Thermal Signal Method Of Soil Thermal Properties Determination

Soil thermal properties are essential parameters in analyzing thermal transfer, and many researches have been focused on finding the simple and accurate estimation method of the thermal transfer parameters. soil thermal properties were studied by experimental method with constant boundary temperature, boundary layer theory and heat pulse, using the combined method of theoretical analysis and laboratory test, based on summarizing the research results of basic theory of soil thermal transfer and determinition method of soil thermal transfer parameter, The results were as follows:1. Soil thermal diffusivity of 4 texture soils for different water content and bulk density were caculated by analytical solution method of heat conduction equation, soil thermal capacity were caculated with soil bulk density and water content, and soil thermal conductivity were caculated based on caculated the soil thermal diffusivity and caculated the soil thermal capacity, based on analyzing thermal transfer characteristics in the condition of the test of constant boundary temperature. At the same time, the variation of soil thermal properties with water content and soil texture was analyzed. The result indicate that with the increasing water content, thermal diffusivity increased first, and then decreased. With the increasing sand content, thermal diffusivity increased. The higher content of sand the more thermal diffusivity peak value, and the corresponding water content was less. With the increasing water content and bulk density, thermal capacity increased. With the increasing water content and sand content, thermal conductivity increased.2. thermal diffusivity theory formular of boundary theory was developed according to thermal transfer boundary theory and thermal diffusivity was determined through the theory formula. the relationship between thermal diffusivity and soil physical properties was analyzed, At the same time, thermal diffusivity determined by analytical solution method and boundary theory was compared, the result indicate that thermal diffusivity determined by analytical solution method and boundary theory have differences in various degree. optimal boundary method suitable for 4 texture soils was obtained.3. Soil thermal diffusivity was determinded using heat pulse theory according to variation characteristics of soil temperature in the condition of heat pulse, and then the variation of soil thermal properties with water content and soil texture was analyzed. Through comparing thermal diffusivity determined by heat pulse and analytical solution, the result indicate that soil thermal diffusivity determined by heat pulse were appreciably larger than the one determined by analytical solution method. But comparing the temperature profile based on thermal diffusivity, the results indicated that a little difference between two methods exists, and the relative error was less than 5%. So it was shown that the determination method of thermaldiffusivity with heat pulse was feasible.4. Comparing the thermal conductivity determined by Campbell empirical formula and analytical solution method, the results indicated that the former was too great. Through modifying the Campbell empirical formula, the result was improved.