

Switching to unleaded gas means we need lower compression ratios, maximum compression ratio is typically about 8-10

-

87, 91 and 93

Octane tells the propensity of a fuel to resist knocking

Bigger cars tend to need higher octane rated gas - it allows it to reduce the knocking more

Octane rating:-

But there are problems with this:

Notes Page 91

High displacement volume gets high workEg: to get 200HP it is much easier with a 4L engine than a 1.5L engineNeed a metric that factors this size out

Other important calculationsWednesday, April 14, 2010

11:46

Notes Page 92

Diesel, Otto, and Atkinson cyclesHW10 assigned - do number 1 with excel

-

How do we get from work in cycle to power?

How do we get to power?Friday, April 16, 2010

11:01

Notes Page 93

If it is cold outside it may not work as wellThey used to use glow plugs - it's a bit of heat that helps it to ignite when it is cold (10-20 years ago)Now we vary the injection - though some use glow plugs

Here we want and need high compression ratios so that state 2 is high temperature and high pressure - this is NECESSARY - once it's ignited it must burn.

Diesel EngineFriday, April 16, 2010

11:12

Notes Page 94

Otto cycle is limited to compression ratios of 8-10Diesel cycle compression ratios are typically around 20 or moreTherefore the efficiency of a diesel engine tends to be higher as a higher compression ratio lets this happen

Note that real ones are not completely perfect

Notes Page 95

4 stroke 4 cylinder diesel engine. Total displacement of 2000cc and operates at 2000 RPM. qH=1800kJ/kg airAir intake has p1=1 bar, T1=15 C, r=20, cutoff ratio is 2.88Find: net work per cycle, the power, thermal efficiency, MEPHint: cold air standard, constant cp, cv and gamma

Example Diesel ProblemMonday, April 19, 201010:59

Notes Page 96

Compresses the incoming air to high pressure

Compressor-

Burns the fuel and produces high pressure, high velocity gas

Combustion area-

Extracts the energy from the high pressure, high velocity gas flowing from the combustion chamber

Turbine-

Three parts:

It is not strictly a cycle - replenishment like in others

Interested in high T, high P gas - need momentum equations for that (ME 310)-

Used on jet planes

We analyze them for power

Modeled as:

Brayton: two isobars, two adiabatsSame as Rankine cycle, BUT we are compressing a gas rather than a liquidRankine had a phase change, which made liquids very easy to pumpBrayton cycle deals with gas, which is much more costly to pressurize from an energy standpoint

Compare to Rankine cycle

Used as backups, occasionally in small power plants-

Even though they are inefficient, you can get a lot of power-

Turbine just recovers the work from the compressor, BWR ~= 1, maybe less□

Interested in the high T, high p exhaust gas for thrust□

Jet engine

Put on car□

Don't really want a lot of work, just enough to compress air□

Turbocharger

Can also use to convert power

Used in applications which demand high power-

Due to this, gas turbines are expected to be inefficient

Gas Turbines (Brayton cycle)Monday, April 19, 2010

11:18

Notes Page 97

d

Notes Page 98

Make it look more like a Carnot cycle1.Increase the temperature at which we add heat2.Decrease the temperature at which we exhaust3.

Brayton cycle (continued)Wednesday, April 21, 201011:01

Notes Page 99

Notes Page 100

Example 1: Regenerator aloneWednesday, April 21, 2010

11:19

Notes Page 101

Notes Page 102

Example 2: Regenerator + Reheat + IntercoolingWednesday, April 21, 2010

11:39

Notes Page 103

Notes Page 104

Stirling cycle with regeneration

Kind of have two adiabatic processes - heat is transferred through regeneratorHowever, it only works properly with low temperature differences, so not particularly practical

Stirling EngineFriday, April 23, 2010

11:15

Notes Page 105

\\ //\||/

Also called inverted Rankine cycle-

Vapor-compression refrigeration cycle

Therefore it consumes work

Note: this is a refrigeration cycle, therefore it goes anticlockwise (as opposed to clockwise for power cycles)

Fluid inside refrigerator must operate at lower temperature than desired temperature - if operating at 100 C, cannot cool to more than 100 CMust reject heat to a temperature lower than the high temperatureThese are refrigerator design constraints

The important thing about refrigeration cycles are the working fluids, called refrigerants

Not on earth - would have to operate at at least 100 C - at typical temperatures it would be nearly a solid, nearly impossible to move

-

Is water an appropriate refrigerant?

