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 Components

Outer Covering

Conducting Layer

Insulating Layer

Outer Covering

Circuit

Heating Element

Battery

Heating Pad Diagram

Battery Heating Element

ThermostatVoltage Regulator

Energy Density Comparison

174.9150.8

68.57 64.0341.95

22.36

020406080

100120140160180200

En

erg

y D

ensi

ty (

Wh

/kg

)

Voltage Regulator

Thermostat Circuit

Circuit Debugging

Voltage Regulator CircuitVoltage drops too low before shutoff

Thermostat CircuitFinding accurate resistance for temperature

set point Inconsistent turn on/ turn off pointHysteresis – 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 SiliconeGreat Thermal Conductivity (0.83 W/mK)Temperature Range -55°C to 200 °CFlame RetardantFlexible

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

CH3OHH2O

(liquid polymer compound) (rigid, rubbery silicone)

Insulating MaterialOuter Material

COHRlastic Solid Silicone RubberThermally 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 mailRTV siliconeBattery 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 ScheduleID Task Name

Feb 2004 Mar 2004 Apr 2004 May 2004

2/1 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

2 Obtaining Materials

14 Testing Materials

Processing/Building

18 Prototype Assembly

Testing and Troubleshooting Prototype

11

5/16

3 Wires

4 PCM

6 Polymer Gel

8 Battery

7 Insulating Material

Start

2/5/2004

3/2/2004

3/2/2004

3/9/2004

3/9/2004

3/9/2004

3/9/2004

4/1/2004

4/6/2004

4/6/2004

Finish

3/18/2004

3/4/2004

3/11/2004

3/11/2004

3/16/2004

3/16/2004

4/8/2004

4/8/2004

4/13/2004

5/6/2004

9 3/16/20043/9/2004Outside Material

10 3/16/20043/9/2004Wire Coating

5 3/11/20043/9/2004Thermal Switch

16 4/8/20044/6/2004Wire

17 4/8/20044/6/2004RTV Silicone

4/8/20044/1/2004Circuit

1 3/11/20043/11/2004Formal Design Review Presentation

4/13/20044/13/2004Initial Prototypes19

5/6/20045/6/2004Last Day of Lab Work

20

22

21

5/13/20045/13/2004Final Presentation/Posters Due

12 4/6/20043/23/2004Outer cover

13 4/6/20044/1/2004Circuit

15