The Concept of Heat Transfer Part II

Heat is capable of transferring from one point to another with or without any material medium through which is transferred. This is what is termed as "Heat Transfer." Heat can transfer through solid medium and in fluid ( either liquid or gas).

The effects of thermal expansion on Solids and Liquids

When is applied to solids or liquid, it expand but when cools it contract. This concept can be practically demonstrated using simple methods.

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Experiment to demonstrate the effects of heat change on solid

For instance a metal ring and metal ball are provided. Upon cooling, the metal ball fix exactly into the metal ring. But when heat is applied to the metal ball, it can no longer fix into the metal ring.This clearly shows that when heat is applied to solid, it expand but when cools it contract.

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Experiment to demonstrate the effects of heat change on liquid

Water is poured into a cooking sliver pot. Upon cooling you see that the water has contracted looking at the meniscus. As soon as it's places on hot flames like combustion of charcoal on coal pot, the convection currents begins to circulate in the container. The molecules collide with each other. The heating of the bottom of the silver cooking pot causes expansion of the liquid.

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Mode of heat transfer

There are three processes by which heat transfer from one point to another. These are conduction, convection and radiation.

Conduction

It's the process by which heat is transferred from one point to another in solids. For example one end of a metal bar is inserted into a hot flame. The heat from the point source of the metal is able to travel through the metal bar to the other end. To really observe this effect, you can place a candle wax at the end of the metal bar. As the heat begins to move through the metal bar, the candle wax will begin to fall. In the diagram below, the "A" will begin to fall before "B" in that order.

Application of conduction

In every day life, blacksmith is able to beat the metal into different shape because of heat applied on the metal to make it soft. Cooking is possible due to heat applied on the cooking pots. Combustion of bushes and houses occur as a result of excessive heat on the environment.

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Convection

Convection is the process of heat transfer from one point to another through material medium of liquid or fluid. The molecules of liquid move colliding with each other. This motion are sometimes in circular way called convection currents. In our everyday life, we heat water. Heat from the bottom of water in the vessel extend upwards through convection.

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Radiation

This is the process by which heat travels through an empty space of vacuum without any material medium carrying the heat. Heat from the sun reaches the earth surface through radiation. The heat coming from the see breeze and microwave oven are all examples of radiation.

Reference 1