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
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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
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200
180
160
140
120
100
80
60
40
20
0
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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
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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
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NiCr 80/20
 Variables
control Resistance (Ohms/ft)
Length
 Gauge - thickness
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 Resistance
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 Power  Heat
P=V2 / R, V is constant = 7.4V
 Trial
and Error - find balance
Minimize resistance
 Minimize current
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Detailed put together
Securing The Wire
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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
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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
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COHRlastic Solid Silicone
Rubber
 Thermally
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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
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Obtaining Parts – lost in mail
 RTV
silicone
 Battery Charger
Finding correct heating wire length and
gauge
 Debugging circuits
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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
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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