Sleeping Bag Comparison

1. 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

3. 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?

4. 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

5. 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

6. 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)

7. 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

8. Results – Thermal images Sleeping bag 1 – Ledge Mummy sleeping bag Qtotal = 8970 W/m2

9. Results – Thermal Images Sleeping bag 2 – Northface Mummy sleeping bag Qtotal = 7890 W/m2

10. 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

11. Appendix – Experimental Measurements

12. Appendix – Preliminary Calculations

13. Appendix – Final Calculations & Results