双针热脉冲测定冻土热特性的数值模拟方法  

Numerical simulation method for measuring the thermal properties of permafrost by dual-probe heat-pulse sensor

作　　者：张媛媛 刘湘君 赵天悦 赫刘台 何海龙 刘刚 ZHANG Yuanyuan;LIU Xiangjun;ZHAO Tianyue;HE Liutai;HE Hailong;LIU Gang(College of Land Science and Technology,China Agricultural University,Beijing 100193,China;College of Natural Resources and Environment,Northwest A&F University,Yangling 712100,China)

机构地区：[1]中国农业大学土地科学与技术学院,北京100193 [2]西北农林科技大学资源与环境学院,杨凌712100

出　　处：《农业工程学报》2024年第11期92-99,共8页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金资助项目(42077008,41771257)。

摘　　要：使用双针热脉冲(dual probe heat pulse, DPHP)测定冻土热特性时施加热脉冲后会导致加热探针周围的冰融化,使用目前常用的仅考虑热传导(忽略融化相变、冰水两相分界面)的解析解处理DPHP温度数据,会导致在-5℃至0℃温度范围内无法准确测量热导率(λ)和比热(C_(v))。为了能够准确测定冻土的λ和C_v,有必要考虑DPHP加热过程中引起的冰融化的相变潜热。该研究基于COMSOL仿真软件模拟了考虑相变潜热、相变区间以及移动冰水界面的DPHP测量过程,采用随温度非线性变化的真实冻土热特性进行模拟,并与真实冻土的DPHP测量数据对比。结果表明:1)COMSOL仿真在不考虑相变条件下与无限线性热源模型结果完全吻合(R^(2)=0.998 9);2)当土壤初始温度低于-5℃时,考虑相变发生的COMSOL仿真能够准确模拟试验结果,表现出较高的相关性(R^(2)> 0.93),在-1~0℃的土壤初始温度范围内,无限线性热源模型的结果与试验测量显著偏离(R^(2) <0.001 3);3)在不同土壤初始温度下,相变温度为-1.5~-0.5℃的仿真结果与试验数据具有较高的相关性(R^(2)> 0.7)。该研究结果检验了有限元仿真用于真实冻土DPHP研究的可行性,可为准确预测冻土热特性的研究提供方法。Thermal properties of frozen soil can be measured to evaluate the engineering construction and agricultural production.However,it is still challenging to determine the thermal properties of frozen soil using a dual-probe heat pulse sensor(DPHP).The thermal pulse can cause the ice around the heating probe to melt during DPHP measurement.The commonly-used analytical solution can only consider the heat conduction,resulting in the less accurate measurement on of the thermal conductivity(λ)and specific heat(Cv)at−5℃to 0℃.The purpose of this study is to test the feasibility of finite element simulation for the frozen soil DPHP.COMSOL simulation was carried out to consider the latent heat and temperature of phase transition in the measurement process of DPHP.The two-dimensional transient fluid module was used for simulation.The three-dimensional of DPHP experiment was simplified to the heat transfer in two-dimensional cylindrical coordinates.The 150 mm×150 mm square was constructed as the study area,where was approximated the DPHP probe with a 0.6 mm circle(ignoring internal probe padding and needle body material),and spaced the probe by 6 mm.The boundary of the study area was set as the adiabatic boundary,the boundary of the circular heat source was the heat flux boundary,which was set as 48.51 W/m,and the heating time was set as t0=8 s,respectively.The parameter settings were consistent with the experimental process.The nonlinear relationships between thermal conductivity and specific heat capacity with temperature was were calculated using the nonlinear relationship between liquid water content and temperature as studied by He et al.2015.These relationships were then set as the thermal conductivity and specific heat capacity of the frozen soil model.Four phase change temperatures were at−0.05-0.05,−2-0,−1.5-−0.5,and−0.5-0℃,corresponding to phase change intervals of 0.1,2,1,and 0.5℃,respectively.Four geometric shapes were constructed around the key solving region(around the DPHP probe),each of wh

关 键 词：冻土 数值模拟 热传导 双针热脉冲 移动边界 

分 类 号：S-3[农业科学] P642.14[天文地球—工程地质学] S225[天文地球—地质矿产勘探]