有限元模拟土壤孔隙对双针热脉冲法测量比热的影响

FINITE ELEMENT ANALYSIS OF EFFECT OF SOIL PORES ON MEASUREMENT OF SPECIFIC HEAT WITH THE DUAL-PROBE HEAT-PULSE METHOD

双针热脉冲(DPHP)方法是目前用来测量土壤比热(c)、热导率(λ)和温度(T)的重要方法。然而,很多因素均会导致双针热脉冲法测得的λ和c存在误差,如土壤孔隙。基于三种不同粒径的石英砂,通过有限元法(FEM)模拟DPHP实验,分析土壤孔隙对DPHP法测量比热的影响,结果表明:(1)土壤孔隙导致测得的温度空间分布存在显著的各向异性,加热针周围6 mm处不同方向的比热(c)之间相对误差达到了23%;(2)DPHP方法测得的土壤热特性标准差随粒径增大而增大,这与实际实验观察的结果一致;(3)土壤孔隙的存在使得DPHP法测得的土壤比热被高估,本模拟中加热针周围6 mm处c值被高估了约6%。

The Dual Probe Heat Pulse （DPHP） method is an important method to measure specific heat （c）, ther- mal conductivity （ A ） and temperature （T） of soil. However, there are a number of factors that may cause errors in meas- urement of both A and c using DPHP, such as soil pores. With finite element method （FEM） simulating DPHP experi- ments, three kinds of quartz sands which different in particle size were used to analyze the effect of soil pores on measure- ment of specific heat with the DPHP method, and the result shows that （ 1 ） soil pores caused significant anisotropy of spa- tial distribution of measured temperatures and led to a relative difference, reaching as high as 23% in c measured between different spots 6mm away from the heater in different directions; （2） the standard deviation of the measurement of the soil thermal properties with DPHP increased with the increasing particle size, which was consistent with the observation during the experiments; and （3） the existence of soil pores led to overestimation of c when the DPHP method was used. In this simulation, the specific heat measured at 6 mm away from the heater was overestimated by about 6%.