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3.082 Final Presentation May 13, 2004 Brie Frame • Sandra Gonzalez • Angela Tong • Chenny Zhu

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.

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3.082 Final Presentation May 13, 2004 Brie Frame • Sandra Gonzalez • Angela Tong • Chenny Zhu

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  1. 3.082 Final Presentation May 13, 2004 Brie Frame • Sandra Gonzalez • Angela Tong • Chenny Zhu

  2. Objective • Design and fabricate a heat therapy device for lower back pain.

  3. Increases Circulation Decreases pain signal transmissions Heat Therapy Creates tension in muscles and soft tissue surrounding spine Reduces tension Strain or over-exert back Restricts proper circulation Pain signals sent to brain

  4. Design Priorities • Long-term reusability • Portability • Heat distribution • Flexibility and comfort • Long-lasting heat • Light weight

  5. 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/

  6. Energy Densities

  7. Electrical Superiority Best Worst

  8. Final Design Schematic Front View Heating Pack Circuit Insulation On/Off Switch Side View Battery Towards Body Cotton RTV Silicone Wire RTV Silicone Insulation Cotton Towards Outside

  9. Voltage Cut-off Circuit • Prevents over-discharging of battery • 7.4V > V > 6 V On • V < 6 V Off

  10. Thermostat Circuit • Switches heating pad on and off based on temperature • Hysteresis • Turns on 38°C • Turns off 42°C

  11. Constructing the Circuit • Design circuit • Assemble components on breadboard • Test circuit • Solder circuit

  12. Testing the Circuit • Voltage Cut-off Circuit • Ensure circuit is opened at < 6V • Thermostat Circuit • Fine tune Set-point temperature • Connect circuits together

  13. Battery • Design Limitations • Voltage cut-off circuit needed • 7.4V • 1300 mAh – limits heating cycle • Need special charger

  14. Battery Charger • Purpose • Prevents over-charging • Requirements • 12V DC power supply • Charge time > 1 hour • Charge Time • 12V, 800mA power supply • 1.6 hours

  15. Heat Lost to Environment Environment Insulatoin RTV Siliconccce Heating Wire Cotton

  16. Heat Flux to Body RTV RTV T = Temperature (°C) L = Length (m) k = Thermal Conductivity (W/mK) A = Surface Area Body RTV Silicone Heating Wire Cotton

  17. 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

  18. H2O CH3OH (liquid polymer compound) (rigid, rubbery silicone) 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

  19. 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

  20. Final Design Charge Time = 75 minutes Heat Time = 130 minutes Weight = 260g

  21. 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

  22. Cost Analysis

  23. 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

  24. Acknowledgements • 3.082 Teaching Staff • David Bono • Hao Wang • Yet-Ming Chiang • Course 6 lab • Course 6 friends

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