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 ModelUsing 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.

Foam Thermoscm m

r1 3.95 0.0395 k,plastic 100W/m*K Cp,water 4.207KJ/kg*Kr2 4.05 0.0405 k,foam 0.012W/m*K Density 995kg/m^3r3 4.25 0.0425 h, air 50W/m^2*KL 12 0.12 Rtot 0.053607

V 0.5L Rplastic 0.000332Rfoam 0.053275

Time (min) Time (sec) T (Freezer) T(h20) q (W)0 0 -10 95 -1958.711 60 -10 94.06415 -1941.262 120 -10 93.13664 -1923.953 180 -10 92.2174 -1906.81

56 3360 -10 53.59938 -1186.4157 3420 -10 53.03253 -1175.8458 3480 -10 52.47073 -1165.3659 3540 -10 51.91394 -1154.9760 3600 -10 51.36211 -1144.67

Model of Foam Thermos

Vacuum Thermoscm m

r1 6.3 0.063 k,vac 0.015W/m*K Cp,water 4.207KJ/kg*Kr2 6.35 0.0635 k,al 250W/m*K Density 995kg/m^3r3 6.45 0.0645r4 6.5 0.065 Rtot 0.975293161L 17 0.17 V 0.5L Ral1 2.96035E-05

Rvac 0.975233954Ral2 2.96035E-05

Time (min) Time (sec) T (Freezer) T(h20) q (W)0 0 -10 95 -107.661 60 -10 94.94856 -107.6072 120 -10 94.89715 -107.5543 180 -10 94.84576 -107.502

57 3420 -10 92.10786 -104.69558 3480 -10 92.05784 -104.64359 3540 -10 92.00784 -104.59260 3600 -10 91.95787 -104.541

Model of Vacuum Thermos

The measured experimental results after one hour in the freezer:Vacuum thermos= 82Foam thermos= 40

Calculated results by excel model:Vacuum thermos=91.9Foam 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.

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!