AIRFLOW DISTRIBUTIONS IN THE FILLET SPACES OF A TIMBER STACK

Abstract

An important requirement for producing evenly dried timber (lumber) in a kiln is that the airflow is uniformly distributed throughout the timber stack. The airflow distribution within the timber stack of a semi-scale kiln, which has multiple fans, was investigated to determine the possible causes of any airflow non-uniformity. Airflow measurements along the length of the timber stack illustrated the importance of ensuring that each fan generates the same flowrate, and that end-baffles are placed on either side of the timber stack to reduce bypass around these edges. Airflow measurements down the height of the timber stack demonstrated the effects of a separation zone near the air-inlet face of the stack, which partially reduced the airflow through the upper portion of the stack, and of non-aligned boards, which generated a saw-toothed velocity profile. Once the data had been smoothed to account for these effects, the down-stack velocity profile took on the expected form, with the maximum and minimum velocities at the top and bottom of the stack, respectively. Comparison of the velocity profiles at the air-inlet and outlet faces of the stack indicated a significant redistribution of the flow through the stack. The prediction of a one-dimensional model of airflow in a kiln was shown to be in good agreement with the smoothed experimental data at the air outlet of the stack.

Keywords:

• Airflow maldistribution
• Fluid dynamics
• Kiln
• Lumber

ACKNOWLEDGMENTS

The authors gratefully acknowledge the funding by BMWi (Bundesministerium für Wirtschaft), AiF (Arbeitsgemeinschaft Industrieller Forschungsvereinigungen), DGfH (Deutsche Gesellschaft für Holzforschung), and the Public Good Science Fund (PGSF) of the New Zealand Foundation for Research, Science, and Technology (FRST). The authors would also like to thank the staff of BFH (Bundesforschungsanstalt für Forst- und Holzwirtschaft Hamburg) and Hamburg University for supplying experimental equipment, and Mr Steve Riley, Forest Research, Rotorua, New Zealand, for providing the data on airflow friction coefficients in stacked timber boards.