Errors Analysis Of Heat Pulse Probe Methods: Experiments and Simulations

Abstract

The heat pulse probe (HPP) method can be used to measure specific heat capacity (c), thermal conductivity (λ), and water content of soil; however, many factors are believed to contribute to measurement errors in both λ and c from the HPP method. The objective of this study was to examine if contact resistance, heat‐driven flow, temperature‐dependent thermal properties, or epoxy fillings affect the estimated soil thermal properties and water content from the HPP method. Heat pulse experiments were conducted on oven‐dry sand, water‐saturated sand, sand saturated with agar‐stabilized water, and coarse snow (large grain size). The results showed that for the sand and coarse snow, the thermal contact resistance did not contribute to the overestimation of heat capacity. There was little difference in measured water contents between sand saturated with water and sand saturated with agar‐stabilized water, suggesting no obvious heat‐driven flow under saturated conditions. Compared with an 8‐s heat pulse with a power strength (q′) >80 W m−1, a long heat pulse of duration 60 s and q′ < 6 W m−1 reduced the overestimation of soil c and water content (θw) on oven‐dry sands. Both temperature‐dependent soil thermal properties and epoxy filling inside the heater needle contributed to the overestimation of c and θw.

Development and Application of the Heat Pulse Method for Soil Physical Measurements

“…These studies together with others served as the basis for many subsequent developments and applications of the HP method. Error analysis of these methods and probe designs were performed and documented (Kluitenberg et al, , , ; J. H. Knight et al, ; G. Liu et al, ; G. Liu & Si, ). It should be noted that HP measurements are based on the assumption of local thermal equilibrium within the duration of the measurements (Roshan et al, ).…”

Single- and Dual-Probe Heat Pulse Probe for Determining Thermal Properties of Dry Soils

“…First, the specific heat of soil is the sum ofthe heat capacities of water and solids (de Vries, 1963); therefore, the specific heat of dry soil is a prerequisite for determining the water content of soil from HP methods. Second, DP methods are known to overestimate soil c (Song et al, 1998;Ren et al, 2003;Basinger et al, 2003;PhÜlips et al, 2005) and the mechanism for the overestimation off is still not well understood (Liu and Si, 2010). The rvalues of mineral soils measured with DSC were between 740 and 840 J kg"' K"' (Basinger et al, 2003;Ochsner et al, 2003), while the c values from DP methods were between 881 and 973 J kg"' K"' from Ren et al (2003) and between 864 and 939J kg"' K"' from Campbell et al (1991).…”

“…Therefore, for a field application with strong diurnal temperature fluctuation, the DP method with a short heating duration is advantageous over the SP method. The mechanism for the well-known overestimation of the specific heat by the DP method (Song et al, 1998;Ren et al, 2003;Basinger et al, 2003;Phillips et al, 2005;Liu and Si, 2010) is still not well understood. In our DP experiments, the overestimation if f was between 19 and 29% (Fig.…”

“…Because the contact conductance was considered by the SP method and was ignored by the DP method, it is possible that the overestimation off by the DP method originated from the imperfect contact between the needles and the surrounding air-dried soil particles. The reason is that, if the model of de Vries (1952) or Kluitenberg et al (1993) was used for the DP method, the existing contact resistance would slow down the propagation of heat from the heater needle, which is equivalent to increasing c (Liu and Si, 2010), and thus will cause overestimation off. Noborio et al (1996) also studied the poor contact between the probe and surrounding soil by using a finite difference simulation model (Riha et al, 1980).…”

“…The DP was a five-needle design (Liu and Si, 2010) that was similar to that of Mori et al (2003). All five needles were constructed from 1.27-mm-o.d.…”