CHAPTER ONE

INTRODUCTION

In large industrial processes, it is necessary to transfer heat between the system and its surrounding and the device whose primary objective to do it efficiently and effectively is the heat exchanger.

          Therefore heat transfer is defined as the rate of exchange of heat between one body (hot) and another cold.

          The most important aim in the chemical engineering sector of any plant is to control the flow of thermal energy between two terminals. It there existing temperature gradient of change.

          In industrial process, the heat exchange is a very important unit in all the processing industries that their design has been highly developed. Designers of heat exchanger must be constantly aware of the difference between the idealized conditions for and under which basic knowledge was obtained and the real conditions of the mechanical expressions of their design and it’s environment.

          The design must satisfy process operational requirement such as availability and maintainability.

          Heat transfer or thermo-kinetics is another chapter of the theoretical fundamentals of heat engineering dealing with the processes of heat propagation. In nature and engineering, the most diverce process of heat propagation are observed and also heat flow from bodies (or their section) of a lower temperature. During the process of heat transfer, from one body to another heat flow continues till their temperature became equal be come to equilibrium state of temperature.

MODES OF HEAT TRANSFER

          Heat is transferred by conduction, convection and thermal radiation. In practice, heat is usually transmitted by two or all the three modes of heat transfer concurrently.

CONDUCTION

          Heat conduction of simply conduction is the transfer of heat by a direct contact between the elementary particles of a body, Viz molecules, atoms, free electrons, when the bodies involved are at rest.

          Pure conduction takes place in opaque or non transpired solid.

          In goses, conduction occurs due to random motion of the molecules (the diffuse from high concentration region to lower region. In this made of heat transfer, it is very common with metals and thus call for high thermal conductivity. Also the heat transfer per unit area is proportional to normal temperature gradient given as:

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