106 MISC. PUBLICATION 5 40 ; U. S. DEPT. OF AGRICULTURE 



Applying law 5a, both capacity and fan speed are directly proportional to the 



16.7 

 specific volume of air. Hence the proper fan speed is 475 X -^=596 r. p. m. 



The power absorbed by this fan (5b) will vary directly as the square of 

 the specific volume, 19 X (16.7 2 /13.3) =29.8 hp. 



It is now possible to predict the actual operating capacity and static pressure 

 of the fan by applying law 5a, which shows that both varv directly as the spe- 



16.7 

 cific volume. Therefore, the actual capacity is 53,200 X ^- 3 =66,5O0 c. f. m. 



16.7 

 and the actual static pressure of the fan is 1.45 X r^-Q=1.81 inches of water. 



BIN-TYPE FINISHING DRIERS 



The bin finisher provides an efficient, relatively inexpensive means 

 of finally drying vegetables to low moisture content. It is compact 

 and has a comparatively high heat use. If it is used as final drier, 

 better use can be made of the preceding dehydrator, whether it is a 

 tunnel, cabinet, or belt type. All of these t} 7 pes use large areas of 

 loading space for the reduced volume of thinly spread, partially dried 

 product. 



If a bin drier is added to a system and, further, if additional heat- 

 generating capacity is available in the preceding drier, then the plant 

 capacity is potentially increased. The shortened retention time re- 

 quired by the preceding driers in reducing the moisture of the product 

 only to a condition satisfactory for bin drying (approximately 10 to 

 15 percent moisture) permits the system to handle additional tonnage. 

 This additional tonnage of course requires additional heat. 



Very little is known of the performance characteristics of bin driers. 

 Their use as an expedient for increasing plant output or for carrying 

 the dryness of the product to low moisture limits is, however, of 

 unquestionable value. As a secondary aid, the bin driers can be used 

 to supplement the plant's finished-product storage facilities. Being 

 relatively simple and easy to build and operate, finishing driers are 

 becoming standard equipment in most dehydrating plants. 



Types of Bin Driers 



There are two basic types of bin driers — the batch-process bin drier 

 and the continuous bin drier. The continuous bin drier usually con- 

 sists of a single unit, whereas the batch-process drier is almost in- 

 variably a multibin drier. 



The continuous bin finisher, because of its operating characteristics 

 and its size limitations, is generally confined to use in small plants. 

 The unit consists of a large storage bin designed for working depths 

 ranging approximately from 3 to 8 feet. Drying air is introduced 

 through louvers at or near the bottom of the bin. The bin must be 

 of airtight construction except for an exhaust port located in the top 

 or at some other position above the active bin level. A gate is provided 

 in the bottom of the bin to permit gravitational removal of the prod- 

 uct in progressive layers. To facilitate removal and to prevent arch- 

 ing, mechanical or electrical agitating or shaking devices are some- 

 times provided. Figure 57 shows a typical design for a continuous 

 bin finisher intended for use with onions. Note the location of the 

 agitator. 



When the bin is in operation, the partially dried material is allowed 

 to enter in a steady stream, at such a rate that it keeps the bin com- 



