Effects of Particle Size and Fines Content on Thermal Conductivity of Quartz Sands

Abstract

The thermal properties of soil have drawn great research attention in recent years. Thermal conductivity is the most important such property, particularly for the design of shallow geothermal systems such as energy piles and borehole thermal energy storage. A newly developed thermo–time domain reflectometry probe was used to measure the thermal conductivity of quartz sands with the peak value method. Three rounded quartz sands with different particle sizes were used in experiments to investigate the effects of particle size and fines content on thermal conductivity. Results revealed that thermal conductivity increased with increasing particle size for uniform sands. The thermal conductivity was lower in fine sands than in coarse sands under dry conditions but higher in fine sands than in coarse sands at low moisture contents. The thermal conductivity of coarse sands was increased to peak value by increasing the fine sands content to the critical fines content corresponding to maximum thermal conductivity. The critical fines content increased with a decrease in the mean grain size ratio of fine sands to coarse sands; the content also was related to the grain shape.

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

“…The authors found that thermal conductivity of pure sands decreased as grain size declined and it was affected by the increase of number of physical contact points, thereby it caused an increment in thermal resistance between sand particles. Zhang et al (2015b) also showed that porosity of 0.50 and fines content of 50 % caused an increase in thermal conductivity of sands with high quartz content (k Ottawa 20/30 = 0.35 W/m K). A sand sample with porosity of 0.36 and the same percentage of fines content showed a decrease of thermal conductivity up to 0.17 W/m K. Moreover, the thermal conductivity of sands with uniform grain size decreased as grain size decreased, while for sands with nonuniform grain size, the thermal conductivity increased as a result of fine particles in sand pores.…”

“…Xing (2014) computed an average temperature of 17.6 °C on soil covered with short grass in Puebla, Mexico. Zhang et al (2015b) studied the effects of grain size and finest content on thermal conductivity of three typical sands with high quartz content. The authors found that thermal conductivity of pure sands decreased as grain size declined and it was affected by the increase of number of physical contact points, thereby it caused an increment in thermal resistance between sand particles.…”

Effect of biochar on desiccation of marine soils under constant and cyclic temperatures

“…7b are merely illustrated in an orderly arrangement to highlight the increase in contact points between the PS-3 biochar-biochar particles compared to a single biochar particle in PS-1. The increased number of contact points would have narrowed the heat flow path and reduce heat flow (denoted by red arrows) between particles as a result of increased thermal resistivity due to limited contact area for heat transfer at the physical contact points [64]. Moreover, as depicted in Fig.…”

“…Furthermore, with reference to Fig. 5d, it could be presumed that (even at slurry state) BAS belonging to the PS-3 category would have possessed the lowest thermal conductivity due to the introduction of more (1) contact points between biochar-biochar and/or biochar-soil particles and (2) tortuous heat flow paths in the BAS matrix [22,64]. Low thermal conductivity would have reduced the magnitude of heat that reached the water molecules within the BAS pores and minimized their evaporation.…”

Thermal Conductivity of Biocemented Graded Sands

“…. Previous studies found that the particle size could greatly influence the thermal conductivity of sands (Lee et al 2015;Xiao et al 2019c;Zhang et al 2019;Zhang et al 2020).…”