多针热脉冲技术测定土壤热导率误差分析

土壤热导率是研究土壤热传输、水热耦合运移的基本物理参数。为了探知多针热脉冲技术的误差，该研究以能够准确测定热导率的单针法作为参比，在4种质地土壤上，对多针热脉冲技术在不同体积质量、含水率和气压条件下测定的热导率进行了分析。结果表明，多针热脉冲技术的热导率结果与单针法总体符合较好，其热导率测定值的平均误差为0.074 W/(m·K)。干土热导率随气压增大呈现对数增长，这是由于气体分子平均自由程下降的原因。多针热脉冲技术的测定误差主要出现在中等含水率区域，关键问题是加热针的温度升高偏大，促进了水汽潜热传输。另外，土壤与探针之间的热接触阻力、探针导致的土壤体积质量改变、温度梯度引起的液水流也影响测定结果的准确性。该研究可为农业水土工程中的土壤热导率模拟提供依据。

Error analysis of multi-needle heat pulse probe for soil thermal conductivity measurement

Thermal conductivity is an essential parameter for studying coupled transport of heat and water in soil. In order to determine the error of multi-needle heat pulse technique, measurement accuracy of a multi-needle heat pulse probe was tested by comparing its data with that from the single probe method in this paper. Thermal conductivity measurements were conducted on four soils of different textures under various bulk densities, water contents, and air pressures. The results indicated that generally the thermal conductivity from the multi-needle heat pulse method agreed well with that from the single probe method, and the method was able to provide accurate soil thermal conductivity data. The mean error of the multi-needle heat pulse probe thermal conductivity was 0.074 W/(m·K). Due to the mean free path of gas decreased, the thermal conductivity of dry soil showed a logarithmic increasing with the increasing of air pressure. The errors of the multi-needle heat pulse probe mainly appeared at the medium water contents, where larger temperature rise near the heater enhanced latent heat transfer of vapor. The contact resistance between the needle and sample, change of soil bulk density near the needles, and liquid water transfer under temperature gradient may also have contributed to the errors in the muti-needle probe method. This study will provide a method for estimating soil thermal conductivity in the soil and water engineering.