Project summary: We are evaluating two thermoses. Using what we have learned from heat transfer we will calculate the temperature of the fluid and compare it with the measured experimental data. In the end we will be able to determine if the statement of the thermos company is correct in that the vacuum thermos maintains your drinks at a much closer temperature than cheaper competitors. Challenges: The fluid temperature inside the thermos is constantly changing therefore we have a constantly changing heat transfer rate.
Method of Excel Model • Using initial conditions we calculated the rate of heat transfer. • We assumed heat left the system at this initial rate for the first minute and approximated the total heat that left the system. • We then calculated a new internal temperature for time = 1 min. • Then we repeated this process for each time step of 1 min.
Results The measured experimental results after one hour in the freezer: Vacuum thermos= 82 Foam thermos= 40 Calculated results by excel model: Vacuum thermos=91.9 Foam thermos=51.4 This is following the same difference as our model. The discrepancy in the two is likely due to the heat escaping through the cap and the bottom of the thermoses. We neglected these due to the complexity of the lids and the inability to see what the design was without destroying the devices.
Conclusion By the results obtained both by calculation and experimentation the vacuum thermos is much better at reducing the amount of heat transfer and therefore well worth the extra money if you would like to have your drink kept at the right temperature. Therefore the claims they make about the quality of a vacuum thermos are correct!