Temperature dependence of thermal conductivity of soil over a wide range of temperature (5-75 degrees C)

The coupled heat and mass transfer in soil can be analysed by examining the temperature dependence of thermal conductivity. We have measured the therm al conductivity of two kinds of soil (Ando soil and Red Yellow soil) as a f unction of both temperature (5-75 degrees C) and water content by the twin heat probe method. From our results we concluded that the thermal conductiv ity resulting from the latent heat transfer can be separated from the appar ent thermal conductivity by subtracting the thermal conductivity at a tempe rature near 0 degrees C from that at a higher temperature. The relation bet ween the phenomenological enhancement factor (beta) and the volumetric air- filled porosity was divided into two parts: beta increases linearly as the volumetric air-filled porosity increases from zero (that is, water saturati on), to the point at which soil water potential corresponds to -320 J kg(-1 ); from that point to oven-dry condition, beta decreased logistically with the volumetric air-filled porosity. From these results, we could generalize the behaviour of beta.