Introduction to Heat Transfer

Importance of Heat Transfer

Heat transfer is all around us. This process is happening from household cooking stove to super hot sun. For an engineer it is important to predict amount of heat transfer occurring in the energy conversion device both qualitatively and quantitatively.

Modes of Heat Transfer

The way heat is getting transferred is different in different cases. There are 3 different mechanisms behind heat transfer, they are.

1. Conduction
2. Convection
3. Radiation

Trolley Analogy

A trolley analogy is used for explaining above 3 heat transfer mechanisms. In trolley example trolley represents molecules, ground altitude represents temperature and hot object represents heat.

Fig.1 Trolley anlalogy used for explaining different heat transfer mechanisms

Conductive heat transfer

It is analogical to a hot object is getting transferred along a slope with help of series of trolley. Here first trolley transfers hot object to second , second trolley transfers the object to third and so on. So all the trolleys remain in its own position, but the hot object is getting transferred from first trolley to last trolley. In world of heat transfer similar to this trolley example one phenomenon happens, Conduction.In conduction heat is getting transferred from high temperature to low temperature region with aid of vibrating layers of molecules.

Fig.2 Analogy between series of trolley example and conductive heat transfer

Convective heat transfer

It is analogical to a hot object is getting transferred along a slope with help of a single trolley. Here in order to transfer hot object from one end to other trolley also has to move with the object.Convective heat transfer is similar to this, where hot molecules actually moves in order to transfer heat from hot region to cold region.

Fig.3 Analogy between single trolley example and convective heat transfer

Radiative heat transfer

Can the hot object move with out help of a trolley? It might be difficult in trolley example, but is possible in heat transfer world. This kind of heat transfer where is medium is not required is known as radiative heat transfer. It happens in form of electromagnetic radiation.Unlike conduction and convection, Radiation is a one-way process.

Fig.4 Transfer of  hot object without a medium/trolley is analogical to radiative heat transfer

Industrial Applications

Heat transfer mechanism forms the heart of industries based on energy conversion. Consider a heat exchanger which produces steam in virtue of hot gases passing inside the tube.Here hot gas passes inside the tube and heat is transferred from hot gas to cold liquid surrounding it. Between hot gas and cold fluid there is a material interface known as heat exchanger. Here mainly 2 modes of heat transfer happens 1) from hot gas to metal interface - Convection 2) from hot metal surface to cold metal surface - conduction 3) from cold metal surface to fluid surrounding it - Convection

How to Build a Career in Heat Transfer?

The opportunities are enormous, its all depends upon your profession and specialization(thermal / chemical). Some of the fields which offer good career opportunities are listed below.

Heat Exchanger Design

This is an exciting area of heat transfer where you have to continuously use all your knowledge in heat transfer. Effect of radiative heat transfer may be neglected for heat exchangers handling low temperature. Main goals of designer are to make a 1) high heat transfer 2) compact 3) robust 4) economical heat exchanger. There are lot of reliable commercial tools available in market, such as HTRI for design purpose of heat exchangers.

Design of heat transfer enhancement mechanisms

There are extensive research works going on in all fields of heat transfer area in order to enhance heat transferred such as use of delta winglets, introduction of turbulent generators and use of heat transfer enhancement additives to working filed. Most of this research works are experiment or CFD based.

Process plant design

Almost all chemical reaction equipments are involved in huge amount of heat transfer. So it is imperative to have good amount of knowledge in heat transfer in order to design it, whether it is a oil refinery or acid reactor. One commonly used software for process plant design in ASPENPlus.

Electronic circuit cooling

Nowadays computer processors are becoming faster day by day. As calculation speed of processor increases it generates more amount of heat. If there is no effective mechanism to carry away this heat, that will damage whole electronic circuit. So design of cooling mechanism which will consume least amount of energy and at the same time will produce effective cooling is need of the hour. ICEPak is a specialized CFD software used in this field.