Abstract
Drying
is very important process applicable for agricultural
and industrial products. Drying is the moisture removing process from the
products. Drying reduces the bacterial growth in the products. It will helpful
for preserving the products for long time. Solar drying is the oldest method of
products drying. Open air solar drying method is used frequently to dry the
agricultural products. But this method has some disadvantages. Therefore to
avoid disadvantages it is necessary to use the other solar drying methods.
Different solar drying methods are direct solar drying, indirect solar drying,
and mixed mode solar drying.The device developed and used for proposed drying
process with application of solar energy is called the solar dehydrator using discarded
beer cans. Solar dryers are also classified with mode of air circulation. In
this project, we developed the solar drying and low cost solar drying
techniques.
Sun drying is still the most common
method used to preserve agricultural products in most tropical and subtropical
countries. However, being unprotected from rain, wind-borne dirt and dust,
infestation by insects, rodents and other animal products may be seriously
degraded to the extent that sometime become inedible. The resulted loss of food
quality in the dried products may have adverse economic effects on domestics
and international markets. Some of the problems associated with open-air sun
drying can be solved through the use of a solar dryer which comprises of
collector, a drying chamber and sometimes a chimney.
The conditions in tropical countries
make the use of solar energy for drying food practically attractive and
environmentally sound. Dryers have been developed and used to dry agricultural
products in order to improve shelf life. Most of these either use an expensive
source of energy such as electricity or a combination of solar energy and some
other form of energy. Drying may be an interesting method in order to prevent
fresh fruit deterioration. There is spoilage of fruits and other fresh foods
that could be preserved using drying techniques in India and other developing
countries. Seasonal fruits like mangoes are not presently dried for export, or
for local consumption during period of scarcity.
fig. Types of solar dehydrator
Advantages of Solar Drying System
Solar
dryers have the principal advantage of using solar energy-a free, available,
and limitless energy source that is also non polluting. Drying most foods in
sunny areas should not be a problem. vegetables, for example, can be dried in
2-1/2.to 4 hours, at temperatures ranging from 43 to 63°Centigrade ( l0 to
l45°Fahrenheit). Fruits take longer, from 4 to 6 hours, at temperatures ranging
from 43 to 66°Centigrade (110 to 150°Fahrenheit). At this rate, it is possible
to dry two batches of food on a sunny day.
A
solar food dryer improves upon the traditional open-air systems in five
important ways:
1).
It is faster:- Foods can be dried in
a shorter amount of time. Solar food dryers enhance drying times in two ways.
First, the translucent or transparent glazing over the collection area traps
heat inside the dryer, raising the temperature of the air. Second, the
capability of enlarging the solar collection area allows for the concentration
of the sun's energy.
2).
It is more efficient:- Since
foodstuffs can be dried more quickly, less will be lost to spoilage immediately
after harvest. This is especially true of produce that requires immediate
drying such as a grain with a high moisture content. In this way, a larger
percentage of food will be available for human consumption. Also, less harvest will
be lost to marauding animals, vermin, and insects since the food will be in an
enclosed compartment.
3).
It is safer:- Since foodstuffs are
dried in a controlled environment, they are less likely to be. contaminated by pests,
and can be stored with less likelihood of the growth of toxic fungi.
4).
It is healthier:- Drying foods at
optimum temperatures and in a shorter amount of time enables them to retain more
of their nutritional value especially vitamin C. An extra bonus is that foods
will look and taste better, which enhances their marketability.
5).
It is cheaper:- Using solar energy
instead of conventional fuels to dry products, or using a cheap supplementary
supply of solar heat in reducing conventional fuel demand can result in a
significant cost savings. Solar drying lowers the costs of drying, improves the
quality of products, and reduces losses due to spoilage.
Disadvantages of Solar Drying
System
Solar
dryers do have short comings. They are of little use during cloudy weather.
During fair weather they can work too well, becoming so hot inside at midday as
to damage the drying crop. Only with close supervision can this be prevented.
As temperatures rise (determined with a thermometer or by experience), the lower
vents must be opened to allow greater airflow through the dryer and to keep the
temperatures down. Rice, for example, will crack at temperatures above 50°C seed grains can be dried
at temperatures no higher than 40 to 45°Centigrade.
Solar Dryer
Applications
Solar
energy is use throughout the world to dry food products. List below are a few representative
item to show the diversity to which the sun’s energy is put to use
·
Grains
·
Vegetables
·
Meat
·
salt
·
fruits
·
fish
·
clothes.
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