G?Love: Heated Gloves*

1
G?Love Heated Gloves
Kristin Brodie, Jeff Colton, Colin Galbraith,
Bushra Makiya and Tiffany Santos
Amount of heat supplied to the hand by the
heating element was determined by calculating the
amount of heat needed to keep the hand
comfortable when walking across the Harvard
Bridge in -10C weather with 15 mi/hr wind.
NiCr High Resistance Wire

• 80 Ni, 20 Cr
• Diameter 0.40mm
• Resistance 0.0807 ?/cm
• 100 cm of wire used in design
• Wire temperature reaches 60?C
• Selected for superior mechanical properties
  compared to other wires (largest elastic region,
  see graph below).
• Other high-resistance wires considered
  60Ni16Cr24Fe and 70Fe19Cr11Ni.

Outer Fabric
100 polyester fleece selected for its good
insulating properties, breathability, and high
heat transfer coefficient. Melting Temperature
260?C Heat transfer coefficient 1.49
W/m2K Good breathability hand will sweat
minimally inside glove. Other fabrics
considered 80/20 and 20/80 cotton/polyester
blends.
Teflon Tubing Insulation

• Poly(tetrafluoroethylene) -(CF2-CF2)-
• High Melting Temperature 327?C
• Thermal Conductivity 0.25W/mK
• Necessary for electrical insulation of wires and
  protection from corrosion.

Phase Change Materials (PCMs)

• A PCM is melted by body heat and the latent heat
  of fusion is stored. When subjected to a cooler
  environment, the PCM crystallizes, releasing the
  stored heat and thus warming the hand.
• It is necessary to encapsulate the PCM into a
  base material such as polypropylene or high
  density polyethylene in order to prevent leakage
  when the PCM melts. Because extrusion facilities
  were not available, uniformly dispersing a PCM in
  either one of these materials proved to be very
  difficult. Therefore less efficient encapsulants
  had to be used.
• PCMs considered Octadecane in Polydimethyl
  Siloxane (PDMS) Resin and Polyethylene Glycol
  (PEG) in Polyethylene.
• Octadecane C18H38
• Molecular Weight 254.5g/mole
• Melting Temperature 27.2C
• Crystallization temperature 16.5C
• (Measured by Differential Scanning Calorimetry)
• Total Heat Capacity 5g ? 283.5J/g 1148J
• Embedded in PDMS Resin
• Thermal Conductivity 0.002 W/mK

Inner Lining Fabric
100 polyester Selected for softness and
comfort. Other fabrics considered flannel
(100 cotton).

Final Gloves (left to right) Inner lining with
battery and resistive heating element, inner
lining with embedded PCMs, and outer glove.
PEG in Polyethylene
Octadecane in PDMS
A comparison of the two encapsulation methods is
shown above. Although polyethylene proved to be a
better encapsulant due to the low thermal
conductivity of PDMS (reduction in efficiency
35 vs. 51), the overall heat capacity of the
octadecane embedded in PDMS resin was greater
(93.1J/g vs. 61.2J/g). This was due to the larger
weight fraction of PCM in that sample and its
higher latent heat storage capacity. Therefore
octadecane was used in the gloves. In the future,
it would be interesting to experiment with heat
sealing octadecane in polyethylene. This could
further increase the gloves efficiency.
Comparison of PCM and Wire Heating Elements 5
grams of octadecane will give off the same amount
of heat upon freezing per cycle (1.7 W) as 100cm
of NiCr wire in 14 minutes.
3.082 Materials Processing Laboratory,
Undergraduate Team Project