Sleeping Bag Comparison

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Sleeping Bag Comparison

• Which sleeping bag will keep you warmer?
• By Kyle Layton and Ben Salazar

2
Introduction

• Camping is fun, but can be cold, especially in
  the winter.
• Many companies make claims that their brand of
  sleeping bag is better at keeping you warm in
  cold conditions
• Research Objective
• We want to compare two sleeping bags that have
  very similar materials and specifications but
  drastically different prices and experimentally
  find out which is more effective at retaining
  heat
• We will do this by deriving a heat transfer rate
  for the different forms of heat loss
• We will then plug in values for each sleeping bag
  that we measure in our experiment and obtain the
  heat transfer associated with each sleeping bag
• We will compare these values and determine which
  brand of sleeping bag is better at keeping a
  camper warm

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Introduction sleeping bags

• Sleeping bag 1 Ledge Mummy Sleeping bag
• Operating temperatures 20º F
• Price 60.00

• Sleeping bag 1 - Northface Mummy Sleeping bag
• Operating temperatures 20º F
• Price 200.00

Which is better?
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Methods

• Materials used
• 2 Small Zip-Loc bags large enough to fit 500 ml
  of liquid
• Beaker
• Water
• Microwave
• Two sleeping bags of the same size and style, but
  different brands
• Infrared thermal laser digital thermometer
• FLIR E5 compact thermal imaging infrared camera

• Assumptions
• Zip Loc bags have uniform surface temperature
• Zip Loc bags can be approximated as as spheres
  with properties of water
• Sleeping bags can be approximated as flat
  surfaces
• Floor can be treated as a semi-infinite solid
• Thickness of material of sleeping bag can be
  neglected due to compression
• 1-D heat transfer

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Methods

• Filled Zip-Loc bags with a fixed volume of warm
  water
• Measured water volume using a beaker 475 ml
  475 x 10-6 m3
• Heated water to 49º C using a microwave
• Measured the temperature of water, the room, and
  the sleeping bag using an infrared thermal laser
  digital thermometer

• Placed Zip-Loc bags in sleeping bags and
  monitored temperature of both the sleeping bag
  and the Zip-Loc bag over a 45 min time interval.
• Took thermal images using FLIR E5 Compact Thermal
  Imaging InfraRed Camera for visualization
  purposes

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Methods

• The bag of water at 49º C is assumed to heat at
  least a small portion of the sleeping bag.
• If we approximate the patch of sleeping bag that
  was heated as a small plate we can use the
  following equations
• Using these values, the Rayleigh number was
  calculated for each corresponding measurement Ra
  Pr(Gr)
• This gave us a way to calculate the average h
  value for surfaces
• Then, using the equation Qair hA(?Tt), we
  calculated the heat transfer between each
  measurement through free convection.
• The total heat loss through the air was found by
  summing values for these Qair values( see
  appendix)

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Methods

• Heat transfer through the ground was calculated
  assuming a semi-infinite solid in contact with a
  uniform temperature surface, using
• For each measurement, similar to the procedure
  outlined for Qair, q values for each time
  interval were calculated and then summed
• Heat loss through the air (Qair ) and through the
  ground (q) were then summed to determine the
  total heat loss

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Results Thermal images
Sleeping bag 1 Ledge Mummy sleeping bag
Qtotal 8970 W/m2
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Results Thermal Images
Sleeping bag 2 Northface Mummy sleeping bag
Qtotal 7890 W/m2
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Conclusion

• A slight difference was detected between the two
  sleeping bag brands
• At Qtotal 7890 Sleeping bag 2 more effectively
  retained heat and thus would keep a camper warmer
• This represents a 12 better heat retention
• Despite its better performance, we do not believe
  this justifies the 140 price difference between
  the two products
• We therefore recommend the use and purchase of
  the less expensive and still effective sleeping
  bag

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Appendix Experimental Measurements
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Appendix Preliminary Calculations
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Appendix Final Calculations Results