HEAT TRANSFER

The transfer of heat can take place by twophenomena known as conduction andradiation.

As a result of conduction and/or radiationoccurring into a fluid media then a transport ofheat may occur called convection.

Heat transfer: the mechanisms

Three mechanisms for heat transfer: conduction, convection and radiation.

CONDUCTION

In conduction heat is transferred through amaterial.

It is considered energy transfer occurs due toatomic or molecular impact which results fromatomic or molecular vibration in the case of solids.

It is also probable that there is some free electrondrift showing an energy flux in the direction ofreducing temperature.

So metals with their more compact molecularstructure show greater thermal conductivity thanliquids.

CONDUCTION THROUGH A FLAT PLATE OR WALL

CONDUCTION THROUGH A COMPOSITE WALL

CONDUCTION THROUGH A COMPOSITE WALL

RADIATION

Unlike conduction, radiation requires notransfer medium between the emitting andreceiving surfaces.

The classic example of energy transmission byradiation is the sun, which transmits abundantenergy to the earth by this means.

It is an electromagnetic phenomenon of varyingwavelengths closely allied to the transmissionof light and radio.

CONVECTION

Heat transfers which occurs as the result of themovement of the fluid.

It cannot take place in a solid. Most of the hot water will eventually pass up into

the pipe and in its passage through the pipe willlose some heat.

It will therefore fall through the pipe as its densityincreases and will eventually reappear at thebottom of the vessel once again to receive heat.

Thus a circulation of water has been createdcalled a convection current.