Theory and practical application of heat pulse to measure sap flow
Theory and practical application of heat pulse to measure sap flow
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DOI：
10.2134/agronj2003.1371
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发表时间：
2003-11-01
期刊：
影响因子：
2.1
通讯作者：
Jardine, B
中科院分区：
文献类型：
--
作者：
Green, S;Clothier, B;Jardine, B
热脉冲方法可用于准确测量植物茎中的树液流量，只要使用可靠的校准程序将测量的热脉冲速度与实际树干流量相关联即可。本文回顾了补偿法和T-max热脉冲法的理论基础，这两种方法使用线性加热器和径向插入植物茎的温度探头。这些探头不仅扰乱了树液流，而且还改变了探头附近边材的热均匀度。干扰程度取决于探头的大小和几何形状以及相应的非导电边材的缠绕宽度。本文采用二维热流和水流模型，推导出适当的修正系数，以考虑探头热性能和流动堵塞的影响。缠绕宽度对热脉冲测量有很大的影响，而传感器材料的影响很小或没有影响。给出了补偿法和T-max法的校正因子表。通过比较柳树(Salix alba L.)树干的热脉冲测量，证实了这些新的修正因子。和一棵杨树(杨树W.Bartram ex Marsh)，对照实际蒸腾速率，通过测量生长在大蒸渗仪中的树木的重量损失来确定。在每天的基础上，两次热脉冲测量都被发现在实际蒸腾的5%到10%以内。补偿法准确地测量了接近2 cm/h的流量。T-max法很难分辨任何速度低于10 cm/h的流量。
Heat pulse methods can be used for accurate measurements of sap flow in plant stems provided a reliable calibration procedure is used to relate the measured heat pulse velocity to the actual sap flow. This paper reviews the theory underpinning both the compensation and T-max heat pulse methods that use a linear heater and temperature probes inserted radially into the plant stem. These probes not only disrupt the sap stream, but they also alter the thermal homogeneity of the sapwood in the vicinity of the probes. The degree of disturbance depends on the size and geometry of the probes and the corresponding wound width of the nonconducting sapwood. A two-dimensional model of heat and water flow was used here to derive appropriate correction factors to account for the influence of both probe thermal properties and flow blockage. Wound width has a large influence on the heat pulse measurements while sensor material appears to have little or no influence. A table of correction factors is presented for both the compensation and T-max methods. These new correction factors are confirmed by comparing heat pulse measurements in the trunk of a willow (Salix alba L.) and a poplar (Populus deltoides W. Bartram ex Marsh), against actual rates of transpiration determined from measured weight loss of the trees growing in large lysimeters. On a daily basis, both heat pulse measurements were found to be within 5 to 10% of the actual transpiration. The compensation method accurately measured flows close to 2 cm/h. The T-max method had difficulty resolving any flows slower than about 10 cm/h.