Thermoelectric Energy Conversion

• Thermoelectric devices use “bulk materials” with low figure of merit, ZT (efficiency)

ZT= S² σT/k • Study of the electrical and thermal characteristics of nanowires, • The objective is to find out whether the nanowires can replace bulk materials, to produce devices with high ZT.

T = average temperature σ= electrical conductivity

S= Seebeck coefficient k= thermal conductivity

The higher the ZT, the higher the efficiency

• SiGe nanowires have lower thermal conductivity than bulk materials.

• As the nanowires get smaller, the thermal conductivity lessens.

• electrical conductance tends to be constant with temperature change, thus the possible efficiency improvement ZT= S² σT/k

Temperature(K)

0 100 200 300 400

The

rmal

con

duct

ivity

(W/m

K)

0.1

1

10

100

Si nanowire 115nm5

Ge nanowire 115nm32

Core-shell Si0.29Ge0.71 NW2(133nm)

Core-shell Si0.50Ge0.50 NW3(181nm)

Core-shell Si0.19Ge0.81 NW1(132nm)

Si Einstein modelGe Einstein model

SiGe Einstein model

Si/Si0.7Ge0.3 superlattice film40

Si0.5Ge0.5 Bulk 15

Si0.4Ge0.6 Bulk15

Core Si0.19Ge0.81 NW1(96nm)

83nm Si/SixGe1-x nanowire41

Si0.9Ge0.1 film40

Core Si0.29Ge0.71 NW2(109nm)

Results

Physics and Chemistry TEKS/TAKS

Physics TEKS 7B – methods of heat energy transfer. Physics TEKS 5D – conservation of energy &momentum. Physics TEKS 6E – design and analyze electrical circuits Physics TEKS 7A – laws of thermodynamics. Chemistry TEKS 5A – changes in matter, the nature of charge, and the forms of energy. Chemistry TEKS 6A – properties of subatomic particles TAKS Objectives 4 & 5

http://www.tea.state.tx.us/index3.aspx?id=3839&menu_id=793

Hook

The Class Project: Energy Conversion and Conservation

Day 1: 1. Hook: Get responses and write on board2. Do the Pre Test. 3. A short PPT on energy, the different kinds,

conservation and transformation using mechanical energy as an example.

4. Discuss the experiment and do parts A (see attached).

Days 2and 3. 1. Do Part B and C and students to finalize data and

graphs and write the report. 2. Answer Part D. (Questions) See attached.Days 4 and 5. 1. Discuss the lab results. 2. Problem Solving WS3. Discuss Liang’s slide4. Post Test

Experiment Set up

http://www.youtube.com/watch?v=h570lWTqXOU&feature=related

The experiment (10 groups of 2 to 3 students per group)

Objective: To measure how the difference in temperature varies with the voltage generated in a thermoelectric module.

Materials (per group) 1 Peltier module 1 clip 2 aluminum plates 1 motor with fan blade 2 transparent plastic containers Hot plate Ice cold water Voltmeter 2 Thermometers    

Part A   1. Place the module between the 2 aluminum plates and secure it with the clip. 2. Connect the wires of the module to the wires of the motor. 3. Place the motor on top of the assembly and attach

the fan blade 4. Pour hot water on one of the plastic containers and

ice cold water on the other one. 5. Place the containers side by side and dip the

aluminum plates, with one side on the cold water and the other side on the hot water. 6. Rotate the fan and observe what happens. Record

your observation

Part B   1. Turn on the hot plate and heat about 500ml of water 2. Remove the assembly from the water. 3. Remove the motor/fan connection. 4. Replace the connection with a voltmeter. 5. Empty the plastic containers and place the assembly in

the containers just like in Part 1. 6. Put ice cold water in one container and hot in the other. 7. Measure the temperatures on both and record. 8. Measure the voltage on the voltmeter and record. 9. Replace the hot water with hotter water from the hot

plate . 10. Measure the temperature and the voltage

11. Repeat the process with different temperatures for

about 5 times. 12. Record and graph your data.  

Part C. Is the process reversible?   1. Using the same materials, design an experiment to check whether the process is reversible. 2. What other materials do you need? List them down

and justify why you need them for. 3. Present the experiment setup and procedures to

your teacher for approval. Include the list of additional materials you would need. 4. When you get approval, perform the experiment

and gather your data. 5. Analyze your data and write out your report. 6. What are some possible uses of the module and

what possible applications can the concept of

thermoelectric energy conversion have in your life?

Part D. Post Lab Assessment

Answer the following questions:

1. What did you observe on the fan when the assembly is placed in the water bath? __________________________________________________________

2. Explain in terms of energy, what is happening?_________________________

________________________________________________________________

3. Explain your data for Part 2. ________________________________________

________________________________________________________________

4. Explain the graph. ________________________________________________

________________________________________________________________

5. Compute for the slope of the graph ___________________________________

6. Is the process reversible? Explain your answer. ________________________________________________________________

Assessment (Pre and Post) Sample Questions:

1. In thermoelectric energy conversion, as the temperature difference increases, the voltage

a) stays the same

b) decreases

c) increases

d) decreases exponentially

2. The conservation of energy states that a) energy cannot be created nor destroyed b) can be transformed from one kind to another c) total energy in a closed system is constant d) all of the above

Acknowledgements

E3 Team Choongho Yu, Ph.D Mechanical Engineering

Dept ,TAMU Liang Yin, Graduate Assistant National Science Foundation Nuclear Power Institute Texas Workforce Commission Chevron