What do you think is Liang doing?

THERMOELECTRIC ENERGY CONVERSION

ROBERTO DIMALIWAT, GALENA PARK HIGH SCHOOLGALENA PARK ISD

PROFESSOR/MENTORCHOONGHO YU, PH.DMECHANICAL ENGINEERING DEPT.TEXAS A & M UNIVERSITY

LIANG YIN, GRADUATE RESEARCH ASSISTANT

Nano-Energy Laboratory Principal Investigator: Dr. Choongho Yu

Graduate Assistants: Liang Yin, Yeontack Ryu, Kyungwho Choi, Marion Okoth, Vinay Naranunni,

Wongchang Park, Daniel Mcleod Research Focus: Thermoelectric energy conversion Photovoltaic energy conversion Energy Storage Thermal Managements Design and Fabrication of Nano MEMS Systems and Biomedical Devices

Introduction

Thermoelectric Energy Conversion • Thermoelectric Effect direct conversion of temperature differences to electric voltage and vice versa.• A thermoelectric device creates a voltage when there is a different temperature on each side. •Thermoelectric devices presently use“bulk materials”.

• While all materials have some nonzero thermoelectric effect, it is typically too small to be useful.

• Materials which are sufficiently cheap and have strong thermoelectric effect can be used for large-scale thermoelectric applications.

• Thermoelectric effect are based on the Seebeck effect and Peltier effect .

Seebeck effect - is the conversion of temp. differences directly into electricity.

Peltier effect - When a voltage is applied to the different sides of a device, it creates a temperature difference

Temp difference = electricity

Voltage difference =Temp difference

Let’s see how it works http://www.thermoelectrics.caltech.e

du/demos_page.htm

The research Thermoelectric energy conversion• Study of the electrical and thermal

characteristics of nanowires, (SiGe). •The objective is to find out whether the nanowires have similar thermoelectric properties as bulk materials.

• OR are there some differences in these materials to make devices that we can use to improve our way of living?

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• The energy conversion efficiency depends on the dimensionless figure of merit of thermoelectric materials, ZT, ZT= S² σT/k• Currently, the low ZT values of available materials restrict the efficient applications of this technology.

• However, significant enhancements in ZT were recently reported in nanostructured materials.

• Higher ZT is mainly due to their low thermal conductivities..

T = average temperature σ= electrical conductivity

S= seebeck coefficient k= thermal conductivity

The higher the ZT, the higher the efficiency

• Thermoelectric devices using bulk materials applications are limited, producing devices with low efficiency.

• If waste heat can be harnessed and used in devices with higher efficiency, then it will economically and environmentally impact the way we use the earth’s resources.

• Exploring the small scale materials can bring answers to the efficiency problem.

That is Y the Research

Experimental Set Up

How does the set up work?

The Micromodule

The micro module under the optical microscope

What measurements are taken?

Independent variables: Temperature differenceControls The seebeck effect constant is

established The electrical conductivity is

establishedDependent variable: Thermal conductivity

ZT= S² σT/kT= average temperature

σ= electrical conductivityS= seebeck coefficient

k= thermal conductivity

http://www.thermoelectrics.caltech.edu/

Present Findings

Temperature(K)

0 100 200 300 400

Ther

mal

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)

• 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 increase.

ZT= S² σT/kZT is inversely proportional to thermal conductivity

This research can lead to the use of nanowires in thermoelectric devices with higher efficiency than devices using bulk materials.

Now, maybe we know what Liang is doing!

The Future

Liang’s car is partially powered by heat generated from its exhaust….cooooool

How will I use this in my classroom? I am designing an experiment using a

Peltier module to show thermoelectric energy conversion, that is, a temperature gradient will produce voltage strong enough to make a motor run. The flip side will be, the students will design an experiment to show that the process is reversible using some of the original materials plus a few additions.

Concepts/TEKS – There is a lot of Physics and Chemistry concepts involved in this activity. I will outline them in detail in the final presentation

Acknowledgements Choongho Yu, Ph.D Mechanical Engineering

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