Multiple-globe thermometer for measuring the air temperature without an aspirated radiation shield
Multiple-globe thermometer for measuring the air temperature without an aspirated radiation shield
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DOI：
10.1016/j.agrformet.2020.108028
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发表时间：
2020-10-15
影响因子：
6.2
通讯作者：
Nakagawa, Hiroshi
中科院分区：
文献类型：
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作者：
Maruyama, Atsushi;Matsumoto, Yoshihisa;Nakagawa, Hiroshi
提出了一个由多个不同大小球体的温度计算空气温度的简单公式，从而消除了辐射对空气温度测量的影响。该公式是由外流中球面的能量平衡和传热理论导出的。使用这个公式，我们开发了一种仪器，它可以从多个热电偶获得空气温度，这些热电偶具有球形尖端（多个球体），而不需要辐射屏蔽和通风。在夏季和冬季进行了田间试验。将具有不同直径（d = 0.25、0.5、1、2、4 mm）的五个球设置在现场，并且使用具有三重辐射屏蔽和5 m/s的抽吸的标准温度计作为参考。所有地球仪的温度都高于白天的空气温度; d = 4 mm时的最大差值为3.3 ℃。使用建议的公式计算的空气温度与使用标准温度计进行的测量结果吻合良好。在该公式中，使计算的空气温度中的误差最小化的与表面几何形状相关的系数m的最佳值为m = 0.5。这一数值与前人在球面上的传热理论和实验研究结果是一致的。提供最高精度的地球仪直径的最佳组合是0.25、1和4 mm。该组合对所有夏季和冬季数据的均方根误差为0.13 ℃。结果表明，所提出的温度计的足够的精度。建议的温度计可用于农田和森林中，在主电源不可用，因此将有助于澄清农村地区的实际温度和小气候。
A simple formula is proposed to calculate the air temperature from the temperatures of multiple spheres of different size and thus eliminate the effects of radiation on the measurement of air temperature. The formula is derived from energy balance and heat transfer theory for a spherical surface in external flow. Using this formula, we developed an instrument with which to obtain the air temperature from multiple thermocouples with spherical tips (multiple globes) without the need for a radiation shield and ventilation. Field experiments were conducted during summer and winter. Five globes having different diameters (d = 0.25, 0.5, 1, 2, 4 mm) were set in the field, and a standard thermometer having a threefold radiation shield and aspiration of 5 m/s was used as a reference. All globe temperatures were higher than the air temperature during the day; the maximum difference was 3.3 degrees C for d = 4 mm. The air temperature calculated using the proposed formula agrees well with measurements made using a standard thermometer. In the formula, the optimum value of the coefficient m relating to the surface geometry that minimizes error in the calculated air temperature was m = 0.5. This value is consistent with the results of previous studies on heat transfer theory and experiments on spherical surfaces. The best combination of globe diameters providing the highest accuracy was 0.25, 1, and 4 mm. The root-mean-square error of this combination for all summer and winter data was 0.13 degrees C. The results demonstrate the sufficient accuracy of the proposed thermometer. The proposed thermometer can be used on farmland and in forests where mains power is unavailable and will thus help clarify the actual temperature and microclimate in rural areas.