Saturday, September 11, 2010

Why do Tea particles keep rising to the surface while making Tea?

Ever wondered about this simple thing, while you're making Tea?
Those tiny Tea particles that give you that immensely refreshing taste, while these get cooked while you are preparing Tea for yourself or others, (well, that doesn't require you to be making Tea yourself thought :P, still...), you might have seen those little pieces rising above to the surface as if they're coming up to catch a breath of fresh air and then deep dive again, or as they say in those cartoon movies, they take heat, get themselves burnt and rise up in pain!
But that's not what happens here, that might happen in a cartoon movie though!
The scientific reason to this small action lies in a simple one letter word which connects us to the theory of Energy-Transfer
It says Energy can be transferred from one body to the other by 3 means

  1. Conduction
  2. Radiation
  3. Convection -- This is the one we're interested in!
The simple reason is Convection!
WikiPedia says,
Convection is the movement of molecules within fluids (i.e. liquids, gases) and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids.
Convection is one of the major modes of heat transfer and mass transfer. Convective heat and mass transfer take place through both diffusion – the random Brownian motion of individual particles in the fluid – and by advection, in which matter or heat is transported by the larger-scale motion of currents in the fluid. In the context of heat and mass transfer, the term "convection" is used to refer to the sum of advective and diffusive transfer.
Convection Current inside the cooking vessel.
Note the flow of the particles.
It is the same that the Tea particles follow
Due to Convection, the particles that take up heat from the bottom, become lighter and start coming up to the surface. These particles then transfer their energy to other particles. Then these particles after transferring their energy become heavier, again go down and again pick up heat. This leads to a continuous flow of the liquid particles up and down in a circle sort. How and in which manner this circle goes about depends on the heat variation and generally starts from the bottom center to outwards and then up again, where these lose energy and then get down to the top center and then back to the bottom.

Another picture from our daily life would illustrate how these particles flow. This is a general picture that we always see when cooking
Observe that the flow is radially inwards
So, the next time you go and make Tea (or maybe, even just observe it), just keep in mind this very word --

Have a Nice Day!
(Do Comment if You Liked, and share the knowledge)

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