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

2. Portable Heat Therapy Objective  Design and fabricate a heat therapy device for lower back pain.

3. 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

4. Portable Heat Therapy Design Priorities  Long-term reusability  Portability  Heat distribution  Flexibility and comfort  Long-lasting heat  Light weight

5. 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/

6. Portable Heat Therapy Energy Densities

7. Portable Heat Therapy Electrical Superiority Electrical Chemical (Sodium Acetate)HybridThermacare © 1. Long-term Reusability 1234 2. Portable 1341 3. Heat Distribution 1112 4. Flexibility/Comfort 1342 5. Long Lasting 2341 6. Weight 2241 Overall Rating 1.32.33.31.8 1 = Best2 = Good3 = Satisfactory4 = Bad BestWorst

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

9. Portable Heat Therapy Voltage Cut-off Circuit  Prevents over-discharging of battery 7.4V > V > 6 VOn V < 6 VOff

10. Portable Heat Therapy Thermostat Circuit  Switches heating pad on and off based on temperature  Hysteresis –Turns on 38°C –Turns off 42°C

11. Portable Heat Therapy Constructing the Circuit  Design circuit  Assemble components on breadboard  Test circuit  Solder circuit

12. 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

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

14. 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

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

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

17. 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 = V 2 /R ) –Length = 26 inches –Resistance = 14 Ω –Current = 500 mA –Power = 3.5W

18. 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 CH 3 OH (rigid, rubbery silicone) H2OH2O (liquid polymer compound)

19. 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

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

21. 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

22. Portable Heat Therapy Cost Analysis

23. 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

24. Portable Heat Therapy Acknowledgements  3.082 Teaching Staff  David Bono  Hao Wang  Yet-Ming Chiang  Course 6 lab  Course 6 friends