Abstract
Drying is a required operation in timber manufacturing industries. Most drying processes utilise convective kilns, which involve coupling between transient heat and mass (moisture content) transfer in solids and convection in a flowing medium. In the present work, the flow field in the kiln is determined using a system approach based on a general head loss equation, whereas the coupling between transient heat and mass transfer in the timber is accomplished by a solution of a local differential model across the timber stack. The scheme is applied to study the effects of distinct geometric kiln configurations and air flow temperatures upon drying rates and moisture content.
Highlights
The technological advancements in the last years have made available to industries several conventional and nonconventional wood drying methods such as radiofrequency heating, press, solar, and dehumidification drying strategies [1]
The process is performed in dry kilns, in which heated air flows through a lumber stack comprising timber layers separated by stickers
The physics of the problem encompasses the hydrodynamic description of the air flow, conjugated heat, and moisture transfer within timber layers and convective heat and moisture transfer at lumberair interface
Summary
The technological advancements in the last years have made available to industries several conventional and nonconventional wood drying methods such as radiofrequency heating, press, solar, and dehumidification drying strategies [1]. The industrial importance of drying processes has been translated by the increasing number of works reporting numerical prediction of temperature distribution and moisture content in convective drying problems. To the authors’ best knowledge, there are no works in the literature based upon a system approach where the convective kiln is modelled in the real (full) scale and air flow is computed using a lumped approximation. The present system approach aims at developing a simpler model and is yet able to obtain good approximations to the physical phenomena Following this route, it is proposed a mixed numerical model (a global approach to determine flow velocities and a local differential model to compute evolution of the timber temperature and moisture content) to predict the effects of distinct kiln configurations and air flow temperature on the evolution of drying rates, moisture content, and temperatures in a full geometric scale
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