title: Use of the correct heat conduction-convection equation as basis for heat-pulse sap flow methods in anisotropic wood.
abstract: Heat-pulse methods to determine sap flux density in trees are founded on the theory of heat conduction and heat convection in an isotropic medium. However, sapwood is clearly anisotropic, implying a difference in thermal conductivity along and across the grain, and hence necessitates the theory for an anisotropic medium. This difference in thermal conductivities, which can be up to 50%, is, however, not taken into account in the key equation leading to the currently available heat-pulse methods. Despite this major flaw, the methods remain theoretically correct as they are based on derivations of the key equation, ruling out any anisotropic aspects. The importance of specifying the thermal characteristics of the sapwood according to axial, tangential or radial direction is revealed as well as referring to and using the proper anisotropic theory in order to avoid confusion and misinterpretation of thermal properties when dealing with sap flux density measurements or erroneous results when modelling heat transport in sapwood.
authors.affiliation: Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium. maurits.vandegehuchte@ugent.be
authors.forename: Maurits W
authors.initials: MW
authors.lastname: Vandegehuchte
authors.forename: Kathy
authors.initials: K
authors.lastname: Steppe
mesh_terms: D016880:Anisotropy; D018481:Convection; D004058:Diffusion; D006358:Hot Temperature; D008954:Models, Biological; D053147:Plant Exudates / Q000502:physiology*; D012212:Rheology / Q000379:methods*; D013814:Thermal Conductivity; D014934:Wood / Q000502:physiology*
chemical_list: D053147:Plant Exudates