A sigmoidal model for predicting soil thermal conductivity-water content function in room temperature.

Area of Science:

• Soil Science
• Geophysics
• Environmental Engineering

Background:

• Accurate soil apparent thermal conductivity (λ) as a function of soil water content (θ), denoted λ(θ), is crucial for modeling heat flow in soils.
• Simplified λ(θ) functions are essential for efficient heat and water flow simulations in various environmental models.

Purpose of the Study:

• Develop a robust sigmoidal model for predicting soil apparent thermal conductivity (λ) across the full spectrum of soil water content (θ) and diverse soil textures.
• Evaluate the performance of the developed sigmoidal model against existing models in the literature for predicting λ(θ).

Main Methods:

• A sigmoidal model based on the logistic equation was developed, with model constants empirically derived from soil sand content and bulk density.
• The sigmoidal model's predictive accuracy was validated by comparing its predictions with measured λ values across a broad range of soil textures.
• Performance comparison involved evaluating the sigmoidal model against the Johansen, Lu et al., and Xiong et al. models.

Main Results:

• The developed sigmoidal model demonstrated high accuracy in predicting soil apparent thermal conductivity (λ), with validation showing measured vs. predicted λ relationships close to a 1:1 slope and zero intercept.
• The sigmoidal model significantly outperformed the Johansen and Lu et al. models in predicting λ across diverse soil textures and water contents.
• Comparative analysis confirmed the superiority of the developed sigmoidal model over the Xiong et al. model as well.

Conclusions:

• The developed sigmoidal model provides a highly accurate and reliable method for predicting soil apparent thermal conductivity (λ) as a function of water content (θ) and soil properties.
• This model's superior performance makes it a valuable tool for enhancing the accuracy of soil temperature and heat flow simulations in coupled heat and water flow models.
• The empirical basis for model constants allows for its application across a wide range of soil textures, improving the generalizability of soil thermal conductivity predictions.