Thermoelectric CoolingThermoelectric Cooling

Team Members:•Mark Campbell•Peter Giles•Andrew Smith•Tom Strapps•Nickolay Suther

Team Supervisor:Dr. Prabir Basu

Client:Greenfield Research

Our ProblemOur Problem

•Create an air bath using thermoelectric modules

http://www.electracool.com

Project RequirementsProject Requirements•Temperature Range

+5°C to +25°C

•Temperature Control +/- 0.2°C

•CostLess than $2,000

ConstructionPhases• Frame• Insulation• Fibreglass inner box• Panels• Heat sink and fan

arrangement • Power supply• Lid

Frame• Constructed of ¾”

square tubing 0.125 wall• Crosspieces cut at 45°

and arc welded• Designed for rigidity and

weight to resist vibration• Dimensions: Width = 35 cm

Length = 50 cmHeight = 35 cm

Fibreglass Inner Chamber

• Used fibreglass because relatively high insulating value and water proof

• Styrofoam plug constructed

• 5 sided Fibreglass cube formed over plug

Insulation

• 2” Styrofoam SM™

• 5 pieces cut and notched to fit inside frame and surrounding fiberglass chamber

• Cut using hot wire with jig

Panels

• Panels constructed of 22 gauge mild steel

• Cut and bent in machine shop

• Holes machined for good fit and appearance

• Aluminum expanded metal spot welded onto fan shrouds

• Two thermoelectric modules• 2 external and 2 internal heat

sinks made from extruded aluminium

• Interior heat sinks each small (50mm) fan

• Exterior heat sinks each with 2 larger 12V fans (80mm)

Heat Sinks and Fans

Power Supply and Display• Back panel cut and

power supply mounted • Sheet metal tray

fabricated and holes punched for ventilation

• Display panel bolted to top panel

• Coloured buttons also on top panel for programming and reset

Lid

• On top for simplicity and better sealing

• Three layers• Sheet metal on top

with handles• Sealed with foam

weather stripping

Testing ArrangementTesting Arrangement

Thermocouple Thermocouple CalibrationCalibration

•Three Thermocouples•Accurate thermometer

•Ice to 30ºC•Sample every 20 sec for 2000 sec

Calibration DataCalibration Data

Read Temperature Record Temperature

Thermocouple Thermocouple CalibrationCalibration

y = 0.9892x + 0.5002

R2 = 0.9995

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Thermometer Temperature (Degrees C)

Th

erm

oco

up

le T

emp

erat

ure

(D

egre

es C

)

Thermocouple Thermocouple CalibrationCalibration

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Thermometer Temperature (Degrees C)

Problem Points due to:•Insufficient mixing•Ice still not melted•Different locations of thermocouples and thermometer bulb

Thermometer Temperature

The

rmoc

oupl

e T

empe

ratu

re

0 5 10

0

5

10

Thermocouple Thermocouple CalibrationCalibration

y = 0.9885x + 0.4944R2 = 0.9999

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Thermocouple Temperature

Th

erm

oco

up

le T

emp

era

ture

Air TestAir Test

•Cool the empty volume•Thermocouple locations

Both interior heat sinksSuspended in the cooler

Air Test DataAir Test Data

0

5

10

15

20

25

0 2000 4000 6000 8000 10000 12000

Time (Seconds)

Tem

per

atu

re (

Deg

rees

C)

Interior Air Temperature

20ºC

5ºC

1.4 hours

0

5

10

15

20

25

0 2000 4000 6000 8000 10000

Corrected Temperature (degrees C)

Tim

e (S

econ

ds)

•Power•Connections•Ventilation•Thermocouple locations

Air TestAir TestAir and Heat Sink Temperatures

0

5

10

15

20

25

0 2000 4000 6000 8000 10000

Corrected Temperature (degrees C)

Tim

e (

Sec

on

ds

)

Heat Sink 1 Heat Sink 2 Interior air

½ ºC difference

Tem

pera

ture

(OC

)

Time (Seconds)

Water TestWater Test

•1L of water •Thermocouple locations

WaterHeat SinkInterior Air

0

5

10

15

20

25

30

0 5000 10000 15000 20000 25000 30000 35000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

ºC)

Water Test ResultsWater Test Results

Water Interior heat sinkInterior air

9 hours23.9ºC

5ºC

Forced or Natural Forced or Natural Convection?Convection?

