Decrease in thermal conductivity with increasing temperature in nearly dry sandy soil

Abstract

To clarify the role of the water bridges between soil particles on the transfer of heat we studied the dependence of thermal conductivity (l) and electrical conductivity (E) on temperature between 278 and 338 K of sand and sand mixed with kaolin in the nearly dry state. The thermal conductivity decreased as temperature increased in the sand at volumetric water contents less than 0.07 m 3 m ÿ3 , but it increased in the sand-kaolin mixture over the measured range of water content. In the sand, the ratio of E in the soil solution to the electrical conductivity of pure water increased gradually with increasing water content at the water contents less than 0.05 m 3 m ÿ3 and was almost constant at larger water contents. The ratio of E of the sand-kaolin mixture increased with increasing water content, particularly at the lower temperature. For both samples the ratio of E decreased as temperature increased, which suggested that the conduction of heat decreased through the decrease in the water bridges as temperature increased. Because the decrease in l with increasing temperature could not be explained by the transfer of latent heat transfer, we considered that the temperature dependence of l was due not only to the transfer of latent heat but also to the thermal bridge of water. We conclude that the condensation, conduction and evaporation in series involved in the latent heat transfer take place mainly through the water films. Our experimental results will help to understand the mechanism of the latent heat transfer in soil with the water films surrounding the soil particles.

Thermal Conductivity of Binary Sand Mixtures Evaluated through Full Water Content Range

“…5-Region II), the lower hydraulic connectivity makes the grain-water paths more tortuous, resulting in heat flow through less and longer thermally conductive grain-water pathways. Consequently, l shows a steep and abrupt decrease at or around the residual saturation where the heat flow is essentially limited to water bridges randomly connected with nearly dry sand grains (Philip and de Vries, 1957;Sakaguchi et al, 2007). In the hydration regime (Fig.…”

“…e.g., Terzaghi, 1952;Skaggs and Smith, 1968), soil type (Van Rooyen and Winterkorn, 1959;Adivarahan et al, 1962;Haigh, 2012), grain size (e.g., Sepaskhah and Boersma, 1979;Tavman, 1996;Midttømme and Roaldset, 1998), and temperature (e.g., Campbell et al, 1994;Hiraiwa and Kasubuchi, 2000;Sakaguchi et al, 2007). In general, l increases with an increase in q (Philip and de Vries, 1957;De Vries, 1963); this is because l of water (~0.58 W m -1 K -1 ) is over an order of magnitude larger than that of air (~0.02 W m -1 K -1 ).…”

Thermal Conductivity of Standard Sands. Part I. Dry-State Conditions

“…Farouki [1] suggested that quartz grain interfacial effects, prompted by a T increase, were responsible for the improved heat transfer. In turn Sakaguchi et al [15] observed an opposite phenomenon in low moisture Toyoura sand, i.e., its λ was decreasing with T . It was concluded that the decrease in λ with an increase in T was mainly due to decreased water thermal bridges.…”

Analysis of the subsurface urban heat island in Oberhausen, Germany

“…Table 2); however, the relationship between soil temperature, soil water content and thermal con ductivity is complex, and other influencing factors (e.g. porosity) have to be considered, as has been indicated by other studies (see Cosenza et al 2003, Sakaguchi et al 2007. Therefore, as a result of a variety of factors, a pronounced SUHI and a UHI have been formed in Oberhausen.…”