How to make Convection in common life


Convection

Convection is defined as that mode energy transfer in which heat is transferred between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion. The faster the motion of the fluid, the more heat is transferred, and hence the more the convection heat transfer. When there is no bulk fluid motion, heart transfer between a solid surface and the adjacent fluid is by pure conduction. When bulk motion of fluid is present, the heat transfer increases between the solid surface and the fluid, but determination of heat transfer rates is complicated.
    Convection is called forced convection if fluid is forced to flow over the surface by external means such as pump, fan, etc. Convection is called as natural (or free) convection if the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid. Those heat transfer processes that involve change of phase of a fluid are considered to be convection because of the motion of fluid which is induced during the process, such as the rise of vapor bubbles during boiling or the fall of liquid droplets during condensation.                                                                                                                         The rate of convection heat transfer is directly proportional to the temperature difference and is conveniently expressed by Newton's law of cooling as
                         

Whereis known as the convection heat transfer coefficient and it is expressed in  w/m2.k,  is the surface area through which convection heat transfer takes place, Ts is the surface temperature, and T infinity is the temperature of the fluid sufficiently far from the surface. In conduction and convection heat transfer material medium is present. In convection, fluid motion is present. Heat transfer through a solid surface is always by conduction. Heat transfer through a liquid, or gas is by conduction or convection depending on whether bulk fluid motion is present or not.
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