The shape of the dryer:

  1. 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.
  2. For even drying of the substrate it is necessary to have a symmetric shape that would distribute air evenly for even drying.
  3. The cylinder is a shape that is symmetric about its axis from where air can be evenly distributed.
  4. 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.