A Numerical Analysis of Heat Pulse Velocity Theory and Practice

Abstract
When the heat pulse velocity method of measuring sap flux in trees is based on idealized heat transport theory, it seriously underestimates actual water flow. Two-dimensional numerical solution of the physical heat flow system demonstrates that both sensor thermal properties and sap flow interruption in the vicinity of implanted probes cause significant departure from the idealized theory. New numerical solutions to the practical heat pulse problem are given and applied to earlier experimental data. Transpiration rates thus determined in conifers agree within 5% of those measured by weighing lysimetry or in a diffuse porous hardwood within 10% of those calculated from a climatized cuvette. A table of numerical solutions applicable to the most widely published heat pulse sensing configuration is given.

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