A boiling point below the target temperaturea.Relatively high enthalpy of vaporization, h fg=hg-hf.b.High density, as then it has low specific volume, so lower pumping/compressing requirementsc.High critical temperature - makes peak temperature closer to average temperatured.

Best refrigerants have certain properties

For refrigerants, play with pressures to make it work

B and C mean you can have lower mass flow rates

This required very high pressures

One of first refrigerants was CO2,-

A very good refrigerant - wonderful

Low boiling point, relatively large h fg

Ammonia smells awful at 5ppm□

It could ruin your lungs if you stayed in it for a long time□

Also flammable□

Why not use it?

Later on NH3 (ammonia)-

Chlorofluorocarbons (chlorofluoronates)

EX: freon

Don't use them anymore because of the chlorine - contributes to ozone depletion

Work pretty well as a refrigerant

Then developing refrigerants, first were CFC's-

Hydrofluorocarbons (hydrofluoronates)

Still have chlorine in them, but less

Still have ozone effects

Will we use these in the long term? Probably not.

Then HFC's (mostly used in USA) - still used-

Next step, probably back to CO2 or NH3 - a very active area of research-

A brief history of refrigerants (not time)

Coefficient of performance-

Efficiency of refrigeration cycles

Can be relatively high, 2 to 3

Compressor - compressing gas-

Throttling valve-

Relatively inefficient processes here

RefrigerationMonday, April 26, 201010:57

Notes Page 106

Will use R134a, has properties in book (along with R22 and NH3)Compressor has isentropic efficiency of 80%Want QC=30kWWant TC=4 CFind: all the states, the operating temperatures, the power requirement, the COP

Example: industrial refrigerator

Notes Page 107

Notes Page 108

1 cooling ton = 12,000 Btu/hour1 Btu = 1055 J1 hour = 3600s1 cooling ton = 12,000*1055/3600=3516.6667 J/s

Cooling ton: this is a unit of power

Units in coolingWednesday, April 28, 2010

11:10

Notes Page 109

Constant p in evaporator

Constant p in condenser

2 isobaric processes-

1 isenthalpic throttling-

1 adiabatic compression, possibly isentropic-

We have

Be careful - pressure is on a log scaleHas density rather than specific volume

T-s an dh-s diagrams do not have that problem

Note: the reference point is different than that used in the tables - therefore one cannot go between the two from the p-h diagram

Ideal system that operates between 10 bar and 0.5 bar.-

Use R-134a-

Minimum cooling temperature

Maximum temperature to reject heat into

COP

Find-

Coming out of condenser it is a saturated liquid at high p

Coming out of evaporator it is a saturated vapor at low p

3 to 4 is constant enthalpy

1 to 2 is constant entropy

Solution-

Example:

Easier way to solve refrigeration problemsWednesday, April 28, 2010

11:14

Notes Page 110

Next HMWK is due on 5 May 2010 - on refrigerationThere will be a 'concepts to know' thing onlineFinal exam is on the Monday, 7pm in normal classroom

Reheat: remember that it goes through the boiler several times - must include this in QH.

Same thing as a refrigerator, except you are interested in the heat you can reject in the condenser-

The Heat Pump

Want huge COP's

If operating at -20 C, then won't work in an area with lower temperatures than that - it wouldn't heat your home

This means you need moderate temperature differences to work

In climates such as Florida, this is a very attractive system - it acts as a heat pump and a refrigerator by merely twisting a valve (both heater and air conditioner)

But such a process wouldn't work in many climates (including IL)

The lowest temperature (outdoors) is TL, The highest indoor temp is TH. -

Throttling

Compressing gas - takes a lot more power than pumping a liquid

If we use absorption refrigeration, we can get around this - it generally uses ammonia, NH3

Inefficient processes-

Caveats of heat pumps

Pumping a liquid rather than compressing a vapor, so work requirement is much lower

-

Advantages

Only works with NH3 - there are problems with ammonia-

But this isn't too high, for the generator heat it could be solar or waste process heat or (portable system) use kerosene

