Transcript E3 Summer Program 2010

What do
you think
is Liang
doing?
THERMOELECTRIC ENERGY CONVERSION
ROBERTO DIMALIWAT,
GALENA PARK HIGH SCHOOL
GALENA PARK ISD
PROFESSOR/MENTOR
CHOONGHO YU, PH.D
MECHANICAL ENGINEERING DEPT.
TEXAS A & M UNIVERSITY
LIANG YIN,
GRADUATE RESEARCH ASSISTANT
Nano-Energy Laboratory
 Principal Investigator: Dr. ChoonghoYu
 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.
Temp difference
=
electricity
Peltier effect - When a
voltage is applied to the Voltage difference
different sides of a
=
device, it creates a
Temp difference
temperature difference
Let’s see how it works
 http://www.thermoelectrics.caltech.edu/dem
os_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?
Y?Y?Y?Y?Y?Y?
Y?Y?Y?Y?Y?Y?
Y?Y?Y?Y?Y?Y?
Y?Y?Y?Y?Y?Y?
• The energy conversion efficiency depends on the
dimensionless figure of merit of thermoelectric materials,
ZT,
The higher the ZT,
the higher the
efficiency
ZT= S² σT/k
T = average temperature
σ= electrical conductivity
S= seebeck coefficient
k= thermal conductivity
• 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..
• 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 difference
Controls
 The seebeck effect constant is
established
 The electrical conductivity is
ZT= S² σT/k
established
T= average temperature
Dependent variable:
σ= electrical conductivity
S= seebeck coefficient
 Thermal conductivity k= thermal conductivity
http://www.thermoelectrics.caltech.edu/
Present Findings
100
Si nanowire 115nm
Ge nanowire 115nm
Si/Si0.7Ge0.3 superlattice film
10
Thermal conductivity(W/mK)
Si0.9Ge0.1 film
5
32
40
Si0.4Ge0.6 Bulk
40
Si0.5Ge0.5 Bulk
41
83nm Si/SixGe1-x nanowire
15
15
Core Si0.29Ge0.71 NW2(109nm)
Core-shell Si0.29Ge0.71 NW2(133nm)
Core-shell Si0.50Ge0.50 NW3(181nm)
1
Core-shell Si0.19Ge0.81 NW1(132nm)
Core Si0.19Ge0.81 NW1(96nm)
Ge Einstein model
Si Einstein model
SiGe Einstein model
0.1
0
100
200
• SiGe nanowires have
lower thermal
conductivity than
bulk materials.
300
400
Temperature(K)
ZT= S² σT/k
ZT is inversely proportional to thermal
conductivity
• As the nanowires get
smaller, the thermal
conductivity lessens.
•
• electrical conductance
tends to be constant
with temperature
change,
• thus the possible
efficiency increase.
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
 ChoonghoYu, Ph.D





Mechanical Engineering Dept ,TAMU
Liang Yin, Graduate Assistant
National Science Foundation
Nuclear Power Institute
Texas Workforce Commission
Chevron