I supported a kickstarter campaign a while back for an innovative idea: Coffee Joulies, stainless steel 'beans' filled with a special 'phase change material' that liquefies at 140 degrees, absorbing energy in the process (cooling your coffee) and later solidifies releasing energy (warming your coffee). Idea is that the coffee cools off to be drinkable sooner, but stays warm longer. Good for long drives, etc.
I finally received them in the mail recently, they look like this:
I did some testing on them and the results were not dramatic. I used matching ceramic travel mugs, with lids, and tested both with 2 thermometers, a coffee thermometer and an over thermometer:
I used exactly 1.5 cups of near boiling water and then charted temp over time. I used 3 of the joulies in one mug, and zero in the other.
There was a mild, noticeable effect. However, it wasn't dramatic. Initial temp was 180 in the non-joulie mug, and about 173 in the joulie mug. At the tail end of the experiment, there was about a 5 degree delta the other way, with the joulie mug being warmer.
So they work, right? Not necessarily.
Having those 3 objects in the mug is going to do two things:
(1) It will cool the liquid off at the outset because there's more heat exchange going on.
(2) It will change the overall volume of the resultant 'coffee + joulies' entity. Since the cooling has to do with heat exchange with the outside air (ok coffee <-> mug <-> air). The mug with the joulies is more full, and since the volume rises exponentially compared to surface area, a larger volume will cool more slowly. For an example of this, see THE MOLTEN CORE OF THE EARTH!
So, to know whether the phase change material actually makes a difference, versus say, throwing a handful of well polished rocks in there (see how medieval people kept their tootsies warm in bed), I'd have to do another experiment. Maybe if I have time in the coming days.
So, I'd say the jury is still out. but I certainly didn't notice a huge dramatic effect. It may have been more pronounced with all five joulies in the cup, but now I'm sacrificing significant coffee volume, and I needs me the java.
[Update: Another thing that occurred to me is that the PCM liquification could probably be verified with the boiled-egg-spinning trick. Heat the joulie up, sit it next to a cool one, try and spin both of them like a top. The one with the liquid center shouldn't spin well]
[Update: Doh! Looks like BoingBoing beat me to posting a review AS I WAS WRITING THIS!. Looks like they concluded roughly the same thing]