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SAE TECHNICALPAPER SERIES 1999-01-2564
Optimized Thermal Design of Small TThermoelectric Generators
James W. StevensMississippi State Univ
The 34th Intersociety Energy ConversionEngineering
Conference
Vancouver, British ColumbiaAugust 2-5, 1999
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1999-01-2564
Optimized Thermal Design of Small T ThermoelectricGenerators
James W. StevensMississippi State Univ
Copyright 1999 Society of Automotive Engineers, Inc.
ABSTRACT
The daily variation in air temperature is large comparedwith the
temperature changes a short distance below thesurface of the
ground. In theory, a heat engine can bearranged to produce
electricity from this temperature dif-
ference. In practice, the thermal efficiency of such adevice
will be low because of the small temperature dif-ferences involved.
An energy harvesting device couldproduce sensor-scale amounts of
electrical power byusing a thermoelectric generator operating
between theair and ground temperatures. This paper describes a
pro-posed ground-air thermoelectric heat engine along with
aprocedure for the approximate optimal design of such adevice.
Simple design and performance equations basedon thermal resistances
of the thermoelectric module andcold- and hot-side heat exchangers
are derived and pre-sented.
INTRODUCTION
Thermoelectric devices are used in a wide variety ofapplications
for portable or remote power generation andheat pumping. Inasmuch
as thermoelectric generatorsfunction as heat engines, they are
subject to the Carnot
limitation on efficiency: . Hence,
many applications seek higher generator efficiency bystarting
with large temperature differences across thedevice. Nevertheless,
some niche applications have beenproposed which might use the
comparatively small Tavailable from waste heat or ambient sources
to power a
thermoelectric generator producing modest amounts ofpower. One
such proposal would generate power fromthe difference between the
fluctuating daily air tempera-ture and the relatively constant
ground temperature. Therelatively small temperature differences
involved (T
