ENGR 102PROBLEM SOLVING FOR ENGINEERS

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March 6, 2018

I N T O / C S U P A R T N E R S H I P

ENERGY & THERMODYNAMICS

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OBJECTIVES FOR ENGR 102

1. Work in a typical US university environment

2. Understand and solve engineering word problems

3. Analyze data and present engineering information

4. Understand several engineering concepts

5. Ability to use an engineering problem solving process

6. Use software tools: Microsoft Excel and MATLAB

7. Describe jobs in different engineering disciplines

8. Describe courses needed to graduate as an engineer

Source: athenadr.files.wordpress.com

Today’’’’s topics:

• Project:

• Energy storage

• Thermodynamics

• MATLAB

• Flowcharts

• Exam 2

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ASSIGNMENT 11(Due before 12 noon on Tuesday, March 6)

1. Number of students in this class = __13__

2. Students with homework on time = __12__

3. Number of students with full credit = __8__

4. Students with all answers correct = __1 almost__

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How to find a typical problem that you’re interested in.

1. Review the job description

2. Think of an interesting task a person working in this job might need to do, . . .

or, something that you think is interesting that demonstrates the skills required for this job.

3. Review your idea with Professor Bert, Cristian, Hein, Julio, or Akbar

Note: you cannot have the same problem as one of the samples.

PROJECT STEP 7, PART 1:Identify a typical problem that you would need to solve if you were hired to do the job you selected for this project.

YOUR PROJECT PROBLEM

NAME JOB TITLE 7-Step Problem (Question 7)

Abdulla Al Hajri Civil engineer/Hull & Associates Needs revision

Al Muataz Al-Mamari Electrical Eng / Boeing satellites Needs revision

Hamad Al-Mohannadi Software engineer/Apple Needs revision

Marzouq Al Kindi Mechanical CAD/ Calmax Maximum & minimum hole clearance

Sylvia (Yuxuan) Dai .NET Software developer Needs revision

Jean Dumas Organic medicinal chemist Needs revision

Haibing Huang Electrical Eng / Dredging robots Needs revision

Michael Liu Avionics for satellites / Boeing How system can fly without crashing

Yiyee Ooi Mechanical design / Tesla Air drag and electric motor efficiency

Fan Si Electrical design / Boise ID Phone can turn off home computer

Minh Tran Mech design / Boeing bombers Energy from hybrid airplane engine

Yuhe Wu Environmental Eng /Los Angeles What will you calculate?

Harry (Wenhan) Zhao Civil engineer / Transit systems Need revision

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Energy: Power:Capacity to perform mechanical work Energy rate (per unit of time)

A. SI energy B. SI power C. Non-SI energy D. Non-SI power E. Other

Watt second (Ws)

Degree Kelvin (OK) Calorie (Cal or kcal) BTU (British Thermal Unit)

Horsepower (hp)

Newton (N)

Kilowatt hour (kWhr)

Foot pound (Ft lb) Joule (J)

Watt (W)

Quad (1015 BTUs)

Exajoule per year

?

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1 kWhr = 3.6 MJ

= 860.4 kCal

= 3410 BTU

1 kg oil = 11.6 kWhr

1 gallon of gasoline = 32.8 kWhr

1 BTU = 1055 J

ENERGY and POWER

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Which is smallest?A. JouleB. kWhrC. Gallon of gasolineD. kCalE. BTU

Which is largest?A. Kg of oilB. kWhrC. Gallon of gasolineD. kCalE. BTU

UNDERSTANDING ENERGY UNITS

1 kWhr = 3.6 MJ

= 860.4 kCal

= 3410 BTU

1 kg oil = 11.6 kWhr

1 gallon of gasoline = 32.8 kWhr

1 BTU = 1055 J

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2000 2040203020202010 2050 2060 2070 2080 2090 2100

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ASSIGNMENT 10

4. Define these words (6 words maximum) per definition:

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a. Potential energy:

b. Kinetic energy:

c. Internal energy:

d. Chemical energy:

e. Nuclear energy:

