Transcript Modeling and Sizing a Thermoelectric Cooler Within a

Modeling and Sizing a
Thermoelectric Cooler
Within a Thermal Analyzer
Jane Baumann
C&R Technologies, Inc.
Littleton, Colorado
Thermoelectric Device
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Thermoelectric coolers are solid-state devices
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capable of generating electrical power from a temperature
gradient - Seebeck effect
or converting electrical energy into a temperature gradient Peltier effect
The ability to use TECs to heat as well as cool makes
them suitable for applications requiring temperature
control of a device over a specified temperature range
Although these devices have been around for years,
they are gaining popularity in the aerospace industry for
providing temperature control within optical systems
and loop heat pipe temperature control
Thermoelectric Cooler
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A typical thermoelectric
module is composed of
P-type and N-type
elements between
ceramic substrates
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typically Bismuth Telluride
several couples connected
electrically in series and
thermally in parallel
When current is applied to the device, heat is moved
from the cold side to the hot side where the heat is
typically removed by a conduction or a cooling loop
Modeling TECs
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Historically, modeling of a TEC device was left up to the
analyst
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Hand calculations were performed external to a model using
sizing charts
Simplified modeling in SINDA/FLUINT using a heater node,
user defined array lookups, or user defined logic
New methods for TEC modeling
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Built into SINDA/FLUINT and Thermal Desktop
Steady state and transient simulations
Enable sizing studies and parametric runs
Proportional or thermostatic control options
SINDA/FLUINT Methods
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SINDA/FLUINT definition
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User defines cold side/hot side nodes
Define conductors between the cold and hot sides
Define arrays containing above node and conductor IDs
Define an array of areas associated with conductors
Define input mode (power, current, or voltage)
Define aspect ratio (area/thickness ration of a couple)
Define number of couples
Thermal Desktop simplifies the input
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Define surfaces for substrate
Define TEC contact between the surfaces
Define input mode, aspect ratio, and number of couples
SINDA/FLUINT Methods
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SINDA/FLUINT calculates cooling capacity and
electrical power required
Heat pumped at cold side
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Maximum temperature differential
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Can define several independent TEC devices
Can stack multiple devices for additional cooling
capacity or create multistage coolers
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An Example
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Sample Application*
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Device to be cooled is 1.525 inch x 1.525 inch
Estimated heat load of 22 watts
Maximum ambient temperature of 25°C
Device needs to be maintained 5+2°C
Convection heat sink with a thermal resistance of
0.15°C/watt
* An Introduction to Thermoelectric Coolers, Sara Godfrey, Melcor Corporation
Thermal Desktop Model
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Model development
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Use surfaces or
solids for ceramic
substrates, device
and mounting plate
Convection off
mounting plate at
0.15°C/watt
Create TEC contact
between substrates
Device to be cooled
Ceramic
substrates
Optional inputs
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Can model core fill
in TEC if desired
Heat sink
TEC Input
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Simple user interface
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Provide input mode
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Current
Voltage
Power
Aspect ratio
Number of couples
Select cold side
Select hot side
Optional inputs
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Generate conductors
Temperature control
Non-bismuth telluride
devices
TEC Sizing Study
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Key input parameters for cooler definition
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Maximum heat load of device to be cooled, 22 watts
Maximum allowable temperature of device being cooled, 7C
Maximum environment for cooling hot side, 25C
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Thermal Desktop can handle complex thermal/fluid connections
Minimum current, voltage, or power, 4 amps (max 6 amps)
Key output parameters
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Temperature of hot and colds substrates
Aspect ratio
Number of couples
Optimum input current, voltage and power
TEC Sizing Study
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Setup design sweeps on key parameters
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Aspect ratio range
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Number of couples
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Looking at TEC specifications, aspect ratios range from 0.1 to 0.4
cm
Single stage coolers typically have between 17 to 127 couples
Preliminary selection of the TEC device
Run a parametric on input current
Aspect Ratio/No. of Couples
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Design point of 5C
for device
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120-130 couples
127 couples
standard
Wish to minimize
aspect ratio to
reduce heat path
through the device
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Aspect ratio less
than .25
Aspect ratio=0.1
Aspect ratio=0.15
Aspect ratio=0.2
Aspect ratio=0.25
Aspect ratio=0.3
Design Point
TEC Selection
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Need to be able to generate a
40C temperature differential
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DTmax > 40C
Design Point
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Maximum cooling capacity
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Qmax between 35-55 watts
TEC Selection
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The Melcor CP1.4-127-06L meets the requirements
and footprint required for our example
CP1.4-127-06L specifications
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Number of couples = 127
Geometry factor (aspect ratio) = 0.118 cm
Imax = 6.0 amps
Qmax = 51.4 watts
Vmax = 15.4 volts
Tmax = 67°C
Steady State Results
Parametric Sweep
Input Current
Design point
Transient Simulation
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Applied a time varying
environment
Set proportional control in on
cold side at 5+2C
Transient Response
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For this sample we can demonstrate full control of the TEC device
when exposed to the defined environment (3C<cooler.T115<7C)
Conclusion
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New capabilities have been added to existing software
tools allowing the steady state and transient modeling
of thermoelectric devices
Access to built-in parametric and optimization methods
in SINDA/FLUINT aid in design sizing and device
selection
New features in Thermal Desktop allow the device to
reside in an overall system model for system-level
steady state and transient modeling
SINDA/FLUINT methods have been validated against
published examples and sizing tools provided by TEC
suppliers