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A Heat Transfer Approach to Sleeping Bag Ratings
Moises Alcevedo
Jordan Ryskamp
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
Modes of heat transfer
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
FactorsRating
Heat Generation Thermal Resistance
Gender Metabolism
Food Exercise level
Hydration Weight
Insulation Clothing
Fit Tent
Shape Moisture
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
Different Standards
• Ratings are given as a temperature
• Manufacturers pick their ratings
• Many are “optimistic”
• No recognized standards
• Make different assumptions– Young male in a tent wearing thermals – Older larger female sleeping under the stars
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
Our Project
• Use heat transfer principles to compare bags• All bags are limited by the amount of insulation• Approximate as cylinder
Sleeping bag, ( Rcond)
Air inside,( Rair in)
Body ( q gen. Ti)
Air out (To, Rair out)
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
Properties and AssumptionsFillings of sleeping bags• Feathers
k=0.02 mK / W
• Polyguard Delta k= .041 mK / W• h= 5
– Why? Rcond < Rconv = 1/ h
• No radiation– Why? Low temperature
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
Thermal Circuit
Rair in Rcond Rair out
Ti To
Rtotal = Rair in + Rcond + Rair out
Rair in = 1/hA = 1/h2RbodyL
Rcond = Ln(Rout s.b./Rin s.b.) / 2kL
Rair out = 1/hA = 1/h2Rout s.b.L
A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping
Bag RatingsBag Ratings
Solution and Conclusion
• qV = ∆T / Rtotal
= Ti - To / Rtotal
To= Ti - qVRtotal
Currently found online at www.littlegreendesigns.com/Sleepingbags.aspx
Model does not give accurate results. However, it does give a good method of comparison.
