1. Can You Heat Me Now? Formal Design Review Brie Frame Sandra Gonzalez Angela Tong Chenny Zhu Department of Materials Science 3.082 Advisor: Hao Wang March 11, 2004

2. Outline of Presentation Objective Overview of Components of Device Phase Change Materials and Data Melting Energy Calculations Battery Selection Power Calculations Hybrid vs. Electrical Design Proposed Circuit Future Work Proposed Schedule

3. Objective Design and fabricate a heat therapy device for lower back pain with a future use for transdermal drug delivery.

4. Components of Device Body Outer Covering High Insulating Layer Heating Core Battery

5. Average Body Dimensions Heating element volume: 6x4x0.25” = 6in 3 or 10x16x0.5cm = 80cm 3 4” 6” 42” Waist Circumference: 37.48” (men) 34.88” (women) 36.18” (average) Back Width (at shoulder): 15.75” Back Length: 15.77” Waist to Hip: 3.93” 12”

6. Heating Core Potential Materials  Tetradecanol  Ethylene Carbonate  2,6-Di-tert-butylphenol (liquid at room temperature)  Cis-Cyclohexane-1,2-dicarboylic anydride (toxic)  Benzylideneacetone X X

7. PCM: Temperature vs. Time

8. Melting Energy MaterialMolecularMWdensity Weight Enthalpy of FusionEnergyElectric Energy UnitsFormula(g/mol)(g/cm 3 ) g (kJ/mol)(J)(W*h) TetradecanolC 14 H 30 O214.390.823 65.84 49.415170.934.214 Ethylene CarbonateC3H4O3C3H4O3 88.061.32 105.6 13.315949.134.430 2,6-Di-tert-butylphenolC 14 H 22 O206.320.91 72.8 16.575846.7241.624 Equation: Energy (W*h) = (ρ*V*ΔH f ) / (MW)

9. Battery Selection

10. Power Estimation Heat loss to environment  q=-k dT/dx  q=-0.0037*(16°C/0.005m)  q=8.88W/m 2  q*A = P = 8.88 * 0.016m 2  P = 0.142W Heat loss to body  q= -0.025*(6°C/0.001m)  q=150W/m 2  q*A = P = 150 * 0.016m 2  P = 2.4W Total heat loss  P = 0.142 + 2.4 = 2.542 W q=heat flux W/m 2 k=thermal conductivity W/mK  Solid Silicone Rubber = 0.0037 W/mK  Cotton = 0.025 W/mK T=temperature  Heat Pack = 41°C  Environment = 25°C  Body Surface Temperature = 35°C x=thickness = 0.005m A = area = 0.016m 2 P = power (W) 0.10m 0.16m 0.005m

11. Hybrid vs. Electrical Power needed to keep temperature at 41°C in air = 2.56W 4.43 Whr to melt 105.6g of Ethylene Carbonate (EC) 1.73hrs to melt 105.6g (EC) 15min for 10g Ethylene Carbonate to cool to 35°C Assuming cooling rate is at steady state, would take ~150min (2.5hrs) for ethylene carbonate to cool to 35°C 2.5hrs + 1.73hrs = 4.23 hrs for one cycle Save 2.5hrs of electrical energy per cycle = 6.48Whr

12. Hybrid vs. Electrical Electrical  Lighter  Constant Heat  Uses more energy Hybrid  More energy efficient- use electrical energy to both heat body and PCM  Staggered Heating

13. Switch Programmable Thermostatic Switch – Analog Devices AD22105  Control temperature by adding resistors  Small – about 5mmx5mmx2mm  Cheap ~ $1 - $3 per switch depending on how many bought

14. Circuit

15. Insulating Material Potential Materials  COHRlastic Solid Silicone Rubber Thermally Conductive R10404  Low Thermal Conductivity 0.0037W/mK  Very Thin R10480  Low Thermal Conductivity  Flexible

16. Future Work Differential Scanning Calorimetry  Properties of 2,6-Di-tert-butylphenol Polymer Gel combined w/ PCM for comfort Fire resistant wire coating Finding resistance for thermal regulation switch

17. Proposed Schedule