Question

Tray dryers operate by passing hot air over the surface of a wet solid that is spread over trays arranged in racks. They are most widely used in the food and pharmaceutical industries. Its main advantage being its simple operation. However, it has the disadvantage of long drying times. From the concepts of drying that you have learned, what will you suggest to lessen drying time for tray dryers?

Answer 1

The tray dryer is a direct batch type dryer.The main advantages of tray dryer is its low maintanance cost,low space requirement, ease of cleaning and provide good drying condition.But there are disadvantages too, suppose if stagnant air pockets are formed which will lead to the non-uniform drying.This leads to uneven drying and drying time increases which is not favourable.

Suggestion;

1) This suggestion is based on the equation based on drying time.

where xi= initial moisture, xc= critical moisture, x* = equilibrium moisture and xf= final moisture.

W= weight of solid ,Nc= rate of drying and a= area for drying.

From the above relation, the only parameter that we have access to change is area of drying , all other parameters are pre-determined and we dont have the rights to change it.

From the above relation, (t is inveresely proportional to area.)That means as area increases for drying t(time for drying) decreases. So inorder to lessen drying time we will increase drying time.

2) Another suggestion to reduce stagnant air pockets and hence reducing time, we will blow large volume of dry air over the trays,ranging velocities from 3 - 4 m/s. We must maintain a maximum temperature by providing low humidity air and as a result high drying rate is obtained.Also it is best for the dryer to be insulated very well so there will be not much heat loss and heat delivered is used for drying