Heat-Facts about the heat. -Heat transfer.- Why does heat transfer from the hot to the cold body? -Three types of heat transfer.- Example with a combination of 3 modes or types of heat transfer.

Table of content

1.  Heat.

2.  Facts about the heat.

3.  Heat transfer.

4. Why does heat transfer from the hot to the cold body?

5. Three types of heat transfer.

6. Example with a combination of 3 modes or types of heat transfer.

Heat:

Heat is a form of energy that travels from one system to another because of temperature differences.

Facts about heat:

There are some facts about the heat that are explained by theories of heat.

·       Whenever heat exchange occurs, heat is consumed (heat lost by the hot body always equals heat gained by the cold body).

·       Heat flow from hot to a cold body.

·       Substance expands on heating.

·       Weight of the body did not vary if the body was heated or cooled.

·       To change the phase of material from solid to liquid or liquid to gases without temperature rise, a certain amount of heat is required.

Heat transfer

The science that deals with the determination of the rate of energy transfer are heat transfer.

What is meant by heat transfer?

As the term heat transfer shows it is the transfer of heat by movement of heat from one substance to another when a temperature difference exists.

How does heat transfer from one body to another?

Heat is the form of energy that transfers from one system to another system because of temperature differences.

When heat transfer occurs?

When there is a temperature difference exist.

·       Energy transfer as heat from higher to lower temperature.

·       Heat transfer stops when two mediums reach the same temperature.

Why does heat transfer from the hot to the cold body?

Heat flows from a hot body to the cold because the molecules or atoms of a hot body have high kinetic energy (which means they move faster) than cold bodies. As we all know, the kinetic energy of a molecule is a function of temperature(more temperature means more kinetic energy). To maintain thermal equilibrium these molecules start colliding with the molecules of the cold body (having low kinetic energy).

Then two variations occur,

1.    Molecules of the cool body get warm (speed up).

2.    Molecules of the hot body get cool (slow down).

So, the flow of kinetic energy from the hot body to the cold body causes heat transfer from the hot body to the cold body. And this is how heat is transferred in solid materials.

why heat transfer from hot body to cold body?

Why heat transfer is important?

In almost every branch of engineering, heat transfer problems are encountered but the concept of heat transfer is not just important for engineering fields, it has its unique importance in every field. Like, sweating is a very good example of heat transfer. Sweating did not concern with engineering, but it happens due to temperature differences between body and environment or due to work out of the body by heat transfer.

Three types of heat transfer or three modes of heat transfer:

Heat transfer which is defined as the transmission of energy from one system to another due to temperature gradient (change in a temperature over a specified distance between two locations) takes place by the following three modes.

·       Conduction

·       Convection

·       Radiation (In heat transfer, we specifically study thermal radiation)

All modes of heat transfer require the existence of temperature differences from high to lower temperatures.

Combination of three modes of heat transfer with example.

In the majority, heat transmission occurs as a result of the combination of three modes of heat transfer.

For example, the water in a boiler shell receives its heat from the fire- bed by direct contact of heat with the shell (conduction) also from the radiation produced from the fire bed. water gets heat from the inner shell wall by contact of shell surface with adjacent liquid (convection).

3 modes of heat transfer.