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My son is stirring a very hot chocolate hard because he thinks it will cool the chocolate down.
I said that stirring the liquid will increase the energy. Who is right?
If it is him, what is the best speed to stir and cool hot chocolate?
If it's me, is it possible to heat it up very quickly by stirring it?
Stirring helps cool the hot drink as it speeds up the convection process by bringing the hottest liquid at the bottom to the top, where it can be cooled by air.
But in fact, the convection will happen soon and you just speed up a little bit.
Experiments show that, unlike traditional mixing methods, the best way to cool hot drinks is actually to lift the spoon repeatedly in and out.
This is because the spoon heats up in the liquid, cools after removal, and absorbs heat from the system faster.
It is understandable to think that a quick stirring will add energy to the drink, but to significantly heat it, your stirring must be so fast that it will cause the drink to be almost anywhere else, but in the Cup.
In general, if you stir hot chocolate hard to resist the risk of overflow, it may be best to weigh the marginal reduction in the cooling time of hot chocolate and let it cool itself.
LONDON, England Corey treenir when hot chocolate slides on the edge of the Cup, it can move in layers when the flow is slow (called the flow), or when its motion is chaotic, for example, when it is stirred by faster stirring, it will be turbulent.
The driving force of heat transfer is the temperature difference between drink and air.
The greater the difference, the higher the rate at which heat flows between them from heat to cold.
The fluid layer has an insulating effect in the laminar flow, reducing heat transfer.
In turbulence, more fresh cold air will be in contact with the hot chocolate surface, resulting in faster heat transfer due to the larger average temperature difference between drinks and air.
Away from the surface, convection and contact with the cooler liquid will cool the hotter part.
"The driving force of heat transfer is the temperature difference between hot chocolate and air," you said adding kinetic energy to the fluid would raise the temperature exactly right.
The proof of this principle is that you can heat the soup by stirring the soup with a strong mixer for a period of time.
However, by the difference between the amount of heat lost in the flow of air and the amount of energy required for hot chocolate to significantly increase the temperature, it is better than any vibrant chocolate to be stirred by hand several orders of magnitude.
So in theory, son 1 parent 1, but in practice, son 1 parent 0. Sorry parent.
Adriana Fernandes in Urrbrae, South Australia, the quickest way to cool drinks is "stew pot", you pour part of the drink into the tea tray and then put it back in the tea tray.
This gives a larger surface area and can stir the liquid.
In my test, the cooker quickly cooled the drink.
Some even sip cooler liquids from the tea tray, a practice that has been around for centuries, but was outdated during World War II and is now considered in some circles
Ron dipode, San Diego, California, USA
An effective way to cool the drink is to blow it dry.
This makes cold air with a fairly low relative humidity in contact with the surface of the liquid and increases the cooling evaporation.
Blowing and stirring together will work the fastest.
Eric carvalenle-
In 2014, undergraduate students at the University of Leicester in the UK calculated that mixing tea would speed up cooling.
There is no doubt that they will come to a similar conclusion with hot chocolate.
Stirring at a rate of 100 revolutions per minute increases the surface area of the tea leaves, simply because the liquid in the resulting vortex is sunken in its center and rises where it meets the side of the Cup.
Undergraduates simulate the top of the liquid as a smooth, semi-spherical surface, but this may underestimate the area where convection cooling occurs.
After all, the surface of the real liquid being stirred will fluctuate and change constantly.
Flipping the liquid will also increase the speed of evaporation and cooling.
In any case, I suspect that simply having a metal spoon in your favorite hot drink will result in a faster cooling by providing another hot path.
Mike follows, Sutton Colfield, West Midlands, and UKWe pays £ 25 for every answer published on New Scientist.
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