Thermos

Challenge: To design a thermos that will keep heat transfer to a minimum.

Parameters: Your device will be made from a set amount of materials, but you do not have to use all of them. The plastic beaker (which must be returned unaltered after the contest) will be your starting point. You can build insulation around it and a lid for it, but the lid must be removable and you must be able to access the interior with a standard classroom thermometer while it is closed (ie build a hole into the lid). It must be able to sit unattended on a classroom balance.

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 thermos in grams

Lowest score will earn the highest rank.

Physics: A known mass of water in a closed system will transfer energy with the thermos, then the environment. The heat capacity of water (C_H2O = 4186 J/kg°C) is large, so a good thermos will slowly gain or lose energy for quite a while! Heat transfer by radiation, conduction, and convection will all have to be limited in order to be successful.

Extensions: The materials that make up your device have mass and will change temperature, so your system is not really “closed” perfectly, and therefore has its own “heat capacity”. You can actually calculate this! If you do, you will be able to use your thermos as a calorimeter, and probably get decent results. A good thermos can keep hot water hot or cold water cold. Ice cubes can make a big difference, and you can calculate that as well! The latent heat of fusion coefficient of ice (L_f = 334 kJ/kg) would be required. I will lead you through the math required to calculate the heat loss coefficient, but you can look it up if you want to get a head start.

Help/Hints: Please take care in the construction of your device. The heat capacity factor mentioned above can be minimized by making your device smaller and lighter, with insulating materials. Make sure not to get water between the beaker and the insulation.

Quiz Topics: Heat energy

Online Textbook: 11, 12.1