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Sap Flow Measuring System through Heat Pulse Method by use of Thermal Multi Couples

使用热多电偶的热脉冲法液流测量系统

基本信息

批准号：
07650495
负责人：
SUGATA Kazuhiro
金额：
$ 1.47万
依托单位：
TOTTORI UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07650495/
关键词：
sap flow transpiration rate thermal method heat pulse multi thermocouples optimum positioning data logger 蒸散流ヒートパルス法

项目摘要

Sap flow measurement in plants shows promise as a method for determining transpiration rate in controlled environment and field condition. The two most common approaches (steady state heat balance and heat pulse method) have been used so far to measure the transpiration in herbaceous plants. The heat pulse method uses the temperature difference between two thermocouples radially inserted into the stem to estimate sap velocity.A major question concerning the accuracy of this method is related to the appropriate use of the measurement procedure when two data are used : one for low and the other for high convective heat velocities.Heat velocity (V,mm/sec) is estimated by equation (1)V= (X_1-X_2) / (2 x t_0) (1)where X_1 and X_2 are the distances (mm) from the heater to the thermocouple junctions above and below the heater, respectively ; t_0 is the time (sec) elapsed from pulse emission to the first re-occurrence of the initial temperature difference. Cohen suggested that above equation may be used for an accurate estimation of low or moderate velocities (0 to 0.17 mm/sec). For higher velocity, he gave another equation by use of the thermal diffusivity of the stem which is not easy to be measured accurately.To cope with the above situation, we proposed the multi thermo couples heat pulse method so that it can cover any velocity to measure sap flows in the stem by equation (1). We made it evident theoretically that three thermosensors and heat pulser are sufficient to measure any sap flow velocity by placing them at the appropriate locations. We gave the theoretical way to determine the optimum positions of thermo sensors.

在受控环境和田间条件下，植物液流测量有望成为测定蒸腾速率的一种方法。到目前为止，测量草本植物蒸腾作用的方法有两种：稳态热平衡法和热脉冲法。热脉冲法利用两个热电偶径向插入管杆的温差来估计液滴速度。当使用两个数据时，一个是低热流速度，一个是高对流热流速度，这个方法精度的主要问题是测量步骤的正确使用。热速(V，mm/s)由公式(1)V=(X_1-X_2)/(2 X T_0)(1)来估计，其中X_1和X_2分别是加热器到加热器上方和下方热电偶结点的距离(Mm)；T_0是从脉冲发射到初始温差第一次重现所经过的时间(秒)。Cohen建议，上述公式可用于中低速度(0~0.17 mm/s)的准确估计。为了更高的速度，他利用树干的热扩散率给出了另一个不易准确测量的公式，针对上述情况，我们提出了多热电偶热脉冲法，使其可以覆盖任何速度，通过公式(1)来测量树干内的树干流动。我们从理论上证明，通过将三个温度传感器和热脉冲器放置在适当的位置，就足以测量任何液流速度。给出了确定热敏传感器最佳位置的理论方法。