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ENHANCED HEAT TRANSFER IN SOLAR WATER HEATER (WITH
PARABOLIC COLLECTOR) USING PARTIALLY REFLECTIVE GLASS
– A NOVEL IDEA
1Karunamurthy
1
3
K, 2Kanakarajan B, 2Chandrasegaran T
Assistant Professor / Mechanical, JJ College of Engineering and Technology, Tiruchirappalli
Students of Final Year B.E (Mechanical), JJ College of Engineering and Technology, Tiruchirappalli
Abstract: Solar energy collectors are
focus on the flowing fluid will result in
special kind of heat exchangers that
high temperature output.
convert the solar irradiation into internal
Keywords: Solar water heater, solar energy
energy of the flowing fluid. It is the
major component of any solar system.
utilization, enhanced heat transfer, partially
reflective glass.
There are basically two types of solar
collectors:
stationary)
non-concentrating
and
concentrating.
(or
The
concentrating type collectors require
tracking
mechanism
for
better
performance. Solar water heaters with
parabolic collectors are very common
type. Line focusing type of collection of
radiation energy is adopted in parabolic
trough collectors. In this paper an
attempt is made to incorporate partially
reflective
glass with
the parabolic
collector. Partially reflective glass will
allow 50% of the radiation to pass
through and the remaining 50% of
radiation will be reflected back. This
reflected radiation along with incoming
radiation is from the source is collimated
to form highly intense radiation. This
high energy radiation, if allowed to
I. Introduction
Nowadays, most(80%) of worlds
energy demand is met from fossil fuels.
massive exploitation of fossil fuels leads to a
real threat to the environment, through
global warming and acidification of the
water cycle. The distribution of fossil fuels
around the world is equally uneven. Middle
East possesses more than half of the known
oil reserves. This fact leads to economical
instability around the world, which affects
the whole geopolitical system. The present
system as it is cannot be maintained for
more than two generations. The impact it
has on the environment as well to the
humans cannot be disputed. So it is
mandatory to switch to renewable resources.
Renewable energy technology produces
marketable energy by converting natural
phenomena into useful form of energy
At the end of 2001 the total
these technologies use the sun’s energy
installed capacity of renewable energy
and its direct and indirect effects on the
system was equivalent to 9% of the total
earth (solar radiation, wind falling water
electricity generation. By applying a
and
renewable energy intensive scenario the
various
plants,
i.e.
biomass),
gravitational forces (tides), and the heat
global
of the earth’s core (geothermal) as the
sources by 2050 would reach 318 joules.
recourses
from
which
energy
consumption
II. Solar Collectors
energy potential, however, they are
diffused
and
Solar energy collectors are special
fully
kinds of heat exchangers that transform solar
accessible, most of them are intermittent,
radiation energy to internal energy of the
and have distinct regional variability’s.
transport medium. The major component of
These
to
any solar system is the solar collector. This
difficult, but solvable, technical and
is a device that absorbs the incoming
economical challenges.
solar radiation, converts it into heat, and
characteristics
not
renewable
is
produced . These resources have massive
generally
of
give
rise
transfers the heat to a fluid (usually air,
Nowadays,
the
water, or oil) flowing through the collector.
efficiency of collection and conversion,
The solar energy Collected is carried from
lowering the initial and maintenance
the circulating fluid either directly to the hot
cost, and increasing the reliability of and
water or space conditioning equipment or to
applicability make significant progress.
a thermal energy storage tank, from which it
Energy conversion system that is based
can be drawn for use at night or on cloudy
on
days.
renewable
improving
energy
technologies
appeared to be cost effective compared
to the projected high cost of oil.
There are basically two types of solar
Furthermore, renewable energy system
collectors: non-concentrating or stationary
can have a beneficial impact on the
and concentrating.
environmental, economic and political
collector has the same for intercepting and
issues of the world.
absorbing solar radiation, whereas a suntracking
A
concentrating
non-concentrating
solar
collector
usually has concave reflecting surfaces to
intercept
and focus the
B. Non-concentrating type collector
sun’s beam
In this type of collector, the
radiation to a smaller receiving area,
radiation is allowed to fall over the
thereby increasing the
radiation flux.
entire surface of the flat plate collector,
Concentrating collectors are suitable for
instead of concentrating at particular
high-temperature
point below figure shows the non-
applications.
Solar
collectors can also be distinguished by
concentrating
the type of heat transfer liquid used
important parts.
collectors
and
its
(water, non-freezing liquid, air, or heat
transfer oil) and whether they are covered
III. Methods to increase the rate of
or uncovered. When solar radiation passes
heat transfer in Solar Water Heaters
through a transparent cover and impinges
on the blackened absorber surface of high
A. Green house Principle:
absorptive, a large portion of this energy is
This principle is used to trap the heat
absorbed by the plate and transferred to
by using evacuated glass tubes, it consist of
the transport medium in the fluid tubes, to
inner copper tube and outer glass tube ,the
be carried away for storage or use. The
glass tube behaves as the green house gas
underside of the absorber plate and the two
which locks the heat, results in increasing
sides are well insulated to reduce the
the radiation.
conduction loss the liquid tubes can be
welded the absorbing plate or they can be an
integral part of the plate. The liquid tubes
are connected in both the ends by largediameter header tubes.
A. Concentrating type Collectors
In this type of solar collectors the
radiation is either concentrated in a
particular point or in a line. So they are
classified into two types namely line
focusing and point.
Fig 1: Water tube in a concentric glass
tube
B. Selective Coating
partially reflective mirror. 50% of
In this type, the receiver surface is
photons passed to the required target,
coated with selective materials in order to
and the remaining 50%enters into the
trap the heat resulting in increased radiation.
source. By multiple reflections the
intensity of the beam gets increased. In
C. Using reflective surfaces
this solar heater, a partially reflected
In this type the collector consist of
glass is placed in between the collector
mirror in order to get a good reflection.
and receiver, when the incident sun light
Schematic diagram shows the collector with
fall on the collector it is passed to the
reflecting surfaces
partially reflective mirror. it send 50% of
radiation to the receiver remaining 50%
return back to the collector, but the
collector
receiving
the
radiation
continuously, thus the intensity of the
radiation get increased, thus very huge
amount of heat is generated.
Fig 2: Parabolic collector with reflective
mirror
D. Physics behind partially reflective
glass
A partially reflected glass is also
known as semi silvered glass which
allows the light partially into the target
and remaining into the source. It is used
in lasers in order to achieve the high
coherent and intense source of light.
Initially small quantity of photon is
generated by optical pumping and the
photons lies in between the partial and
fully reflected mirror, and then the
generated photon is allowed to strike the
Fig 3: Schematic diagram of collector
along with partially reflecting mirror
[6] Stu campell-build your own solar
water heater, garden way publishing
IV. Conclusion
The paper shows to increase the
radiation by this way we have to improve
the efficiency of solar water heating system
using partially reflective glass. Using this
system we have generate a heat with in the
fraction of seconds in a small area.
References
[1] P.L.knight & A. miller- measuring
the quantum state of light, Cambridge
studies in modern optics.
[2] Alastair I.M.Rae-quantum physics
illusion or reality, Cambridge university
press.
[3] G.D Rai- non conventional energy
sources-khanna publication-2007.
[4] Barry L.Butler, golden, colo- light
weight diaphragm mirror module system
for solar collectors, US PATENT, 1985.
[5] David K. Fork, Palo Alto, Calif-laser
beam
conditioner
using
partially
reflective mirrors, US PATENT, Jan,
1999.
charlotte, Vermont 05445