The behaviour of a thermal flow sensor attached to the wall of a square tube is examined, exposed to gas flow for Reynolds numbers in the range 0-4.1 x 10(4). Consisting of a polysilicon heater and a pair of thermopiles, the sensor's three output signals (heater power, its electric resistance and the thermopile signal) are analyzed as a function of Re. Employing three different modes of operation (constant power (CP), constant voltage (CV) and constant temperature (CT)), it was found that the sensor sensitivity maximizes in CT mode. Heater power and its resistance vary with Re-a where a changes significantly for Re > 2000. The thermopile signal, which corresponds to the streamwise temperature gradient across the heater, in contrast to the other two signals, is more sensitive in detecting flow disturbances. Its fluctuations increase with a high rate close to Re = 1800, a value which is smaller than the corresponding increase of the other two signals. The probability density function (pdf) of its fluctuations is negatively skewed consistently for the range 1500 < Re < 11,000 while for Re > 11,000 it turns to a symmetric one. The pdf of the other two signals do not show any systematic trends with Re. The most striking difference of the thermopile signal behaviour compared to the other two is its multivalued relationship with Re in the range 2000 < Re < 11,000. (C) 2008 Elsevier Inc. All rights reserved.
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机译：检查了附着在方管壁上的热流量传感器的行为，暴露在气流下雷诺数范围为0-4.1 x 10（4）。由多晶硅加热器和一对热电堆组成，将传感器的三个输出信号（加热器功率，电阻和热电堆信号）作为Re的函数进行分析。通过使用三种不同的操作模式（恒定功率（CP），恒定电压（CV）和恒定温度（CT）），发现传感器灵敏度在CT模式下最大。加热器功率及其电阻随Re-a的变化而变化，其中Re> 2000时变化很大。与其他两个信号相反，热电堆信号与加热器上的流向温度梯度相对应，与其他两个信号相比，它更敏感。其波动以接近Re = 1800的高速率增加，该值小于其他两个信号的相应增加。在1500 11,000的范围，则变为对称对称。 Re的其他两个信号的pdf均未显示任何系统趋势。与其他两个相比，热电堆信号行为最显着的差异是其与Re的多值关系在2000 展开▼
