I am arguing with my friend about this ice cream scoop. He argues that this magical liquid inside of it (see product description) makes it cut through hardened ice cream better. I argue that it’s actually the fact that it’s made of a conducive metal, and that metal conducts heat well. Any help?
Per the site:
They seller says its the liquid. They make no mention of the metal.
An ice-cream scoop, sir?
The product description doesn’t name the magical liquid inside the scoop, but if the liquid comprises at least some water, that might contribute toward a larger heat capacity than an otherwise identical scoop made entirely of metal. Higher heat capacity means that the scoop’s temperature will stay above the ice cream’s temperature for a longer time, thus making it easier to cut through the ice cream. The same effect can be achieved, perhaps more cheaply, by keeping a set of all-metal scoops in a hot water bath, and returning each scoop to the bath after dispensing the ice cream.
You are a marketer’s dream.
That’s pretty much my thesis; that if the liquid does anything, it’s only because it prevents the metal from getting cold quickly when the ice cream touches it. The liquid doesn’t really have any amazing properties that water doesn’t have; it’s just a buffer to prevent the metal-- which conducts heat very well-- from getting cold. If the scoop was made of plastic, this wouldn’t do anything.
That’s similar to my method. I’ve got a metal scooper and rinse it under a hot water faucet before starting and between scoops. Works great.
I remember seeing as a kid at Baskin Robbins them keeping the scoopers in holders filled with recirculating hot water.
Maybe the “heat-conducting liquid” is water.
I have two ice-cream scoops that look like that. Once sloshes when you shake it, the other doesn’t. The one that sloshes works slightly better.
Yeah, heat capacity. Something like aluminum is an excellent heat conductor, but doesn’t have much heat capacity, whereas the heat capacity of plain water is enormous. A brief poke about suggests that the liquid isn’t just water, it’s got something like antifreeze in it. The main reason for that would probably be to prevent the liquid in the handle from freezing solid eventually, say if you accidently left the scoop in the ice cream when you put it back in the freezer. I suppose if it froze, the expansion of the ice might rupture the handle.
The heat capacity of water is around four million joules per cubic meter kelvin, where as metals are usually around two million. It isn’t enormous. I think ABS polymer is about the same as water, and if somebody put plastic in the handle, you wouldn’t expect any magic.
Heat capacities of solids and liquids are generally around a couple million in these units. If you base heat capacities on mass instead of volume, they vary more widely, but only because densities vary over a wide ratio.
The water could be a better conductor if it convects, for example because you’re moving the handle around. Convection really IS a huge multiplier.
If it’s the substance we care about, without regard to its phase, we should consider that for most substances the liquid phase is only about half as conductive as the solid phase.
If it’s using heat from your hand, that suggests a heat pipe, not just a reservoir. And a lot of heat pipes contain a substance which goes through a phase transition at an appropriate temperature.
Of course, if it really does work using heat from your hand, that means that your hand is going to get really cold, dishing up the ice cream.
You should dry your scoop before use to avoid having ice crystals form in you ice cream.
Actually I kind of like the ice crystals 
I have an ice cream scoop like this and another reason to think that it’s not just water in it is that the instructions specifically said not to put the scoop in the dishwasher (or heat it to more than 140 degrees), because the heat would affect the heat conductive fluid
I don’t know what’s in it, but if water is in a sealed container and heated to more than 140[sup]o[/sup]F, it would certainly be “affected.” I don’t know what pressure could build up but I suppose it’s possible the thing could crack open.
I have this ice cream scoop. Without the liquid in there, heat transfer from the “handle end” to the “scoop end” would occur very slowly. With liquid in there, and only partially filled, the liquid can transfer the heat much faster. But you have to manually slosh the liquid between the two ends for this to occur.
My impression is that ice crystals are the result of thawing and refreezing ice cream.
Um… Are you talking about a few ice crystals from water left on the surface of the ice cream, or ice crystals throughout?
The metal is a good way to transfer heat, but I would not say that plastic would not work at all, and perhaps a ceramic scoop would work better then metal. But it seems like it’s the magic liquid more then the metal. The metal is more acting as a container so the fluid is held in proper shape. If it were possible to have the fluid held by surface tension alone that would probably be superior to all 3,** so the metal is a hindrance just less so then plastic.**
I though the ice crystals are a result of sublimation and refreezing, AFAIK my freezer maintains temps below freezing and there should be no melting/refreezing.