Experimental Study and Modelling of the Thermal Conductivity of Sandy Soils of Different Porosities and Water Contents

Abstract

This paper at first reports an experimental work to test the thermal conductivity of formulated sandy soil specimens of different porosities and water contents. Both needle probe and hot-plate methods were conducted and compared. It has been confirmed that the needle probe method has a better accuracy for the measurement of unsaturated soil thermal conductivity, and that the pore size distribution plays an important role on unsaturated soil thermal conductivity. Secondly, it gives out an extensive review on the modelling work, and investigates two major types of empirical models in detail. Two generalized formulas have been suggested to mathematically characterise the two types of models and tested using the experimental data. Finally, in terms of the intrinsic relation to the pore size distribution and the similarity between the thermal conductivity and water retention characteristics of unsaturated soils, a soil water retention model has been suggested and tested to describe unsaturated soil thermal conductivity.

Predicting the thermal behaviour of sands considering its moisture content and grain size with applications to geothermal heat pump installations

“…The nature of soils includes texture, mineral composition, shape and size of soil particles; the structural condition covers porosity and particle arrangement; finally, the physical condition is comprised by water content, temperature and pressure. Jin et al (2017) also affirmed that the empirical and mathematical models have demonstrated an underperformance because it is difficult to describe all the material characteristics connected with the thermal conductivity of sands, such as the particle geometry, pore size distribution and the arrangement of the water bridges between grains. The authors suggested a theoretical model to compute soil thermal conductivity considering the effects of porosity, degree water saturation, average pore size, the nature of the respective interfacial interaction of the pore water and vapour phases with the solid phase at the pore wall surface, the pore structure and the material nature of all phases (solid, liquid and gas).…”

“…Meline and Kavanaugh (2017) concluded that soil moisture affects the heat flux in the upper end of boreholes in Vertical Geothermal Heat Exchangers; however, it is uncertain what takes effect at depths between 61 m or 152 m. The models currently being used in the aforementioned studies provided limited insight because they do not consider other important physical factors such as grain size, sand color and grain shape in their analysis. Jin et al (2017) classified the influence factors of soil thermal conductivity in three groups: the first group is the nature of soils, the second factor is the structural condition and the third influence is the physical condition. The nature of soils includes texture, mineral composition, shape and size of soil particles; the structural condition covers porosity and particle arrangement; finally, the physical condition is comprised by water content, temperature and pressure.…”

A Simulation Model for Coupled Heat Transfer and Moisture Transport under the Action of Heat Source in Unsaturated Soils

“…Following are the basic assumptions of this model: The soil is homogeneous; The moisture content consists of pure water; Gravity is neglected; GHE has a constant temperature; The influence of air is neglected due to its limited impacts 24 ; Soil thermal conductivity and heat capacity are both constant. …”

Signal Processing for In-Situ Detection of Effective Heat Pulse Probe Spacing Radius as the Basis of a Self-Calibrating Heat Pulse Probe

“…The Heat Pulse Probe (HPP) is widely used to determine thermal conductivity (Abu-Hamdeh, 2001;Abu-Hamdeh and Reeder, 2000;Jin et al, 2017;Li et al, 2016;Liu et al, 2007;Ochsner and Baker, 2008;Penner, 1970;Yun and Santamarina, 2008), thermal diffusivity and heat capacity (Bristow, 1998;Ham and Benson, 2004;Kluitenberg et al, 1993;Liu et al, 2007;Ochsner 25 et al, 2001;Zhang et al, 2014) of soil. HPPs have been used to measure the thermal conductivity (Morin et al, 2010;Sturm and Johnson, 1992) and density of snow (Liu and Si, 2008); a review is presented by Kinar and Pomeroy (2015).…”