For absorber can just use cooling water

Need to add heat to generator and take it out at absorber -this can be an issue

-

Much more complicated - have to pay the initial cost for all these parts - may not be worth it

-

Disadvantages

Working fluid is always a gas-

No phase change-

EXAMPLE: Brayton refrigeration cycle-

Gas refrigeration systemsCan get to really low Temperatures

Refrigerant: air

Have lower cooling capacity-

Dealing with air, so not taking advantages of a refrigerant-

BUT it isn't very efficient

Because that is when air condensesMain advantage is the possibility of extremely low temperatures (~70 K)

Finishing Refrigeration - Other refrigeration systemsFriday, April 30, 2010

10:59

Notes Page 111

Because that is when air condensesMain advantage is the possibility of extremely low temperatures (~70 K)

This is a closed system now, so it is actually a thermodynamic cycle.

Notes Page 112

There WILL be questions on the exam about this

3 important concerns: performance, safety, pollutants-

The bigger it is, probably safer, and higher power, but less fuel efficiency, and pollutes more

Over past 40 years needed to balance these competing pulls-

Huge driver of trends in automobiles and transportation

Often against market forces

Less pollutants and more performance are generally good□

Ideas that are used to be summarily dismissed now are needed to be researched, optimized and implemented

□

Challenges and opportunities (by government…)

Regulations have required the amounts to go down very low - about an order of magnitude multiple times - NOx, PM, Sulphur

Currently Europe is pretty strict, US pretty low - California higher, in between S. Korea, Canada, Australia, China, Japan close to EU in MPG converted to CAFÉ

Regulation-

C8H18+12.5O2=>8CO2+9H2O□

Take combustion of iso-octane:

BUT we live in air, have to add 47N2

What if we are not stoichiometric

Stoichiometric: have just enough fuel and oxidizer to complete combustion

Equivalence ratio:

Lean(Fuel lean): Φ<1: more oxidizer than fuel

Rich(Fuel rich): Φ>1: more fuel than oxidizer

Can control Φwith the carburetor in real life

If we have only 10 O2 molecules for every molecule of iso-octante□

C8H8+10O2+37.6N2=>3CO2+5CO+9H2O+37.6N2□

BAD - now have CO rather than CO2□

Could have other bad molecules□

Also haven't gotten all energy available□

What happens if we burn rich:

If we have 15O2 molecules for every molecule of iso-octane□

C8H18+15O2+56.4N2=>8CO2+2.5O2+9H2O+56.4N2□

Doesn't look bad BUT□

Combustion temperatures may be low□

Are going to end up getting NOx□

What happens if we burn lean

CO, Aldehydes, PAHs - all poisonous□

C2H4, - not harmful to humans, but harmful to plants - a ripening agent□

These come from burning too cool or too rich - not enough oxygen□

Unburned hydrocarbons

Increased respiratory symptoms

Decreased lung function

Asthma

Bronchitis

Irregular heartbeats

Heart attacks

~10microns

This is the actual smoke you see□

These are highly regulated, even those which are 2.5 microns (these are highly regulated too)

□

Formed from low temperature or rich conditions□

Particulate matter (PM)

NOx is the general term for NO, NO2, NO3□

NO is safe, but NO2 is a poison□

NO+O3=>NO2+O2

NO2+sunlight=>NO+O

NO2+O=>NO+O2

Contribute to ozone depletion□

Contribute to acid rain - like sulphur dioxide does□

Thermal NOx - high temperature, slow reaction, lean conditions

Prompt NOx - more quickly than thermal NOx, CN and HCN hydrocarbons, rich conditions, low T conditions

NNH

Bound to your fuels - interesting because companies are currently nitrogenating their fuels in an attempt to make it better (but it also produces NOx)

Formed by four mechanisms□

NOx

1970's and 1980's: LA catalyst for getting smog under control - much better today□

Pictures from outer space often a catalyst□

Secondary pollutant - formed by reactions of other pollutants□

NOx+unburnt HCs + sunlight => PM +O3□

PM is the hazy smoke, ozone near ground level is bad□

Smog

Pollutants-

Historical Perspective

Conflict final on Thursday 13 May 2010 at 13:30 in 256 MEB

Novel Automotive TrendsMonday, May 03, 2010

11:01

Notes Page 113

Exam: Monday 19:00 in 1310 DCL

NOx is the biggest deal now - four mechanisms on previous pageWhat does this mean for engines

Catalysts are surfaces that help reactions without being consumed-

Ceramic core, honeycomb structure, etc.

