18 



CIRCULAR -413, U. S. DEPARTMENT OF AGRICULTURE 



1.500 % the inlet volume is about three times greater than the volume at 

 discharge. Therefore, a drier with an evaporative capacity of about 

 3,000 pounds of water per hour should allow the passage of about 10.S00 

 cubic feet of air per minute at the inlet. The entrance velocity should 

 not greatly exceed 1.500 feet per minute. For a drier with a thermal 

 efficiency of 60 percent the evaporation of 3.000 pounds of water will 

 require about 5.500.000 British thermal units (B. t. u. ) . This quantity 

 of heat would be supplied by 40 to 45 gallons of fuel oil or 5,500 cubic 

 feet of natural gas. 



In practice, final dilution of furnace gases takes place at the second- 

 ary air inlet. This inlet is so arranged that the atmospheric air is 



-'-'- e 



laryar 



axes I — 



5- :■ 



: □_ 



":-:■ e - 



■ -= :- :■ 



:-': = ? « = 



Burner 



D 



Figvre 9. — Dutch-oven furnace. 



SLIDING RINGS 



S*ee!x 



Sliding rings 



Figure 10. — Cylindrical furnace, with sliding rings for controlling air flow. 



