The shape of the dryer:
- The dryer works by sending warm air over the substrate which then loses moisture by gaining latent heat from the warm air and gets dried.
- For even drying of the substrate it is necessary to have a symmetric shape that would distribute air evenly for even drying.
- The cylinder is a shape that is symmetric about its axis from where air can be evenly distributed.
- Hence the drying chamber will be made cylindrical.
The dimensions of the dryer:
The dimensions of the dryer were calculated using the following assumptions,
- Onion which has 89% water by weight will be the substrate
- The air heater has 20% efficiency i.e. It absorbs 20% out of the total incident solar radiation.
Total incident solar radiation = 19584 KJ /m^2 /day
Assuming 20% efficiency = 0.2 * 19584 = 3916.8 KJ /m^2
total surface area of air heater = 12.6 m^2.
hence Total available heat per day = 3916.8 * 12.6 = 49351 KJ
water removel capacity per day:
latent heat of evaporation of water = 2260Kj / Kg.
With 49351 Kj of available heat,
49351/2260 = 21.83 = 22 Kg of water can be evaporated per day
Onion has 89% water by weight hence onion weighing 24.72 Kg can be dried in a day.
Required surface area:
To calculate the required surface area for drying 24.72 Kg onion, onion weighing 130gram was cut and spread on a flat surface and the surface area was measured to be around 0.09 m^2.
Hence to dry 24.72 Kg onion 17.11 m^2 area would be required.