Airflow direction
Due to the simple symmetrical design and standard sub-floor, the dual-plenum airflow directions can be tailored to meet specific drying characteristics for the vast majority of products on the
market today.
The ability to manage airflow directions, and the importance within that
flexibility, depend solely on the drying constraints of a specific product—size,
shape, density, cell structure, etc.
One school of thought
For example, one school of thought is that if the airflow for a given
product/dryer is “air up” at all sections, then the bottom strata of the
product bed will be at a lower moisture than the top strata. Knowing that
the greatest amount of moisture is more easily retracted from product in the
initial 25% of the dryer, it is conceivable that the product that begins the
drying process on the top-most layer of the product bed will exit at a higher
moisture, even though most dryer applications are of a dual-pass design and
the product is “tumbled” or agitated during the conveyor transition.
The logic behind this is that the air will pick up moisture from the product
on the bottom layer of a bed of product and possibly deposit it within the
product on the top layer (of a single bed of product). This thought process
has merit, though the typical moisture variance is usually insignificant.
However, if a specific product has a non-typical drying curve (due to its
processing and/or composition), then airflow manipulation may be required
to ensure critical moisture parameters are met.
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Figure 6. Dual-plenum airflow directions

All Air up
All Air down

Air Up // Air Down

Air Down // Air Up

Airflow directions can be tailored to meet specific drying characteristics for most products
on the market today.