Experimental determination of the convective heat and mass transfer coefficients for wood drying |
| |
Authors: | Carl Tremblay Alain Cloutier Yves Fortin |
| |
Institution: | (1) Research Scientist Wood Drying Lumber Manufacturing Technology Forintek Canada Corporation 319, rue Franquet Sainte-Foy, (Qc), Canada, G1P 4R4 e-mail: carl.tremblay@qc.forintek.ca Fax: +1-418-659-2922, CA;(2) Associate Professor, Département des sciences du bois et de la forêt, Faculté de foresterie et de géomatique, Université Laval, Québec, (Qc), Canada e-mail: alain.cloutier@sbf.ulaval.ca Fax: +1-418-656-3177, CA;(3) Professor, Département des sciences du bois et de la forêt, Faculté de foresterie et géomatique, Université Laval, Québec, (Qc), Canada e-mail: yves.fortin@sbf.ulaval.ca Fax: +1-418-656-3177, CA |
| |
Abstract: | The knowledge of the convective heat and mass transfer coefficients is required for the characterization of the boundary
conditions of the heat and mass transfer equations of a wood drying model based on water potential. A new experimental method
for the determination of the convective mass transfer coefficient is presented. This method is based on the measurement of
the moisture content, and indirectly the water potential, at the surface of a wood specimen at different drying times. Drying
experiments were performed on red pine (Pinus resinosa Ait.) sapwood from nearly saturated to dry conditions at 56 °C, 52% relative humidity and air velocities of 1.0, 2.5 and
5.0 m s−1. The results show that the convective mass transfer coefficient is constant until the wood surface moisture content reaches
about 80% and then decreases more or less gradually as the moisture content decreases further. The convective mass transfer
coefficient increases with air velocity. A regression analysis shows that there is no significant improvement in considering
the water potential gradient near the wood surface when the difference in water potential between the surface and the surrounding
air (ψs − ψ∞) is used to determine the convective mass flux at the surface. Also, ψs − ψ∞ is more appropriate than the water vapour pressure difference (pvs − pv∞) as the responsible driving force of the moisture flux leaving the wood surface. The convective heat transfer coefficient
was determined during the same experiments. A plateau is observed at high values of moisture content corresponding to the
constant drying rate period.
Received 27 February 1998 |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|