Which of the following is not a continuous drier ?

ANS:D - Tray drier

The tray drier is not typically considered a continuous drier. Here's why:

• Drum drier: A rotating drum is used to spread a thin layer of the product over its surface, and hot air is passed through the drum to dry the product as it rotates. This process is continuous as new product is continuously fed onto the drum and dried product is continuously removed.
• Spray drier: A liquid feed is atomized into small droplets, which are then dried by hot air in a chamber as they fall through it. This process is continuous as the liquid feed is continuously sprayed into the chamber and dried product is continuously collected.
• Tunnel drier: Products are conveyed through a long tunnel on a continuous belt or conveyor system, and hot air is passed over or through the product to dry it as it moves through the tunnel. This process is continuous as new product is continuously fed into the tunnel and dried product is continuously removed at the other end.
• Tray drier: In a tray drier, the product is spread out on trays or shelves, and hot air is circulated around or through the trays to dry the product. However, tray driers are typically operated in batch mode, where a fixed amount of product is loaded onto the trays, dried, and then unloaded once drying is complete. While multiple trays may be used simultaneously, the process is not continuous because loading and unloading are batch processes.