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Published On: Fri, Aug 30th, 2013

How solar dryer system works.

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Drying agriculture products was never a pain for farmers in the past since ample heat energy was available from sun. But as time passed by and technologies widened farmers realised that direct sunlight exposure of the produce was not good as the drying was not uniform. In a country like India we use sun’s energy from drying washed clothes to even concentrating pickle juice by exposing pickle jars to the hot sun.

Solar drying can be called as an integrated phenomenon of sun drying. As far as Asian nations are concerned we resort to high temperature during summer and our spices are dried mostly using this heat. But many at time exposure to un-controlled direct exposure may lead to case hardening, where hard outer shell is developed on the produce and moisture still pertains in the inside.

A solar drier could be the answer for such a dilemma. We know that black bodies absorb radiation. A solar drier mainly consist of such a black surface on which the produce is placed for drying. This surface can absorb radiation from sun. The black body surface is placed inside a chamber having glass covering on the side exposed to sun and walls at other three sides as shown in the figure. A small provision for air circulation, like a vent; is also provided so that convective or forced heat transfer takes place inside the chamber producing uniform heat flow.

Solar dryers broadly classified as High and low temperature dryers. High temperature dryers are mainly used when fast drying is desired whereas in low temperature dryer’s moisture content of the produce is uniformly brought in equilibrium with drying air by constant ventilation.

Solar dryers are also classified as:

Direct solar dryers
Direct solar dryers are those machines that expose the substance to be dehydrated or dried to direct sunlight. They have a black absorbing surface which collects sun light and converts them to heat, the substance that needs to be dried are placed directly on the surface for them to be dried. The direct solar driers may have enclosure, glass covers and vents to make the process of drying really efficient.

Indirect Solar dryers
In-direct solar dryers a black absorption-surface absorbs sunlight and converts them to heat. A vent allows air to flow across the hot surface thus the flowing air gains heat as it passes over the absorption surface. Hot air is then made to pass through the substance that needs to be dried. The air takes off moisture from the substance thus dehydrating it and is removed of via a chimney.

Video of solar food drier.


 

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Credit of the pic to : http://www.fao.org/

Author: Mr. Thomaskutty Jaison

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