That`s why I love plastic ice cubes. Keep in the freezer for some time so the water inside will freeze and enjoy your non-watered down drinks!
Cooling a cup of coffee with help of a spoon
31–40 of 45 posts
Re: Cooling a cup of coffee with help of a spoon
#32Earlier quoted context omitted.
Surely there are some regular motions which could be approximated using a spoon which would more efficiently move the hottest parts of a liquid to the surface than random turbulence? My intuition says sliding the spoon down the side of the mug, then turning the flat side upward and lifting it in the middle of the mug would be one such more efficient motion. Does anybody have a supercomputing cluster we could use to r…
I got one, but unfortunately it's still working on the milk-or-tea-first conundrum.
>milk-or-tea-first
Ahhhhh, the one debate more divisive than emacs-or-vim.
Re: Cooling a cup of coffee with help of a spoon
#33Feynman would get a cup of coffee, a spoon and a thermometer.
Re: Cooling a cup of coffee with help of a spoon
#34I also remember my grandfather using saucering to cool hot tea down, I finally have an explanation for why it works. I wonder why the practice went out of fashion. Do paper doilies send a signal that the saucer is not to be used to hold liquids?
From reading the Laura Ingalls Wilder books, when I was a young'n, I remember that 'saucering' was considered rural, unrefined behavior. That kind of thing goes out quick; I bet none of the Silver Screen movie stars were seen saucering their tea.
Re: Cooling a cup of coffee with help of a spoon
#35I always stir my coffee in a random way so that you see turbulent movement in the cup as opposed to the whirlpool you get from moving the spoon in smooth circles. My intuition tells me that this should give more efficient cooling. I basically have nothing to back this up. Thinking about it, it probably makes more sense for dissolving the sugar than cooling the coffee.
Your aim is to make sure that every bit of the coffee eventually makes it to the surface (so that the highest-energy molecules there can escape and cause cooling). If you stir regularly then (roughly) each bit of the coffee just moves in a circle, and parts that start out below the surface stay below the surface. If you stir it at random, then (this is probably a theorem, if you define "random" with a bit of care, an…
Right, what I remember from Thermo II 20 yrs ago is that heat transfer in turbulent flow is higher than in laminar flow. Heat transfer is basically deltaT * someFactor, with someFactor depending on a ton of parameters. One of them is whether it's laminar or turbulent.
Re: Cooling a cup of coffee with help of a spoon
#36I always stir my coffee in a random way so that you see turbulent movement in the cup as opposed to the whirlpool you get from moving the spoon in smooth circles. My intuition tells me that this should give more efficient cooling. I basically have nothing to back this up. Thinking about it, it probably makes more sense for dissolving the sugar than cooling the coffee.
Someone on physics.stackexchange already mentioned that we should probably ask chemists. IIRC, the most commonly used stirring method in industry is, basically, figures-of-8.
Re: Cooling a cup of coffee with help of a spoon
#37I remember similar physics puzzle from high school days. Given a cup of hot tea and few spoons of sugar how does one go about sweetening the tea so that it would cool off the most in the process.
First, remove your sugar crystals from the thermos of liquid nitrogen...
Should you crush the sugar crystals (to promote rapid cooling) or should you use the largest possible crystals so there are more bonds to be broken?
I'm going to guess that there's a sweet spot in there somewhere; a priori it seems you want the maximum size that will dissolve completely.
Re: Cooling a cup of coffee with help of a spoon
#38Earlier quoted context omitted.
Your aim is to make sure that every bit of the coffee eventually makes it to the surface (so that the highest-energy molecules there can escape and cause cooling). If you stir regularly then (roughly) each bit of the coffee just moves in a circle, and parts that start out below the surface stay below the surface. If you stir it at random, then (this is probably a theorem, if you define "random" with a bit of care, an…
Surely there are some regular motions which could be approximated using a spoon which would more efficiently move the hottest parts of a liquid to the surface than random turbulence? My intuition says sliding the spoon down the side of the mug, then turning the flat side upward and lifting it in the middle of the mug would be one such more efficient motion. Does anybody have a supercomputing cluster we could use to r…
>My intuition says sliding the spoon down the side of the mug, then turning the flat side upward and lifting it in the middle of the mug would be one such more efficient motion.
You're still going to be getting laminar flow unless you're lifting fast enough to eject the tea from the cup (which I assume is contrary to the rules). I use a forward and backward motion going from low down at one side to high up at the other (especially when stirring hot soup for my little nearly 2yo) - I'm trying to produce a ragged (turbulent) collapsing void of air, maximising the surface area exposed particularly in producing as much turbulence as possible at the surface. One tends to get spiralling voids at either edge of the spoon.
I wonder if you can stir fast enough to produce cavitation and what effect that would have on the results.
Also can I design my own spoon to use?
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Re: Cooling a cup of coffee with help of a spoon
#39This is related to the phenomena that tea leaves tend to group in center of cup when you stir it with spoon.
Due to centrifugal forces the level of water near the border is higher that at the center so the water start to flow from borders to center at the bottom of the cup.
This speed up heat exchange as the water gets constantly mixed in addition of usual thermal exchange flow.
Re: Cooling a cup of coffee with help of a spoon
#40Earlier quoted context omitted.
I didn't understand that comment... was he insinuating physicists don't know thermodynamics? The original question is pretty basic.
I think he was saying that although physicists generally understand the principles involved, a chemist might have a better sense of the relative magnitudes of the different effects that come into play in cooling a solution, since chemists have to perform this task routinely.
I suppose, but any physicist worth anything should be able to remember enough high school chemistry to deduce the answer.