Towards reduced heating duration in the transient thermal dissipation system of sap flow measurements
The TTD10 method is an empirical evolution of the constant heat dissipation method of Granier (1985). By contrast to Granier, it uses a transient heating of 10 minutes, and it can be applied to a single-needle probe (Do et al., 2011). This system saves energy and cost and reduces thermal interference due to heat storage and passive thermal gradients. However, the heating duration increases the time resolution of measurement, i.e., 20 min with cooling, and assumes a relative stability of the flow rate over 10 min. Hence the objective was to reduce the heating time and measurement cycle. Previous multi-media laboratory data with both dual-needle and single-needle probes were used to test a generic calibration with the maximum temperature taken at 5 min. A calibration with similar sensitivity and accuracy to TTD10 was obtained under two conditions. The first condition used the difference between the maximum temperature and an offset temperature taken at 30 s. The second defined a new thermal index called K2. This new TTD5 system with single-needle probe enhances the previous advantages of low energy, low cost and simplicity of TTD method, well adapted to large sampling experiments.
Do, F.C., Puangjumpa, N., Rocheteau, A., Duthoit, M., Nhean, S. and Isarangkool Na Ayutthaya, S. (2018). Towards reduced heating duration in the transient thermal dissipation system of sap flow measurements. Acta Hortic. 1222, 149-154
xylem sap flow, single-needle probe, tree water use, transient heat dissipation