12 BULLETIN 1330, U. S. DEPARTMENT OF AGRICULTURE 
COMPARTMENT DRIERS 
Compartment driers (fig. 5) have a drying chamber divided by 
partitions into several compartments, each holding one or two stacks 
of trays. These trays can be handled most conveniently on trucks. 
Air is carried from the heaters through a main duct, from which por- 
tions are diverted to each compartment. Circulation in a vertical 
direction through the tier necessitates a shifting of the trays during 
drying, inasmuch as the contents of the trays farthest from the 
source of the air supply dry more slowly than the material on near-by 
trays. For this reason circulation of the air across the trays is prefer- 
able. The air is discharged from each compartment into a recircula- 
tion duct, to be either reheated or discharged from the drier without 
passing through any other compartments. 
Fic. 5.—Compartment drier 
TUNNEL DRIERS 
In tunnel driers (fig. 6) the drying is done in a long chamber or 
tunnel, in which both the materials and the air move horizontally for 
the most part. A concrete slab floor, hollow-tile walls, and a rein- 
forced-concrete ceiling make a durable and fireproof drier. Many 
driers, however, have wooden floors and double walls and ceilings of 
tongue and groove flooring nailed to a skeleton framework of 2 by 4s. 
Although the dimensions and capacity of the tunnels vary, a typical 
tunnel is about 40 feet long, 6 feet wide, and 6 feet high, capable of 
holding a single line of 10 trucks, each truck carrying a double stack 
of trays 214 feet square. Handling the trays on trucks is more 
