G Love
Prototype Presentation
Kristin Brodie
Jeff Colton
Colin Galbraith
Bushra Makiya
Tiffany Santos
DMSE 3.082
Presentation Topics
•
•
•
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Materials Selection
Processing
Testing
Future Work
DMSE 3.082
Materials Selection: Fabrics
Key Properties: Heat transfer coefficient, good
breathability, lightweight, low cost, good durability.
•100% polyester (fleece)
• 80% polyester, 20% cotton
• 20% polyester, 80% cotton
• 100% cotton (flannel)- intended as inner lining
Cotton ignites at 250C
Polyester melts at 260 C
DMSE 3.082
Materials Selection: Heating Element
Key Properties: High resistivity, mechanical strength,
large elastic region.
Calculated Stress
(ksi)
Length of Elastic
Region (inches)
Load at end of
elastic region (lbs)
DMSE 3.082
Ni:Cr
80:20
wt%
121
Ni:Cr:Fe
60:16:24
wt%
107.8
Stainless Steel
Fe:Cr:Ni
70:19:11 wt%
102.2
~4
~3.5
~2.5
13
10
7
Materials Selection: Wire Coating
Key Properties: High electrical resistivity, high thermal conductivity,
high Tm, low water absorption, good ductility, good weather resistance.
• Teflon (CF2) is the best candidate.
• Polyethylene has too low Tm and may melt.
• Braided tubing will allow water through.
• Glass is not flexible enough.
• Silicone rubber has low thermal conductivity.
DMSE 3.082
Teflon: Resistivity
>1018 ohm*cm
Tensile strength
21-34 MPa
Tm
327 C
Thermal conductivity 0.25 W/m*K
H2O Absorption
<0.01%
Materials Selection: Battery
Key Properties: Flat, flexible, rechargeable, high capacity, weight.
Alkaline
Batteries
Voltage
1.5 V
Energy Density 80
W*hours/kg
Physical
cylindrical
Characteristics
Rechargable?
no
DMSE 3.082
Lithium Ion
Liquid
3.6 V
>120
W*hours/kg
flat, hard
casing
yes
Lithium Ion
Polymer
3.74 V
>120
W*hours/kg
flat, flexible
yes
Materials Selection: Temperature Sensor
Key Properties: Fast reaction time, good temperature control, cost.
thermistor
Sensitivity
Reaction Time
Cost
DMSE 3.082
< 1
slow
low
bimetallic
thermal switch
< 1
fast
low
polymer thermal
switch
< 1
fast
free
Materials Selection: Phase Change Materials
Key Properties: Tm near that of human body,
high heat of crystallization, ease of processing.
Octadecane
Tm (C)
Heat of
Crystallization (J/g)
DMSE 3.082
27.2
-283.5
Polyethylene Glycol
(900g/mole)
26.63
-150.8
Materials Selection: PCM Base Materials
Key Properties: Flexible, hydrophobic, easy to process,
contains microspheres, thermal conductivity, high Tm.
PDMS resin:
• Used as the base material for octadecane.
• Easy to process-when mixed with a crosslinker it sets into a flexible rubber overnight.
DMSE 3.082
Polypropylene:
• Can be made into fibers or sheets.
• PEG can be incorporated directly, rather than
fabricating microspheres first.
• Atactic polymer should be easy to process.
• High solvent resistance.
PCM Processing: Microsphere Fabrication
• Microspheres increase surface area, releasing heat faster.
• Small particles can be incorporated into the fabric easily.
SEM image of octadecane microspheres. They appeared to
have melted and recrystallized during fabrication.
DMSE 3.082
PCM Processing: Incorporation
1) Embed microspheres in a base material.
• Octadecane microspheres were embedded in PDMS.
• There was no difference in DSC results compared to a
regular piece of PDMS resin. This could be due to the
quality or quantity of the microspheres or to properties
of the PDMS.
2) Incorporate PCM directly into base material
(polypropylene) and form into flat sheets.
3) Coat fibers or fabric with the PCM.
DMSE 3.082
Testing
Heat transfer coefficient of fabric
Place heating element in gloves
Use thermistor to measure inside/outside temp.
Measured to be 1.1-1.5 W/m2K
Equilibrium time ~5 min
Next Step:
Repeat this experiment with gloves containing PCMs
DMSE 3.082
Thermal Testing
• h = I*V/[A*(T1-T2)]
= 3.6*0.55/(.04*DT)
• As h goes up, less heat is
lost (small DT)
• Polyester has the highest
value for h
• Graph for values with
3.6V and 100cm of wire
D T (K)
Tem perature Difference vs Tim e
100P
100P*
20C 80P
0
5
10
80C 20P
Tim e (m in)
h
DMSE 3.082
50
40
30
20
10
0
100P 100P*
20C 80P
80C 20P
1.12
1.35
1.08
1.49
Power Requirement
603672
W*h
2.835
141988
5.101
597980
4.416
Oper. Length(min)
@16F
90.4
162.6
Required Power vs Temperature
140.8
@21F
91.9
165.4
143.1
@32F
94.9
170.8
147.9
Required Power
(W)
Serial #
20C 80P
2
100P
1.5
1
240
20P 80C
100P*
260
280
Temperature (K)
DMSE 3.082
300
Future Work
• Improve octadecane fabrication process, make more
microspheres, test a larger piece of silicone rubber with more
microspheres.
• Test PEG as an alternative PCM, either by making
microspheres or by directly incorporating it into a
polypropylene sheet.
• Continue heat transfer testing of gloves. Test gloves with
PCMs incorporated.
• Coat or insulate wires (Teflon tubing is in the mail).
• Test and incorporate thermal switch (in the mail).
• Connection of wires to battery.
• Cost analysis.
• Continue working on quantitative heat transfer analysis
DMSE 3.082