Alumina overcoat - increases surface area

Precious metals - gold, rhodium (most prevalent), platinum, palladium

There is an underground market for stealing these for the precious metals

Require high surface area structures coated with a special metal - typically-

1980's

2NOx=>xO2+N2□

Reduce NOx

2CO+O2=>2CO2□

Oxidize CO to CO2

Numerous reactions□

Oxidize unburned HC's

TWC works pretty effectively on 3 reactions□

Simple to install□

Advantages

Need to have tight control of temperature and concentration for optimal performance□

Need to run a little rich (wastes gas)□

Hard to take care of NOx on a diesel, but you need catalysts for the soot□

Catalyst poisoning□

Disadvantages

Three way catalyst-

Common now, will be more in future - on most cars

Widely used since 1970's

Some of the exhaust is recycled back into the intake

Instead of just air you now have CO2 and H2O as well, increasing specific heat and lowering temperatures

□

Lower exhaust temperatures - lowers thermal NOx□

Advantages

Inclusion of CO2 and H2O lowers mixture γ, which lowers efficiency□

Increases the amount of PM in diesels□

Smaller power density (can be an advantage, especially in Ottos)□

Disadvantages

Exhaust Gas Recirculation - EGR-

Otto's are great, but have low compression ratio

Diesels are great, but the fuel is injected and burns when it wants, thus little control of temperature or equivalence ratio. Also, typically burns rich and sooty.

Highly volatile□

Mixed well with air in Otto cycle□

Plenty of air everywhere to react□

Premixed□

Gasoline

Not mixed well, fuel has to meet up with air□

Local areas of high concentration fuel□

Diffusion flame□

Diesel

Automotive trends

Next step?-

Ways to fight these

More Novel Automotive TrendsWednesday, May 05, 2010

11:01

Notes Page 114

Higher compression ratio, higher efficiency

Otto to Diesel □

High degree of control

Accurate stoichiometric combustion

Low soot

Low NOx

Three way catalyst

Diesel to Otto□

Yes

Direct injection of gasoline (GDI)

HCCI and other LTC strategies

Are there regiments in between these that could be interesting?-

Gasoline Direct Inject

Instead of mixing gasoline up in the carburetor, only air is brought in and then injects gasoline in a hollow cone of injected fuel

Excellent control of injection and equivalence ratio□

Lower fuel consumption□

Multiple injections□

In theory can do higher compression ratios (in practice gains are lower than anticipated)

□

Less worry about knock□

Advantages

Cost□

Complex components, gasoline fuel injectors□

Higher pressure materials□

Disadvantages

GDI-

Homogeneous Charge Compression Ignition

Ignites in multiple points in the piston-cylinder assembly

Works with any fuel - gasoline, diesel, biofuel…

High compression ratios (r~15)□

Really lean conditions□

Lower fuel consumption□

Low temperature□

Low NOx - almost none□

Advantages

Knock□

Spotty ignition□

Low temperatures mean unburned hydrocarbons□

Higher pressure materials□

Really lean conditions can mean less power□

Lots of factors to control - like valve control□

Disadvantages

Being actively researched - many challenges, but increasingly useful

HCCI-

Notes Page 115

Chapter 1

– closed system – open system/control volume – surroundings – boundary

• Systems and identifying them

– extensive property – intensive property

• properties

– state– process (path)• SI unit system, conversion of units• Specific volume, density, specific gravity• Pressure

Kelvin, Celsius, Fahrenheit and Rankine scale–• Temperature (Zeroth Law of Thermodynamics)

Chapter 2

– kinetic energy– potential energy– internal energy

• Forms of energy

– heat transfer– work– sign convention

• Modes of energy transfer

• First Law of Thermodynamics – Energy conservation Various forms of 1st law:

Q = W + U (particularly useful for constant volume systems) why?

Q = - VdP (particularly useful for constant pressure systems) why?

