Theoretical principles of experimental methods for determining the thermal diffusivity of soils.

摘要

Mathematical models for predicting the heat transfer in soils are used for the management of the soil thermal conditions; the development of different soil constructions; the analysis of the thermal effects related to the loosening or compaction of the surface soil layers, the sanding of peat, and the application of friable mulching materials; and the description of many other phenomena and processes. The experimental support of the development and functioning of these models is provided by the function of thermal diffusivity, which describes the thermal diffusivity as a function of the water content and can be derived using the methods based on the solution of direct and inverse problems of heat transfer. On the basis of the different boundary conditions and sine-shaped daily and annual temperature cycles, a number of equations were proposed for calculating the thermal diffusivity that contained logarithms, arctangents of amplitudes, and the phase shift between the daily temperatures at two depths. A mean-integral solution was obtained for the estimation of the average temperature in a specific soil layer. A number of methods were developed starting from the analysis of the temperature dynamics on the basis of four daily observations at the same depth with 6-hour intervals, and nomograms were given for the rapid and simple calculation of the soil thermal diffusivity at a specific depth. The developed methods can be used for assessing the soil thermal diffusivity under natural conditions, which should improve the reliability, accuracy, and adequacy and expand the application range of predictive mathematical models for the thermal regime of soils.