The External Drying Environment

Lumber is prestaeked and moved into the kiln on flatbed trolleys. The individual stacks are usually 2.4 m wide. A kiln may have a single track or double track (with two stacks side-by-side). In the stack boards are packed tight - without gaps - within 

Early in the schedule the drying rate at the outlet side can be less than half that at the inlet faee. There are two factors at work the increasing humidifieation and eooling of the airstream as it passes across the stack and the gradual thiekening of the boundary layer between the wood surface and the rapidly moving airstream. 

A boundary layer of retarded flow is zero at the leading edge and builds up gradually with distanee as flow is hindered by skin frietion. The mass-transfer 

Uneven heat transfer across individual boards 

The overall consequence is that despite over-drying a load of lumber some boards will still not achieve the desired end-moisture content. Merely extending the drying schedule does not solve the problem of airflow maldistribution and uneven drying this is especially true when drying permeable species using low air velocities of 3.5 m s  

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To learn more about the external drying environment. 

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