Consumes or produces work–Direction–

• Energy analysis of thermodynamic cycles

Chapter 3• Phases of pure substances (solid, liquid, gas) • Phase, p-v and T-v diagrams• Enthalpy When to use it?• Specific heats

EOS–What does this say about enthalpy and IE?–

• Ideal gas model

• Closed system process relations (isothermal, adiabatic, const. volume, const. pressure)

Critical point properties, reduced temperature and pressure–• Compressibility factor

– quality– saturation temperature – saturation pressure– superheated vapor

• Two-phase, liquid–vapor mixture

• Using steam tables to determine properties

Chapter 4• Mass flow and volumetric flow rate• Conservation of mass – mass rate balance• One-dimensional flow

How control mass is a special case of general energy law–• Energy rate balance (THE most general eq. of the 1st Law)

Why enthalpy matters and not just internal energy–• Flow work

heat exchangers–throttling devices–nozzles and diffusers–mixers–

• Passive devices (no work)

– turbines– compressors– pumps

• Active devices (work involved)

• System integration (also using entropy considerations to solve these)

Chapter 5• Thermal reservoirs

Clausius (cannot have a system with only result of HT from cold to hot)

Kelvin-Planck (cannot produce work from interaction with one reservoir)

• Second law statements

Causes of irreversibility

reversible processes

• Reversible vs. irreversible

How you make a thermal Carnot cycle (2 adiabats, 2 isotherms)

Maximum efficiency (for any cycle at the two reservoir temperatures)

What this means for real cycles (lower efficiency)

real substance, ideal gas, ideal gas + const. specific heat

power, refrigeration, heat pump

• Carnot Cycle

Chapter 6

Two sources (reversible heat transfer and irreversibilities)

• Definition of Entropy Change

App. 1.5 times length of hour exams - time shouldn't be as much of an issue as on midtermsHMWKS will be available tomorrow in Office hours (10,11,12) -15:00All solutions are online (except tests…)

Final Exam InformationWednesday, May 05, 201010:41

Notes Page 116

Two sources (reversible heat transfer and irreversibilities)

Area representation of HT (and when not appropriate)

Carnot cycle on these

Particularly for active deviceso

Solving processes

• T-s and h-s diagrams

Incompressible substances

Real substance

Ideal gas

• Change of Entropy

• Entropy balance for closed system (entropy production/irreversibility)

directionality

Entropy transfer by flux of mass

• Entropy rate balance for open and closed systems (entropy production)

turbine, compressor, nozzle

• Isentropic efficiencies

Chapter 8

Analyzing Vapor Power systems

turbine, condenser, pump, boiler, heating rate, fuel consumption

thermal efficiency

Deviation between actual vapor power systems and ideal

• Ideal Rankine cycle

Superheat

Boiler pressure

Condenser pressure

reheat

regeneration (open/closed feedwater heaters)

Cogeneration

Integration with other cycles, topping cycle

• Improving performance of the Rankine cycle

Chapter 9

Diagram, displacement volume, stroke, bore, CAD, MEP, etc.

• Engine Terminology

• Thermodynamic model of reciprocating internal combustion engine

How is this not officially a thermodynamic cycle. Why?o

Efficiency, work, power, etc.

• Otto and Diesel Cycles

How is this not officially a thermodynamic cycle. Why?o

Adding non-ideal compressors, turbines, etc.o

• Performance improvements to gas turbines– Intercooling, regeneration and reheat

• Brayton Cycle - gas turbine

• Stirling cycles

• cold air-standard analysis, constant specific heats, ratio, etc.

Why we use throttling valves instead of a turbine?o

Refrigeration cycle vs. power cycle

Environment requirements on condenser and evaporator temperatures.

Loads, cooling tons, etc.

Historyo

Refrigerants

Adding non-ideal compressors, etc.o

P-h diagramo

Analysis of the ideal inverse rankine cycle

COP

Heat pumps, combined heat pump/refrigerators

Absorption refrigeration

Gas refrigeration cycles

Chapter 10

Power requirementso

NOx

Unburned hydrocarbons

PM

Pollution Remediationo

Regulation

TWC-three way catalysto

EGR-exhaust gas recirculationo

HCCI-homogeneous charge compression ignitiono

LTC-low temperature combustiono

Developments and combat strategies

Combining the best components of Otto and Diesel cycles.

Automotive trends:

Notes Page 117