Estimation of Field Soil Heat Diffusion due to Crop Residual Burning and Flaming by Semi-Infinite Solid Method

Effect of long period and seasonal heat regimes on field soils were studied by the researchers who work on thermal soil physic. Although, they were presented some suitable models, they are not applicable for short-time heat transfer evaluation in the shallow field soils. In this paper transient heat transfer during residual burning and flaming on field soils were analyzed by using the semi-infinite solid method. Field soil was assumed as a semi-infinite object by considering the ground surface as a boundary condition and depth of soil as an infinite direction. Thermal diffusion in soil layers due to residual burning and flaming was analyzed mathematically by simplification based on the physical condition and the results of other researchers. The complex derived mathematical equations were simplified by statistical models. These models were function of soil moisture content and texture. Finally the resulted models were verified theoretically by empirical experiments of other studies. The presented model that was called SDE (Soil Diffusivity Estimator) showed that flame remaining time period and soil conditions (moisture content and texture) are more important than surface flaming heat intensity. Minimum heat transfer occurred at dry and low sandy soil, and maximum heat transfer was at dry but high sandy soil. Therefore, the resulted model of this study can be used to find the best soil moisture content, depends of soil texture, during residual burning for minimum heat diffusivity in the soil. Another result showed that in conventional condition, the effect of heat flaming was not diffused lower than 0.5 cm depth of the soil. But during residual burning, although the fire temperature was low, the effect of surface temperature was up to 2.5 cm soil depth. At the worse condition, during residual burning, the maximum depth thermal diffusivity was lower than 5 cm, which soil micro organisms were affected by critical temperature (50°C was assumed in this study) at maximum depth of 4 cm. In flaming operations, because of short period heating time, depth of heat diffusivity was limited to 12 mm and this condition was not harmful for micro organism at lower than 7 mm. The results of this study can be used for understanding the mechanism of short-time heat transfer in shallow field soil and increase our knowledge about the condition of thermal rate diffusivity. Also the derived graphs from the model can be used to estimate the harmful condition in residual burning and flaming. Also, the field conditions can be managed for minimum damage of soil micro organism during those thermal treatments.