10-08-2013, 12:59 PM
Study of Desert Cooler
Introduction
Evaporative cooling technique is very old and easy method of cooling. Humans have
been using this technique for their comfort and convenience. In many old monuments we can
find this type of cooling technique.
But because of systems inefficiency and some constraints we are not using this technique so in
this seminar report, focus is made to understand the system working and improve its efficiency
by using latest cooling pad and also make a study how to design desert cooler for a particular
region.
History
Civilizations throughout the ages have found ingenious ways to combat the heat in
their region. An earlier form of air cooling, the wind catcherwas invented in Persia(Iran)
thousands of years ago in the form of wind shafts on the roof, which caught the wind, passed it
over subterranean water in a qanat and discharged the cooled air into the building.
Wind Catcher:
It uses the principle of the evaporative cooling. Room is isolated from the outside
environment so when stream of air passes it create low pressure zone in the room. At the base of
the room there is water reservoir called qanat. Water flowing in the qanat has low temperate. Due
to the pressure difference air entered in to the qanat and gets cool because of the evaporative
cooling. At the top of the room there is a wind tower which allows hot air to go out and helps in
air circulation
Surface evaporation
Evaporative cooling is a physical phenomenon in which evaporation of a liquid,
typically into surrounding air, cools an object or a liquid in contact with it. Latent heat, that is the
amount of heat needed to evaporate the liquid, is drawn from the air. And air gets cooled. This is
evaporated because partial pressure on the water vapor at the top of the layer is very small so its
boiling point temperature is also very small.
Evaporative pad material
There are many materials available to make pads. Like wood wool, coconut coir, steel wire
mesh, khus pad, synthetic foam sheet. We are mostly using the wood wool &coconut coir
because the gives more cooling efficiency of cooling than steel wire mesh, khus pad, synthetic
foam sheet. But now days there are new pads available called as Cel-Dek pads which gives very
high efficiency of cooling near about 90%.
Performance curves of CELdek pads
Based on different designs of pad its flute angles and width the gives different cooling efficiency
and this can be plotted on graph. Depending on our requirement we can select suitable pad for
our cooling purpose. These are performance curves for CELdek pad here D indicates the depth
of the pad in side view. If we observe we will find that pad 7090-15 has max efficiency of the
cooling for air velocity less than 1 m/s and it is near about 96% So depending upon our
requirement and cost consideration we can select proper pad and required depth of the pad
Conclusion
Base on above study it is found that these pads are more efficient than that of
conventional khoos pads and other pads. CELdek pads are highly efficient they have maximum
cooling and humidification low pressure drop less costly to operate. It requires low maintenance
self cleaning specially treated, algae resistant substance. In these pads routine maintenance can
be performed while the system is operating.