Joule heating of logs for phytosanitary purposes and timber processing pre-treatment

Abstract

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.

Anisotropic electrical conductivity of green timber within $$20-90^{\circ }\hbox {C}$$ temperature range

“…However, above FSP, the effect of temperature on EC becomes dominant (Nursultanov et al 2017), with the effect of MC being negligible (Stamm 1929(Stamm , 1964Nursultanov et al 2017). The effect of temperature on the longitudinal EC of green P. radiata is near linear, similar to aqueous solutions of salts below water's boiling point (McCleskey 2011;Haynes 2014), while in the radial and tangential directions, the effect remains nonlinear (Nursultanov et al 2017).…”

“…Growing interest in various plant and wood related technologies such as precision irrigation (Oletic and Bilas 2020), earlier plant disease detection (Khaled et al 2018), electrical heating of wood (Hoover et al 2010;Heffernan et al 2018), and sapwood/heartwood identification in living trees (Guyot et al 2013) require holistic understanding of wood properties. However, some of the wood properties such as electrical conductivity (EC) have been studied partially, with most of the research done on wood below fibre saturation point (FSP), which is commonly assumed to be around 30% MC (Berry and Roderick 2005), and at near room temperature.…”

“…This correlation formed the basis for all electrical moisture meters. However, to develop and improve emerging technologies such as Joule heating (Heffernan et al 2018), a holistic knowledge of EC is desirable, below and above FSP. Only then, such knowledge, coupled with suitable electrodes (Heffernan et al 2018), would enable accurate determination of sapwood and heartwood proportions of green logs and live trees, temperature/temperature distribution measurement of heated logs and, in conjunction with a computational model, prediction and control of Joule heating of logs for phytosanitary (Nursultanov et al 2019) or other conditioning purposes.…”

“…However, to develop and improve emerging technologies such as Joule heating (Heffernan et al 2018), a holistic knowledge of EC is desirable, below and above FSP. Only then, such knowledge, coupled with suitable electrodes (Heffernan et al 2018), would enable accurate determination of sapwood and heartwood proportions of green logs and live trees, temperature/temperature distribution measurement of heated logs and, in conjunction with a computational model, prediction and control of Joule heating of logs for phytosanitary (Nursultanov et al 2019) or other conditioning purposes. In addition, knowing wood EC above FSP would allow improvement in the accuracy of established technologies such as electrical resistance tomography (ERT), which estimates electrical resistivity (the reciprocal of EC) distribution computationally (Guyot et al 2013;Luo 2019).…”