Hot Potato By David Weston Larissa Cannon Background

Hot Potato! By: David Weston Larissa Cannon

Background • Potatoes cook by absorbing heat through radiation and convection. The heat is then transferred through the potato by conduction. • The “perfect” temperature for a baked potato is 210 °F • Aluminum foil has a shiny side and a dull side. These two surfaces have different emissivities, meaning that the potato will absorb different amounts of radiative heat when the different sides of the foil are facing outward while cooking.

Hypothesis • A potato will cook faster if the shiny side of the aluminum foil is touching the potato than if the dull side is touching the potato.

Approach qconv Aluminum foil Potato qcond qrad

Approach cont… • We estimated the potato as a cylinder and solved for the time required to heat it to a specified “ideal” temperature of 210°F

Assumptions • We assumed that the aluminum foil would reach very near the temperature of the oven almost instantaneously • We assumed the potato to be a perfect cylinder • We assumed the presence of the aluminum foil would be tantamount to an instantaneous change in surface temperature for the potato and used an infinite Biot number to calculate the transient heat transfer

Experiment • We wrapped one potato with the shiny side in and the other potato with the shiny side out. • After allowing the oven to heat to 350°F, each potato was heated separately for the predicted time required to reach 210°F.

Experiment cont… • Once the potato reached the predicted time, we measured its center temperature using a thermocouple. • Our prediction? The potato with the shiny foil touching it will finish cooking in less time!

Results Side Touching Potato Predicted time Required to reach 210°F Predicted temp Actual temp Shiny 24. 2 min. 210 °F 122. 6 °F Dull 33. 2 min. 210 °F 143. 0 °F NOT 210 °F like we predicted

Results cont. . . • Since the measured temperatures did not match our predicted values, we measured the temp of each potato after the SAME amount of time Shiny side wins!

Improvements • Core a perfect cylinder out of the potato so that the transient heat transfer equations are more applicable • Use a thermocouple that can withstand the heat of the oven so that we can leave it in the potato and get the temperature profile for the entire heating process

Conclusion • Yes, if the shiny side is touching the potato, it will cook faster, so wrap it right! • The shiny side cooks faster because it absorbs more radiation from the oven and reflects more radiation back into the potato due to the difference in emissivity between the shiny and dull sides of the aluminum foil.