Modeling and Sizing a Thermoelectric Cooler
Within a Thermal Analyzer
Jane Baumann
C&R Technologies, Inc.Littleton, Colorado
Thermoelectric Device
Thermoelectric coolers are solid-state devices 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
A typical thermoelectric module is composed of P-type and N-type elements between ceramic substrates 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
Historically, modeling of a TEC device was left up to the analyst 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 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
SINDA/FLUINT definition 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 Define surfaces for substrate Define TEC contact between the surfaces Define input mode, aspect ratio, and number of couples
SINDA/FLUINT Methods
SINDA/FLUINT calculates cooling capacity and electrical power required
Heat pumped at cold side
Maximum temperature differential
Can define several independent TEC devices Can stack multiple devices for additional cooling
capacity or create multistage coolers
An Example
Sample Application* 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
Device to be cooledCeramic substrates
Heat sink
Model development 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
Optional inputs Can model core fill
in TEC if desired
TEC Input
Simple user interface Provide input mode
Current Voltage Power
Aspect ratio Number of couples Select cold side Select hot side
Optional inputs Generate conductors Temperature control Non-bismuth telluride
devices
TEC Sizing Study
Key input parameters for cooler definition 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
Thermal Desktop can handle complex thermal/fluid connections Minimum current, voltage, or power, 4 amps (max 6 amps)
Key output parameters Temperature of hot and colds substrates Aspect ratio Number of couples Optimum input current, voltage and power
TEC Sizing Study
Setup design sweeps on key parameters Aspect ratio range
Looking at TEC specifications, aspect ratios range from 0.1 to 0.4 cm
Number of couples 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
Design point of 5C for device 120-130 couples 127 couples
standard Wish to minimize
aspect ratio to reduce heat path through the device Aspect ratio less
than .25
Design Point
Aspect ratio=0.1
Aspect ratio=0.15
Aspect ratio=0.2
Aspect ratio=0.3
Aspect ratio=0.25
TEC Selection
Need to be able to generate a 40C temperature differential DTmax > 40C
Design Point
Maximum cooling capacity Qmax between 35-55 watts
TEC Selection
The Melcor CP1.4-127-06L meets the requirements and footprint required for our example
CP1.4-127-06L specifications 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
Applied a time varying environment
Set proportional control in on cold side at 5+2C
Transient Response
For this sample we can demonstrate full control of the TEC device when exposed to the defined environment (3C<cooler.T115<7C)
Conclusion
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