Determination of Thermophysical Parameters of the Soil according to Dynamic Data on Its Temperature

Methods for determining the thermal diffusivity coefficient from point temperature records in soil of a given thickness have been developed. Data on the dynamics of soil temperature measured at the same depth eight times per day with an interval of 3 hours are used. The proposed methods are based on solving inverse problems of the heat transfer equation (with two harmonics on the soil surface). Experimental studies on the temperature of the layers (0, 5, 10, 15, 20, and 40 cm) of gley alluvial soil (Calcaric Gleyic Pantofluvic Fluvisol) in the Igdır region (eastern Turkey) were carried out using Elitech RC-4 sensors during the summer season. Using the obtained data, various methods were used to calculate the thermophysical properties of the soil, namely thermal conductivity, thermal diffusivity, attenuation depth, heat transfer, and heat flux. Based on statistical criteria, it has been proven that the proposed point model is the best one. It has been established that for the studied soil, the thermal diffusivity κ is 1.1035×10^–6 m²/s, thermal conductivity λ is 1.7612 W/(m ^оС), damping depth d is 17.42 cm, and thermal effusivity e is 27.9431 W h^0.5/m² °C. In addition, in accordance with the model obtained, it was determined that the largest heat flux on the soil surface occurs at 12:00 pm (q = 106.85 W/m²), and the lowest heat flux, at 03:00 am (q = –64.62 W/m²).