VEGETABLE AND FRUIT DEHYDRATION 



83 



Against the theoretical advantages of this type of dehyclrator must 

 be set the fact that it is complex to build and operate. The trucks must 

 fit very tightly into the tunnel to avoid short-circuiting of air through 

 useless channels, and the numerous changes in direction of air flow 

 increase the fan horsepower required and impose difficult problems 

 of equalization of flow. 



The temperature conditions suitable for successive sections of this 



200 



180 



y- 160 



140 



120 



100 



80 



\ Air 



Temperat 



ure 





\ Parallt 

 \ Flow 



1 















Wet-Bulb 



1 / 



| / Cou 



nterflow 





Tempera- 

 ture 



y 



i 

 I 









i 



1 Wet- 



Bulb /-> 





Tempe 



-ature 





10 20 30 



DISTANCE FROM WET END (FEET) 



-5 

 S'| 4 



O ^ -x 



















MOISTURE C 

 (LBS. /LB. B( 



























10 20 30 



DISTANCE FROM WET END (FEET) 



Figure 46. — Drying conditions in a heavily loaded combination parallel-flow and 

 counterflow tunnel. Time, 7.6 hours ; relative capacity, 1.43 ; final moisture 

 content, 5 percent. 



type of tunnel are similar to those in a single cabinet dehydrator dur- 

 ing successive equal periods of time. (See section on cabinet dehy- 

 drators.) For example, if there are six sections, the temperature in 

 the first section must be maintained at conditions suitable for a cabinet 

 near the end of the first sixth of the total drying time ; conditions in 

 the second section must be similar to those in the cabinet at the end 

 of the first third of the drying time ; and so on. 



