VEGETABLE AND FRUIT DEHYDRATION 



81 



contains as much as 50 to 60 percent of moisture. High air circu- 

 lating capacity and high heat input are provided. The counterflow 

 tunnel may be longer, but the air flow and heat input will be sub- 



200 



^ 180 

 u.' 







UJ 



or 



= 160 



< 

 or 



Ul 

 0- 



2 .„« 











\ Air Te 



mperaturf 















uj 140 

 120 



Wet 



-Bulb ^ 







Temp 



2rature y 







10 20 30 



DISTANCE FROM WETEND(FEEP 



~ 5 

 ui q 4 



CO 

 CO • i 



































7Z » ' 



O co 

 S _J ^ 











^ 









Figure 42. 



10 20 30 



DISTANCE FROM WET END (FEET) 

 -Drying conJitions in heavily loaded parallel-flow tunnel 

 13.4 hours ; final moisture content, 10 percent. 



Time, 



stantially less, since comparatively little evaporation will be required 

 there. In some designs the air exhausted from the counterflow 

 tunnel, being warm and still comparatively dry, is used to make up 

 all or a part of the "fresh" air required by the parallel-flow tunnel. 

 Division of the drier into two separate tunnels necessitates an 

 additional handling of the trucks, and therefore some increase in 





BLOWER 



HEATER FRESH-AI 



R INLETS 

 WW 



4 





HEATER 



FAN 







/\. 



5 



3> 



1 





/ 



i 



^-^J, 



: 



i 



-,\ 

























WET 



s - 









V 















DRY 



MATERIAL 









V 















MATERIAL 













/ 



~* \ 



















EXHAUST-AIR STACK MOVABLE PARTITION 



Figure 43. — Combination of counterflow and parallel-flow arrangements. 



labor cost. Consequently there are several designs of dehydrators 

 that combine both parallel-flow predrying and counterflow finishing 

 into a single tunnel structure. Figures 44 and 45 illustrate two 

 such arrangements. They are generally termed "center-exhaust" 



569074 — 44 6 



