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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?
• 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
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
Present Findings
Temperature(K)
0 100 200 300 400
Th
erm
al c
on
du
ctiv
ity(W
/mK
)
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!
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