Why heat transfers

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In order for two substances to affect each other, they must be in thermal contact with each other. If you leave your oven open while turned on and stand several feet in front of it, you are in thermal contact with the oven and can feel the heat it transfers to you by convection through the air.

Normally, of course, you do not feel the heat from the oven when you're several feet away and that is because the oven has thermal insulation to keep the heat inside of it, thus preventing thermal contact with the outside of the oven. This is of course not perfect, so if you stand nearby you do feel some heat from the oven. Thermal equilibrium is when two items that are in thermal contact no longer transfer heat between them.

The basic effect of heat transfer is that the particles of one substance collide with the particles of another substance. The more energetic substance will typically lose internal energy i. The most blatant effect of this in our day-to-day life is a phase transition, where a substance changes from one state of matter to another, such as ice melting from a solid to a liquid as it absorbs heat. The water contains more internal energy i.

In addition, many substances go through either thermal expansion or thermal contraction as they gain and lose internal energy. Water and other liquids often expands as it freezes, which anyone who has put a drink with a cap in the freezer for too long has discovered. The heat capacity of an object helps define how that object's temperature responds to absorbing or transmitting heat. Heat capacity is defined as the change in heat divided by the change in temperature.

Analogies All three molecular transport equations are identical. In the mass transport two components are being transported by relative motion. In heat transfer, molecules are relatively stationary and transport is taken by electrons. Transport of momentum is occurred by several types of mechanism.

Driving forces Thedriving force momentum, temperature,or concentration difference becomes smaller as timeprogresses, and eventuallybecomes zero when nomore transport takes place. The Reynolds Analogy is popularly known to relate turbulent momentum and heat transfer.

That is because in a turbulent flow in a pipe or in a boundary layer the transport of momentum and the transport of heat largely depends on the same turbulent eddies: the velocity and the temperature profiles have the same shape. From Wikipedia, the free encyclopedia. The turbulent Prandtl number Prt is a non-dimensional term defined as the ratio between the momentum eddy diffusivity and the heat transfer eddy diffusivity.