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Introduction

The discipline of Heat Transfer is science about the methods of distribution of
thermal energy in space and in time. In the simplest of terms, the discipline of heat

transfer is concerned with only two things: temperature, and the flow of heat.
Temperature represents the amount of thermal energy available, whereas heat flow

represents the movement of thermal energy from place to place.

The theory of heat transfer is younger than engineering thermodynamics. Its was

created at the end of 19 age and at the beginning of a 20 age. It was time when began to

build many thermal machines power (engines). Its loss a lot of heat through the walls of

cylinders of machines and the walls of a boiler. The losing heat influenced on efficiency

of engines. Thus it was needed to calculate these losses, and then to avoid them. So due

to these problems science of heat transfer is created.

On a microscopic scale, thermal energy is related to the kinetic energy of molecules.

The greater a material's temperature, the greater the thermal motion of its constituent

molecules (manifested both in linear motion and vibrational modes). It is natural for

regions containing greater molecular kinetic energy to pass this energy to regions with

less kinetic energy. Several material properties serve to modulate the heat transferred

between two regions at differing temperatures. Examples include thermal

conductivities, specific heats, material densities, fluid velocities, fluid viscosities,

surface emissivity’s, and more. Taken together, these properties serve to make the

solution of many heat transfer problems an involved process. Thermal energy is related

to the temperature of matter. For a given material and mass, the higher the temperature,

the greater its thermal energy. Heat transfer is a study of the exchange of thermal energy

through a body or between bodies which occurs when there is a temperature difference.

When two bodies are at different temperatures, thermal energy transfers from the one

with higher temperature to the one with lower temperature. Heat always transfers from

hot to cold.

Heat transfer: energy transport because of a temperature difference. Thermal

energy is transferred from one region to another.

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