DEFINITIONS, EQUATIONS, AND EXAMPLES

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DEFINITIONS, EQUATIONS, AND EXAMPLES

a. Potential energy: gravity, springs, magnets, capacitorsmgh (for gravity), ½kx2 (for a spring), (position can do work)

b. Kinetic energy: velocity can do work½mv2

c. Internal energy: temperature difference is usefulQ=mC(∆T) Internal energy can also be defined as “heat”

d. Chemical energy: burning, photosynthesis, batteriesExample: CH4 + 2O2 = CO2 + 2H2O + 802 kJ/mole

Changing molecular bonds can do work

e. Nuclear energy: atom bomb, fusion, fission

E=mc2

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SAMPLE WORD DEFINITIONS

Internal energy

force x distance

Never created or destroyed

Entropy cannot decrease in closed system

Useless energy

Useful output/input

Energy/time

Useful cooling/input

Mass exchanged with environment

Mass does not cross boundary

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ASSIGNMENT 11(Due before 12 noon on Tuesday, March 6)

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SOLVING THERMODYNAMICS PROBLEMS

1. Make sure you clearly understand the problem.

2. Draw a diagram of the energy flows.

3. Write the equations (theory).

4. List any assumptions.

5. Solve the equations.

6. Check answer for right units & significant digits.

7. Make any further comments, if needed.

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EFFICIENCY

Figure 16.6Energy losses in a typical steam power plant

Overall Efficiency =Useful output

Total input

This steam plant uses 1 unit of fossil energy to produce 0.33 units of work available at the generator.

There are further efficiency losses in the electrical generator.

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FIRST LAW OF THERMODYNAMICS(Conservation of Energy)

In a non-nuclear process, energy can never be created or destroyed.

Closed System Open System

Heat (Q)Work (W)

Heat (Q)Work (W)Mass (E2-E1)

Examples: Sealed balloon Example: Gasoline engine

Equation: 1Q2 = (U2-U1) + 1W2

Where: 1Q2 = heat added

1W2 = work done

(U2-U1) = change in internal energy

Equation: 1Q2 = (U2-U1) + (E2-E1) + 1W2

Where: 1Q2 = heat added

1W2 = work done

(U2-U1) = change in internal energy

(E2-E1) = change in energy from mass flow

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Overall (System) Efficiency = (Engine Efficiency) x (Generator Efficiency)

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Overall (System) Efficiency = (Engine Efficiency) x (Generator Efficiency)

About ½ of input power lost in

engine

About ½ of remaining power lost in generator

About ¼ of initial power is available

as electricity

Note: many light bulbs are less than 10% efficient in producing light.

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SECOND LAW OF THERMODYNAMICS

The energy not available to do useful work can only increase.

Entropy

Give some examples of conserved energy, but increased entropy:

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SECOND LAW OF THERMODYNAMICS

The energy not available to do useful work can only increase.

Entropy

Examples of processes with conserved energy and increased entropy:

• Friction (work converted to heat)

• Mixing materials at different temperatures without extracting work

• Creating heat by deforming a material (work converted to heat)

• Electrical resistance (batteries heat when charged because of this)

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CARNOT EFFICIENCY, REFRIGERATION AND HEAT PUMPS

• Carnot process: an ideal process that converts thermal energy to work with no increase in entropy.

• Carnot efficiency is a function of the relative absolute temperatures between two objects.

• Carnot efficiency = 1 – TL/TH in degrees K

• What does this mean for heat engines, heat pumps, & refrigerators?

Source: universe-review.ca

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CARNOT CYCLE(Theoretically most efficient thermodynamic process)

From 1 to 2:-- Reduce pressure

-- Keep temperature same (high)

-- Requires adding heat

-- Removes work from system

From 2 to 3:-- Reduce pressure

-- No heat added or removed

-- Pressure decreases

-- Removes work from system

From 3 to 4:-- Increase pressure

-- Keep temperature same (low)

-- Requires removing heat

-- Requires adding work to system

From 4 to 1:-- Increase pressure

-- No heat added or removed

-- Pressure increases

-- Requires adding work to system

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Carnot engine efficiency formulas can calculate the maximum heat energy available to do useful work. They are based on temperature differences.

