Electrical conductivity (EC) of the unseasoned timber of three softwood species (Pinus radiata, Pseudotsuga menziesii, and Sequoia sempervirens) and one hardwood species (Eucalyptus globoidea) was studied over the temperature range of 20 − 90 • C . EC was measured in sapwood, transitional wood, and heartwood in the three principle grain directions. All species exhibited similar behaviour: (1) heartwood EC was lower than that of sapwood and (2) EC increased with temperature. P. radiata samples from two regions of New Zealand's South Island showed variation of EC by a factor of two in the longitudinal direction; however, in the radial and tangential directions, the EC variation was less pronounced. This work seeks to provide possible explanations for EC variation in green wood and to propose suggestions for future research.
Joule heating has recently been investigated as a potential alternative to chemical fumigation for phytosanitary treatment of Pinus radiata logs exported from New Zealand. The research was driven by concern regarding the effects of methyl bromide release to atmosphere, following fumigation, as highlighted by the Montreal Protocol. The work has involved creating 1 dimensional and 3 dimensional computer models of the Joule heating process in P. radiata, building a laboratory-scale log test rig with suitable instrumentation and control systems, heating approximately 60 P. radiata logs and using the measured data to refine and validate the models. While engaged in this work it became clear that the process could also potentially be applied to heat veneer peeler logs. This paper describes the application of the 1 dimensional model and laboratory-scale test rig to a typical P. radiata export log and to a Eucalyptus nitens log prepared for veneer peeling. The results demonstrate that, despite the heterogeneities of the timber, the technique is capable of achieving the required temperature profiles for both applications and that the model is a sufficiently good representation of the process to provide a viable control method.
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