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Performance Enhanced Natural Convection Solar Dryer For Fruits And Fruit Products

Dr. Reghu Rama Das, Mitraniketan, Thiruvananthapuram, India

InSIC's first Call For Grant Applications was launched in September 2019. Out of the three eligible applications received by the deadline of the Call, the Evaluation Working Group of InSIC selected one project for funding. Project titled as Performance enhanced natural convection solar dryer for fruits and fruit products is implemented by Mitraniketan, a non-profit organization located in Kerala, India. Read below the first news about the ongoing project and the development of the solar drier.

Drying, a process of moisture removal from a natural product in order to reach the standard specification moisture content is an energy intensive operation. To accelerate drying various methods are adopted like direct sun drying and using driers. The common method is convective drying by circulating hot air over the mass. Hot air heats up the product and conveys released moisture to atmosphere.

The driers work on the following principles:

  1. Increasing the air temperature, and thereby increasing its moisture holding capacity.
  2. Improving the air flow (convection)

THE DESIGN
Our design covers both the key aspects for drying. Under the project we incorporate the following features to the existing tunnel design for improving the performance of the drier:

  1. Pre-heater: Pre-heater plates are flat plate solar collectors with darkened substrate and transparent top to harvest maximum amount of heat. Increasing the inlet air temperature causes drop in relative humidity. In other words, unit mass of air can retain more amount of moisture by increasing the air temperature. Heating will be carried out in two stages- in the air pre-heater, as well as the drying chamber.
  2. Air circulation: To improve the airflow in and out of the drier unit, a solar chimney is introduced at one side of the tunnel which creates a draft. The pre-heater plates will be provided with air intake holes or apertures through which fresh air is introduced into the main drying chamber.

FABRICATION
Frames are manufactured from mild steel square tubular sections of 20x20x1.4 mm. The transparent panels for the main drying chamber, air pre-heater as well as the solar chimney were cut out from readily available poly-carbonate sheets. The drying plates that come in contact with food is made of food grade aluminum sheet.

See the presentation here: