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I know that there is asked questions about something like cooling down cope of coffee..etc, but this one is little different.

My friend was watching TV program of English eating etiquette, and they mentioned that it will be faster to move teaspoon back and forth in a line instead of in a circular way (what we doing usually) will force sugar to dissolve much faster!

But I'm very suspicious with that, and my argument taken from my observation that all of the mixers I saw in industrial level was moving in a circular way, and I believe that they optimized their productivity as much as possible.

So is there any physical reasons that explains which motion will produce the best vortexes for sugar dissolving?

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You should note that sugar doesn't melt - it dissolves. This makes a difference, since melting requires transfer of thermal energy, while dissolving depends on the saturation level of the liquid near the solid. –  Chris White Feb 5 '13 at 8:06
    
Yes thx, sorry for that, it's my English, corrected. –  TMS Feb 5 '13 at 8:12
    
I wonder who downvoted this question, and why? –  Bernhard Feb 5 '13 at 20:21
    
@Bernhard, I got used for such unreasonable behavior here :) –  TMS Feb 5 '13 at 20:53
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up vote 2 down vote accepted

Dissolving depends on several parameters, one of them is the amount of matter already dissolved in the medium. You can't dissolve any amount of sugar in a cup of tea, at some point it stops dissolving.

When circling, the stuff moves all the time pretty the same path thus you don't mix sugar and water too much comparing to each other, they move the same direction because of inertia. Thus the concentration of sugar in some parts of water may be higher and sugar dissolves slower.

In back-and-forth "style", you always change the direction the particles move and thus you mix them more effectively, so you can't have areas where sugar is more concentrated. Which means it should dissolve faster.

That's my assumption :)

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The term you are looking for, is turbulent diffusion: en.wikipedia.org/wiki/Turbulent_diffusion –  Bernhard Feb 5 '13 at 9:12
    
Thanks, didn't know that term –  ctapobep Feb 5 '13 at 9:39
    
It seems logical for me, anyway we still don't know if moving the spoon back/forth needs less (what I doubt) energy than moving it in a circular way. –  TMS Feb 5 '13 at 14:31
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The question was about speed of dissolving, not about energy.. Of course you'll spend more energy because you'll be moving spoon against inertia. If you want to save energy, then just don't use spoon, sugar will dissolve on your own. –  ctapobep Feb 5 '13 at 20:09
    
Yes, I just wanted to make sense of the industrial mixers. –  TMS Feb 5 '13 at 20:55
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