Monday, August 24, 2015

Reflections on a mug of tea

A question for students (its good to have an open ended question sometimes):

A ceramic mug of hot tea sits on a wooden table. Discuss how it cools. (Yes I know the picture does not show a wooden table... :) )

Convection from the surface is important.
Conduction through the sides and then cooling by convection significant too.
Cooling by radiation happens too although the temperature difference is small.
Conduction through the base not important as the ceramic is a poor conductor and the wood is worse.

How can the cooling be enhanced?
Convection is easily speeded up by a higher flow of air (blowing, fan, breezy location etc).
Putting a spoon in the cup increases conduction loss.
Using a black mug will help a little.
Drastic methods! (if you are late for work) - pour into another vessel, add ice etc.

Tuesday, August 11, 2015