NUMERICAL MODELING OF A THERMAL-CONDUCTIVITY MATRIC SUCTION SENSOR

Thermal conductivity matric suction sensors appear to be a promising d evice for the measurement of suction in soil. The technique indirectly measures matric suction by measuring the thermal conductivity of a ce ramic block. This paper uses both a spherical and a cylindrical porous medium to simulate the heat flow in a thermal conductivity matric suc tion sensor. It is found that, although the transient temperature at t he center of the sensor is heavily dependent on the material of the th ermocouple and the heating device, the steady-state temperature is pri marily determined by the thermal conductivity of the ceramic block. Th erefore, accurate measurements can be obtained by using a longer heati ng period or by selecting a lower-heat-capacity material for the therm ocouple and the heating device. Optimal sizes of the sensor for given heating rates and heating periods are calculated using a finite differ ence method. A multilayered sphere was also used to simulate the situa tion where the size of the sensor is not sufficiently large and an err or occurs due to the influence of the surrounding soil. The numerical model is verified by comparison with the theoretical solution of a spe cial case.