The first stage involves removing water from the surface of the wood; this can be accomplished by drainage or other external mechanical forces (centrifugal force, pressure). However, this method allows only the removal of free water from porous wood. Another mechanism is evaporation, in which free water is present within the wood cells in a manner similar to capillary systems.

The first stage involves removing water from the surface of the wood; this can be accomplished by drainage or other external mechanical forces (centrifugal force, pressure). However, this method allows only the removal of free water from porous wood. Another approach is evaporation, in which free water is present within the wood cells in a manner similar to capillary systems.
Phase Two: Water moves from the inner part of the wood outward—for example, from a water-containing region into a drying region. As drying continues, the saturation point decreases, and water transitions from one channel to another, evaporating through the pores. When drying wood that has not been impregnated with water, water diffusion will begin precisely at the onset of Phase Two. Initially, water penetrates inward, and then it evaporates between the cell walls.
Stage 3: When moisture has spread throughout the entire thickness of the wood, wood drying enters the third stage.
The goal of wood drying is to reduce the moisture content and achieve the final required moisture level of the wood as quickly as possible. The drying process must be cost-effective and consume as little electricity as possible.
Drying speed
The drying rate is determined by the following factors:
1) Wood structure and density
2) Wood thickness (plate length and width)
3) Wood drying temperature
4) Drying humidity range
5) The drying gradient, which is the ratio of the wood’s moisture content to its equilibrium moisture content in the drying chamber.
VMK
Gradient = %
ANGLE
6) Organization of airflow in a wood stack
7) Furnace design and selected drying criteria
Influence of structure and density
Low-density wood (that is, wood with a low-density cellular structure) offers much less resistance to water flow than high-density wood. To properly dry wood of the same density (for example, heartwood), it is necessary to adjust the drying time according to the wood’s density and the degree of direct air exposure.
The influence of wood thickness
The thicker the board, the more attention should be paid to its drying process. The moisture content of wood varies from the center to the periphery. Of course, the length and width of the board also affect the drying time, since the edge surfaces of the wood (for example, short wooden blocks) will release a large amount of water.
Effect of temperature
The effect of temperature is the most important factor determining water movement in wood. As the temperature rises, the drying process accelerates, since the movement of water within the wood—from the interior to the outer surface—speeds up. The higher the wood temperature, the faster the water flow (at 80 ℃, the rate of water movement in wood is five times greater than at 25 ℃), and the more water is released. As long as this does not negatively affect the future use of the wood, the temperature can be raised as much as possible.
Influence of the water content range
The general rule is that the longer the wood-drying process lasts, the more moisture needs to be removed; however, wood with a moisture content above the fiber saturation point requires significantly less time to remove the same amount of moisture than wood with a moisture content below the fiber saturation point.
The effect of the drying gradient
If the drying gradient is low, highly saturated air finds it much more difficult to absorb additional moisture than water does—i.e., to leave the wood. Conversely, if the drying gradient is high, the air can more easily remove moisture from the wood’s surface. Therefore, it is important to select appropriate drying gradients according to the wood species and thickness in order to prevent drying defects.