Heat can be defined as the energy transferred from one body
to another body due to the difference in temperature. Heat
can flow spontaneously from an object at higher temperature
to another object at lower temperature.
It is
denoted by Q. Heat transfer to the system is taken +ve and
heat transfer from the system is taken as –ve`.
The
heat is measured in joules.
METHODS
OF HEAT TRANSFER:
There
are three methods of transfer of heat from one object to
other.
Conduction:
It is
the most significant means of heat transfer in a medium
(solid, liquid and gases). In this method the hot and
vibrating atoms come in contact with the neighboring atoms
and molecules, transferring a part of heat to these
neighboring atoms. It can be shown as
Q = kA
(t_{1}t_{2})/l
Where Q
is the heat transfer rate, t_{1}t_{2} is
the temperature difference, A is the area of the heat
transfer surface and k is the thermal conductivity of the
material.
Convection:
In
conduction the heat transfer takes place by fluid flow. As
we give heat to the fluid, it will transfer the heat to its
neighboring molecule and so on. There are two types of
convection.
1.
Free convection: In force convection the fluid moves
under gravity.
2.
Forced convection: In this type of convection we take
help of fan or blower to move the fluid
Radiation:
It is the heat transfer process in which there is no medium
present for the heat transfer from one body to another body.
It is the transmission of heat in the form of radiant
energy. It occurs in the vacuum because the medium will
affect the rate of heat transfer. The equation for radiation
heat transfer given by the StefanBoltzman is
E_{
}= σAt^{4}
Where E
is the energy radiated, σ is the StefanBoltzman’s constant,
t is the temperature of the surface and A is the area of the
surface.
