This personality causes the product to respond to dehydration in a unique manner, unlike any other product. The Hot End or high-pressure end begins at the fan wall and extends the length of the air deck, down through the air deck gap and back through the first few cars on the ground level. Distinguished by high static pressure and high process air temperatures, the hot end is where the dry product exits from the dryer when drying in the counter flow configuration. The wet cars enter the dryer from the hot end. The hot process air passes through the trays in the same direction, as the cars are moving inside the Tunnel Dryer.
Parallel airflow is used when production requirements outweigh quality concerns.
The hot air from the fan reaches the fresh product first. To counter the potential for case hardening, another car full of fruit is placed upstream of the first car at a specifically timed interval. The cooling action of the moisture driven off the upstream car re-hydrates the original car slightly, thus averting case hardening. This is the cause of the quality issue. Parallel Flow is an adaptation of the original Counter-Flow methodology.