1. MODULE-1
According to thermodynamic concept ,
the energy that is transferred as a result
of a temperature difference is called
HEAT
THREE DIFFERENT TYPES OF HEAT
TRANSFER:
1.CONDUCTION
2.CONVECTION
3.RADIATION

2. Itmportances of heat transfer:
1.electrical engineerg:cooling system for
motors,generators and transformor
2.chemical engineering:
evaporation,condensation,heating and cooling
of fluid
3. civil engineering: constructions
dams,structures,building design.
4.mechanical engineering:heat transfer in
internal combustion engine,steam
generations,refrigeration and heating and
ventillation.

3. Conduction:it is the process by which heat flows from a
region of higher temperature to a region of lower
temperature within the substance. Conduction take
place by two mechanism:
a)by lattice vibration:molecules at higher temperature
imparts energy to adjacent molecules at lower
temperature.
b)by free electrons: transfer of heat by free electrons,
the free electrons concentration in non-metals is very
low.Hence conduction is found in solids

4. Convection:it is possible only in the presence of
fluids( liquid and gases).As fluid passes over hot
objects,they pick up heat energy and carry it to
colder area.
Two types of convection:
1.free convection
2.forced convection

5. RADIATION:RADIATION HEAT TRANSFER
BETWEEN TWO SUBSTANCES TAKE
PLACE EVEN WITHOUT ANY MEDIUM
THROUGH ELECTROMAGNETIC WAVES

6. Heat flux: it is the amount of heat flow
per unit area through a body=Q/A
W/m2
the materials having higher thermal
conductivity are conductors, while
material having lower thermal
conductivity are called as insulators

7. Radiation is the only way that heat can
move through a vaccum.Radiant heat
can be felt by holding a hand near any
hot object,higher the temperature of
the object, more energy being
released. The denser the solid, the
faster heat will be transferred from the
hottest regions to coldest.

8. Convection: Is the way heat flows
through fluids, whether they are
liquids or gases.

9. THE LAWS OF HEAT TRANSFER.
1.Fourier’s law of heat conduction.
The rate of heat flow is proportional to
the product of the area of flow A, and
the temperature gradient (-dt/dx),the
constant of proportionality being the
thermal conductivity k, which is a
property of material.
Unit is j/s or W
Qx=-kA(dt/dx)

10. 2.NEWTONS LAW OF HEAT
CONVECTION
Q=hA(t1-t2)
heat transfer is occuring from a
surface area A at temperature t1, to a
fluid at a lower temperature t2.
h is the convection co-efficient in
w/m2K

11. STEFAN-BOLTZMANN LAW OF RADIATION:
Q=EσAT4
T-absolute temperature,
A-surface area,
E-emissivity
σ-stefan boltzmann constant,5.67*10-8w/m2k4
It states that the radiant energy emitted by a black
body is proportional to the surface area and fourth
power of its absolute temperature.

12. Thermal conductivity:
thermal conductivity, k is the property
of a material's ability to conduct heat
PURE METALS HAVE HIGHER VALUES
OF THERMAL CONDUCTIVITY WHILE
GASES AND VAPORS HAVE LOWEST.

14. K for a pure metals decreases with
temperature.
K=ko(1+bф+cф2)
where ф=T-Tref.
K for a non homogeneous materials
increases both with increasing
temperature and increasing density.

21. Thermal conductivity: it is defined as
the ability of a substance to conduct
heat. It is expressed in w/m-k or
w/moC.
Heat transfer co-efficient(h): ability of
the fluid carry away heat from the
surfaces which in turn depends upon
velocities and other thermal
properties.unit w/m2 k or w/m2oC