Stay Warm

Challenge:  To design an insulated container that will keep heat loss to a minimum.

Parameters:  Your device will be made from a wide variety of materials that some people might call garbage, but we will call “re-purposed”.  It must be able to securely hold a ceramic crucible whose dimensions are approximately 10 cm in diameter and 4 cm in depth.  It will come out of an oven at a high temperature, but less than 100°C.  You can build insulation around it and a lid for it, but the lid must be easily removable so we can read the temperature just before closing, and just after opening 20 minutes later.  It can have a temporary thermometer port for finding out its cooling curve and its heat-loss coefficient, but you can seal that port up before the competition.  

It must be able to sit unattended on a classroom balance, so a flat bottom would be helpful.

Scoring:  Your score will be determined primarily by the heat loss coefficient of your device, and secondarily by the mass of your device.  

Score:  | heat loss coefficient | • (100 + m/50)

m is the mass of your device in grams

Lowest score will earn the highest rank.

Physics:  A known mass of a pure substance in a closed system will transfer energy with the system, then the environment. The heat capacity of a known mass of a pure substance, for example water (CH2O = 4186 J/kg°C) can be used to calculate how much energy is being gained or lost as temperature changes.  Heat transfer by radiation, conduction, and convection will all have to be limited in order to be successful in this project.

Extensions: The materials that make up your device have mass and will change temperature, so your system is not really “closed” perfectly. You can actually measure something called the “calorimeter constant” for your device.  If you do, you will be able to use your device as a calorimeter, and probably get decent results.  Ice cubes phase change to liquid requires a ton of energy, and you can calculate that as well!  The latent heat of fusion coefficient of ice (Lf = 334 000 J/kg) would be required.  I will lead you through the math required to calculate the heat loss coefficient.

Help/Hints:  The scoring formula mentioned above can be minimized by making your device smaller and lighter, with insulating materials, but it is not the biggest part of the score.  Be careful using reflective aluminum foil as it will work really well preventing heat loss by radiation, but is extremely conductive and will not prevent heat loss by conduction!  

Quiz Topics: Heat energy

Online Textbook:  11, 12.1