Can You Heat Me Now? Initial Prototype Brie Frame Sandra Gonzalez Angela Tong Chenny Zhu Department of Materials Science • 3.082 • Advisor: Hao Wang • April 13, 2004 Outline of Presentation Objective Benefits of Heat Therapy Desired Device properties Components of prototype Energy sources comparison Circuits Insulating material/Outer layer Encountered problems Future work Objective Design and fabricate a heat therapy device for lower back pain with a future use for transdermal drug delivery. Benefits of Heat Therapy Relieves Pain Enhances recovery by stimulating thermoreceptors (block transmission of pain signals to brain Decreases Stiffness Relaxes Sore Muscles Source: www.thermacare.com Desired Device Properties Long Lasting Heat Competitive Cost Flexibility/Comfortability Portability Battery Operated Heat Pad Satisfies All The Constraints! Device Schematic Heating Element Heating Pad Diagram Battery Voltage Regulator Heating Element Thermostat we rd ou bl e 200 180 160 140 120 100 80 60 40 20 0 Th er m ac ar e So di um Ac et at e Te tra de ca Et no hy l le ne C ar bo 2, na 6 D te i-t er t-b ut ylp he no l Th un de rp o Energy Density (Wh/kg) Energy Density Comparison 174.9 150.8 68.57 64.03 41.95 22.36 Voltage Regulator Thermostat Circuit Circuit Debugging Voltage Regulator Circuit Voltage drops too low before shutoff Thermostat Circuit Finding accurate resistance for temperature set point Inconsistent turn on/ turn off point Hysteresis – turn on / turn off Heating wire NiCr 80/20 Variables control Resistance (Ohms/ft) Length Gauge - thickness Resistance Power Heat P=V2 / R, V is constant = 7.4V Trial and Error - find balance Minimize resistance Minimize current Detailed put together Securing The Wire RTV Silicone Great Thermal Conductivity (0.83 W/mK) Temperature Range -55°C to 200 °C Flame Retardant Flexible Source: http://www.mgchemicals.com Chemistry of RTV Silicone RTV = Room Temperature Vulcanization Cures in absence of heat Moisture from the air activates cross-linking agents Reactions produce non-acidic byproducts H2O (liquid polymer compound) CH3OH (rigid, rubbery silicone) Insulating Material Outer Material COHRlastic Solid Silicone Rubber Thermally Conductive R10404 Thermal Conductivity 0.0037W/mK Outer Material Cotton/Polyester blend Cotton has a thermal conductivity of 0.03 W/mK. An order of magnitude higher than COHRlastic! Problems Obtaining Parts – lost in mail RTV silicone Battery Charger Finding correct heating wire length and gauge Debugging circuits Future Work Find correct length and gauge heating wire Coat circuit with hot glue to prevent short circuits Sew outer band Put together all components Proposed Schedule Feb 2004 ID Task Name Start 2/1 1 Formal Design Review Presentation 2 Obtaining Materials 3/11/2004 3/11/2004 2/5/2004 3/18/2004 3 Wires 3/2/2004 3/4/2004 4 PCM 3/2/2004 3/11/2004 5 Thermal Switch 3/9/2004 3/11/2004 6 Polymer Gel 3/9/2004 3/11/2004 7 Insulating Material 3/9/2004 3/16/2004 8 Battery 3/9/2004 3/16/2004 9 Outside Material 3/9/2004 3/16/2004 Wire Coating 3/9/2004 3/16/2004 3/9/2004 4/8/2004 3/23/2004 4/6/2004 4/1/2004 4/6/2004 4/1/2004 4/8/2004 10 11 Processing/Building 12 Outer cover 13 Circuit 14 Testing Materials Mar 2004 Apr 2004 May 2004 Finish 15 Circuit 4/1/2004 4/8/2004 16 Wire 4/6/2004 4/8/2004 17 RTV Silicone 4/6/2004 4/8/2004 4/6/2004 4/13/2004 4/13/2004 4/13/2004 18 Prototype Assembly 19 Initial Prototypes 20 Testing and Troubleshooting Prototype 4/6/2004 5/6/2004 21 Last Day of Lab Work 5/6/2004 5/6/2004 22 Final Presentation/Posters Due 5/13/2004 5/13/2004 2/8 2/15 2/22 2/29 3/7 3/14 3/21 3/28 4/4 4/11 4/18 4/25 5/2 5/9 5/16