Three mechanisms transfer heat: conduction, convection, and radiation. Conduction involves heat transfer through a material due to atomic vibration. Radiation requires no medium and examples include heat from the sun. Convection occurs through fluid movement and circulation, like convection currents in water heated in a vessel.

1. HEAT TRANSFER
 The transfer of heat can take place by two
phenomena known as conduction and
radiation.
 As a result of conduction and/or radiation
occurring into a fluid media then a transport of
heat may occur called convection.

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

5. CONDUCTION
 In conduction heat is transferred through a
material.
 It is considered energy transfer occurs due to
atomic or molecular impact which results from
atomic or molecular vibration in the case of solids.
 It is also probable that there is some free electron
drift showing an energy flux in the direction of
reducing temperature.
 So metals with their more compact molecular
structure show greater thermal conductivity than
liquids.

6. CONDUCTION THROUGH A FLAT PLATE OR WALL

13. CONDUCTION THROUGH A COMPOSITE WALL

15. CONDUCTION THROUGH A COMPOSITE WALL

20. RADIATION
 Unlike conduction, radiation requires no
transfer medium between the emitting and
receiving surfaces.
 The classic example of energy transmission by
radiation is the sun, which transmits abundant
energy to the earth by this means.
 It is an electromagnetic phenomenon of varying
wavelengths closely allied to the transmission
of light and radio.

24. CONVECTION
 Heat transfers which occurs as the result of the
movement 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 will
lose some heat.
 It will therefore fall through the pipe as its density
increases and will eventually reappear at the
bottom of the vessel once again to receive heat.
 Thus a circulation of water has been created
called a convection current.