CAJ | 학술논문

在利用热脉冲方法测定热特性时，通常对探针形状做理想化处理，即假设探针为线性热源，热导率无限大而热容量为零。在实际应用中，探针本身的有限特性（有限半径以及有限热容量）会导致热特性测定误差。为了研究探针有限特性对热脉冲技术测定土壤热特性的影响，该研究采用改进的热脉冲探针（直径2 mm、长度40 mm、间距8 mm）测定土壤热特性，并分别使用PILS（pulsed infinite line source，无限长线性脉冲热源）和ICPC （identical cylindrical perfect conductors，近似圆柱形完美导体）2种理论估计土壤热特性，比较分析了探针有限特性对热脉冲技术测定热特性结果的影响。结果表明：1）与PILS理论相比，利用ICPC理论拟合得到的温度升高曲线，可以有效减少探针有限半径和热容量对土壤热特性测定结果的影响。与 ICPC 理论相比，在0.03～0.25 m3/m3的含水率范围内，用PILS理论得到的砂土热扩散率和热导率分别偏低11.8%和5.2%；与模拟热容量相比，PILS和ICPC理论分别将热容量高估16.1%和7.9%；2）探针有限特性对土壤热特性的影响与含水率有关：在干土上最大；随着土壤含水率的增加，其影响逐渐降低。该研究对提高热脉冲技术测定土壤热特性的准确性具有指导意义。
재이용열맥충방법측정열특성시，통상대탐침형상주이상화처리，즉가설탐침위선성열원，열도솔무한대이열용량위령。재실제응용중，탐침본신적유한특성（유한반경이급유한열용량）회도치열특성측정오차。위료연구탐침유한특성대열맥충기술측정토양열특성적영향，해연구채용개진적열맥충탐침（직경2 mm、장도40 mm、간거8 mm）측정토양열특성，병분별사용PILS（pulsed infinite line source，무한장선성맥충열원）화ICPC （identical cylindrical perfect conductors，근사원주형완미도체）2충이론고계토양열특성，비교분석료탐침유한특성대열맥충기술측정열특성결과적영향。결과표명：1）여PILS이론상비，이용ICPC이론의합득도적온도승고곡선，가이유효감소탐침유한반경화열용량대토양열특성측정결과적영향。여 ICPC 이론상비，재0.03～0.25 m3/m3적함수솔범위내，용PILS이론득도적사토열확산솔화열도솔분별편저11.8%화5.2%；여모의열용량상비，PILS화ICPC이론분별장열용량고고16.1%화7.9%；2）탐침유한특성대토양열특성적영향여함수솔유관：재간토상최대；수착토양함수솔적증가，기영향축점강저。해연구대제고열맥충기술측정토양열특성적준학성구유지도의의。
Soil thermal properties, including volumetric heat capacity, thermal diffusivity, and thermal conductivity, are basic physical parameters for determining the change rate of soil temperature, heat storage and transfer. The heat pulse technique, with the advantages of relative easy operation, minimal soil disturbance, and making repeated and automatic readings, has been used widely for measuring in-situ soil thermal properties. A heat pulse is emitted from a line source enclosed in a stainless heating needle and the temperature rises with time at a shorter distance from the heater are recorded for a few minutes. Soil thermal properties are then estimated from the temperature change by time data. For simplicity, the heat pulse probe is normally considered as a line source with infinitesimal probe radius and zero heat capacity when soil thermal properties are calculated. In reality, the finite properties of the probe itself, including finite heat capacity and finite probe radius, can lead to biased thermal property estimations. In this study, we compared the results of soil thermal property estimations with the PILS (pulsed-infinite-line-source) theory and ICPC (identical cylindrical perfect conductors) theory, to evaluate the influences of finite properties of the probe on soil thermal property estimations. The heat pulse probe consist of 3 needles with a diameter of 2 mm and a length of 40 mm. Heat pulse measurements were conducted on a sand soil with water content varied from air dry condition to field capacity, and soil heat capacity, thermal diffusivity, and thermal conductivity were estimated with both the PILS and ICPC methods. In addition, heat capacity estimates with the de Vries model were used to evaluate the accuracy of heat capacity measurements. The results indicated that compared with the PILS theory, the ICPC solution significantly reduced the errors in soil thermal property estimations from the temperature change-by-time curves. For water content ranging from 0.03 to 0.25 m3/m3, the PILS theory underestimated soil thermal conductivity and thermal diffusivity by 11.8%and 5.2%, respectively. Compared with the theoretical values from the de Vries model, the PILS theory and the ICPC theory overestimated soil heat capacity by 16.1%and 7.9%, respectively. Further analysis showed that that the influences of finite probe properties on thermal property estimations were most significant on dry samples, and the errors were reduced linearly with increasing soil water content. The experimental results from this study support that the theoretical analysis including finite heat capacity and finite probe radius improves the accuracies of soil thermal property estimations. The conclusions also have implications in optimizing the design of heat-pulse probes, especially for probes with relatively larger diameters.