•Remove one set of fans•Install thermocouples on both exterior heat sinks

We Need FansWe Need Fans

0

10

20

30

40

50

60

800 1000 1200 1400 1600 1800 2000

Time (Seconds)

Te

mp

era

ture

(D

eg

rees

C)

HS w/o Fan Interior Heat SinkHS w Fan

54ºC

36ºC

ResultsResults

10 mins

Time ConstantsTime Constants

•Time Constant, = 63.2% of temperature difference• = 0.5 hours

0

5

10

15

20

25

0 2000 4000 6000 8000 10000 12000

Time (Seconds)

Tem

per

atu

re (

Deg

rees

C) 20ºC

5ºC

10ºC

~ ½ hour

Cooling of Air

Control CircuitryControl Circuitry

LCD Display

Micro Controller

Analog/Digital ConverterUser Input

(3 Buttons)

TemperatureSensor

PrecisionVoltage

Reference

TemperatureTemperatureControlControl

Water Heat Sink 2Heat Sink 1

0

5

10

15

20

25

0 5000 10000 15000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

Deg

rees

C

elsi

us)

1L Water Setpoint: 10oC

TemperatureTemperatureControlControl

Water Heat Sink 2Heat Sink 1

Control

9

9.5

10

10.5

11

11.5

12

12000 13000 14000 15000 16000 17000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

Deg

rees

C

elsi

us)

TemperatureTemperatureControlControl

Precision

11.65

11.67

11.69

11.71

11.73

11.75

11.77

11.79

12000 13000 14000 15000 16000 17000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

Deg

rees

C

elsi

us) 0.12oC

Water Temperature

TemperatureTemperatureControlControl

Precision

11.65

11.67

11.69

11.71

11.73

11.75

11.77

11.79

10000 11000 12000 13000 14000 15000 16000 17000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

Deg

rees

C

elsi

us) +/- 0.06

oC

Water Temperature

TemperatureTemperatureControlControl

Steady State

0

5

10

15

20

25

7000 9000 11000 13000 15000 17000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

Deg

rees

C

elsi

us)

1hr 40minutes

Water Temperature

TemperatureTemperatureControlControl

Water Set PointActual

Accuracy

8

10

12

14

16

18

20

22

24

0 5000 10000 15000 20000

Time (Seconds)

Co

rrec

ted

Tem

per

atu

re (

Deg

rees

C

elsi

us)

1.8 oC

Costs

Category Amount ($)

Construction 581.24

Heat Transfer 415.27

Control 487.01

Total 1,483.32

Budget 2,000

Surplus 516.68

Safety FeaturesSafety Features

•Solid State Relay–Isolates Power Supply from the Controller

•Thermal Switch–Protects from overheating

•Protective Shrouds

Thermal Switch

Future ConsiderationsFuture Considerations

Recalibrate Set PointRecalibrate Set Point

Present:

•Set point off by ~1.8 oC

Future:

•Virtually no offset

Synchronize Fans to controllerSynchronize Fans to controller

Present:

•Fans are always on

Future:

•Fans turn on/off with TE modules–Less heat pumping into device–Increased efficiency

Additional ThermoelectricsAdditional Thermoelectrics

Present:

•Two modules are in the device

Future:

•More then two modules are used–Decrease cooling time–Increase temperature range

Heating the DeviceHeating the Device

Present:

•Device can only be used for cooling

Future:

•Heating and cooling will be possible

Special Thanks ToSpecial Thanks To

•Albert Murphy •Angus MacPherson•Stuart Carr•Greg Jollimore•Trisha Laws •Dr. Prabir Basu•Greenfield Research

Source: www.dal.ca &www.greenfieldresearch.ca

Air Time ConstantAir Time Constant

0

500

1000

1500

2000

2500

3000

3500

4000

0 2000 4000 6000 8000 10000 12000

Time (Seconds)

Tim

e C

on

stan

t (S

eco

nd

s)

Average time constant ~ ½ hour

Water Time ConstantWater Time Constant

0

5000

10000

15000

20000

25000

0 5000 10000 15000 20000 25000 30000 35000

Time (Seconds)

Tim

e C

on

stan

t (S

eco

nd

s)Average time constant ~ 2.75 hours