Sleeping bag comparison
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Sleeping Bag Comparison. Which sleeping bag will keep you warmer? By: Kyle Layton and Ben Salazar. 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

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Sleeping Bag Comparison

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Sleeping bag comparison

Sleeping Bag Comparison

Which sleeping bag will keep you warmer?

By: Kyle Layton and Ben Salazar


Introduction

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


Introduction sleeping bags

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?


Methods

Methods

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

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


Methods1

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 InfraRedCamera for visualization purposes


Methods2

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(ΔT*t), 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)


Methods3

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


Results thermal images

Results – Thermal images

Sleeping bag 1 – Ledge Mummy sleeping bag

Qtotal = 8970 W/m2


Results thermal images1

Results – Thermal Images

Sleeping bag 2 – Northface Mummy sleeping bag

Qtotal = 7890 W/m2


Conclusion

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


Appendix experimental measurements

Appendix – Experimental Measurements


Appendix preliminary calculations

Appendix – Preliminary Calculations


Appendix final calculations results

Appendix – Final Calculations & Results


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