Abstract
Heat equation of mixed material is developed based on three hypotheses. The first hypothesis is introduced to express condition of the mixture. The second hypothesis expresses flowing part of each component. The third hypothesis requires the temperature is the same in each material at a place. As application of developed equation, four types of heat equation of soil system is derived. Soil system is classified generally by both flow/no-flow conditions and saturated/unsaturated conditions of water.
There are two parameters characterizing energy flow: apparent thermal diffusivity and coefficient of flow rate. Experiments were conducted to evaluate applicability of the equation. The experiments were planned to measure sectional flow rate of soil-water and thermal diffusivity by phase differences corresponding to two different angular frequencies of input-temperature-signal. Measured thermal diffusivities are different from the theoretical values. The differences between measured and theoretical diffusivities come from apparent thermal conductivity of the mixture. Mechanism of the difference is not clearly explained by the effects of both heat bridge among soil particles and convection of heat. As the result, the developed heat equation can be applied to mixed material under the condition that the thermal conductivity is constant.
