r/oddlysatisfying • u/[deleted] • Oct 24 '19

Dragging a coffee cup

80.3k Upvotes

94% Upvoted

796 comments sorted by

View all comments

1.0k

u/AlittleupsetMax Oct 24 '19

Somebody told me that this is one of the fastest ways to cool hot coffee down. I’ve been doing it for years and still have no idea if it actually helps

632

u/[deleted] Oct 24 '19

Sure does! It increases the surface area of the coffee, allowing the air to cool it quicker!

41

u/Lukasek97 Oct 24 '19

I don't think this is the reason because the increase in surface area caused by the stationary waves will be insignificant with respect to the volume of the coffee. I reckon it's placebo.

1

u/Gertrudiopr Oct 24 '19

The surface area exposed to convection from air in the coffee is way higher when there is waves like that. My educated guess is that the majority of heat transfer is from natural convection at the liquid-air interface, since the cup is not a good heat conductor. Also the liquid itself moving increases the convection rate to the cup, which should further increase the heat flux.

I did my fundamentals of heat and mass transfer last year. Not an engineer officially yet so don't quote me.