TO ZIP OR NOT TO ZIP By Jeremy
TO ZIP OR NOT TO ZIP? By Jeremy Alsup and Mark Daniel
Purpose � Mark’s wife often complains of being cold, but refuses to zip up her coat. We wanted to see how much zipping up would help to keep warm.
Method � Developed a model of the torso with a jacket zipped up and one unzipped. � Torso: Cylinder with. 25 meter diameter ½ inch layer of insulation with the properties of water surrounding a core at a constant temperature 36. 7°C Adiabatic surfaces on the top and bottom Generates 50 W (estimated from 1 Met, or 105 W, generated by the entire body) � Jacket: ½ thick with the properties of blanket and batt (Incropera, et al. Table A. 3, pg. 936) No space between skin and jacket
Method � Zipped Jacket completely surrounds the torso � Unzipped Jacket surrounds half of the torso �While the jacket really surrounds more, this simplifies calculations and accounts for the convection that goes on for the areas that are not directly exposed. � Assumed that there was no other insulation but the jacket (This is a man, so it’s ok)
Method � Assumed a cold day with a breeze � Temp = 0°C � h = 10 W/m 2*K
Results � Zipped � Calculations show 37 W leave the jacket, keeping 13 W trapped in the jacket and warming the wearer � Unzipped � Calculations show 58 W leave the jacket, with the wearer losing 8 W and feeling cold
Conclusions � � If you are cold, zip up your coat! Possible improvements to the model: � Better representation of the torso (not a cylinder) � Include arms � Mass transfer (and thus convection) at top, bottom, and arms of jacket � More accurate values of constants for coat and skin
- Slides: 8