CarnotEngineHot side

(TH)

Work

Qheat2

Qheat1

Cold side (TL)

Maximum work: Work = Qheat1 (1 – TL/TH)

Maximum efficiency:

Work/Qheat1 = 1 – TL/TH

Conservation of energy:

Qheat1 = Work + Qheat2

ASSIGNMENT 11(Due before 12 noon on Tuesday, March 6)

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ASSIGNMENT 11(Due before 12 noon on Tuesday, March 6)

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ASSIGNMENT 22(Due before 12 noon Friday, October 25)

Gasoline engines operate like a Carnot engine, but aren’t as efficient. Efficiency = (rate of work out)/(rate of heat value in):

Engine

Rate of

work out

Qout

Rate of heat

value inEfficiency: Wout / Qin

Conservation of energy:

Qin = Qout + WoutQin

Generator

Electrical

Power out

Qout

Wout

Rate of

work in

Win Pout

Efficiency: Pout / Win

Conservation of energy:

Win = Qout2 + Pout

A generator is the same as an electric motor operating backwards:

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MEANING OF CARNOT EFFICIENCY, REFRIGERATION AND HEAT PUMPS

• Heat engines: convert heat to mechanical work: Hotter engines are generally more efficient Efficiency limited by max material temp for turbine engines

• Refrigerators/air conditioners: work to heat flow Can produce more useful cooling out than the amount of

mechanical work put into them. Maximum ratio is a function of temperature Refrigeration Efficiency = RE = 1 / (TH/TL –1) Example between 0OC and 20OC: RE = 1 / (293/273 –1) = 14

• Heat pumps: convert mechanical work to heat flow Converting high temperature fuel to electricity and then using

an “air conditioner in reverse” is more efficient for heating a house if the outside temperature is not too cold.

Hot side

(TH)

Carnot engine efficiency formulas can calculate the maximum heat energy available to do useful work. They are based on temperature differences.

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CARNOT ENGINE EFFICIENCY & REFRIGERATION EFFICIENCY

CarnotEngineHot side

(TH)

Work

Qheat2

Qheat1

Cold side (TL)

Maximum work = Qheat1 (1 – TL/TH)

Maximum efficiency:

Work/Qheat1 = 1 – TL/TH

Conservation of energy:

Qheat1 = Work + Qheat2

Refrigerator or Heat Pump

Work

Qheat2

Qheat1

Cold side (TL)

Maximum Qheat2 = Work / (1 – TL/TH)

Maximum refrigeration efficiency:

Qheat2/Work = 1/(1 – TL/TH)

Energy conservation:

Qheat1 = Work + Qheat2

Refrigerators and heat pumps run opposite of a Carnot engine. They take work and produce a temperature difference. The maximum efficiency calculations are also based on temperature differences.

An electric motor converts electrical energy to mechanical work. There are losses (friction, electrical resistance, etc) that result in heat.

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ELECTRIC MOTOR EFFICIENCY & HEATER THERMODYNAMICS

ElectricMotorElectrical

energy

(Joules or kWhr)

Work

Qheat1

Qin Work = Efficiency • Qin

Conservation of energy:

Qheat1 = Qin- Work

Qheat1 = (1-Efficiency) Qin

Energy conservation:

Qheat = QinHeater

Chemical or

electrical

energy

(Joules or kWhr)

Qin Qheat

A normal heater, such as a natural gas heater, converts chemical energy to heat. An electric heater converts electrical energy to heat.

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ASSIGNMENT DUE THURSDAY(See www.engr102.com)

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WHAT’S NEXT(See www.engr102.com)

• Assignment 12: due noon Thursday, 8 March Matrices, MATLAB, and vocabulary

• Assignment 13: due noon Tuesday, 20 March Practice exam

• Exam 2: Thursday, 22 March

• Project Part 2: Thursday, 27 April