Energy transfer deals
with the transfer of heat energy which take place from one body to another body as a
result of temperature difference. There are many transport process
which occurs in nature and in the devices
man in which flow is driven or modified by density differences caused by
chemical composition differences, radiation and material or phase
Heat is a transport of thermal energy due to temperature gradient.
transfer phenomena play an important role in many industrial and environmental
The study of temperature distribution and heat transfer is
great importance to engineers and scientists to design, operation and
maintenance of any thermal system in order to
transfer specified amount of heat in a
time. The optimal design of heat exchangers such as , boilers,
condensers, radiators, heaters, furnaces, refrigerators, and solar collectors
analysis of heat transfer .
The basic modes of heat transfer are
The flow of Conduction is heat energy
occurs in a substance, from a region of high temperature to the low temperature
by direct molecular interactions and the drift of electrons. The exchange of energy
from molecules at a relatively high level energy to adjacent molecules with
lower energy levels.
heat transfer conduction in gases and liquids ,occurs due to the diffusion and collisions of the molecucles during their
random motion. In solids, it is due to the
combination of free electrons
and lattice vibrations. Copper,
Silver, Iron, Steel are good conductors of heat. Wood, air, paper, Styrofoam
are poor conductors of heat.
The convection is the heat
transfer in which the energy is transported by moving fluid particles. The
convection heat transfer consists of of two system. First is transmit of energy
due to random molecular motion and
second is the energy transmit by mass or macrospic motion of the fluid. The
molecules of fluid are moving collectively or as aggregates thus take energy
from high temperature region to low temperature region.
If heat transfer between the
fluid and the solid surface occurs by
motion of fluid particles due to
the density differences caused by the temperature differences between the surface
and the fluid, then the Convection heat transfer process is classified according to
the nature of the flow as forced convection and free or natural convection.
If heat transmit
between the fluid and the solid surface occurs by fluid motion created by process
of an external work then the mode of heat transfer is termed as
“Forced Convection’. Like fan or
blower, heat exchangers, nuclear
reactors, air conditioning apparatus are examples of devices functioning based on
Free Convection is one of the modes of transfer of heat
between a surface and fluid moving over it. This is only possible in a fluid
medium. When a fluid flows inside a duct or over a solid body and the
temperature of the fluid and surfaces are different, heat transfer .
convection flows have been studied most extensively because they
found frequently in nature as well as in engineering applications. The process
in nature include a photosynthetic mechanism, calm-day evaporation,
beings, while the engineering applications include cooling of electronic
such as power transistors, TVs, and VCRs; heat transfer from the
refrigeration coils and power
Natural convection effects are also
encountered in mass transfer. For example,oceanic convection is driven by
density differences due to varying salinity. Here warmer and saline water sinks
and colder fresh water rises,
reversing theCustomary transport of heat. Convective mass transfer
an important role in meteorological phenomena, drying process, the design
chemical processing equipment.
general, a free convection heat transfer is generally much smaller compared to
a forced convection heat transfer. It is important only when there is no
All physical substance emits thermal radiation is based on
electromagnetic waves due to irrational and rotational moves of the molecules
and atoms which make up the substance.
Characteristics of radiation
1.The rate of emission increases with temperature level.
2.No material medium required for electricity transfer to
All particles with a body temperature above the absolute zero level
continuously emit energy in the form of radiation.
Sparrow et al . Cess, (1961) have analyzed the effect of a magnetic
field on free convection heat transfer. Das
et al. (1996) have obtained solutions
for the radiation effects on flow past a an impulsively started vertical
infinite plate. Hossain et al.
(1996) analyzed.Radiation effects on mixed convection along an isothermal
verticalplate . Raptis
et al. (1999) have discussed the effects of thermal radiation
and free convection flow past a moving vertical plate. Kesavaiah
et.al (2012)found the effects of thermal radiation and
heat generation on moving infinite vertical plate in the presence of variable
temperature and viscous dissipation.
The theory of mass transfer considered as the mass
transition occurs due to a species concentration in a mixture and is used in
many areas like the working system in home humidifier, evaporation of liquid
refrigerant etc, biological applications like oxygenation of blood, food and
drug assimilation, respiration mechanism and
in many more fields .
Chamkha et al . (2001) considered
Radiation effects on free convection flow past a semi-infinite vertical plate
with mass transfer.
Magneto convection plays an important
role in various industrial applications such as magnetic control of molten iron
flow in the steel industry, liquid metal cooling in nuclear reactors, salt
water, collision (transformed) fewer plasmas and magnetic suppression of molten
Soundalgekar et al.
(1979) has analyzed an exact
solution of the flow past an infinite isothermal vertical plate with mass
transfer by taking into account the free convection current. Soundalgekar et al.
(1986) solved free Convection effects on MHD flow past an
impulsively started infinite vertical isothermal plate.
Das et al. (1996) was presented the mass transfer
effects on the flow past an impulsively started infinite vertical isothermal
plate at constant rate in the presence of species concentration. Mazumdar et al. (2007) presented MHD flow past an impulsively
started infinite Vertical plate in presence of thermal radiation. Palani et al.(2009) Free Convection
MHD Flow with Thermal Radiation from an Impulsively-Started Vertical Plate.