Examination of Auxiliary System Stability in Wood Drying

The commonly employed conventional dry kilns achieve the desired changes in wood moisture content with their hardware sub-systems and properly chosen drying schedules, which determine the required times depending on the value of the humid air parameters. Drying kilns predominantly make use of subsystems providing dehumidification, humidification, and heating. Optionally, some other variables, such as air flow, can also be controlled. The operation of each of the mentioned subsystems can be described in terms of the physical processes of heat and mass transfer. Variation in the process parameters (air humidity and temperature), previously defined by the chosen drying schedule, might result in instabilities in the integrated system. In order to examine such possibilities, a simulation was performed using a mathematical model and the corresponding matrix transfer function with the aim of determining the system's stability and the conditions to attain this in terms of the control laws.