3.082 final presentation may 13, 2004 brie frame • sandra gonzalez • angela tong • chenny zhu
DESCRIPTION
3.082 Final Presentation May 13, 2004 Brie Frame • Sandra Gonzalez • Angela Tong • Chenny Zhu. Objective. Design and fabricate a heat therapy device for lower back pain. Increases Circulation. Decreases pain signal transmissions. Heat Therapy. - PowerPoint PPT PresentationTRANSCRIPT
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Portable Heat Therapy
3.082 Final PresentationMay 13, 2004
Brie Frame • Sandra Gonzalez • Angela Tong • Chenny Zhu
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Portable Heat Therapy
Objective
Design and fabricate a heat therapy device for lower back pain.
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Portable Heat Therapy
Heat Therapy
Strain or over-exert
back
Creates tension in muscles and soft
tissue surrounding spine
Restricts proper circulation
Pain signals sent to brain
Increases Circulation
Decreases pain signal transmissions
Reduces tension
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Portable Heat Therapy
Design Priorities1. Long-term reusability2. Portability3. Heat distribution4. Flexibility and comfort5. Long-lasting heat6. Light weight
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Portable Heat Therapy
Potential Portable Heat Therapy Designs
Chemical– Employ Phase Change Material (PCM)– Freezes at room temperature releases heat
Electric– Uses battery only
Hybrid – PCM melted by battery
http://www.hotsnapz.com/
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Portable Heat Therapy
Energy Densities
22.3041.9564.01
174.91
2050
0
500
1000
1500
2000
2500
Thermacare Thunder PowerDouble
Tetradecanol EthyleneCarbonate
2,6-Di-tert-butylphenol
Energy Density (Wh/kg)
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Portable Heat Therapy
Electrical Superiority
ElectricalChemical (Sodium
Acetate) Hybrid Thermacare ©
1. Long-term Reusability 1 2 3 4
2. Portable 1 3 4 1
3. Heat Distribution 1 1 1 2
4. Flexibility/Comfort 1 3 4 2
5. Long Lasting 2 3 4 1
6. Weight 2 2 4 1
Overall Rating 1.3 2.3 3.3 1.8
1 = Best 2 = Good 3 = Satisfactory 4 = Bad
Best Worst
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Portable Heat Therapy
Final Design SchematicFront View
Heating Pack
InsulationC
ircui
t
Side View
Towards Body
Towards Outside
Wire
On/OffSwitchBattery
RTV SiliconeRTV SiliconeInsulation
Cotton
Cotton
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Portable Heat Therapy
Voltage Cut-off Circuit
Prevents over-discharging of battery• 7.4V > V > 6 V On• V < 6 V Off
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Portable Heat Therapy
Thermostat Circuit
Switches heating pad on and off based on temperature
Hysteresis– Turns on 38°C– Turns off 42°C
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Portable Heat Therapy
Constructing the Circuit
Design circuit Assemble components
on breadboard Test circuit Solder circuit
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Portable Heat Therapy
Testing the Circuit
Voltage Cut-off Circuit– Ensure circuit is
opened at < 6V Thermostat Circuit
– Fine tune Set-point temperature
Connect circuits together
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Portable Heat Therapy
Battery
Design Limitations – Voltage cut-off circuit needed– 7.4V – 1300 mAh – limits heating cycle– Need special charger
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Portable Heat Therapy
Battery Charger
Purpose– Prevents over-charging
Requirements– 12V DC power supply– Charge time > 1 hour
Charge Time– 12V, 800mA power supply – 1.6 hours
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Portable Heat Therapy
Heat Lost to Environment
RTV
Sili
conc
cce
Cot
ton
Envi
ronm
ent
Insu
lato
in
Hea
ting
Wire
W
AkL
AkL
AkL
AkL
TTqPower
env
env
ton
ton
insultion
insulation
RTV
RTV
tenvironmenwire
3
cot
cot
1046.4 −×=
+++
−==
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Portable Heat Therapy
Heat Flux to Body
RTV
Sili
cone
Cot
ton
Bod
y
Hea
ting
Wire
WAk
LAk
LTTqPower
ton
ton
wire
wire
skinwire
754.0cot
cot
=×
+×
−==
T = Temperature (°C)L = Length (m)k = Thermal Conductivity (W/mK)A = Surface Area
RTV
RTV
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Portable Heat Therapy
Heating Element
High Resistance Wire– NiCr 80/20– 30 Gauge (0.010 in.
diameter)– Resistance = 6.5 Ω/ft
Heat Power (P = V2/R )– Length = 26 inches– Resistance = 14 Ω– Current = 500 mA– Power = 3.5W
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Portable Heat Therapy
RTV Silicone RTV = Room Temperature Vulcanization (cures in
absence of heat) Flexible, thermally conductive (0.83 W/mK), and flame
retardant Property retention at temperatures of -55°C to 200°C Moisture from the air activates cross-linking agents Reactions produce non-acidic byproducts
CH3OH
(rigid, rubbery silicone)
H2O
(liquid polymer compound)
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Portable Heat Therapy
Insulation and Outer Layer
Solid Silicone Rubber (Insulation)• Produced by COHRlastic• Low Thermal Conductivity 0.0037 W/mK• Flexible
Cotton (Outer Layer)• Comfort• Low cost
http://www.tapecase.com/tc/rubber.asp
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Portable Heat Therapy
Final Design
Charge Time = 75 minutesHeat Time = 130 minutesWeight = 260g
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Portable Heat Therapy
Safety Concerns
Must use in dry environment Battery
– Only use charger provided– Watch battery while charging– Charge Battery in non-flammable area– Don’t short the battery
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Portable Heat Therapy
Cost Analysis
Product Cost Dimensions Reusable?One Cycle of Heat (hrs) Cost per Month
Thermacare $3.50 4x10 no 8 $69.90
Zap Pac $44.95 4x10 yes 0.75 $44.95Heat me
Now $65.00 4x10 yes 3 $65.00
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Portable Heat Therapy
Future Work
Longer lasting – Use battery with larger Ahr
Decrease size of chip– Surface mount chip
Convenient battery charger– Build simple to use charger– Attach car adapter
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Portable Heat Therapy
Acknowledgements
3.082 Teaching Staff David Bono Hao Wang Yet-Ming Chiang Course 6 lab Course 6 friends